measurement and modelling of noise emission of road
TRANSCRIPT
Hans G. Jonasson
Measurement and Modelling ofNoise Emission of Road Vehiclesfor Use in Prediction Models
Nordtest Project 1452-99KFB Project 1998-0659/1 997-0223
SP Swedish National Testing and Research InstituteSP AcousticsSP REPORT 1999:35
-..
.
.—
2
Abstract
The road vehicle as sound source has been studied within a wide frequency range. Welldefined measurements have been carried out on moving and stationary vehicles.Measurement results have been checked against theoretical simulations. A Nordtestmeasurement method to obtain input data for prediction methods has been proposed andtested in four different countries.
The effective sound source of a car has its centre close to the nearest wheels. For trucksthis centre ,seems to be closer to the centre of the car. The vehicle as sound source isdirectional both in the vertical and the horizontal plane. The difference between SEL andLpFn,aduring a pass-by varies with frequency. At low frequencies interference effectsbetween correlated sources may be the problem. At high frequencies the directivity oftyre/road noise affects the result. The time when LPF.,Uis obtained varies withfrequency. Thus traditional maximum measurements are not suitable for frequency bandapplications.
The measurements support the fact that the tyreh-oad noise source is very low.Measurements on a stationary vehicle indicate that the engine source is also very low.Engine noise is screened by the body of the car. The ground attenuation, also at shortdistances, will be significant whenever we use low microphone positions and have some“soft” ground in between. Unless all measurements are restricted to propagation over“hard” surfaces only it is necessary to use rather high microphone positions.
The Nordtest method proposed will yield a reproducibility standard deviation of 1-3 dBdepending on frequency. High frequencies are more accurate. In order to get accurateresults at low frequencies large numbers of vehicles are required. To determine the soundpower level from pass-by measurement requires a proper source and propagation model.As these models may change it is recommended to measure and report both SEL andLpFnlanormalized to a specified distance.
Key words: Noise, emission, road vehicles, measurement method, source modelling
Swedish National Testing andSP Research InstituteSP Rapport 1999:35 SP Report 1999:35ISBN 91-7848-794-3ISSN 0284-5172Bor5s 2000
Postal address:BOX 857, SE-501 15 BO~S,SwedenTelephone +46 33165000Telefax +4633 135502e-mail: info @sp.sehttp:llwww.sp.se
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DISCLAIMER
Portions of this document may be illegiblein electronic image products. Images are “produced from the best available originaldocument.
Contents
Abstract
Contents
Preface
Conclusions
2
3
5
6
,,”
11.11.21.3
22.12.22.32.42.52.6
33.13.23.33.3.13.3.23.43.53.63.6.13.6.23.73.7.13.7.23.8
4
55.15.25.35.45.5
66.16.2
77.1
IntroductionAim and backgroundList of symbolsSome basic theory
Some preliminary considerationsGeneralSource heightGround interference and instantaneous sound pressure levelsInterference effects and SELMeteorologyDiscussion
Some pass-by measurements on single vehiclesGeneral description of the measurementsVertical directivity and interference effectsDistance dependenceSound exposure levelMaximum sound pressure levelEngine noise versus tyre/road noiseIntegration timeTime historyCarTruckGround attenuationSound exposure levelMaximum sound pressure levelAerodynamic noise
Some measurements with parabola
Some further measurementsMeasurement siteHigh exhaustScreening of engine noiseMeasurements with a barrierMore examples at another test site
Measurements on stationary vehiclesDescription of measurementsAnalysis of the results
Determination of SEL, LpFmaxand LwDifference between SEL and LpF.a
7777
10101010131414
151517202022242626262829293336
38
414141424345
484848
5151
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4
7.2 Calculation of Lw and LpFmx
8 Discussion and conclusions
9 Comparison measurements using Nordtest method9.1 Introduction9.2 Results
10 References
Annex Proposal for Nordtest method
52
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565657
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63
5
Preface
The work accounted for in this report have been financed by 3 different projects:
Nordtest project 1452-99 Measurement of noise emission of road vehicles has financedthe comparison measurements and the elaboration of the Nordtest method,Swedish Transport & Communications Research Board (KFB) project 1998-0659 NewNordic prediction method for road trafic noise - Acoustic source modelling of roadvehicles and KFB project 1997-0223A new test method for the noise emission of carshave financed the other measurements and the theoretical work. In addition everythinghas been discussed and planned within the frame of the current Nordic project Nerd 2000aiming at making a new generation of prediction methods for environmental noise.
The following people have been actively involved in the projects:
Steind6r Gudmundsson, Icelandic Building Research InstituteJorgen Kragh, Birger Plovsing, Delta Acoustics & Vibration, DenmarkSvein Storeheier and Truls Berge, SINTEF, NorwayJuhani Parrnanen, Technical research Centre of FinlandHans Jonasson, Tomas Strom, Geir Andresen and Xuetao Zhang, SP Swedish NationalTesting and Research Institute.
Volvo Truck Corporation supplied a truck with driver for some of the tests.
The help of the above individuals and organizations are gratefully acknowledged.
Most of the work was earned out in 1999 but the report was not finalized until December2000.
Bor%, December 2000
Hans Jonasson
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6
Conclusions
The effective sound source of a car has its centre close to the nearest wheels. For trucksthis centre seems to be close to the centre of the car.
The vehicle as sound source is directional in the vertical plane. Between 100 and 800 Hzthere seems to be some decrease of sound at all positions above the bottom of the carbody. This is probably due to screening of the engine. At high frequencies there seems tobean increased directivity upwards. Both effects seem to be less than about 2 dB fordistances and heights practical to use for emission measurements.
The vehicle is also directional in the horizontal plane. The difference between SEL andLPF.Uvaries with frequency. The time histories of pass-bys verify such a frequencydependence. At low frequencies interference effects between correlated sources maybethe problem. At high frequencies the directivity of tyre/road noise affects the result. Thetime when LPF.U is obtained varies with frequency. Thus traditional maximummeasurements are not suitable for frequency band applications.
The measurements support the fact that the tyre/road noise source is very low.Measurements on a stationary vehicle indicates that the engine source is also very low. Itseems that a source model using three different point sources yields reasonably goodresults. For passenger cars the three sources can be used throughout the frequency range.For trucks, however, the lowest source should only be included above 2000 Hz. At highfrequencies there are large statistical variations.
The significant frequency dependence of the difference between SEL and LPF~mmakes itdifficult to measure only one of the quantities. Nor is it easy to calculate one quantityfrom the other. In order to be able to do so we need an accurate source model. Such amodel is also required to calculate the sound power level.
The ground attenuation, also at short distances, will be significant whenever we use lowmicrophone positions and have some “soft” ground in between. Unless all measurementsare restricted to propagation over “hard” surfaces only it is necessary to use rather highmicrophone positions.
To determine the sound power level from pass-by measurement requires a proper sourceand propagation model. As these models may change it is recommended to measure andreport both SEL and LPFn,mnormalized to a specified distance.
The Nordtest method proposed will yield a reproducibility standard deviation of 1-3 dBdepending on frequency. High frequencies are more accurate. In order to get accurateresults at low frequencies large numbers of vehicles are required.
7
1 Introduction
1.1 Aim and background.,.-
The aim of Nordtest project 1452-99 Measurement of noise emission of road vehicles isto define a measurement method suitable to use to obtain input data for road vehicles inprediction methods.
The aim of Swedish Transport& Communications Research Board (KFB) project 1998-0659 New Nordic prediction method for road trafic noise - Acoustic source modelling ofroad vehicles is to describe the road vehicle as one or more point sources which mayeither be omnidirectional or have a specified directivity. In combination with pointsource sound propagation theory traffic noise can the be calculated accurately.
KFB project 1997-0223A new test method for the noise emission of cars aims atanalyzing problems with the current noise emission method ISO 362, [3], in relation topractical trafllc noise conditions. The results of this project reflects the fact that theoriginal budget was cut by 50%.
The first two projects are essential for the Iongterm Nerd 2000 project which aims at newprediction methods for environments noise, including road traffic noise.
1.2 List of symbols
a, d= the shortest distance to source (m);C(v) = calculated difference between sound exposure level and sound power levelh,, height above ground of receiver;h$,height above ground of source;LE, sound exposure level (dB);LPF~u,maximum sound pressure level with time weighting F,Lw, sound power level, in dB;n, number of sources;p, sound pressure (Pa);t,time (s);P, sound power (W);v, speed (m/s);ALi = the increase in sound pressure level due to the presence of a sound reflectingground surface (dB);cz open angle (radians);Z time constant (s);
1.3 Some basic theory
Assume that each vehicle has n different omnidirectional sources, each emitting adifferent sound power Pi. When passing the microphone, ignoring all excess attenuationin excess of free propagation and possible ground interfere~ effects, each source willyield, see e.g. [7], the sound exposure level LE;
LE,i = Lpmx,i+ 10lg(tr) – 10lg(v) + 10lg(Ad) (1.1)
. .—.-. —— ,.
8
where a= the shortest distance to source i (for simplicity a is assumed to be equal to allpartial sources), v= the speed (m/s) and zla= the sector angle (radians) covering the timeof integration, see figure 1 LP~m,jin (1. 1) is the true maximum measured with a very shorttime weighting.
v-------1 u ~------(-----J
I 1
\,1------I/
. /‘\ I.
/’/’1
Figure 1. Basic geometry of a pass-by
Eq. (1.1) also gives the difference between sound exposure level and maximum level inthe ideal case with no excess attenuation:
LE,, – LPmx,i = 10lg(a) –lOlg(v) +lOlg(Acz) (1.2)
The total LE from all partial sources is obtained by adding all the different contributionson energy basis. Thk adding can be carried out automatically by measuring the soundexposure level, LE, during a complete pass-by by all partial sources of the vehicle.
For an omnidirectional source Lp~a,iis given by
L,mx,i = Q,i -101g~z(a2 + (h, - h~,i)’)]+ AL, (1.3)
where LIK,= the sound power level of source i, h,= the height of the receiver and h,,, =the height of the source i. ALi is the ground effect which can take any value between -COand +6 dB depending on the geometry, the ground surface and the phase relationshipbetween the direct and the reflected wave. If the difference in travelled distance betweenthe direct and the reflected wave is small compared to the wave length and the ground istotally reflecting, ALi = +6 dB. This is for instance the case at all low frequencies, evenif hs is great when h~is small or, for all frequencies at all receiver heights, if h~is close tozero. In these two cases we get approximately by assuming that h/a <c 1:
4,= LE - lolg(a) + 10lg(v) - 10lg(A~) + 101g{4m(a2 + h:} -6 (1.4)
In practice eq. (1.4) will be complicated. A complete source and propagation model hasto be used in order to predict the sound power model from a pass-by measurement of thesound exposure model.
In the following the notation C(v) will be used for the difference between sound exposurelevel and sound power level:
c(v) = LE – Jq (1.5)
The notation C(v) is used to indicate that C is a function not only of frequency but alsoof speed. From (1.4) we can see that, for a given spectrum
{)c(v) = C(vo) + 101 ~Vo
(1.6)
where V. is the reference speed for which C has been determined using the source model.
At noise emission measurements the maximum A-weighted sound pressure level duringpass by is often interesting. Normally time weighting F as defined in IEC 651 is used.However, in the Nordic countries time weighting S is also often used. Because of thisconfusion it is of interest to calculate the maximum level with different time weighings.By definition the time weighted sound pressure Ievel is given by
[
1 ‘0P2(0 (Ho)/T~tLp(to) = 10lg ~~~e 1 (1.7)
where the time constant z= O,125s for time weighting F and 1,0s for time weighting S.
Assuming we have a source consisting of a number of point sources, for example wheels,each wheel, will contribute, neglecting the ground attenuation, according to
p’(t) = 10%/10
P: 2z(a2 + (vt - dl~)’)(1.8)
where Llyflis the sound power leveI of wheeI n. v= the speed of the vehicle, ciln=thedistance between the first wheel(n=l) and wheel no n. t= Ocorresponds to the first wheelbeing closest to the receiver.
— . >.<.,.... .. . . . —,,
10
2 Some preliminary considerations
2.1 General
The aim of the Nordtest project is not only to get reproducible but also correctmeasurement results as well. It is, e.g., possible to get reproducible results by specifyingmeasurement distance and microphone height with narrow tolerances. However, if theseparameters cause systematic errors which are not known, the results cannot be used forinput into accurate prediction models. The problems to overcome are much more difficultnow than they were in the past when we worked primarily with A-weighted soundpressure levels, but now the aim is to work with one third octave band calculations.
Current prediction models use several different source heights. Some examples: In [1]0,5 m is used for A-weighted sound pressure levels and in [2] both zero height fortyre/road noise and 1,8 m for the other noise sources is used. Logically the truth must bemore complicated than that. As will be obvious from the following the selection ofsource height is critical. The problem is also difficult as we may have to use severaldifferent source heights combined in different ways depending on the relative strength ofthe sources.
For practical reasons the number of microphone positions for standard measurementsshould not exceed two in order to make it possible to use conventional 2-channel real-time analyzers.
2.2 Source height
A vehicle has several different noise sources: tyre/road interaction, engine, transmission,air intake, exhaust, aerodynamic noise, body and wheel vibration. The tyre/road source isvery low, close to O.In [8] it is concluded that the source is between 0,01 and 0,05 m andno distinction is made between engine and tyreh-oad noise. In stead the conclusion isdrawn that engine noise, if any, is also emitted from under the car. In different predictionmodels engine noise is often assigned a source height which may vary between a fewcentimetres up to several meters for large trucks. It is important to find a measurementprocedure which can deal with all these source heights. Tyre/road noise is dominated byfrequencies above 500 Hz while the other sources are more important for the lowerfrequencies. It must also be considered that tyreh-oad noise, although normallydominating, may be less important if there are low screens close to the vehicle.
2.3 Ground interference and instantaneous soundpressure levels
The method should not have any bias for any frequency band between 25 Hz and 10000Hz. This is a rather tough requirement. Interference between the direct and the groundreflected sound wave will always depend on source height, measurement distance andreceiver height as well as on the properties of the ground between the vehicle and thereceiver.
The problem is illustrated in figure 2 which shows clearly that if we have a high soundsource, in this case 1,0 m, the commonly used microphone position at 1,2 m, used in [3-4], above ground yields substantial systematic errors at 250 Hz and above. If, in stead, we
11
select a low microphone position, the problems move upwards in frequency, see figure 2.Obviously the low position is more predictive. However, it will have problems with theground attenuation. Both figures assume perfectly reflecting ground. The calculationshave been carried out using “smoothing” according to [5] for one third octave bands. Thecar propagates along a line from-50 m to +50 m and passes the microphone at x= Om.
80
78
76
74
5’
72
70
68
66-40 -30 -20 -10 0 10 20 30 40
m
Figure 2. Instantaneous sound pressure level during pass-by, third octaves,height 1,0 m, receiver height 1,2 m, distance 10 m. caI-pass(20,1,0,10,1 .2,k3
80
78
76
74
/5
72 \
70 “y
...68 F’
66-40 -30 -20 -10 0 10 20 30 40
m
source
Figure 3. Instantaneous sound pressure leveI during pass-by, third octaves, sourceheight 1,0 m and receiver height 0,1 m. caI-pass(20,1,0,10,0,1, k’)
As the source height is not known and may vary from vehicle to vehicle, at least forengine and exhaust noise, the most logical choice of microphone position would be tohave one position on the ground yielding +6 dB relative sound propagation in a free fieldcorresponding to the example in figure 3. This ground position is rather unproblematicfor low frequencies but sooner or later the ground attenuation wilI affect the resuIt as thefrequency increases. It is necessary to identify the lowest frequency to yield +6 dB. Aswill be shown later this position also has the advantage of keeping wind noise at aminimum.
.——
12
If the microphone height is increased we get other effects which are illustrated in thefollowing figures. Figure 4 shows that for a high source, 1,0 m, and a high receiver, 4,0m, there are strong, unpredictable interference effects below 1000 Hz but at and abovethis frequency we get a more predictable result approaching +3 dB relative the free fieldsound pressure level.
80 f ,1z
I~ i76 - i
1
74I
I.5’ !
!1
68-
-40 -30 -20 -lo 0 10 “20 30 40m
Figure 4. Instantaneous sound pressure IeveI during pass-by, third octaves, sourceheight 1,0 m and receiver height 4 m, measurement distance 10 m. carpass(20,1,0,10,4,’n’)
Now the question is what will happen when the source is very low, like the tyre/roadcontact point which may be close to O.This problem is illustrated in figure 5 and 6 forthe receiver height 4,0 m and 1,2 m respectively. Obviously we are back to the sameinterference problems as we had for low frequencies at 1,2 m microphone height. Thefigures are, however, purely theoretical products. In reality we may have severaI differentsource heights “smoothing” the result. Experimental results have to be analysed beforeany conclusions can be made.
