27-11-2014
1
Room acoustic measurements
Jens Holger Rindel
Odeon A/S, Scion-DTU, Denmark
Background
• Room acoustic measurements have become
easier than ever
• From the most simple (hand claps)
• To the most sophisticated (new parameters for
open-plan offices)
26 November 2014 Room acoustic measurements 2
Related standards
• ISO 3382-1:2009, Acoustics - Measurement of room acoustic parameters -
Part 1: Performance spaces
• ISO 3382-2:2008, Acoustics - Measurement of room acoustic parameters -
Part 2: Reverberation time in ordinary rooms
• ISO 3382-3:2012, Acoustics - Measurement of room acoustic parameters -Part 3: Open plan offices
• ISO 9921:2003, Ergonomics – Assessment of speech communication
• ISO 14257:2001, Acoustics - Measurement and parametric description of
spatial sound distribution curves in workrooms for evaluation of their acoustical performance
• ISO 18233:2006, Acoustics - Application of new measurement methods in building and room, Acoustics
• IEC 60268-16:2011, Sound system equipment – Part 16: Objective rating of speech intelligibility by speech transmission index (Edition 4.0)
26 November 2014 Room acoustic measurements 3
Contents
• The reverberation time – development of
methods for measurement
• Snap-shot (survey) or sine sweep (precision)
• Sources of error in measurements
• Other room acoustic parameters for auditoria
• Comparison of measurements and simulations
• Calibration of sound source
• STI measurements
• Measurements in open-plan offices
Room acoustic measurements 426 November 2014
Sabine’s set of organ pipes (1906)
Room acoustic measurements 526 November 2014
Frequencies:
64 Hz – 4097 Hz(7 octaves)
W.C. Sabine, Collected papers (1922)
Decay time with 1-4 organ pipes
26 November 2014 Room acoustic measurements 6
6 dB louder sound with 4
pipes instead of 1 –
Sound in heard longer (Δt)
T60 = 10 Δt
W.C. Sabine, Collected papers (1922)
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2
Measurement setup in reverberation chamber 1919
26 November 2014 Room acoustic measurements 7
Ref.: J.W. Kopec, The Sabines at Riverbank (1997)
First standards on RT
• 1963: ISO R 354 Measurement of absorption coefficients in a reverberation room
– Loudspeaker, interrupted noise or warble tone
• 1975: ISO 3382 Measurement of reverberation time in
auditoria
– Loudspeaker, interrupted noise
– Organ pipes (all semitones in each frequency range)
– Impulses from pistol shots
– Orchestra, fortissimo passages followed by long pauses
26 November 2014 Room acoustic measurements 8
Decay of interrupted noise
26 November 2014 Room acoustic measurements 9
Brüel & Kjær made a level recorder with logarithmic potentiometer (1949)
Decay of impulse response (1978)
Room acoustic measurements 10
Portable setup for measuring reverberation time using a pistol shot and level
recorder (Ref. K.B. Ginn (1978). Architectural Acoustics, Brüel & Kjær, Denmark).