80 , a # ,
I78
76 -
74 “ ]5
72
70
66-40 -30 -20 -10 0 10 20 30 40
m
I?igure 5. Different low point sources with a high receiver.
13
80 ,
1oocj Hz
74 -
5
72 i
70
~
I66
-40 -30 -20 -lo 0 10 20 30 40m
Figure 6. Different low point sources with a medium high receiver.
A comparison between figure 5 and 6 shows that the interference effects are greater athigh frequencies for high receiver positions. This is a problem as low positions may givetoo much ground attenuation.
2.4 Interference effects and SEL
Infigure 7 and 8 some examples for the sound exposure level are shown. Figure 7illustrates that the problems are small when the source height is 1,0 m. We have a rathernice +6 dB case close to the ground and an equally nice case at 4,0 m.
95
94
93
m-0~-92
C/Y
91
90
89 .10’ 103 104
Frequency, Hz
Figure 7. Source height 1,0 m. Measurement distance 10 m. Different receiverheights.
Figure 8, however, indicates the problem with a low source height. The only predictableheight is 0,0 m which cannot be used in practice because of possible ground attenuation.
,, -
,’,,
,-‘.
------- .,>7-- ..,. ,. -. . . . . . .. ... . . . ?.,.. .- ,.,.. .. . T> ..,,,_, ...
., - . .—————. . . .. —
14
95 I I I 1 , , t k
mu
w
Ii Ii
89102 103 104
Frequetwy, Hz
Figure 8. Source height 0,1 m. Measurement distance 10 m. Different receiverheights.
2.5 Meteorology
Wind induced noise is critical at low frequencies, in particular for ordinary cars whichemits mainly high frequency tyre/road noise. This fact is another reason to select a lowmicrophone position for low frequencies. The wind speed is significantly smaller close tothe ground.
2.6 Discussion
It is obvious that low frequencies are best dealt with using a low microphone positionand very high frequencies using a high position. However, the most important mediumhigh frequencies are more difficult to deal with. Experiments are needed to get the bestsolution. One problem with high frequencies may be the directivity. If high microphonepositions are used the sound pressure level measured may not be representative for morehorizontal propagation.
15
3 Some pass-by measurements on singlevehicles
3.1 General description of the measurements
All car and truck measurements have been carried out on a flat air field using an asphaltrunway with surrounding grass land. The asphalt surface was very hard. As the cargenerated rather little low frequency noise the sound exposure levels below 250 Hz arenot always reliable, at least not for the high microphone position. The truck used was aVolvo FH 12 heavy truck with and without a 3 axles trailer, see figure 8 and the car usedwas a new vw Passat. station car, see figure 10. unless otherwise indicated each
measurement represents the energy average of 3-5 pass-bys. The microphonearrangements can be seen in both figures. The special ground microphone very close tothe ground is shown in figure 11.
1.
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Figure 9. The Volvo truck used for the measurements
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Figure 10. The VW Passat used for the measurements
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Figure 11. The ground microphone
17
3.2 Vertical directivity and interference effects
Car, 50 Imr/h, 3 m96,0. , , , , , # , , , ,
94,0 -- 1 -J--L-J--I-.-L-J-- L -J--l--J-l--l--J--l_- L +0 .L --I.-1111111 !Ilt 11
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------ ~- - +--;--}-+--:--;-+ --:-- +--:--.: +0,8 +_ -;--
88,0 L -J--L--I-.-I-- L --I--L-2-J-- L –x-- 1,2 ------
84,0
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r34,0 - .1--l--_l_L--L-l-J__ L-J--I-- L--I--L-J--I--L-J--I- -1--1--L-J-N1111111 111!111 1111111 1.,
eo -n--l-- r-q--r-t--,-- ~-q--,--~-q-- p-,--,--r-<-- ~-T--,-_r-q-J
00,0 -+.--;--+-+.--}.-+.--;-- +-;--;--+--;--}-+--:-- ;-;--:--{--:--}-;--:--w
m,o -4--1--J---I--I- -b--l--l--J--l-- A-A--L-4--I-- J.--I--L-4-A-- l__4-A-i!
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Figure 12. Carpass-byat3 m. Propagationover asphaltonly. Thezeroheightmicrophone is 0,5 m from the nearest wheel whereas the 3 m distance is measured fromthe centre line of the car, that is 2,25 m from the nearest wheel.
Figure 12 illustrates that the SEL-level drops off when the direct distance increases. Thesmaller difference at high frequencies indicates an upwards directivity at highfrequencies or, alternatively, screening of low frequency engine noise. The theoreticalfall off of 10 Ig(distance) is illustrated in table 1 assuming that we have a point source,integrated during its pass-by, on the road surface under the middle of the car. The resultsindicate that the major sound source is rather at the distance 2,25 m than 3,0 m, that isthe nearest wheels are the most important sources. The astonishing results below 100 Hzare probably due to wind induced noise from the vehicle pressure wave.
Table 1. Distance dependence of SEL at the distance a and the height h,.a
~olg(T) ‘r a ,O,g(m)2,25
3 0,0 0,4 2,25 0,13 0,1 0,8 2,25 0,33 0,3 1,2 2,25 0,53 0,8 2 2,25 1,3
I 3 1,5 I 3 I 2,25 2,23 2,2 4 2,25 3,13 2,9 5 2,25 3,9
‘ ,-
...
: .. .
---- -..- ., ... .. .—.-. —--ma...
.—
18
Truck without trailer, 70 kmlh, 3 m100.0. I , r , , I , c , 1
mv2“wf.e
98;096,094,092,090,088,086,064,082,080,078,076,074,072,070,068,066,064,062,060.0
Frequency, Hz
Figure 13. Truck pass-by without trailer at 3 m distance with the exception of the zeroheight microphone which was about 0,5 m from the nearest wheel.
Figure 13 shows that the behaviour of the truck is very close to that of the car. The onlymajor difference is that the close to zero height microphone has much higher values atlow frequencies which is an indication that engine noise is relatively higher for the truck.
Figure 14 shows a bus pass-by at a short distance. The 4,5 m microphone position seemsto give about 2 dB lower levels at low frequencies. Qualitatively this is in agreement withthe theoretical calculations for a longer sound path. Thus the screening effect, if any,seems to be lower for the bus than for the other vehicles.
Distance: 4,9 m
88
Ml
_________-________---=f::;l----- ------ ---- ---- ----- ------------ --
86 ------
64 ---- --- ------------------ ---- ---- -----
_.$ 78
v~ ~
----- ---------- ---- ---- ------------- ---- ---- ---- -
= 76 ----- ----- -------- ----- ---- ------- ---- ------- --ar~ 74 --- --- -- --------- ----- - ------ ------- ----
: 72 -- ------ --- ---- - ------ ---- ------- ---- -
~ 70 --------- -- ----- ------------- ----- ---- ----
~ 68 --------------- -------- --------------- ------ -----
3 66 -------- ------- --------- ----- ----------- --------- -
(%64 ------ ----------------- ---- ---- ---- ---- ---- ----- -
62+--- _------- __---- ___--- ____---______ -______ -\~____{6O}--------------------------------------------->~--{
56+--------------------- ‘-------------------- ‘-----\W
Frequency, Hz
Figure 14. 2-axles buspass-by. Sound exposure 1evel.
19
Distance: 7,5 m‘.
76- -.-------- ------------ ------- -----
u_- 70~al> 681~~ 66- -L$ 64- - --------------------------------- -
!j 62- -
: 60+---------------------------- -----------&~-------j
c3
r??
56}----------------------------- ------------>}------+
52 ---- -------- --------- ,---- - ------------------------
50
Frequency, Hz
Figure 15. 2-axles bus pass-by. Soundexposure level.
Figure 15 also indicates thatthe lowfiequency SELisl-2dB lower atlowfrequencies at4,5 m than it is at 1,2 m. At high frequencies ground attenuation affects the result. Infigure 16 the difference in pathlengths to the two microphone positions is negligible butstill the 4,5 m microphone yields about 1 dB lower values, which may support thescreening hypothesis.
Distance: 22,1 m
60-
76- -
76- -
74- -
72- -
70- -----------------------------
~- 66
~ 64
0 62- -
: 60- -
$$56- -
=56- -ue54- -s0 52- -
m 50- -
48- -
46- - -----------------------------------------
44- -
42- - --------------------------------------------------
40 T
Frequency, Hz
Figure 16. 2-axles buspass-by. Sound exposure level.
. . ..
20
3.3 Distance dependence
3.3.1 Sound exposure level
-1.25 -0.75 0.75 1.25 1.65 265 4.15 5.65
Figure 17. Test set up
Car pa.ssby at 70 Ianlh, different dlsbnce% Oheight78,0-
76,0- - -- +---.;___ ;---+--+ --_; ---lr -.-:__-\- -------- :---+- -+ ___
74,0- - -- ~ ---l ---l--- I.---I--A---L- -L _- -4 _ --l------ -1---
-v--_-_-
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58,0- -
56,0- -, --1---1 __ -l___81111 11111 11
54,0- -
52,0- -“11
------__-’___ Hxk’[ +!::~:: &:-
11--AT--,-__’---
50,0- -“;;;; ;;;;;:,II
48,0- - --J--4---I--- L--4--..1---I- --4---I---I- --L--11
46,0- -1111
--T--T__-;--- r--~---l---r--J__tl Ill
~---_;-;__..;__ ~---l--_r--;___
44,0, I I I I I ! I I I I I I I I I I
g~gggg~$Zsg
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Frequency, Hz
Figure 18. C~pass-by withzero height microphone atdistances shown in figurel7.Simultaneous measurements at all distances.
A comparison between figure 18 and the calculated distance attenuation 10 lg(distance)given in table 2 for the distances described in figure 17 shows that the sound sourcegiving the best fit is not the car centre line but the nearest wheels. These measurementsconfirm the results shown in figure 12 and table 1. The results are confirmed by figure 19which shows the same car at 90 kmih.
Table 2 Calculated distance dependence of SEL in figure 18.K2=1,65 K2=0,90K3=2,65 K3=1,90K4=4,15 K4=3,40K5=5,65 K5=4,90
10 lg(K3/K2) 2,1 3,210 lg(K4/K2) 4,0 5,810 lg(K5/K2) 5,3 7,4
.
21
Car WAY at 90 Ian/h, different distance% Oheight00,0. , 8 , I I , , , 4
78,0- - II II------------------------------11111 Ill
-. -..+--- :- __\__ ; --..-:--- + --.-:---- I_
~ 6s,0
60,07 --;111111 1
5a,o
“11 \--;---:---;--;---:--;--.~--.+.--;--+;--;--+__;-_;-_:58,0 j ; ~ ; ; ‘ \!------------------- ;___;___ lr__ +.--_;---- Ir -- + -__:___ } -- -- , --
\
1---I---L--J---L--1 --J---Ll-l---l--_L__ J_-_!-_-L_-J- -L-54,0 --, ,II 11111 111!1 11
52,0 -- J---_L-JL--J---L --L--J---I---L ---I---L--J---I--- L---l--- --Illt
.50011111 1!111 I
-- + ---,--- 1- -- -1 ---!- -- + -- +---+ -- + -- +---- # -- + ---,___ * -- + -__,_-
Frequency, Hz
Figure 19. Cupass-by withzero height microphone atdistances shominfigue2O.Simultaneous measurements at all distances.
In figure20andtable 3thecorresponding informationisgiven fortheVolvotruck. Inthis casethe best fitseems tocome fromhaving the truckaxis asreference forthedistance.
Truckpass-byatdiffemnt dlsemc%satas+eed of70kmlhand mlcmphone height 0,4 m
92,0
90,0
ea,o
M,o
%0
02,0
60.0
78,076,0
74,0
~ 7Z0~ 70,0
~ Ixoo
66,0
64,0
02,0
00,050,0
56,0
54,0
52,0
50,048,0
a;$l s ~% ~ ~ g g! : $$s33gggggggggggj
Frequency (Hz)
Figure 20. Truck pass-by at 3 different distances with microphone height 0,4 m.
Table 3 Calculateddistance dependenceofSEL infigure20.K2=3 K2=2
I I K3=6 I K3=5 I
In figure 21 thecorresponding figure for4mreceiver heightis given.
. .
,,.-
i .
,—--..,.. _ . .. . . . !.-. . . .. ... ., ,., . . .. . . . —.
.—— -. -— ———-----
22
Truck pass-by at different dl-nces at a speed of 70 kmlh
and microphone height 4 m90,0
660
%,0
64,0
62,0
60,0
78,0
76.0
74,0
~ 72,0
g 70,0
ij 66,0
@ 66,0
64,0
62,0
60,0
66,0
66,0
54,0
52,0
50,0
Frequency (Hz)
Figure 21. Truck pass-by at 3 different distances with microphone height 4,0 m.
Figure 20 and 21 indicate that the major sources for trucks at 70 lm-dhare close to thecentre of the vehicle.
3.3.2 Maximum sound pressure level
Carpasbyat70km/h
620 , , i i I , 0 , 8
60,0- ---
7a,o. - -_; _--:___l 1 IT . --- l --- r -- ;__-:---- )-
l---ti L- J___l__l_ --l -- J--_ L__ J _--L---_--J-_ _L -_
58,0- - -- i---l---r-- -1 --- l---t---, --- l--- q---,- --f---l---p- -% ---,
66,0. -,, ,,-- J--- 1---!. ---l --- l___L ___l ---111111 1111. ,
54.0- -
52,0- - -- +--- :---!. ---1-__ l___i ___l _- -L -- J___ l___L ___l _ -- l--- J___ l_-, _L __11111 1111, ,,, .,
50,0- ---+---l---*--1---1- -- + ---l --- l--- +---,--- + ---, --- l----f ---,- --’ f.,--i4,0- --- + ---; --- + --:---:--- +---~---;--+---;---:- --; ---: --: ---: ---:---
40,0 * /
g~gg::~~g ~g~ $gg~gg. .Fraquency, Hz
Figure 22. Carpass-by withzero height microphone atdistances shown in figure2O,Simultaneous measurements at all distances.
23
...... ..
...Table 4 Calculated distance dependence of LPF~musing 6 dB/doubling.
K2=1,65 K2=0,90K3=2,65 ~ K3=1,90K4=4,15 K4=3,40K5=5,65 K5=4,90
20 lg(K3/K2) 4,1 6,420 lg(K4/K2) 8,0 11,620 lg(K5/K2) 10,6 14,8
Table 5 Calculated distance dependence OfLpmu using eq. (1.8) and (1.9).
K2=1,65 . K2=0,90.K3=2,65 K3=1,90K4=4,15 K4=3,40K5=5,65 K5=4,90
LoF.u(K~-Kz) 3,1 4,7LP~ma(G-Kz) 6,3 8,7L.c. . ...K.)-K.) 8.7 11.4
It seems to be difficult to draw any firm conclusions from these measurements andcalculations. The point source description is probably not accurate enough. However,also in this case the shortest distance to the car seems to come closest to the truth. Theproblem will be discussed further later on in this report in connection with directivity andtime-history during pass-by. ,,
Carpa*yat671an/h6?,0 - , am,o -
-r --,--
~ Es,o --1 -- - 1- .-...&’=-$__
~ 61,0- -
S3,0 . -;;\l_ --------: ---: --.-; -- + --.-;---; - .- .-:---.; _ -;_--;--- ;-------
%,0 . -N
54,0. --- L--J--J---I---L--1- -J--J__-L--
S2,0 - - _ - ; -- ; ---.: --_;-
520. - -- > ---1 ---1 ---1--- L - .- A ---I ---1--- I--- L -- J. ---I ---I---
40,0. - .-- + --+-.-._; -.-- ;---+ -.-+.-..-:- --: ---;--- :-- +-.-+ ---; ---;---- +-- +-.’-.
46,0 ‘1
gg~g~~gg~ gg~ $$$$$:F-
Fraquency, Hz
Figure 23. Car pass-by with zero height microphone at distances shown in figure 17.Simultaneous measurements at all distances.
.— ,= ——-
24
3.4 Engine noise versus tyre/road noise
Figure 24 was measured in 1999 and the following figures in 1998.
78,0
76,0
74,0
72,0
70,0
68,0
66,0
64,0
% 62,0
~ 60,0
58,0
56,0
54,0
52,0
50,0
48,0
46,0
44,0
Car paaa-by with and without engine ewitched on
i , , , , , , , IIll 111
-- 7--7---.,---.;-- ~__11111
‘cr -- ., .---,--- ,--_ r_- J
--_l ---l___11
_--l ___ L--11
-- d--- l---11I------ ;---II------ ;---11---l---:---
I — -fL:-w.#L-_4--*-_!11L --l---l--IllL--l ---1--IllL-- 1--J--Ill---1 ---l--!IllL-_l- --1--Ill--_+--_; --11
---+---: --I1
;-._;.---.: --
II-l---L-
11_l_--L_
,,
---- L-11
-l---L-11
-1---1- -II
+_- l--1
1-,--- l--1
L1—KWoff _
~ K410ff
_ KYoff -
--x--K2/on -
-+-KWon -
--+-KUM -
----KYon-
- + --_: ---;-
- + _--; ---:-
- ~ --_:--- :_
------------------
J.-
1 I I I I 1 I I I I I I I I I I
Frequency, Hz
Figure 24. Cmpass-by with(70 M)mdwithout (67~)engine switched on.Simultaneous measurements with microphone height: 0,0 m. Propagation over asphalt.
Figure 24 shows very little difference between engine/on and engine/off which indicatesthat tyre/road noise dominates.
Car, engine switched off, 70 kmlh, 3 m
86,0
84,082,080,078,076,074,072,070,088,066,064,0
> 62,060,0 J------+-’--’-l--’--’-l--’--’-”
y_-:-y-;__:-.:-:__;_-*-y58,0- --
~:fi
L --I--I--L-J--I-- L-J--I--L-J-
56,0- - -W::~:W::[:::::: :;::~:j::~::~:j::~:: ~:j::[::~:j::::_ ‘ ‘54,0- -
-l--l -- L_ J--l-- L- 1 - J-- L-J-J--L --I --I--L-J--I-- L-J--L.-L-52,0- -,, ,,, , !111111 111111150,0- - _T --,-_’ ~ -,--,--~-~--,-- ~ -,--,--r-~--,-- ~_T--,-_r-7--,- -T-748,0- - -L_ J-_ L- J_ J--L-l --I__L-J--I__L-J--l__ L- J--I-- J- I--I- _L - _I -
46,0- -: %--.--;__ } - + --:_ - ; - + -_;-- } - { _-:_- } - + __;-- } - + __;_- ; - + __:_- ; - + __,-
44,0-‘-*--’--P-7--’--P-’--’--’-+--’--*-” --’--’-i--’--+-i--’--”-i--’--?
42,0- -, - J __I__ L-J_-l--L_J_-l--J_Jl-l-- L-J__l--L-J__l_-L-J__l_ -L-J__L-L--
40,0- -111111! 1111111 1111111
~-,--,--~-,--1--~-, --l--r-,--l--r-,--,-- ~_7_-1--r_,--r--r-T -_T__;-_’ ‘
28.0 +
Frequency, Hz
.“
Figure25. Carpass-by at 3mwith engine switched off. The zero heightmicrophone iscloser, 0,5mfrom nearest wheel. The strange effects atl,2,2and3 mat low frequenciesmaybewindinduced pass-bynoise.
25
>
Car paas by, engine on, 70 Ion/h, 3 m distance94,0 a t I , I I I , 1 , I , t t I , I , I \ 1
h92;0 -~--; -- l---+ --l--t--l--l-- + --I--I--+--I-- !---l --1--t--
90,0 1 --I--L-J--I--L-J--I-- 1- J--I--1--1--L-J--I-- L-
88,0 ‘ --~--~-;--~--;-{--~--’ ‘ ‘86,0 -
~--,--;--;--:;_:-_--:-_ ;----*-+--,--+ -+--,--+-+__ *-+--,--*-+ --,--~-
84,0 - - - .1_-1--L-J--J--J. --I--I---L-.-I--L- J--l--L-
-A;:
82,0 ; ; ‘--;--}-;--;--;-;--~--;--;--}---------
80,0 -,--.,--; -,--~-7--T--T-T --r-T--l_-r-T -,-78,0 -.4--I--L- - I-.-L--I--I--4-J--I- -.$-4--
78,0 :k-!--:-~-, -+-+-_:.--+_:-..-’-_+_ I_
-L-
x
II-4--l--&--l--l- -Om -J-_L-L-J__l_1111 I -9-0,4m -
‘--’--r-’--’- +0,8m ~+--l--i---l--l-J--l--L___L_L
J--L-l._J_-L-
-r_7-q--~-q~--~ -,-y,:, -<--]
L-+---I--I- * -1 --1--
52;0 - -’””””””- +--l--l--+--l-- * -+--l--+--l-- l-- +--l--l--+--l-- i-- +--l--t-+-- 1-
50,0- -- L --I--L-J--I-- L -J--I--L-J-- I-- J-J--L-J--I-- L -J--1--L.-J-- l--
48,0- - .- + --;-.-.;- + -_:-_+--: --:--. +-.-:-- :--+ --:.--fr -{--:--;- + --. :--}--: --:-
48,0- - _, _-,-- ~-,--,--~-~-- ,-- * - q--,-,--, --r-,--l--r- ~--,--r_n__r -T-=_44,0- - - A--l--l---l--l-- L- -I --I-.-J.--I--!--4--I-- L-.I.-_l-- l-- J_ -l-_ L --I--L-L--I-- L
42,0+!!!!!!!! !!!:::::!: ::!!!!!:lr.g~~g g.~gg~~ ggggggg ggggggg g
z . ..N 6* UYOMON Qs :’z$lggg. ..- >?
Frequency, &
Fiwre 26. Pass-by by the same car as in figure 25 but with engine switched on. N.B. ‘Tie zero height mi~rophone is closer, 0,5 mfrom nearest wheel. The strange effects at1,2,2 and 3 mat low frequencies maybe wind induced pass-by noise.
In figure 27 a comparison is made between figure 25 and 26 for two heights. When thedifference between the curves is less than 3 dB tyre/road noise dominates and when it isgreater than 3 dB engine noise dominates.
82,0- , , 1 , 4 , , 1 i , 0 , I t t 1 , , a t i , #
80,0- --+--]-- ;-; --; -+--; --}-+ --;-- +--; --;-+--:- -- ‘ : : ; : :_______________ +--:-_
78,0 ; - _J__L_L _J-_L_L__l__L _J_.J-_L-_:__:_J-. -L_J - _l--l-_ L_ J__l__L__l _-It 1111111
76,0- -’!111111 .111
4--1--t- -- I--4--I--I-- -1 --l--+--l-- - - l-- t--l-- 4 --l--4-l--l--+--l--
74,0- --’ --:--; -1 -L-: --:--: --l--’ -v 4--1111 111111
-,--,--f-<—-l- _-, -_ ~_q__,--*-+ --
72,0- -“-’-1111111 I_T _ ;_ :_’_-:_-.:-’- ‘ --, _r -+__:_ r--, --- - --r —,--,- _r_ 7-_
70,0 ‘ : : , , ‘ , -J : ; , : : ,--’ -+--, -7 ~:+--:-- +--:----------------- ------------
“~
88,0 :- -:-J- --:--L188,0 - --l-- +-4--
,l__:_;::;:;::*m;-: -~-:::::!:;::-.+- - i---l--l--
184,0 _,_ , _r_; -~ Ir-l r-r-1--r --1 -T_ q_-
m
~ &’,o 1 1 - “-1--~-,--1- -1 ,--~--,- -om/Engin~~n ‘~- ‘-1 ‘~-1 ‘~-- i--!--
J- 80,0 I~IIJ-&*+--~--Li--i--l- lotiEnginedf ~~$~-~-j~_L-:lJ-
~_-l__l. _J__L_A..*.-A(l -_l_l___ L--l.-% 58,0-1,,,,, ,,1, ,,
58,0 _+_.l__A:_+ _l__+_ ‘ _+4rn/Engine on I
_+__,.-- +_+__~ _ + _ -,__ +_+-_,--- +_+-
54,0 ‘1111111
\
—x-4m/Engine off I I I I I_, __;-_ T-7-- r- T--_r_ 7__;_;_- ;-;_ -r- T-a--’r ;.- -_*_;_
52,0’’” _,-. -l_ -r-,_-:-+-_:_- ;_; -_~__ + --;- _} -;-_:__: _; .--: _ + __:-- _}_,_.-,- +_ -:__
1--I--L-J--L-1--I--L- J--I--L--I--L-J--)--;- : --:-.+--:--:-;--:-- ;50,0 -,,,,,,,, ,,, ,,, ,
\
----
48,0 -, J-- 1-- L--I--L - J--l--l---l--l-- L--l -- L_.l --l-- L_ J_- L_.L _-l-- L_ -l_ _L - _-1111111 Itlll[l l]llltl II
48,0 -+ --l--+ -+ --l--+ --l --l--+ --, --+--, -- l--+-- ,-- +-+-- +- +--,-_ +_+__*- _+-
44,0’’’’”t 11111111 1111111
-T __,-- r-l-- r- T--: __; _l -_:__
\
~ -7--r-T--l-- ~-T_-r-T-7_- ~-7_ -r-r_ 7_-
42,0 -+__ :__ +__: __lr _ +__[__ :_ +__ :_ -+__{ __!r _ +_ .-[__ +__l __ lr_+__: .--}- +- .-:-- ;-. -,-
L-_l--L-J--l-.l --1--L-J--L-L- J-- L-J--L-L-J -- L-I--I--L-J--I-- L--l --40,0 -,,,,,,,, ,,, ,,, ,,, ,, ,,, ,,,
Frequency, Hz
Figure 27. A comparison between rolling noise and rolling+ engine noise.
,.-,,,.
‘.
‘ ,-
,~,
, -.
.. —..—— ,~~ . . . .—
26
3.5 Integration time
LE as a function of integration time (or angle) is given by eq. (1.1). Theoretically theangular fimction 10 lg(Act!)= 5 dB, 4,4 dB and 4,0 dB for the three cases shown in figure28 which gives experimental results. We can see that the agreement is good for the lowfrequencies where we can expect the source to be omnidirectional. The differencebetween SEL and SEL 5d is 1 dB and between SEL 5d and SEL 3d is 0,5 dB whichcorresponds to the theoretical differences. For the higher frequencies the agreement is alittle worse. Because of the higher directivity of the high frequencies the contributionfrom far away is smaller and thus the differences between the cases decrease. Theconclusion that we either have to measure at least along A 5d of the road or we have tocorrect the measured values theoretically.
98-I 1 I I
s6-- --- --- --- ---- --- --- --- - --- ---- .- “+SEL - ---
+SEL 3d94- -
A
92- - --- --- ---
sO- -
--- --- ---- ---~.
%s6 --- --- --- ---- ---- --- --- ---- ---
Ie4- - --- ---- --- --- ---- --- --- --- ---- --- --- ---
82- - -- --- --- --- ---- ---- --- --- --- ---- --- --- ---- ---
eO- - --- ---
78 ----- ---- --- --- ---- ---- --- --- --- ---- --- --- ---- ---- --- --- --
76 *
Zzs’:: : ;g~g.-,-,-
ggggg Zg g--- Ncu Zv
Frequency, Hz
Figure 28. Evaluation of sound exposure level using different integration intervals.Station car, 70 kdh, distance: 15 m, microphone height: 5 m.
3.6 Time history
3.6.1 Car
Figure 29 and 30 show the sound pressure level during pass-by as a function of theposition of the car (Om corresponds to front of car crossing the normal to the direction ofpropagation through the microphone). The theoretical curve is the curve to be expectedhaving two uncorrelated equally strong point sources located on each wheel axle. Therather flat curves at high frequencies indicate some directivity forwards and backwards(horn effect). The more complicated behaviour at low frequencies could possibly dependon interference between at least two correlated sources. Please observe that themicrophone is on the ground, that is there are no nonstationary interference effectsbetween the direct and the reflected wave .
27
Rolling, 70 km/h
75m;“ 70
$ 65
m
: 50
‘“ 45 I 1 I ! ! I ! 1 I , , I# [ I
r+125 Hz
-R- 500 Hz
-A- 1000 Hz
++ lBOO Hz
-30-25-20-15-10 -5 0 5 10 15 20 25 30
Position, m
Figure 29. Pass-by at 5,65 m across asphalt pavement with microphone on the ground,70 ludh, VW Passat Variant-98. Measured at Hasslosa 990519. Leqduring 0,17s.
Car, 70 km/h, cruising, 306
75
45
-1 I 1<1 J&L=I+P+125 Hz
+ 500 Hz
+ 1000 Hz
+ 1600 Hz
,s-
,.-.,-
-30-25-20-15-10 -5 0 5 10 15 20 25 30
Position, m
Figure 30. Pass-by at 5,65 m across asphalt pavement with microphone on the ground,70 km/h, VW Passat Variant-98, 5* gear. Measured at Hasslosa 990519. L.q during 0,17s.
A possible explanation to the strange directivity at low frequencies is given in figure 31which shows a theoretical simulation of two correlated point sources 2,5 m apart passingby. As the result is similar both with engine on and off such sources might beaerodynamic noise sources.
.-. .vr. . . . . . . . . . . . ,. .,,,, .?--,=. %k.. . .. . . . ..-.’ . . . -. . ... . . .. ... L. --- , . . . . . . . . . . .. J,>.,.-.
~..
. . . . . . . . . . . . . . . . . . . . . . . z.—
.— —.
28
mu
-5
-10
-15
-20
-25
-30
-35
1 I I 1 II ! 1 1 I1 1 1 1 11 I 1 1 1 I
------- : - _ --- .-- ;------1 11 I1 !I 11 1
. ------ L------ -1-----I 1
A-------IL ------ :----
----- -- } -.------;__111 ~1!1
------- ~------- *---
1 11 I1 11 11 1, ,
Ir --------------- ~_______
1 11 1
I I I1 I 11 1 1
----.---L ------- L--------1 I 1III1
--L-- ---- -11111
-- ;-
1 1 1I 1 1I I 11 I 1I 1 1
--i---------l-------- *-------I 1 I1 1 11 [ 11 1 1I 1 1
-30 -20 -10 0 10 20 30
Position, m
Figure 31. Simulation oftwo equally strong pointsources 2,5 fromeach otherpassing5,65 mfromthe microphone.
3.6.2 Truck
Figure 32 and 33 give the time history of a pass-by at 3 m and 10 m respectively.It isdil%cult to draw any firm conclusions. However, it seems to be clear that there isassymetry.
Truck passby (Volvo FH12 with 24 tons 3-axles single wheel trailer) at 30 Irm/h at 3 m distance and 1,2
m microphone hsight
, a , i11!11 11 11181 1
w.
40
11111 I ‘/-:--uA---:---:---~ ---:---l---l ----l---t --- I----I ---4 ---1-
---, - --, - -- f-- -~ ~-fl---~.
11111 ,r
}
1“. ---4-”--4-- -+---l----l- -- 4---1----
IUi \ll , , , , , , , , ,-1! 111 1111
lVV
1?J ---;---:----;-.--;-- -;---;---J.---1---L- --l---J---L--
n;;lllll 1~~:~:: ‘1
‘w:,’ )’, vi “’-kw 1-. “1”11 I Ill!! !!!!! I
29
Truck pasby (Volvo FH12 with 24 tcma3-exles single wheel trailer) at 30 kmlh at 10 m distance and1,2 m microphone height
82807876
~ 74z. 72? 70; 68: 66; 64; 62~ 60; 58
5654525046 -,--,2--:~~~:--:----:---:---: ---:--J-:--~u~~~46
L
-- i----, ---+--- + --- &__+--- ~--- _. ,-
1 1 1 w
- “~#,,1-
44 ---1-- --:--- L---:---- ;-- .-:--- :---L- -. _:--- J---: ----- .
42 ---, --- -1--- + ---l----l --- +---+--- l----l ---+--- ● ---l---+-- r
Figure 33.
3.7
3.7.1
Tid(lOms*n)
Time history of a pass-by at 10 m distance.
Ground attenuation
Sound exposure level
Figure 34 illustrates the ground attenuation. It is obvious that low microphone positionscannot be used above grassland and similar “soft” surfaces.
Car pass-by,10 m aephal~ 5 m gta~ 80 krnlh66,0
66,0
64,0
62,0
60,0
58,0
56,0
54,0
~ 52,0
~- 50,0
@ 46,0
46,0
44,0
42,0
40,0
28,0
36,0
34,0
32,0gg~ g:~ g~jj %gg g~$~ gg
Frequency, Hz
Figure 34. Propagation above 10 m dense asphalt and 5 m grassland. 4 differentreceiver heights.