26 November 2014
Obs: Method not allowed after revision of ISO 3382 (1998)
Integrated impulse response
26 November 2014 Room acoustic measurements 11
Schroeder’s integrated impulse response method (1965)
Chu: JASA 63
(1978)
Backward integration of impulse response (1982)
26 November 2014 Room acoustic measurements 12
Reading: 0.60 s from -5 to -25 dB
Result: T20 = 1.80 s
Tape recorder – change of tape direction and speed –
B&K real time analyzer with long integration time - B&K level recorder
20 dB
0.60 s
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3
New method – New problems
• Influence of background noise
1. Using full record length
2. Using truncated record
3. -
4. Using full record length
with subtraction of
background noise
26 November 2014 Room acoustic measurements 13
Chu: JASA 63 (1978)
Using a sweep signal
• Method developed by
A.C. Gade (1984)
• Each sweep covers one
octave
• Applied for 6 octave bands
(125 Hz – 4000 Hz)
26 November 2014 Room acoustic measurements 14
Sweep and
frequency response
Impulse response
after deconvolution
ISO 18233 (2006) New methods
• MLS signals
– Periodic maximum length signal + cross correlation +
octave filter + integration =
decay curve
– Length of sequence ≥ RT
– Only for time-invariant systems – quite sensitive to
changes during the
measurement (OBS)
– Distortion causes
increased noise floor (OBS)
26 November 2014 Room acoustic measurements 15
• Sine sweeps
– Single sweep + decon-volution + octave filter +
integration = decay curve
– Longer sweeps give
reduced noise floor
– Exponential sweep ~ pink spectrum
– Only for time-invariant systems – less sensitive
than the MLS method
– Harmonic distortion
separated from impulse
response
6 s sweep length
E, MeasuredgfedcbNoise floorgfedcbOnset timegfedcbTruncation timegfedcb
C:\...\Arb-vaerelse\Impulse response file.ImpRespFile0.wavRaw decay curve at 250Hz
time (seconds)0.70.650.60.550.50.450.40.350.30.250.20.150.10.050
SP
L(d
B)
-35
-40
-45
-50
-55
-60
-65
-70
-75
-80
-85
-90
-95
-100
-105
-110
-115
-120
Odeon©1985-2013 Licensed to: Odeon Restricted version - research and teaching only!
Noise floor
26 November 2014 Room acoustic measurements 16
60 s sweep length
E, MeasuredgfedcbNoise floorgfedcbOnset timegfedcbTruncation timegfedcb
C:\...\Arb-vaerelse\Impulse response file.ImpRespFile1.wavRaw decay curve at 250Hz
time (seconds)0.70.650.60.550.50.450.40.350.30.250.20.150.10.050
SP
L(d
B)
-35
-40
-45
-50
-55
-60
-65
-70
-75
-80
-85
-90
-95
-100
-105
-110
-115
-120
-125
Odeon©1985-2013 Licensed to: Odeon Restricted version - research and teaching only!
Noise floor
Factor 10 –> 10 dB
26 November 2014 Room acoustic measurements 17
300 s sweep length
E, MeasuredgfedcbNoise floorgfedcbOnset timegfedcbTruncation timegfedcb
C:\...\Arb-vaerelse\Impulse response file.ImpRespFile2.wavRaw decay curve at 250Hz
time (seconds)0.70.650.60.550.50.450.40.350.30.250.20.150.10.050
SP
L(d
B)
-35
-40
-45
-50
-55
-60
-65
-70
-75
-80
-85
-90
-95
-100
-105
-110
-115
-120
-125
Odeon©1985-2013 Licensed to: Odeon Restricted version - research and teaching only!
Noise floor
Factor 5 –> 7 dB
26 November 2014 Room acoustic measurements 18
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4
Measurements
Obtain an impulse response using an impulse signal
• Sweep method
• Start pistol, hand clap, popping a balloon or a paper bag
Derive ISO 3382 parameters
Implementation in Odeon12 – our aims:
– Automatic
– Reproducible
– Give warnings when needed
Room acoustic measurements 1926 November 2014
• DEMO
26 November 2014 Room acoustic measurements 20
P1
1
2
3
4
5
6
7
8
9
P1
Odeon©1985-2013 Licensed to: MULTICONSULT AS, Norway
Snap shot (handclap)
• Hole Bo – room at
elder centre
• Visit includes:
• Talking to people
about the acoustical
problems
• Taking some photos
• Recording some hand
claps
26 November 2014 Room acoustic measurements 21
Demo
26 November 2014 Room acoustic measurements 22
Recording of impulse response with a smart phone
Simulated Avr.gfedcbSimulated MingfedcbSimulated MaxgfedcbSimulated Std. dev.gfedcbMeasured Avr.gfedcbMeasured MingfedcMeasured MaxgfedcMeasured Std. dev.gfedc
Statistics
Active receivers: 2,5
Frequency
63 125 250 500 1000 2000 4000 8000
T(2
0)
(s)
1,5
1,4
1,3
1,2
1,1
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
Odeon©1985-2013 Licensed to: MULTICONSULT AS, Norw ay
Acoustic survey made with hand claps
10 10% absorbentgfedcb 10005 Glass, large gfedcb 1002 !Brick, unglagfedcb 3002 Wood parquet gfedcb 4044 2*13 mm plastgfedcb 20 20% absorbentgfedcb 12100 (Example 1210gfedcb 3075 Panel, 13 mm gfedcb 4058 Adjusted mategfedcb 11057 Chairs, lightgfedcb 3004 Wooden f loor gfedcb
Absorption coeff icients
Frequency (Hz)
63 125 250 500 1000 2000 4000 8000
1
0,95
0,9
0,85
0,8
0,75
0,7
0,65
0,6
0,55
0,5
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
Odeon©1985-2013 Licensed to: MULTICONSULT AS, Norw ay26 November 2014 Room acoustic measurements 23
Model with initial materials
Simulated Avr.gfedcbSimulated MingfedcbSimulated MaxgfedcbSimulated Std. dev.gfedcbMeasured Avr.gfedcbMeasured MingfedcMeasured MaxgfedcMeasured Std. dev.gfedc
Statistics
Active receivers: 2,5
Frequency
63 125 250 500 1000 2000 4000 8000
T(2
0)
(s)
1,5
1,4
1,3
1,2
1,1
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
Odeon©1985-2013 Licensed to: MULTICONSULT AS, Norw ay
10 10% absorbentgfedcb 10005 Glass, large gfedcb 1002 !Brick, unglagfedcb 3002 Wood parquet gfedcb 4044 2*13 mm plastgfedcb 20 20% absorbentgfedcb 12100 (Example 1210gfedcb 11057 !Chairs , lighgfedcb 3004 Wooden floor gfedcb 13100 (Example 1310gfedcb 4058 Adjusted mategfedcb
Absorption coefficients
Frequency (Hz)
63 125 250 500 1000 2000 4000 8000
1
0,95
0,9
0,85
0,8
0,75
0,7
0,65
0,6
0,55
0,5
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
Odeon©1985-2013 Licensed to: MULTICONSULT AS, Norw ay
26 November 2014 Room acoustic measurements 24
Model with adjusted materials
Acoustic survey made with hand claps
27-11-2014
5
Coming soon
• ODEON ver. 13:
• Generic algorithm to optimize absorption
coefficients of unknown materials to match a set
of measurements
26 November 2014 Room acoustic measurements 25
Error sources in RT measurements
• Wrong onset time
• Influence of noise floor
• Distortion from loudspeaker
• Faulty impulse response (disturbance)
• Temperature and humidity
26 November 2014 Room acoustic measurements 26
Measuring correct resultsOnset of impulse response?
Room acoustic measurements 27
Omni microphonegfedcbOnset timegfedcbTruncation timegfedcb
F:\Users\Claus\Documents\Odeon f iler\Measurements\ExtraPreImpulseA.w av
Ray Impulse response at 1000Hz
time (seconds)
21,510,50
p
10
8
6
4
2
0
-2
-4
-6
-8
-10
Odeon©1985-2013 Licensed to: OdeonElectromagnetic transfer
Time delay = r / c
r
26 November 2014
Measuring correct resultsOnset of impulse response?