.,-!.
‘.
, -..,.
-- ——
30
Car pass-by at 90 km/h, 10 m asphalt72,0- , , , , , I , I # , 1 t # , , , I 8 I , I I a
70,0- --1 , , , , , , , , , , , , , ,11!1118
68,0- -
04,0- -
62,0- - -;-+ -; --: --:-- :--:-- ;-+- ;--;- -;-+ -1
* ecJ,o- - - L-I.-J--I..
:. 5a,o- -L- l-J--
-q-.., --,--p-F -7 , --r--,--,--l-- ~ - f - y-q-q--,- -1-
40,0-!.-.!- -!--l-_ 1--1--1-- L- 1-l --1--1-- I--IL-!. -L-l--l --1--1-- I-- L-L -1--1
36,0
%’QZ s%~g?s:z:?zz~gs~g $Egi$igz
Fraquency, Hz
Figure 35. A-weighted frequency bandvalues. Propagation above dense asphalt only.10 m distance and two different receiver heights. Please ignore low frequencies at 4 m!
Figure 35-38 show propagation over 10 m mixed ground with different ratiosasphalt/grassland. Propagation over dense asphalt only is shown in figure 35 which alsoshows that the background noise at low frequencies is significantly higher at 4 m than at0,2 m. It also shows that the sound pressure level increases with height above 1000 Hzalthough the distance to the higher position is longer. There are two possibleexplanations for that. Either there is some ground attenuation even when propagatingover the very dense asphalt only or the source has a higher directivity upwards. Anotherinteresting result is that the two microphone positions yield identical results between 250Hz and 800 Hz. This is an indication that the sound source is low. This is logical as weknow that tyre/road noise dominates at this speed.
Car paas-by at 90 km/h, 7,5 m asphalt and 2,5 m grassland72,0- , , , 1 I I I i 1 , I , , , , I t t , k , , I
70,0. -
5a,o - - -;-+ --: --; --:-- :--;- +--: --: -- ;-- ;--+-
60,0- -------------------------- ----- ----------
60,0- -1111
- r-,-<--,-- ,--
~- 56,0- -- L -l-J--l--l--1-111111
~--,-- r-, _7_7 - -- r-T-.
~ 52.0- --:-; A_-l-_l--L-L-.l _ A
+ 50,0-11111 [11 Ill
--- ;-- Ir -;- ;--: --; ----- :--+- +--;- -: --:-- ;-+- +-. +-- ;---
40,0,1111111 1111111 I
30,0- -- r - ~--i-m--r ‘ r-r-7-7--l-- r-r-~-~-~--)--r- r -T-7-y--I--I-- r-r
34,0 -i I I ! ! I I , I 1 , I 1 , 1 ! ! I 1 , I I 9 , 1 I
%--ZZZ zg~g:: ;g;;:g: g[~:ggzsG --- 3s g
Fraquency, Hz
.
#
Figure 36. A-weighted frequency band values. Propagation above 7,5 m asphalt/2,5 mgrassland. 10 m distance and two different receiver heights.
31
Figure 36 indicates clearly a significant ground attenuation above 1000 Hz already withonly 2,5 m grassland with a very low microphone position. Compared to figure 35 thereseems to be no difference for the 4 m microphone position.
Car pa+y at 90 Ian/h, 5 m a~halt and 5 m gra~and70,0- 1 I , 8 1 I , , , 1 1 , t , I
ea,o - -- L_-l_J_ .1--L-L- L_-t _ -I --l--L-L- -t. L_-l--l__L_L. l- J--
6s,0 - - - $ -;-; --:- _:-- ;- +_; _-:__:_-} _}_+_
64,0- --;- - l -- l --l --l--l--+ --l--l--l--b-t- 4-4
62.0- - _T_+ __: --: --:__ ;_;_ +_ -:__ :__ :__ ;_;_lnul-i-
&),o -+-~-y-+--~-p - +-q--j--,--p-+ -*
~\/
+_+--,--+-*-* -<- --l--t-t-+-_L-J_J--l__l__ :-+_; __; __;_- j-- !. I I : I : ; ; ; -:-:-.:-:-------------------
Ill 111_T_T_7--,--r- _T_7_ q--,-- ~_7_q_-l_-
-L_J _ _-1-- l-_L _- r - ~ --r --l--,- -r-*-7-
J_-l- -L- _l_J _ _l- _J. -L--l __l_- -L-L-J-111
-~--r , --:__ }_;_+-,_11 11!
-,--. r.-r.-, _l__:r_:--r - -.,__;__\_’_;-.;_
-*- -4--I-.-I--L-L- -1 --1--L-I.-J--I- -I-- I--L-L-J J --!--I--L L-.I-
-: +-4--’- - T-,-;--{--}-;-;-+--:--:-- ;-+-+__l 1--:__:_l-.;_
-+--t- -1--l-- k-+-+--l--l-- l-- +-+--l--l--l-- l-- +-+--l--l -+ -+-+ +-
--- _; __:-- ;-. -.;.- +- +-_: --. :__ ;__+- +--; --: -_l-- \-+_ +__:-_ :-- 111
----- -111
.wo+z<+-- l--l-- l--l--t --t --l--l--i--t-i--i--l--l-- I--t--r-+--l--l-->-*-*\+
40;0rL - 1 - J--I-- I-- L - 1 - 1-J--I--L -L-1-J-J--L-L-J.-1- J--L -L-L J._J-
3S,0-+-’’’’’” “’’’’’”
\]
1111117 -7--l--r-T-T ‘7-7--I--r-r- -r -7--I--r--r-T --r--I--r--r-r- -T-
33,0 - L-2_ J--l--L-L _l_ J -J--l--L_ L_l-J--l-_t-_L _L_J__l _-1--L- L_L _ -
34,0 -: _;_;--;--:-_;_+_; __:__;__l ~_#_+_; __:__ {-_:_lT -+-4--:--:--}-;-T
Frequency, Hz
Figure 37. A-weighted frequency bandvdues. Ropagation above 5masphalti5mgrassland. 10mdistance andtwodifferent receiver heights.
Figure 37 confw the result of figure 37 as do figure 38 below..
Grpasbyat 90 kmlh, 7,5 m as#halt and %5 m graaSandqo - 1 1 1 I 1 I I 1 , , I i 1 , ,70,0. - - +-+--l--l--l--l-- +-+-+--l--l--l--l- -1--+ --l--l--l--l--+- ● +--i--
64,0- - - 1.-~-~-~--,--,-- ~-~-T-.r_q__l__r _r
62,0- ----------------------------
m 5&o- - - ~-~-,-,--1--,-- ~-r-T-,-T__,_ ~ -~-j--’,-,-,--,---,__ ~ ~_ T_ T_,__
- +-+--l--i--l--l-- l--+-+--l--l-
S 5Q,o- -11111
.cs 4a,o- -
- r --r --l--, --l-- r--r--T _T-$.-.4-I--I--I--I- -!--l-- .!. --t-
$46,0- -- f.-+ ____ I__ L_ L_l_l_J__I__l__L - L - 1 -:-J-----
d 44,0- - _T _ ~ _}_+_;.-;__;__:__ }_; _+_, _;__; __l__
42,0- -
________________________________________________
26,0 I ‘ T-T-l-l--t--l--24,0- -
_L_l-J_ J__l__l-_L-L_L _J_J_-J--L _22,0- -,, ,,, ,,, ,,, ,,, ,,, ,,, ,,, ,,L_ L_l_d_J _-l_ -l__ L_L _ L_4_
“03:ss38g$~g3:5~33 g:~g~gggggg?
.. N’N C-l *o
-.
>.,.,.. ..
Fraquency, Hz
Figure 38. A-weighted frequency bandvalues. Propagation above 2,5masphalti7,5mgrassland. 10 m distance and two different receiver heights. Measured after the lunchbreak.
Figure 35-38 have been compared with calculations using the coming Nordic predictionmethod forenvironmental noise, [10]. Thesound power of thevehicle has beendistributed to 3, 0,01; 0,15 and 0,3 m, and 1 omnidirectional point source, 0,01 m,respectively. The flow resistivity has been assumed to be 20000 krayls for the roadsurface and 100 kRayls for the ground surface. The impedances were measuredaccording to NT ACOU 104, [11]. The results are shown in figure 39 and 40.
. .
, ...
., - . -.—m- ., ,:----- . ,...? ---- ,. . . ..=--.... . . . . . . ,. ,., .
—.——. :.
32
‘hs=O.01,0.15,0.320000/100kRavls.20,0
-5,0Inoloorooolnoo Ou’)oooooooo 0000000CQCIWU)WWONUI Olin. oacoooul Ooo1oooooo
,-.-QNCNJWJW mmmo~mo m.-OOO-JOOl-1-. @JoJ co* Inwa Jo
Frequency, Hz
Figure 39. Calculated differences between SEL at 4 m and 0,2 m respectively.
The results of figure 39 and 40 can be compared with the measurement results reportedin figure 35-38. Bearing in mind that we study the very extreme case with the receiver at0,2 m and an impedance jump the agreement is not too bad. By introducing vertical andhorizontal directivity the values at high frequencies will increase 1-2 dB and theagreement will become even better. Actually the worst result seems to occur at theseemingly easiest case, that is propagation over asphalt only. By limiting the sources toone only at 0,01 m we can improve this case a little, see figure 40. However, for the othercases there is no improvement. The general shapes of the curves seem to be better usingthree sources at different heights.
hs=O.01 20000/100 kRayls20,0 —
15,0- — —
Em.o 10,0 -— —-!Illa
f 5,0- — —wu)
0,0- ~ ~
-5,0- ~U)cuoocoo,olnooo !430000000000 00000‘*-”” ”:2S8R3SS%S88888 288888
t-t-l- cucumwul cocoa
Frequency, Hz
Figure 40. Calculated differences between SEL at 4 m and 0,2 m respectively.
>
33
75.0
70.0
65.0
60.0muJ- 55.0wm
50.0
45.0
40,0
35.0
, , , I 1 n , , 1 , I , , , , , , , , # # , t ,
~~=~+;~d’~~~’~~;;--r7-~~:!:T:;-n:;-#;-;-l-;-;-l-:%-l-;-;-!-
~r1!1 III l?;111111111 !1Ill I 11111111 11!1
-,-,- ,-+-r -, r-t-7 -r-r 7-r-l-7 -T .l -T-J-1111Ill _;&--$3\,:,~:;;;;;:;;;: ::::
--
/
%-1--1 -t -l--l-+-l--l-+-t -1- +-t-l-+-t-l-+ -i--l--i +-1-
111111111 1111111111 11 !.!
\-
1111!1111 !! 11111111 1111J L-l-J-L-l-A-L-l_ J- L-!-A-L-I-J-L -I- J-L-I-J-L
1111111 1111 !111 1111111 141//1/1 I 1 1 1 1 1 1 1 II 1 Ill 1 11 1 1 1 1 1 INI
Frequency, Hz
Figure 41. A-weighted frequency band values. 4 different measurements at 4 mmicrophone height.
Figure 41 shows that the 4 m value is essentially the same for all configurations at andabove 250 Hz. However, if we don’t accept errors greater than 1 dB we have to excludeat least the 7,5 m grass case although the slightly higher values around 1000 Hz for 2,5m asphalt/7,5 m grassland may depend on changed conditions. The measurement tookplace a few hours after the other measurements.
3.7.2 Maximum sound pressure level
In figure 42-45 the maximum sound pressure level during pass-by using time-weighting Fis shown for some different cases. The spread in data is confusing at low frequencies. Asbefore a possible explanation is wind induced pass-by noise and background noise.Comparing figure 42 with figure 35 indicates that the directivity at high frequencies issignificantly less for the maximum level than it is for the SEL level. The explanation isthat the horn effect is not as efficient perpendicular to the direction of propagation.
Car pasby ●t 90 Iunfh, 10 m asphalt70.0- , , n i , # 1 I , , , I , r ,68,0. - -I--I--I-4-4-+- + -I--I--I--I--!-4 -+-k -1-+--i-+-+-i- -+ -l--
moo- -64,0- -::::;:;;: ;’&20 --60,0. - -b-l--l--l-+-+-l- - I--I--I--I--!-4
l-l._L_L_L-
--j --t - r - l-- l--,--,- q-n_7 ~_ r-~-,--
% 520- -
Ii------- +_ +_: -:_ -;_-; --:-.:- +_+
s 4.9,0--s?
_l-l_J. _L_L_l__l _ _l-J-.L -L_ L_!-- l__l _ J_ J_ l-L-L-
.to,o -- -,-~-~-~-*-~-~ -,--, -~-,-,-~-r - r-l--l-T-,-T-r -r -r-,I-- I-4--I--I-+-L -I--I--I-4--I-4- t - !-- > -l--l -+--l -+-+-l--!--l-
-l__l__l_J_J-l_L_L -l-_l_J_ J_ J- L- L-l- _l__l _ J_-l_L_L_L_L -L-
Frequency, Hz
Figure 42. A-weighted frequency band values. Propagation above dense asphalt only.10 m distance and two different receiver heights.
,,.-.
:,
‘ \-
,,
..
.,.
:.. -. __, —.. —....’. . . .
34
CarpasLyat SW 7,5 m aqimlt and &5 m gmsdand
j 44,0
t!t?O’dt i’’’”” “’’’’’’’’” ‘kqi-----l--i --i-+-+-l-- ●hi_;__;_;-;-;-;-:-%-I--I--L::::+:+ ~‘l-l-T-~-~-~-~-,--,- ,-,-~-~-r-i-~--~--”-
430. --l
\
\-: --;--: -; -.+ -+. -: -. :--;__ ;__;__~ -+-+ -+-: -Ir-:--. :-. +.-{ -;_l _;
{3s0 -- ~-l--, -T- T-.f - ~-r-r-r-,--l- ~-~-,-r-r..r -,--, --I-T-7-T -T-
--I--J - 4 - + - I-- I-- I--I--I --I- ~-~-+-~-~-l--l--+-J--J- +-+-
320+!!!!!!!!! !!!!!!!!!!! !!!!! [
Freqwwy, R?
Figure 43. A-weighted frequency bandvalues. Propagation above 7,5mdense asphaltand 2,5 m grassland, two different receiver heights.
Car pass.byat 90 bW1’$5 m a@alt and 5 m grasiandXlo , , , , , , , I , , I 8 I , i 1 1 I , , I
630
1-1--l--J -J- L- L_L_L -L_t__l_J_J_l_L -
A
-L-I-J--J-J-.I- L-L-L-
E6,0 ‘ ‘ ‘ ‘ ‘ ‘ ‘ 1 ‘ ‘ ‘ ‘ ‘ ‘ ‘ ;--’--l:; ,2; :l,\; -l--\-~ -,--l-3-,-T-T -r-r -,--, _T -,-T -r
64,0 -L -I--I-J-J-L -L_ L- L-l__l_J --1-1- -L -L-- -- 1--1
a.
-L-;
E20” -r -,- -’-, ;.-; -+_; _;_: -[-_:_ ;- +-; 1 I I I II +-4m
r- r-r-r-t T-7 -}-:
MO _l--l-J--l_J_L - L - L - L .-I--I--! -J- -L-L-L-I--I- - A-J-L-L-L-,11111111 11111111 11111111 Ii
1MS3.0, ;””------
/
, , -, - T - T - r-r-,--l_ ,-
;. 56,0 _LJ-J_J--l_L_L_L -L-l--l- -J-
g54,0 -:--: -;-;-;-;-;-;-;-- -’ ‘ ‘~ 52,0 _F-:_-:_.&_:_:*g+-:-:--fi-j-’.mq 46,0+ -,--1-)$- ~-fi
~-r- -r-x+ ----
1I -1--,-r-r-r-
-I- J-J-J J-L-L-L-11111111
1111n:yp”-”’”-”-”7 7 T r r-r-r-l-7-7-T-r-r- r-l--I--t-7--r- y:~;- J-A-J-A-L-L-L -1- J-. -A- L-.L -I.-L- L -l--l-A-A-A-& L L ,
;M--,--, ,--- i -T-~-~-l--;--l--l-~-T -T-r -l--,- _l__l- T-7-T_ ~ ~-
L-,--,--J-4-4- L-L-L-I--I-J- J-1-L-L-L-I-J- J-J-J-J.-L- -!
Frequency, Hz
Figure 44. A-weighted frequency band values. Propagation above 5,0 m dense asphaltand 5,0 m grassland, two different receiver heights.
.
35
m‘n
CarpasAy at 90 Ian/h, 2,5 m asphalt and 7,5 m grasdand72,0- 1 I I , n # 1 1 1 i I # i I #70,0- --: -: -:--p -l-- L - J- J - l--l-- l---
6a,o - -,,,,;’------------ ,--:_; --: -_:-_ :_-lr -- r_{ _-: --:-- l__l_-L -
m,o - -- *-*--I--I--I--F-+ -+--l--l--1--F-+-+-1-J-J-J--L-L-L-J- J_-1--L-L64,0- --, , , , , ,
62,0- - -~-,-,-~--,--r -;-;-1111
~_-,__,--r-;-
lxl,o - -
,_T--,_-l--r-T-
-&-L--t--l--l-- L-L.-.$--I-A--I-- L-I. .l-4-4_-1-_l-- &_ --I--I--I--I--L --
58,0- ~’ - ~ - + --: --:--;-- :-- + _ + --; --;--:-_ Ir - - + - + -_:-- :_- :-,- } _ + -;.2
1/\56,0 -t-+-+--l--l--l--+-+ -+- -1-- -+-+--i- --l--l--l--+--l -l--l--l--t-
L_L-J-_I-_l--L-L-J- -1 -!- -L. -L%,o -,
Y
1- --l- I--L-L--l-J_ l__l--L-L-
g52,0 -r-;-;--;--:--:-;-;- -,--;--}-;-T-;-.-:--, -\-:-;-;-_l -:--}-;-
Q60,0 -b-~-~-~- --- -~--1--1--~-~-~- J-d--l-- -~-~-~--t-- -~-~-=~48,0 ; : ; :- -- ------ -1--- ___-l --f-_f-- IL- !. -1 - J -_f--f-- IL- .! --l --l__l- -- L -
946,0 -r-T-,- --’ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘-&;--’-;--~-~-,-q--,-- ,--,p-r-T-,-q --l--r-r-T-
~ 44,0 - L-1- - --l--L-L_J_J--!-_I__ L-L-1-J-J--I--L-L- 1--!- l__l__L_ _
42,o ‘ ‘-r_
40,0 -+l--;--;--;-;;;-;--;--;- -;-;-;-;--;--;--:-; _+-;_-.,_ I__\-r
- -1 - -1--l--+ - + - 4 - -1--l--l-- & - + - + - -1 - +--1--> - 1- - + - -i --1--1- !- - t -
28,0 - ’ -+-:--:--:--:-+-+-+--;--;--;-+-,+ -+--;--;--:-;-+-+--:--:--l -+-
26,0 r--r--l--r--l-- I--T-7--I--I-- l--r-r--t--l-l --,--l--l---?--l --,--,--1-- - i
Frnquency, Hz
Figure 45. A-weighted frequency bandvalues. Propagation above 2,5mdense asphaltand 7,5m grassland, two different receiver heights.
In figure 46 the geometry of figure 45 has been used to calculate the theoreticaldifference between the two heights using the same method as the reported earlier for theSEL-level. The agreement is very good in this case. Notable is the fact that the sourceposition seems to be very low at high frequencies and at low frequencies the location ofthe source is not very critical.
16,0
14,0
12,0%.~- 10,0
=- 8,0?$E 6,0
0,0
-2,0
2,5m/7,5m 20000/100 kRayls ,-,<’.4 . .
!:. ”
Frequency, Hz
Figure 46. Theoretical calculation of figure 45 with different point sourceconfigurations.
Figure 47 shows the time-weighted F time-history for selected 1/3 octave bands duringpass-by by a passenger carat 7,5 m and 70 km/h. The microphone was on the ground inorder to avoid uncontrolled interference effects at low frequencies. We can see that theA-weighted level has a broad maximum during about 0,6s, a time during which the 63I% value may vary about 10 dB. In figure 46 the difference between the true maximumand the maximum when the A-weighted value has its maximum is shown.
,.-,
.. .. -17--,m.-..-.?.. ,.. ._. ,,:,.,. .. ---- . . . . . . . .- - , . --- .-———— —& ,- .’,-., ,. —-
m-0
——. ——— — ————..——
36
Pass-by at 7,5 m and 70 km/h
75,0
70,0
65,0
60,0
55,0
50,0
45,0
40,0
I I I I I I
I I
I k7’ I I
fI xl I I
h’,, ,
—31.5
— 63. . . . . 125
— 250. . . . - “500
— 1000
—2000
—4000
— A-weighted
3 4 5 6
Time, s (1 s= 19,4 m)
Figure 47. Time-history during pass-by of a passenger car.
9,0
8,0
7,0
6,0
5,0
4,0
3,0
2,0
1,0
0,0
< \+7,5 m, mean
\—————
~15 m, meanR
U-Jm-oocooou)o Oomoooooo 00000000004 WU3acoomlmoul .Oo moo moo O1ooooooz --- CN OJ m w u-la co o ml w o In? o 0 co o 0
. . . m N mm’ mm coo
Frequency, Hz
Figure 48.Difference between truemaximum (LPF~x)andmaximum atthetimeofmaximum A-weighted level.
3.8 Aerodynamic noise
By chance we happened to measure one day with strong winds exactly parallel with ~he--road. The result is shown in figure 49. We can see that the low frequency sound pressurelevels are considerably lower in the downwind case. As the high frequency tyre noise is
37
the same the results indicate that aerodynamic noise may be the difference unless theextra load on the engine makes the difference.
95
90
85
80
sgg 75
3
70
65
60
55
Reference 2: Gear 5/2500 rmp (100 km/h), Wind: around 8 m/s
1 I I 1 I i I I 1 1 I I I I I I I i I I 1 1 I 1 III 111111 Ill 111111 1111111111111111 111111111 11111111
111 1 II
\
. -.--L---J--11
11 1111 1111----- +- _.-:__11II tII 1111l-l---”--+ --1--11 II11 1111 11I-l----- J__11 1 \-11
;\11II 11-p,---- _,-----
11 1111 11
11 11! 111 111111
-: _-:__: -.:+++ +_____ ;--.-.;_ +_ }.-:.. :-
!1 111111 11111111111111 111111II 111111 111111
q --,- q - ~ *, * * -----,--- p- +-r-,-~11 111111 11! 11111 1 [1111 11111111 111111 111111111 11
J--l_-l-~~JJ~---__l-_- ~_J-LJ_l_l_l-l----- J---l -_11111111 Ill! 11111 II11111111 1 11111111 111
It Ill-l- J..I -I-l
111!1 i11111111111! 111_, -----
!111111111111111111
-I-+-l-l+111111111111111
-!-~~1~11111!11!11! 11111111
\
l- l-i-l-l1111111!
!1!IJ
-1-11 1Ill1111111
.-I- T1l+18111l!tll11111
25 50 102 250 500 103 2000 4000 104
Frequency (Hz) hrl =0.2m, T= 1.3
Figure 49. Difference in sound exposure level between up and downwind. The windspeed was about 13 mls. (Not 8 rnls as indicated on top of the figure).
:,. .. .,.
— —
38
4 Some measurements with parabola
In order to find out whether or not the sound radiation is about the same for all wheelssome measurements using a parabola antenna were carried out. The measurementdistance was about 10 m and the parabola which is highly directive above about 800 Hzwas directed towards the wheelhoad interface. Some of the results are shown in thefollowing figures.
The conclusion of the measurements are that all wheels radiate about the same soundpower although there are large statistical variations. There is no strong indication that thedriving wheels make more noise than the other wheels when the vehicle is cruising atconstant speed.
lD19JOng container truck
58s0
93s9
S4sa
9293
9303
mm
C-WI
g M.cO
: 82.CUm
woo
7803
7003
74.nO
T2.co
70.M
Figure 50. Truck with 5 axles of the type shown in figure 51.
.“.
..
Figure 51. Truck with 5 axles
Figure 52. Truck with 5 axles
Figure 53. Bus with 3 axles
000821_i~_bwk(MJJ)
02,ca , I
I . Yea,oo A \
8s,20 / PA\./i f\ A IJYY
Et4,m f I \ dY k-’
8200. d AA Al \M,C17- Al \l”v ‘78,M
v{\A
a74,C0 \/
72.M I-. IOI-. u)):z~:: g~z~~$;gq~?j:=T [1/S3S) .0.5 m
Figure 54. Truck with 1 + 1+3 axles, 81 Ian/h
-’
.— ~ —.-.-.—-- .. ... ~—— —.
,.
40
000821-1 91_truck(90-2)
Kc?@/} I+1 k.w.
Figure 55. 1 + 2 + 3 wheels, 90 knih000821-55-car(100.0)
lm.m.
/6.3,c0 /~1 * A.v@W94,03 fll
70.02 \ / \
mm \/\ k
70.m 4 I1234567891011 !213! 41516171819202122 232425262726 Z92JJ
T [1154S) Bask
Figure 56. Passenger car, 100 Ian/h.000821-88-car(l 16JJ)
tm.m. ~ -
S6.co
94.03. / / \\
52.03- \/
60.02. / I \\s~ 2S,CU
% ~m i \w.I
12345675 91011121314151S 1718192cI
T(I15Os) +0s m
. ..— ,
Figure 57. Passenger car at 116 lcdh
41
5 Some further measurements
5.1 Measurement site
All measurements reported in this chapter were carried out along a motorway. Themeasurement site was a checkpoint to test the weight of heavy vehicles. There was a 2 mhigh earthberm along the motorway. The unscreened measurements took place in a 15 mgap in this berm just in front of the bermfront.
5.2 High exhaust
Normally it is not possible to distinguish between exhaust and engine noise by usingsimple pass-by measurements. However, there is one exception and that is when theexhaust is on top of the vehicle. Figure 58 and 59 indicate that there is a qualitativeagreement between predicted and measured behaviour.
Viared Konlrollplats, 2000-08.08, at the opening100, e
11 1111111 11 I 111111 11 111111
95 ; -I-;;;%:---+--:-;-: ;;}:----;--:-;-::;: III Illlhll 1 11111111 11
9rJ-;-}+ ++l+\; :---- +--; -’-_J; L:_-- _-;--:_1111111I 1111111 11
_l_~JJ~l_l__ -_~-_l-
80 -
I 111111
1 1111111 11 1111111
I !1111!1 11 1111111
65 -;-l; ;;-l; l---- ;--;; ;;; ;;; ,;----; --,-1 1111111 11 1! 11111 11
60 -}-\; -l; ;+:---- +--:-:-;;;::--_-;--;-
0 hrl=O.2 m l[lll’’ 111’55 __~--l-_l_~JJ~l-l-__- ~--r_
— hr2.1.75 m ,,, ,,, ,,, ,,— hr3.4 m 11111111111
250 500 ,.3 2000 ~
I 1 11111
J11111-----111!111111
-l_~l_r_l1111111111
-l_ LLl_l1111111111
-. LLLLI1111111111
-- r-r-l-l11111!1111
-rrrrl11111
1111-t i t-i
Ill.l-~~
1111~!! 111
)0 104Freq. (Hz) 10 m asphalt 85 kmlh u=2T3d = 2.56s) 5+(1) asles
Figure 58. High exhaust. Measured values.
Calculated pass-by at 10m from source at 3,5m height95 r
Ill lUtllthr=O,O1ll 11111u u 11111111
---- y_o-~_&r-l I Ill, ~~~ ~,-----, ---,--,- ~-,-,-,~
t..rllllll~mili 1111111111
II IAIIII1ll III 111111111
‘111111 111 111111 1!111!1111111
88 7-17 TI-----; --:- ;-:-:: ;:-----:---;--:-;-;-;-;;11111 111 111111 11111111
11111111111111111111111-_--~--_~_l_~~~~~ l_l--_--l_ l_ll-J-l-l_l_l-l661++++: , , , 111111 1!! 11111
11111 111111111 11111111
85 ! , , t , , , , , ! t 1 , , , , , ,
102 103 104Frequency, Hz
Figure 59. Simulation of pass-by by a 3,5 m high source.
!,. .
1-
,.
.. . ..-. . l.r_..-_.. ... —’
42
5.3 Screening of engine noise
In 3.2 some measurements were reported from measurements on an airfield. Below someadditional results are reported from measurements on freely flowing motorway trucks.Figure 60 seems to have the same behaviour as figure 58 which indicates that also thistruck has a high exhaust. Both figures indicate clearly that the high microphone positiongives lower levels at low frequencies. This supports the hypothesis that engine noise isscreened at high positions.
Viared Kontrollplats, 2000-08-08, at the opening
I , r90 .l-J-LJ JAJL----L--L-L-L JJJLL---- L-- LLAJ1LAJ1.
11111111 111111111 1111111111111181 111111111 111111!1
Pi
11111! 185 _;-l-:; JJJ ;----:- - -L JJJJ L-.---:--L-: -~;:;:-
11111111/,’’’’”
1181111111111111 111118 11181111
8 ‘v’’’” ‘ ‘ ‘-.+
i\
++----+--+- +-111
Ill 1!1111111 Ill
7 --t- t--t--t-Z 111~ 11
~711
--1- ---- -r-T-
co 111Ill
114+111111111111
-1 -i-l-l11111111
11111++ +-4+111111111111111 1
65 -;-;-;;;;;;----+--;-+-11111111 Ill!1 111111 Ill 11
60 -;-;-~J-’-’+~----+--;-+-11111111111111 111111111
--- hrl.O.2 m111111111 111!
55 - -- l-_ L- J- LJJJJ L----
-0- hr2=l .75 m “’’1’’’’’” ‘“+ ht3=4 m
111111111111111111 1111118
50 t t , , , , , , , I I I , , , , I 9 ,25 50 ,02 250 500 ,.3 2000 4000 104
!1117-111111111111111----111!
ti-lt-111111111111
T_tlT-111111!11111
T_17T111111111111~71T -
Freq. (Hz) 10 m asphalt 74 km/h ~=2*T3d = 2.92 s) 4+(1) axles
Figure 60. Screening of truck engine
Viared Kontrollplats, 2000-08-08, at the opening85
80
75
~ 70~-1w03 65
1)! 111111111111
Go :-;-:;;;:!1 111111111111
111111111!
111111111111181
----L--L-L-I- L11111111111111!
Ill
\
11111111l-u-----l---l--l- -1 -1-1-1111 1111111Ill 1111111Ill 11111!1111111
55 -!1111111
--- hrl. O.2 m
P
111111---~--~-~,-rr ~ l-, -----,.--, --,- ~,_,
-e- ht2=l .75 m ‘;’’’’’’’”; ““
+ hr3=4 m111111 111118
11111 !111 11! 11111,
50 , , # , , ! ! 125 50 ,02 250 500 ,03 2000 4000 104
Freq. (Hz) 10 m asphalt 68 km/h (l=2”T3d = 2.46s) 5 axles
)
#
Figure 61. Screening of truck engine
Figure 62 shows the corresponding results for a passenger car. Also here we have a clearindication that the low frequency sound pressure level decreases with the height of thereceiver.
80
Lit
Ill!11
70 +-; -:111111
g~;’265 :- J.-
W 11u)”;
60
55
Viared Kontrollplats, 2000-08-08, at the openning
II 111111 11111111
A
1111111111 111111 1! 111111 1111111111 111111 1111111 111 !111111 111111 111 111!1 11111111
-L-l-LIJ-ll-11111!1
11111 1 II Ill 11111Illti 111! 1111111111111 111! 111111111
1111 T----T--T ‘T -rll TT --11111 11111111111 1111111II11 111111
J.-L_LLJ-l*-
11 111111 Ill 111111 1111 111111 111111111 IllII 111111 1 11 111111 111 LII Illltl 111 1111!1 1111
F ~ [[::::::11111111
11111 11111111111 l!ll! 1111
-+’’.-LJ!!-+!----+-- + -+-;::.!++-.---.+-- +!1! 1111
I +- nrl=
.oE&smn,,,,,,,,, ,,,,,)j ,.. --~---r--r-l--i-i, ,y----~--~-T- ~,
,0.2m , , , 111111 111111111-n_hr9=l.T5~ I I 1111111 1 I 111! I
111 111111 111111Ill 1!!!11 Ill 11111
-25 50 102 250 500 103 2000 4000 104
Freq. (Hz) 10 m asphalt 108 km/h (T=2*T3d = 2s)
Figure 62. Screening of car engine.
5.4 Measurements with a barrier
As the measurement site used in 4.3 happened to have a barrier with a height of 1,75 msome measurements were made to see whether barrier measurements could be used tofind out the positions of the equivalent point sources. Unfortunately the barrier had a lowprotection fence in front of it and together with a grass covered barrier top it turned outto be difficult to use the data. The fence obviously affected the high frequencymeasurements considerably .Nevertheless some of the measurement results are reportedin the following 4 figures. The position hr= 1,75 m refers to a reference measurement onthe same vehicle but before the barrier starts. The height corresponds to that of thebarrier.
Viared Kontrollplals, 2000-08-08, barrier (hr6 is at the line of sight)1 I 1 I i , , , , 0 , , , 0 0 , 1 , , 1 1 1 I (11 111111 1111111111 111111
/’%” [ \ :[[\\\11111111..
11 111111 1!1 111:111>11,4111~
75 {-j-~jj~j~----+--+- ~-r~m77r--.+-~--~-~-~ +~j~11111111 Ill 1//-!!11 y;;;;;:;;
\
70\\;;’’’’”
--*,--T’-+-:-+;{+,x, ,,, ,,,,\
s ,>: ::::;:
: 65uW
6011111 ml-al l’\lllll
50
;::::; m-------------1
~> hr7=3.3 m ~;:;-Y- hr2=l .75 m Itlltllll 111 11111’, , , a , I ,
25 50 102 250 500 10’ 2000 4000 1o“Freq. (Hz) 10 m asphalt 108 kmlh (T=2”T3d = 2 s)
Figure 63. Measurements on a passenger carat different heights behind the barrier.
-—,
44
Viared KcmtrcJp4ata, 2flWB03 ,bdnfer(ls6 iaatthelirwofsi@t)
~ \-l- LL1-lJL_-_:_-+_l_Li !.lJL___;_;-~JJJ~i1111111 1111111 181111
I 111111111 11111 !4111 1,, ,,1 Illlllllkl ,,, ,,, ,,, , ,,, ,
~u______;-i.iii_l i___ i--T_;!’
25 50 ,.2 250 SX11032C IYJ4C?33104
;;;;;11111
777r8-11111811111111111111
+++1-1-11111111111111111111
,J J L L1.
k
1111II!
<b- - ,.11 I\{
J ~li>
Ftsq, (Hz) 10m@talt 74 knvh(E?T?d. 2.92s) 4+(1) axlaa “-
Figure 64. Measurements on a truck at different heights behind the barrier.
Viared Kontrollplals, 2000-08-08, banier (74 ktih, 4+(I ) axIes)
-:~
-- +-+-+ + -, ++-,---- ,-- *-,-++ *I+.
25 r---------- ;--; -; -’-’-’~ ~’----~--}-~-}::~;
-1E, 11111141111 Itlil 11 II; ii;li’=, 1111111111! 11111111 ,, ,’,
~20 L- I- LLLIJ L--- L- J-* J-I JILI-— ——I— — L—I—L. J,!1 1111111111 111111
0.ml
.Freq. (Hz) hr2 (raferance)=l.75 m & hr8 ia al the fine of sight
Figure 65. Measurements on a truck at different heights behind the barrier. Soundpressure levels relative the unscreened reference position with sign changed.
Viared Kontrolfpfats, 200Q.08-08, Carl 00, 108 kmlh25 11111111111
--*-- l-i-l-,- l* F, ----l-- e-,-p+~j+
1 [111111181111 [111
.=
n.In 11111111
F&
111----111IllIll
-1- L I.Ill!11111==--
%l---T lTllTr, r,----,-- ~ -r~
Ki!lll, ,111 l,, ,,r 11- T1lYI III 1 1 1! 11111111
n.(n I LLLLIL ---J-J -1 J_l JILl__ --l-- L_l_
Ot: -1-l 11111 1111111111 1 ,%
Ill11[111i I:111II!l-u.111111111rm-111IllLIJ.
*1
11111! 1111 1111111111111111111 1111,1
;;~p
Y-5 F -I- I- I- I- I-I I----*--- ++-, -4+ M---- ;--:-,- *+*,111111!11 111181111 181111
1 111111111 11! 1111111 11111
-10 l-l-! LI-I-IL ---L --1-1 _l_l_ll Ll__-- I-- !-_ l_LLL l_l! , , , ,, , , , , t , I ! I , , t , t
2 50102
250 5W103
2LM0 4000104
,
Freq. (Hz) hr2 (referance)=l .75 m & hffi i3 at the tineof sight
Figure 66. As figure 65 but on a passenger car.
45
5.5 More examples at another test site
Figure 66 shows another test site. The width of the road to the fws grass was 2,6 m, theditch was 6,1 m wide with its deepest point 0,7 m below the level of the road surface.The flat grassland was 0,2 m below the road surface and the microphones were 9,75 mfrom the ditch that is 18,45 m from the,nearest wlieels. The ground imped~ce wasmeasured and it turned out to be quite soft,rthe flow resistivity was 160,kRayls. Thecalculations were carried out according to the latest Nerd 2000 method using twodifferent source models. One used three source heights: 0,01; 0,15 and 0,30 m, and the
Figure 67. Test site. The truck is in its right path.
A typical registration of a pass-by is shown id figure 68. The upper curve is a referenceclose to the road while the three come from microphones in the stand farthest away fromthe road. In the following we will only look at the difference between 4 m and 0,5 m.
Volvo Bori%, 2000-09-05, 2.6 m asphalt + 15.65 m grassfield with ditch
80 1 I I 1 1 1 I 1 1 I I I I I [ 1 I 1 I 1 I 1 I 1 1I 1*.11111 !11 1111! 1,111 1111111
/
Iyllll 111111111 lltllltlt
‘?! ‘
,5 ;--: :’’i::;: \ : ;“’’” ; : :::::----------- ~-r-L.LJ Jl !____ ~-_-l-._;_ ; -,-,-,-,-1- 111 111111,
Ill ,111 111111111 111111111111!11 111 !11111 1111! 111
111 111111I-I-----1---L-L-I-I. -I-IL
70 -:-:j::-1~,:: I I I I ; ; #\----:--:--l-Wl-,., ,,, , 1111 11111111
‘;5 50 102 250 500 103 2000 4000 104Freq. (Hz) car023, near track
!,.. .~.
1.~.
‘t.
Figure 68. A typical pass-by registration.
._— .—— ., /...
46
20
15
mv
.
g. 100J
%
45
du.!u)
o
-5
._ ”.”
U)oaoomooloooo Lnoooooooooo 00000OJm=rmfocoomlmoln I-00C900UIOOOUY 00000
7 77 ol am w Uy w co o a Wo m 1- 0 0 m o 0-1-l-mJt3Jm*ln mmo
Frequency, l-lz
Figure 69. Measured differences between 4 m and 0,5 m for 6 different passbys.
Figure 69 shows measured differences for 6 pass-bys. It indicates very little differencebetween the passenger cars and the trucks. The only exception is between 1000-4000 Hzwhere the difference is smaller for the trucks. In figure 70 a comparison is made withdifferent source models. The agreement is rather good between the 3-source model andthe passenger cars. However, it is rather bad for trucks around 2000 Hz.
20,0
15,0
Emo- 10,0Jwu):
: 5,04wto
0,0
-5,0
:
\
U)cuoomoolnooo In Oooooooooo 00000Olmwu)coao(uu)oul l-oo@loomooouJ 00000
rt-. oJoJc9*uy facoooJ@omP Oo(r’joo.e. oJoJlxJw u-j @mo
.
1-
FrequencyjHz
Figure 70. Measured and calculated values from 3 car/truck pass-bys at the test siteshown on figure 67.
47
20,0
15,0- –
m-a
.
~. 10,0 -–
:wv)
; 5,0- –-4Illu)
0,01 ~.
-5,0- r
,,t’.
Frequency,l+z
Figure 71. Measured and calculated values from 3 truck pass-bys at the test site shownon figure 67.
Infigure71 different sourcemodelsarecompared with3truckpass-bys. Upto2000Hztheagreementis verygoodwitha sourcemodelusing twosonrces, one at0,15 mandoneat 0,3 m. Above 2000 Hz figure 70 indicates that the result improve by adding one moresource at 0,01 m.
-..
.s . . . . . ,. . ... . . . . . . . . . . . . . . . . .. . . . . . . . .,....,,=,, .-
.,. ..,, ,., . . . . .. . . . . —-
:.. .
48
6 Measurements on stationary vehicles
6.1 Description of measurements
The car was located on a grit surface and grassland respectively. The engine was runidling at 3000 rpm and the measurements were carried out at 7,5 and 15 msimultaneously on 4 different heights, the lowest of which was 0,3 m.
6.2 Analysis of the results
In figure 72 a comparison between calculated and measured results are shown. The freefield + 6dB level has been taken equal to the level above a grit surface which is probablynot quite correct at high frequencies. The measured values are from measurements on thestationary car on grassland and the calculations have been made accordingly.
‘\i,
Source height I
---- I/0,3 /
i,
\ /0t
/‘o
\/Measured , 00’2
/0 +----+.----
6’ +0,10 /
+
-1- /-
/0,05
0,0
I I I
10’ 102 103 104
.
Frequency, Hz
Figure 72. Level re free field+ 6db 15 m in front of a Hyundai passenger car
10’
,Ill 111111 1! 1111111 Ill IIllt11!111!11 111 111111 11111111111 111 [11 111111111 P!111!11
I1
1 11! 111 II I ‘1 Ik1 I I I I I I Measdx! 1-!/1111
. -$ -l- & l- !-l------ l--- +--l-+-l-l-l-l ● l- L~-l. L-k-+ -L. 4-i-4
1 ii 111111 11111 111111 1lfltllttl 1111)111- )/1 1,1/1111
-----l---i--l-Ill liltiiIll 1111111111111!1t II 111111f 11 111111111! 11111
111111
----4---4--1- - $ -l -l -l -l-l----- l--- +--l-+1
f
-,+4 -Z-Z-Y-L11 111111 1111 ‘1111 1
111111111 Ill 111! rdiii!i1111 111111 111/ 11111 11 I.l .1111111 11(111. 11 illllt I
111111 ;s=6,5’? ; : : :II 111111 111! 111!
---- J_-d_-l- J_ L-L LLl_____ L-_ L- J_l J-l-lJJ _----l--- L- 1.-l-l111 111111 111111111 !1111111 1111(1 111111111 11111111 111111 1! 1111111 11111111 11! 111 111111111 11111ll!ll! 111 111111111 11111111111111 11111 !111 11111, , , I , , , , I I , , t t , , , , , I , , t , , t
102 103
Frequency, Hz
Figure 73. Difference between 7,5m and 15 m at the receiver at 0,3 m.
5
0
mu
m--5
-0w+
: -loGalalJ=al: -1593
-20
-25
10’
_lJ11II1]IIIIII
-lJII)1
4!11
11! 111111 111111Ill 101111 111111111 !11111 1! 1111111111111111111!11
11 I 1 I@l&[\[[\
-__-;- 1 I I 9I LL-----J--L-1-LJ-1.111111111 111111111111111 11111111 111111 IIll 111111Ill 111111I 111111
-- ;--:-J-LLLLL11
11
Ill
---- 1
111 111111111 11111111 IAII III11
--_- L--~ -l- J-l- LLl-l--L_- f_- f-~~{-----1111111111! 1111111111111111 111 l\ll
111 l\tl
11111 !11111111 !111111 !11111
---- L-_ J- J- J_t-LL Ll --111 111111Ill 111111111111111111111111111111111Ill 111111
---- L-_ J_ J- J_l_LL lJ --Itl 11111111111 !111111111111111 111111111111!11 111111Ill 111111 111111I , 1 , , ! , , , , , f ,
\
1111111111111111
--- L-- L- J-LJ 1-111!11111[1! 11111111111111111111
--- L-- L- J- LJ-l111111111111111111111111 (
102
104
I I 11111!11II 1111111111 1111111111 1111111111 11111111It)J-----;_::;;:_::;;:.11 Illllltl11 1111111!11 11111111!1111
11II 11111111111.IJ-___-I---l_ L- LIJJJ.1111 I11 11111 8!1 I
II11 11111111111
11 Ill 11111
11 11811111!t 0: :1; ;[; ;
11111111, t , , L103 104
Frequency, Hz
Figure 74. Level re free field +6 db at 15 m and 0.3 m receiver height, 150 krayls and0.3 m source height
Figure 74 indicates a very good a~eemeht at medium high frequencies. However, theagreement is not good at low and high frequencies. As to the high frequencies analternative model using sound absorption might be used in stead. In figure 75 the soundabsorption of the two ground types is shown and in figure 76 the result is illustrated. Itseems that the ground absorption models in this c,aseworks better than the propagationmodel.
1
0.9
0.8
ucg 0.3u-l
0.2
0.1
0
——. . ———. —
50
,
102
1 1! 11111 IO”= dlffusei i i i i i ii1 111111111 11111 I I I - = perpenhicularl I I I I I I
----- __ ;_---.-; --_lr__; _-; -+- ;+ -;-- -----_; -.---+ ---; _- L-l,-- ! Al
I 11111!1!1
1I
1t1
I
1 Y
I 11 .& ..)’,,
11! 111119’:::
------- ‘~_-._-.l--.-l 1 I l-l I 1~-, --,-, ~,-1--------~---- +n --,- ~- ;-r-,-r
11111111 ~1 11111111111111111111!
----- --r---- ,--- r -<--,-q-l-< _, ----- ~,--$~:::::l --- ~---,--t-t- ~-1-~
1[1 [1111 111111111111111111111
------- >----1 ---l---l--l-+-l. 4,lo-:___; ~ I :::;:- 1----+---!--+- +-l--l-l-111!1 1111111
1 !8111
II11 1 /’7
: ~>; :1751111 Yls; ;;;:’” 1},1----- -- l-----l --- L-J -J -- _--l----J--J-- L- J- L&lLL
II , C)<-; ;-:-- , , , ,;~;:::: II 1~:1:
!111111
I1
1111111
11111 1! 11111!1111111111111
-------1 ---- 4 ---I--+-4-L .-l-b
, , , 9 , ! ! I , , , , I
103 104
Figure 75.
Frequency, Hz
Calculated ground absorption for grassland and grit surface respectively.
12
10
8
6
m
‘- 4aoc
$2~n
o
-2
-4
-6
10’
Difference gravel-grass at 7,5 m
/2,5 m, measured,,, 4 m,,<me}st
102 103 104Frequency, Hz
Figure 76. Difference between grit and grassland using statistical absorption theory instead of propagation theory.
51
7 Determination of SEL, LpFxnaxand Lw
7.1 Difference between SEL and LpFma
The prime descriptor of road trafilc noise is Lw. This means that the most 10gicalmeasurement quantity for individual vehicles should be the sound exposure level (SEL).However, for practical reasons it would be convenient to measure LPFmax and to calculate
SEL as SEL measurements require more from the test environment. In order to be able todo so we need a source model which works well enough. Using the simplified modeldescribed by eq. (1.2) we get the differences between SEL and LPFmax as shown in table G
for passenger cars with 2 axles 2,5 m apart. For longer vehicles with more axles SEL willincrease more than LPFmav
Table 6 Calculated difference between SEL and LpFmm at G 10 m and V= so ~
Range of integration SEL - LpFmmA 1,5 a (1,97 radians) 1,7~ 3 a ( 2,50 radians) 2,7+ 5 a ( 2,75 radians) 3,1
A 10a ( 2,94 radians) 3,4+ 100a ( 3,12 radians) 3,6
Table 5 shows the result to be expected assuming that the tyre/road radiation isomnidirectional in the horizontal plane and that the distance between the two wheel axesis 2,5 m. From figure 77 we can see that the point source model seems to workreasonably well for the frequency range 200-1000 Hz. Within this range the difference isbetween 2,3 and 2,9 d13compared to a calculated difference of 2,7 dE. The higherdifference around 2000 Hz probably depends on the horn effect between tyre. Moresound power is radiated forwards than sidewards.
5,5
5,0
4,5
4,0
3,5
# 3,0
E 2,5u.~ 2,0
J1 1,5w(0 1,0
0,5
0,0
-0,5
-1,0
-1,5Lnt.noomoomooo Inoooooooooo 00000N ~-qlnco coomlcoo ml-o Omoomooomooo 00
m s-7-,1- ml fNm-i-u)co moNcDoml-oo C900l-1-l- fNoJc9-a-mca coo
Frequency, Hz
Figure 77. 9 pass-by measurements on passenger cars at 50 * 3 km/h and 10 m distanceand 4 m microphone height. SEL integration during+ 3 a
..,,.”
;,-!“
-..
- ——. .- ... ,,. . ,,,. ... . . . . ..- -“.. ,,, f,..~. ... ‘., --- .--— ---
.—. .—— —
52
Another conclusion from figure 77 is that it is not possible to calculate the soundexposure level from the maximum level without introducing some directivity in thehorizontal plane. In addition the maximum sound pressure is difficult to use in any case.As was shown in 3.7.2 the maximum level will occur at different times or positions fordifferent frequencies. Thus, even in the simple case for passenger cars, it seems moreappropriate to use the sound exposure level than the maximum sound pressure level.
In figure 78 the corresponding pass-by measurements on two medium trucks are shown.we can see that the curves are quite different compared with the passenger cars.
4,0 , m 1
3,5
3,0
0,0
wmaocooomooo KJoooooooooo 00000ml ~--lnmwoolwoul I- Oomoomooo U300000
m ..70JoJcf)d-uy WCoonlwom. Oo moo. ..nlnlm% Ulco coo
Frequency, Hz
Figure 78. 2 pass-by measurements on medium trucks with 3 axles at 53 and 60 kmrespectively and at 10 m distance and 4 m microphone height. SEL integration during ~ 3a.
7.2 Calculation of LW and LPF~~X
According to eq. (1.5) the sound power level is obtained from
Lw = LE -W~ – C(v) (6.1)
where C(v) is calculated theoretically using a point source model coupled to propagationtheory. Correspondingly we can calculate the maximum sound pressure level from
LP~mx= Lw – cm(V) (6.2)
,
In table 6.1 below these calculations have been carried out modelling the vehicle with 3point sources at the heights 0,01; 0,15 and 0,30 m and assuming that the ground surfacehas the impedance 20000 kRayls. For the maximum sound pressure level the distance ofcalculation has been the shortest distance, that is 10 m.
53
Table 7 Measured and calculated values for a passenger car as reported in figure 64.Calculated fromsource/propagationmodel
Frequency Lw– SEL LW- maxi%
2531,540506380100125160200250315400500630800100012501600200025003150400050006300800010000
A-weighted
C(50)23,923,923,923,923,923,923,923,924,024,024,124,224,424,625,025,526,327,428,428,126,425,225,927,427,128,128,9
cm(50)25,725,725,725,725,725,725,825,825,926,026,226,526,927,528,228,828,828,127,828,727,726,828,728,928,529,930,6
Measured Calculated9 pass-bys at 50~3 Ian/h
SEL(El
69,467,769,973,068,664,862,961,662,362,664,362,961,662,863,064,967,366,063,460,458,555,252,650,047,144,240,873,5
(i&5,35,126,264,186,6
4,483,172,842,561,421,691,551,021,441,261,571,561,661,421,371,011,3
1,551,711,952,041,88
LPF-dB
69,667,769,272,468,564,261,960,260,260,962,360,759,360,661,663,365,563,159,556,855,451,349,846,844,242,039,171
LwdbB5,5 93,35,3 91,66,7 93,84,2 96,96,7 92,54,7 88,83,7 86,82,6 85,52,5 86,31,4 86,62,7 88,42,5 87,12,2 85,92,5 87,42,3 87,93,2 90,42,2 93,62,4 93,52,3 91,82,3 88,52,2 85,02,0 80,52,1 78,42,3 77,32,9 74,23,0 72,32,7 69,7
LPF-dlil
67,665,968,171,266,863,061,159,760,460,662,260,659,159,959,761,664,865,463,959,857,353,649,748,445,742,439,172
Table 7 shows that the standard deviation of the sound exposure level is significantlysmaIIer than that of the maximum leveI. This is another indication why it more suitable towork with sound exposure levels. The results are also illustrated in figure 79.
—- ——
54
75,0
70,0
65,0
%? 60,0#
EL= 55,0-1
50,0
45,0
40,0
_ Calculated *
‘k \
35,0 f
Frequency, Hz
Figure 79. Difference between measured and calculated levels for a passenger car.
From figure 79 we can see that the agreement is quite good, possibly with the exceptionof 1250–3150 Hz where the calculated values are systematically about 2 dB higher.This is probably due the homeffect, [9], between tyre and road surface. As more energyis radiating along the path of the car the maximum level which has been calculatedperpendicular to the car is overestimated as the sound power has been distributedomnidirectionally.
In order to improve the result for 1250-3150 Hz it is possible to introduce a directivity tothe earlier sound power level without changing the sound exposure level. If, e.g., thefollowing sound power level is used
Lw + 7abs(cos(q)) – 1,7 (6.3)
the maximum sound pressure level perpendicular to the vehicle will become 1,7 dBlower although the SEL-level will remain the same.
55
8 Discussion and conclusions
The measurements in clause 3.2 and 3.3 indicate that the effective sound source of a carhas its centre close to the nearest wheels. For trucks this centre seed to be closer to thecentre of the car. Assuming a shortest meas~ement distance around 7,5 m a variationbetween these two distances will cause an error in the sound exposure level of about 10lg(7,5/6,5) = 0,6 dB. Because of this problem it is not recommendable to measure at tooshort distnces.
The vehicle as sound source is directional in the vertical plane. Between 100 and 800 Hzthere seems to be some decrease of sound at all positions above the bottom of the carbody. This is probably due to screening of the engine. Maybe the result will depend onthe position of the exhaust but that has not been tested. At high frequencies there seemsto be an increased directivity upwards. Because of the horn effect this directivity is mostlikely most pronounced in the direction parallel’to the wheels. Both effects seem to beless than about 2 dB for distances and heights practical to use for emissionmeasurements.
The vehicle is also directional in the horizontal plane. The difference between SEL andLPF.Uvaries with frequency. The time histories of pass-byes shown in 3.6 also verifies afrequency dependence. At low frequencies interference effects between correlatedsources may be the problem. At high frequencies the dnectivity of tyre/road noise affectsthe result.
The time when LPFn~ is obtained varies with frequency. Thus traditional maximummeasurements are not suitable for frequency band applications.
Low frequency background noise is a problem below about 63 Hz. It seems to be a goodand practical solution to use a low microphone position for these frequencies.
The measurements support the wellknown fact that the tyre/road noise source is verylow. At high frequencies the source is probably only a centimeter or two above the roadsurface. At low and medium high positions the source height is not as critical as at highfrequencies. The measurements on the stationary vehicle in 4 indicate that the enginesource is also very low. At very low frequencies, below about 100 Hz, the location of theexhaust mouth is important.
The significant frequency dependence of the difference between SEL and LPF.mseems tomake it worthwhile to measure both quantities. On the other hand the maximum level has.a high standard deviation and it is not always relevant for long vehicles.
With a proper source model it is possible to calculate the sound power level from pass-bymeasurements, at least in the direction of propagation. If the directivity is known themaximum sound pressure levels can be calculated from the sound power level.
The ground attenuation illustrated in clause 3.8 will be significant whenever we use lowmicrophone positions and have some “soft” ground in between. Unless all measurementsare restricted to propagation over “hard” surfaces only it is necessary to use rather highmicrophone positions. If these positions are too high directivity effects may affect theresult.
,.-.-
-.. .,. ., . .. . .... ....... . .. ....>. .,,5...... . . . . . . . . . . ..?,., . . . .,. ——.— — .-
— — —— ——.——
56
9 Comparison measurements using Nordtestmethod
9.1 Introduction
A first proposal for Nordtest method was elaborated. The measurement method wasaccording to the method given in annex A. However, the evaluation procedure was notdecided upon until after the measurements.
It was decided to carry out the measurements at a suitable flat road section with anaverage speed around 50 km/h. The road surface should be dry, in good condition andwith asphalt concrete. It was also decided to concentrate on light vehicles in order to geta sufficient number of vehicles. VTT did not carry out any measurements according tothe method. In stead they used some older measurements of which only 3 could be usedwithin the frequency range 50 t 2,5 kdh. The microphone height was 1,5 m in stead of 4m and no frequency band data were taken for LpF~a.
The measurement results also indicated that the low microphone position at 0,4 m may beis not necessary, at least not for passenger cars. However, too little data at present isavailable to extrapolate that conclusion to heavy vehicles.
Traditionally A-weighted sound pressure levels are presented as a function of speedusing regression analysis. In the present Nordic prediction model the SEL dependence onthe speed follows 25 lg(v) and 30 Ig(v) for light and heavy vehicles respectively above 40and 50 km/h respectively. The problem with this presentation is that we assume a certainbehaviour, that is a constant slope, which may not always be true, in particular not ifengine noise and tyre/road noise get different weighings. For trucks we have a breakingpoint at 50 lcrdh and assume a constant level below 50. Using regression only will not beable to identi~ such breaking points.
Another disadvantage with regression analysis is that the result may depend on the speedrange used for the evaluation. The problems get worse if we require data in frequencybands. Each frequency band must have its on regression line and breaking points, if anymay vary from band to band. For these reasons the Nordtest method recommends apresentation primarily vehicle by vehicle and secondarily as energy average determinedfrom all measurements within ~ 2,5 km/h. Using a slope of 25 lg(v) at 50 km/h thiscorrespond to a 1 dE difference between the extremes of the range.
57
9.2 Results
In the following only the results at 50 km/h are reported. All SEL-values have beencorrected to correspond to an angle of integration corresponding to ~ 5 times themeasurement distance.
Figure 80 and81 indicate that the Icelandic results deviate from those of the other Nordiccountries. A possible explanation is that the the conditions are different. There are e.gmany more terrain vehicles on Iceland. Figure 82 indicates that the measurementuncertainty improves at low frequencies if the speed interval is increased. This could betaken as a proof that a very large number of vehicIes are required in order to get accuratelow frequency data.
50 km/h+2,5km/h
80,0 , I I I I I I I I I I I I I I I I I I I I I I I I I I I
55,0
50,0
45,0
40,0
Frequency, Hz
Figure 80. Normalized sound exposure level, LE,lo~.Energy average of all vehicleswithin 50 Ian/h t 2,5 kmfh.
—--i,.. --7— -----
58
SEL, 50 km/h,+- 5 km/h
80,0
75,0
70,0
55,0
50,0
45,0
40,0
bx r I I I I I I
! ! I I I I I
I I I I I I I
I 1 l+slm,~+ Delta
I 1 I I I I I I I 1
I I I I I I I I I Im
I I I I I I I I I I i
Intqoo mootno 0001 WU3cowocucoow
z . . . CNcd
U)ooooooo 00000000 -0I-00C300LO0 Oomooooo 0)CO-3 u) al co o N a o In - 0 0 co o 0=
.-. Cumlccl=tu)cocoo ~.—
!?4
Frequency, Hz
Figure 81. Normalized sound exposure level, Lfi,lO~.Energy average ofall vehicleswithin 50 Icm/h~ 5 kndh.
Sound exposure level
10,0-
9,0 t- —
8,0-
7,0
6,0 ~
5,0-
4,0- —
3,0- —
2,0- — —
1,0
0,0
, ,
m u-)-o o m o 0 In o 0 0 to o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 *N =tU-Jmmoolao O.oocooom Ooolnoooo 0<
z -r. cuNmwlnuJcoo OJcoou).oocg 00Frequency, HZ l--w a ccl -3 In mm o
Figure 82. Standard deviationoftheenergy averages reported in figure 80(excludingVTT)and81.
SEL-LFmax, dB
2531,5
405063
80100125160
&
200 &lrn
250315
s3
~ 400 Q.: 500
; 630 #~ 800
0x
k;~os3
160020002500
31504000
500063008000
10000A-
LpFmax, dB
co w s $. Cn m mo Cn o c-n o m o-1 , 4 , i
L-----L-----L-----!-----+-----4------I!-----i------i------:-------l-----;------l
l------i------i-----+------l-----+------l-1------i------!------:------:-----+-----i
I:;------,------,-----+------+------:----------.-j----.-+.----.-:----.--~------1 -----
---- --l--- ---:-- ---- ;----- -: ---- ---:- ----11w:--------.-.---,-.----..-:------{------:-----------------------------------:-----------l------l------l- --- .- +-. ---: --------
J-----------: --- --. -.: ------: -. -. .----:--- --1I
l------i------i------l------l-----:------l
I------~------:------;------:-----;-----------1---- -J--- ---:-- ----l-- --- J-----, I 1
1------------------------l----- J-----I I I I
----- -1 ---- -- 1------1 ------1 ----- J, I 1 1
-----!
-1------~------i------!------:-----ti-----i---- .---1------1-- ----1 ------1 ----- J------
I 1 I I 1
----- -1----- -1 ---- -- 1--- --- 1--- -- J-- ---I I I I 1
----- -1 ---- -- l--- --- l-- ----1- -. ----l -----I 1 I 1 1
... !, . . . . . ,., , .“, - ,-’ : .>” ,., .,-
.—— -.
60
50km/h k 5 kmlh
80 a , , , , , I I 8 , i I t 1 , I , , I11111 !11, 1111 ,1,,, ,!, ,,, ,,11111111 Inn, n,, 1,, ,,, ,,
75- :I:y,w:;:;w: :;::::::;:
70
65
50
45
40
35tnoNW
0000008omul
00ma Soo. . N %’Coom too. . N-t
000
%0Wo
Frequency, Hz
Figure 85. Normalized maximum sound pressure level,vehicles within 50 km/h ~5 km/h
LPF~a,lo~.Energy average of all
LpFmax
12,0
10,0 TPQJ=+45-55 km/t
i
I
—
—
—
—\
—
—
—
—
1’8,0
6,0
4,0
2,0
0,0
——
—
—
<
T~m-oocooom OoolnWU-)(DCOOOJCQO !nl-
FI --- CNcvm
00000Ooc?loo-mw.OJo
Frequency, Hz
000000000 OuLnoooloooo OoaCuwou-). oom oo~~-wNm-d’wJw mom- .-
Figure 86. Standard deviation of the energy averages reported in figure 83 and 85.
61
10[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
References
Vagtrafikbuller, nordisk berakningsmodell, reviderad 1996,Naturv&dsverket, Rapport 4653FHWA Traffic Noise Model, FHWA-PD-96-O1O,DOT-VNTSC-FHWA-98-2, US Department of Transportation, 19981S0362:98 Measurement ofnoise efitted byaccelerating roadvehicles -Engineering methodSS-1S0 11819-1:97 Acoustics-Method for measuring the influence ofroad surfaces on traffic noise. Part 1: Statistical pass-by methodC.I. Chessell, 1977. Propagation of noise along a finite impedanceboundary, Journal of the Acoustical Society of America 62,825-834Tomas Strom, Hans Jonasson, Bestamning av bulleremission frilnstadsbussar, SP RAPPORT 1998:29.H.G. Jonasson; 1973, A theory of traffic noise propagation with applicationsto L,~; JSV 30,289-304J-F. Hamet et al, Acoustic modelling of road vehicles for traffic noiseprediction: Determination of the source height, ICA-ASA conngress,Seattle, 1998.W. Kropp, F-X B6cot, S. Barrelet, On the sound radiation from tyres,manuscript, Chalmers, Sweden.Birger Plovsing, Nerd 2000. Comprehensive outdoor sound propagationmodel. Part 1: Propagation in an atmosphere without significant refraction.To be published.NT ACOU 104, Ground surfaces: Determination of the acoustic impedance.
— .
.- . .X . .
62
2000-11-0663
ANNEx
Proposal for Nordtest method
Vehicles: Determination of irnrnission relevant noise emission
Contents
11.11.2
2
33.13.2
3.3
3.4
3.53.6
3.7
3.83.93.10
44.14.24.34.4
55.15.25.35.4
66.16.26.3
77.17.27.37.47.57.6
8
9
SCOPE AND FIELD OF APPLICATIONGeneralMeasurement uncertainty
Normative references
Definitionsmeasurement distance, dsound pressure, p:
sound pressure level, Lp:
maximum sound pressure level, LPFmax:
normalized maximum sound pressure level, LPFmax,lom:
sound exposure, E
sound exposure level, LE:
normalized sound exposure level, LE,lom:frequency range of interest:background noise
InstrumentationGeneralCalibrationVehicle speed measurement instrumentationTemperature measurement instrumentation
Categories of vehicles and road surfacesGeneralVehiclesRoad surfacesDriving conditions
Test siteGeneral requirementsSurface between the road surface and the microphonesBarriers and reflecting objects
Test procedurePrincipleMeteorological conditionsMicrophone positionsMeasurementsCriterion for background noiseEvaluation of the measurement results
Statement of the results
Information to be reported
Annex ABibliographyAnnex B Format for test results
646464
64
656565
65
65
6565
65
656666
6666666666
6767676868
68686969
69696969707071
71
72
:’..-
. . ..—-—— -----,-.>..,, .. .., .. ... .. ..?-. -. .
————.
1
1.1
64
SCOPE AND FIELD OF APPLICATION
General
This NORDTEST method specifies how to determine the noise emission of vehicles toobtain input data to be used in prediction methods for road traffic noise. The vehicles aremeasured one at a time. The method is applicable to all types of operating conditions andto all types of vehicles on all types of road surfaces provided that the measurementconditions are under control and reported. Many of the features of this NORDTESTmethod has been taken from ISO 11819-1.
1.2 Measurement uncertainty
The measurement uncertainty is given in table 1. The reported uncertainty is an expandeduncertainty based on a standard uncertainty of ORmultiplied by a coverage factor of k= 2,which provides a level of confidence of approximately 95Yo.The measurementuncertainty refers to the energy average of at least 20 vehicles within the speed intervalto be investigated.
Table 1 Measurement uncertaintyCR Expanded measurement uncertainty
25 Hz 6 f 1231,5-63 Hz 4 ~880 Hz – 1000 Hz 3 *61250 – 10000 Hz 2 f4A-weighted 1,5 f3
Note The measurementuncertaintyhasbeen estimatedfromcomparisonmeasurementscarriedout at 4 differentplacesby 4 differentNordic laboratorieson vehiclesof type 1aat 50kmfh.
2 Normative references
The following standards contain provisions which, through reference in this text,constitute provisions of this Nordtest method. At the time of publication, the editionsindicated were valid. All standards are subject to revision, and parties to agreementsbased on this Nordtest method are encouraged to investigate the possibility of applyingthe most recent edition of the standards indicated below. Members of IEC and ISOmaintain registers of currently valid international standards.
1S0 11819-1, Acoustics - Measurement of the injluence of road surfaces on traffic noise- Part 1: Statistical pass- by methodIEC6065 1:1979, Sound level meters.lEC 60804:1985, Integrating-averaging sound level meters.LEC60942:1988”, Sound calibrators.IEC 61260:1995. Electroacoustics, Octave-band andfiactional-octave bandfilters.
64
65
3 Definitions
3.1 measurement distance, &
the horizontal distance between the microphone and the centre line of the vehicle)
3.2 sound pressure, p:
A fluctuating pressure superimposed on the static pressure by the presence of sound. It isexpressed in pascals.
3.3 sound pressure level, Lp:
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure tothe square of the reference sound pressure (20pPa)
3.4●
maximum sound pressure level, LpFmax:
the highest instantaneous sound pressure level measured using time weighting Faccording toIEC6065 1.
3.5 normalized maximum sound pressure level,LpFmax,lom:
the maximum sound pressure level normalized to the reference distance 10 m.
3.6 sound exposure, l?:
,.”
,,
The time integral over a stated time-interval, T, of frequency weighted squaredinstantaneous sound pressure Pz(t), expressed in pascal-squared seconds.
T
E = Jpyt)u’t (1)o
3.7 sound exposure level, LE:
sound exposure level: Ten times the common logarithm of the ratio of sound exposure, E,to the reference sound exposure, Eo, expressed in decibels.
where, in air, E. is 400 ~Pa2s.
3.8 normalized sound exposure level, LE,lom:
the sound exposure level normalized to the reference distance 10 m.
(2)
6s
%
. ..—— -. -. —.
--- ,.. . --.—— —. .. .. ,. .._.
66
3.9 frequency range of interest:
For general purposes, the frequency range of interest includes the l/3-octave bands withrnidband frequencies from 25 Hz to 10000 Hz.
Note. The frequencyrangeof interestmayhave to be restrictedin eitherdirectionbecauseof too highbackgroundnoise.
3.10 background noise
noise from all sources other than the source under test.
NOTE Background noise may include contributions from airborne sound, structure-bornevibrationand electricalnoise in instrumentation.
4 Instrumentation
4.1 General
The measurement equipment shall meet the requirements of a class 1 instrumentaccording to IEC 60651 and IEC 60804 and the filters shall meet the requirements ofIEC 61260.
4.2 Calibration
During each series of measurements, apply a sound calibrator with an accuracy of *0,3dB (class 1 according to IEC 60 942) to the microphone for checking the calibration ofthe entire measuring system at one or more frequencies over the frequency range ofinterest.
Verify the compliance of the calibrator with the requirements ofIEC60942 once a yearand the compliance of the instrumentation system with the requirements of IEC 60651 atleast every two years in a laboratory making traceable calibrations.
Record the date of the last check and confirmation of the compliance with the relevantIEC standard.
4.3 Vehicle speed measurement instrumentation
The vehicle speed shall be measured with an uncertainty of less than 3Y0.Measuringdevices which rest on the road surface and are activated by the passage of vehicle tyresshall not be used.
4.4 Temperature measurement instrumentation
The temperature measuring instruments shall have a maximum error of 1°C. Metersusing an infrared technique shall not be used for air temperature measurements.
46
67
5
5.1
Categories of vehicles and road surfaces
General
In order to have complete control of the measurement data it is necessary to keep track ofas many parameters as possible. In the following the minimum requirements are given. Insome cases it maybe appropriate to include even more parameters.
5.2 Vehicles
As a minimum the vehicles shall be divided into the following classes:
Main Sub Category name Objective descriptioncategory category
1 Carsla Passenger cars excluding other light vehicles 4 wheels, two axleslb Other light vehicles: cars with trailers or 4 wheels, two axles or 6
I Icaravans, light utility vehicles, minibuses, vans, Iwheels, 3 axlesmotor homes, recreational and utility vehicles
2 Dual-axle heavy vehicles. 6 wheels, two axles2a City buses 6 wheels, two axles2b Light and medium trucks 4-6 wheels, two axles
3 Multi-axle heavy vehiclesl)3a Large city buses 8-10 wheels, 3 axles3b Medium trucks 8-10 wheels, 3 axles3C Heavy trucks 4-5 axles3d Very heavy trucks >6 axles
4 Motor cycles5 Mopeds ,,.
) Trailers, if any, included
Note Category1 is equal to that of ISO 11819. The other categories are different.
Indicate also if the vehicle has studded tyres. If the observer is uncertain about theclassification of some passing vehicle, it shall be disregarded or put in a “special class”.
. .
67
—-—,.. , ,4,.,,,...-r~-~~+ . . . . . . . . . . . . . . . . . . -. . . ...’ .-..- . . . . . . .
5.3
.—. . ——. —
68
Road surfaces
As a minimum the roa
Main ISub
3 3aI 3bI 3CI 3d
4 I 4aI 4b
+=
5 5a5b
6 6a6b
I 6C7 I
8Note The diffel
i surfaces shall be divided into the following 8 main categories:Name
Asph. concr., dense, smooth (<12-16 mm) IAmh. concr.. dense. smooth (< 8-10 mm) IMastic asphalt (SMA) (max 12-16 mm)Mastic asphalt (SMA) (max 8-10 mm)Chipped asphalt (BCS) (“hot rolled asph.”)Chip seal, single (Yl), max 16-20 mmChip seal, single (Yl), max 10-12 mmChip seal, single (Yl), max 6-9 mmChip seal, double (Y2), max 16-20 mmChip seal, double (Y2), max 10-12 mmPorous asph., max 14-16mm (*20%voids)Porous asph., max 8-12 mm (*20% voids)Cem. concr., dense, smooth* 20-80 mmCem. concr., dense, smooth, * 12-18 mmCem. concr., ground (grinding not worn)Paving stones, cobble stones (older type)Cement block pavement (interlocking)
mt categories have been taken from the Nordic prediction method for roadtraftlc noise.
Indicate also if the road surface is dry, wet, icy or snow covered. In addition indicate thetemperature of the road surface. Describe or photograph the surface.
Preferably use also sub categories together with the age of the road surface and the yearlytraffic flow.
5.4 Driving conditions
Category Name Objective description1 Cruising Constant speed and gear2 Acceleration Continuous acceleration)3 Deceleration Continuous deceleration)4 Uneven Both acceleration and deceleration
1)E.g. aftercrossings,trafficlightsor speed limit signs2)E.g. beforecrossings,trat%clightsor speed limit signs
6 Test site
6.1 General requirements
The road shall be essentially level and straight.The road section shall extend at least 3 times the measurement distance on both sidesof the microphone locationThe number of vehicles shall be sufficient to get a representative sample and at thesame time small enough to avoid disturbing background noise from vehicles otherthan the vehicle under test
68
69
. The road surface shall be in good condition unless the intention is to study the effectof the condition
6.2 Surface between the road surface and themicrophones
The ground attenuation between the edge of the road and the microphone shall beminimized for any frequency band of interest. With the measurement procedure of thisNORDTEST method this requirement is considered to be met if at least half the areabetween the centre of the test lane and the microphones have acoustical propertiesequivalent to (or “harder” than) those of the road surface used for the tests.
Note It is easier to complywiththeserequirementsif the measurementare carriedout onvehiclespassingby on the lanefarthestawayfromthe microphones.For vehicleswith a screenedexhauston one side it maybe necessaryto measurein two directions.
6.3 Barriers and reflecting objects
There shall be no barriers, such as solid safety barriers, guardrails of metal beams orembankments between the path of the vehicle and the microphones. Transparent wire orcable fences are allowed.
No reflecting obstacles which may influence the measurements by more than 0,5 dB areallowed unless the obstacle is a large facade on which the microphones are mounted, seeclause 7.3.
7 Test procedure
7.1 Principle
,.-
,,’
-.
The principle is to measure individual vehicle pass-bys under representative conditionsand to obtain data affected as little as possible by the ground attenuation between thevehicle and the microphone. The method uses two fixed microphone positions, thebottom and the top microphone respectively. To minimize the risk of underestimating thesound pressure level due to unforeseen interference or directivity effects the highestvalue, after distance correction, of the two microphone positions is taken as the result ofthe measurement. All measurement results are corrected to the reference distance 10 m.
7.2 Meteorological conditions
The wind speed shall not exceed 5 rds when measured at a height of 1 m above theground.
Note 1 To minimize turbulence due to thermal and wind gradients it is recommended tocarry out the measurements when the sky is overcast and the wind speed low.
Note 2 At low frequencies the wind may affect the noise emission from the vehicle due toincreased aerodynamic noise or increased load on the engine.
7.3 Microphone positions
Select a measurement distance, d, as close as possible to 10 m. The distance selectedshall be within the interval 7,5-15 m. d shall be kept within A 0,5 m if the variations are
69
,
.
70
reasonably evenly distributed around the centre line and within ~ 0,3 m if the variationsare unevenly distributed around the centre line. If the variations are greater each vehiclehas to be assigned its own d.
Note A short distance is to prefer when the background noise is high or when theconditions on maximum ground attenuation cannot be met. Else a longer measurement distance isto prefer.
Use two microphone positions , one at 0,2 m and one at 4 m. Measure the heights alongthe normal to the surface of the average ground plane. When defining the ground planeexclude vegetation such as grass. Direct the microphones towards the tyre/roadintersection.
Locate the microphone either away from all reflecting surfaces or fastened directly on alarge reflecting surface parallel to the road. When flush-mounted its axis shall be parallelto the plane of the facade and directed upwards or downwards or with its axis pointingtowards the test specimen along its normal. The distance from the facade to the centre ofthe 13 mm microphone membrane shall be 7 mm or shorter if the upper frequency limit is5000 Hz or 3 mm or shorter if the upper frequency limit is 10000 Hz, if the axis of themicrophone is parallel to the test surface. If the axis is normal to the test surface thedistance shall be half of that of parallel mounting. In order to achieve distances shortenough it is necessary to mount the microphone embedded in a plate or board. Iffastened, the microphone shall be fastened to the test specimen with a strong, adhesivetape. Equip the microphone with a hemispherical windscreen, see figure 2.
Figure 2. Flush-mounted microphone
7.4 Measurements
Measure the speed of the vehicle, the temperature of the road surface, L~ and LP~- duringeach pass-by and record the category of vehicle and the driving conditions.
Note LPF- will occur at different times for different frequencies. Thus the measured A-weighted maximum level will differ from the A-weighted maximum level calculated from themaximum of the different frequency bands.
Start the measurement when the vehicle is at the distance 3d in front of the normal fromthe microphones to the road or earlier, but not earlier than 5d, and stop it when it is at thesame distance or later behind the normal.
In order to achieve the measurement uncertainty stated in this Nordtest method measureon at least 20 vehicles within each speed interval to be investigated.
7.5 Criterion for background noise
70
71
For each frequency within the frequency range of interest the background noise shall beat least 6 dB and preferably at least 10 dB below the level of lowest sound pressure levelduring a pass-by. No corrections are allowed.
Note The background noise level at the highest microphone position maybe significantlyhigher than that of the lower position.
7.6 Evaluation of the measurement results
For each individual vehicle, for each one third octave band and for each microphoneposition, calculate the normalized sound exposure level using the following equation:
L~,lom = LE + 10 lg
M(=F .Io,g[‘a]
10 2 arctan(5)
where
LE= the sound exposure level measuredd= measurement distance, in mw = the axle width of the vehicle (= 0,75 m for cars and 1,25 m for trucks unless otherinformation is available)h,= height of the microphone (0,2 m and 4 m respectively)ZICZ= angle of circular sector covering the line of integration, in radians
The result is given by the highest value from the two microphone positions.
Note 1 If the sound power level is to be calculated it may be necessary to distinguishbetween values obtained from the high and the low microphone respectively.
Note 2 At low frequencies wind and background noise will often influence the soundpressure level more at 4 m than at 0,2 m. Thus it is important to make sure that the highest soundpower level calculated, if derived from measurements at 4 m, is not affected by background noise.
The normalized maximum sound pressure level is calculated from
L LPF.+UW “pFInax,lom =
H
10(4)
Note For long vehiclesthis formulamaynot be as accurateas the correspondingformulafor the soundexposurelevel.
8 Statement of the results
State the result of each individual vehicle pass-by using the format given in annex B.In addition, for each frequency band, calculate the energy mean value of each speedinterval defined by a centre speed, evenly dividable by 5, ~ 2,5 Ms. State the result withone decimal together with the standard deviation and the number of measurements withineach interval.
71
>,.
-—-. . . ... ... ..r. . . . . . . . . . . . . . . .. ---- . . . . . . . . ... -7— . . . . . .,,
———— ——
72
9 Information to be reported
a) State that the measurements have been carried out in full conformity withthis Nordtest method. Any deviations shall be reported.
b) State, for each individual vehicle, for each third octave band and A-weighted, the sound power level, the sound exposure level and themaximum sound pressure level.
c) State the temperature of the road surface either as an average, or, if thevariations are greater than 5°, or for each individual vehicle pass-by
d) State, for each vehicle, vehicle category, driving conditions and speed.e) State road category.
72
73
Annex ABibliography(Informative)
Hans G. Jonasson, Measurement and modelling of noise emission of road vehicles foruse in prediction models, Nordtest project 1452-99, I@B-project 1998-0659, KFBproject 1997-0223, SP REPORT 1999:35
,,
. .
73
—. --- .. . . . .. . . ~ — --
Annex B – Format for test results (informative)Test conditions Mic height
VehicleHalf axle widthRoad surfaceDistanceDaSpeedhast ml-sKorsattAir tempRoad tempCloudinessWind speed
Measured SEL, dB 2531,5
40506380
100125160200250315400500630800
1000125016002000250031504000500063008000
10000A-weighted
Normalized (10 m) SEL 2531,5
40506380
100125160200250315400500630800
1000125016002000250031504000500063008000
10000
A-weighted
41A
0,75lb9
2,5648
13,31
18,629,880%<5
75,373,871,971,577,668,471,164,262,664,066,663,762,662,763,667,768,165,163,159,757,154,551,947,143,940,537,174,074,973,471,571,177,268,070,763,862,263,666,263,362,262,363,267,367,764,762,759,356,754,151,546,743,540,136,7
73,6
0,21A
0,75lb9
2,5648
13,31
18,629,880Y.<5
7774,372,573
79,169
72,365,162,965
66,763,462
62,263,868,168,566,365
60,759,557
53,950,447,142,339
76,573,872,072,578,668,571,864,662,464,566,262,961,561,763,367,668,065,864,560,2
56,553,449,946,641,838,5
Max(0,2 m, 4 m)76,573,872,072,578,668,571,864,662,464,566,263,362,262,363,367,668,065,864,560,259,056,553,449,946,641,838,5
74