Room acoustic measurements 28
E, MeasuredgfedcbE, IntegratedgfedcbE, Correctedgfedcb
F:\Users\Claus\Documents\Odeon filer\Measurements\ExtraPreImpulseA.wavDecay curves at 1000Hz T(30) = 1,91 seconds
time(seconds)21,81,61,41,210,80,60,40,20
SPL(d
B)
45
40
35
30
25
20
15
10
5
0
-5
-10
Odeon©1985-2013 Licensed to: Odeon
Wrong onset time
T(30) = 1.91 s
E, MeasuredgfedcbE, IntegratedgfedcbE, Correctedgfedcb
F:\Users\Claus\Documents\Odeon filer\Measurements\ExtraPreImpulseA.wavDecay curves at 1000Hz T(30) = 1,91 seconds
time(seconds)1,81,61,41,210,80,60,40,20
SPL(d
B)
45
40
35
30
25
20
15
10
5
0
-5
-10
Odeon©1985-2013 Licensed to: Odeon
Correct onset time
T(30) = 1.91 s
EDT = 2.23 s
C(80) = -26.6 dB
EDT = 1.98 s
C(80) = -0.6 dB
26 November 2014
Measuring correct resultsTruncation time of impulse response
Room acoustic measurements 29
D:\Measured Impulse responses\isra_measurements1\Auditorium21GEorgeClaus15feb2013\s1r1_4000.wavRaw decay curve at 4000Hz
time (seconds)3.83.63.43.232.82.62.42.221.81.61.41.210.80.60.40.20-0.2
SPL(d
B)
-8
-10
-12
-14
-16
-18
-20
-22
-24
-26
-28
-30
-32
-34
-36
-38
-40
-42
-44
-46
-48
-50
-52
-54
-56
-58
-60
-62
-64
-66
Odeon©1985-2013 Licensed to: Odeon A/S
Noise floorTt
Truncation time
26 November 2014
E, MeasuredgfedcbE, IntegratedgfedcbE, Correctedgfedcb
F:\Users\C laus\Documents\Odeon filer\Measurements\Auditorium 21\RevisedOdeon12\ISRA_measurementsAuditorium21_8March\Low Gain\S1R5_sweep8000.wavDecay curves at 1000Hz T(30) = 10,61 seconds
time(seconds)3,83,63,43,232,82,62,42,221,81,61,41,210,80,60,40,20
SPL(d
B)
-35
-40
-45
-50
-55
-60
-65
-70
-75
-80
-85
-90
-95
-100
-105
Odeon©1985-2013 Licensed to: Odeon
E, MeasuredgfedcbE, IntegratedgfedcbE, Correctedgfedcb
F:\Users\Claus\Documents\Odeon filer\Measurements\Auditorium 21\RevisedOdeon12\ISRA_measurementsAuditorium21_8March\Low Gain\S1R5_sweep8000.wavDecay curves at 1000Hz T(30) = 1,90 seconds
time(seconds)1,41,31,21,110,90,80,70,60,50,40,30,20,10
SPL(d
B)
-32
-34
-36
-38
-40
-42
-44
-46
-48
-50
-52
-54
-56
-58
-60
-62
-64
-66
-68
-70
-72
-74
-76
-78
-80
-82
-84
-86
-88
-90
Odeon©1985-2013 Licensed to: Odeon
Measuring correct resultsInfluence of noise floor
Room acoustic measurements 30
T(30) = 10.6 s T(30) = 1.9 s
Evaluation range for T(30): -5 dB to -35 dB
26 November 2014
27-11-2014
6
E, MeasuredgfedcbNoise floorgfedcbOnset timegfedcbTruncation timegfedcb
F:\Users\Claus\Documents\Odeon filer\Measurements\Auditorium 21\RevisedOdeon12\ISRA_measurementsAuditorium21_8March\S1R1_sweep4000.wavRaw decay curve at 1000Hz
time (seconds)3210
SPL(d
B)
-30
-35
-40
-45
-50
-55
-60
-65
-70
-75
-80
-85
-90
-95
-100
-105
-110
Odeon©1985-2013 Licensed to: Odeon
Measuring correct resultsCompensate for truncation & background noise
Room acoustic measurements 31
1) Truncate at noise floor
2) Option: add truncated decay
Subtract noise floor
26 November 2014
Measuring correct results
26 November 2014 Room acoustic measurements 32
Measured with exponential sine sweep according to ISO 18233
Longer sweep means
lower noise floor
Derived T30 at 1000 Hz with different S/N ratios
without and with corrections
Non-linear decays
• Non-linearity parameter
– Warning if ξ > 10 ‰ Look at the decay curve!
• Degree of curvature
– Warning if C > 10 % Look at the decay curve!
26 November 2014 Room acoustic measurements 33
ISO 3382-2: 2008 Annex B
[‰] )1(10002
r−=ξ
( ) [%] 110020
30 −⋅=T
TC
Measuring correct resultsWarning for suspisious impulse response
Room acoustic measurements 34
3382-2 Reverberation time in ordinary rooms - the degree of non-linearity:
• r is the correlation coefficient for linear regression line
• ξ > 10‰ : warning that decay may be suspicious – visual inspection recommended
)1(10002
r−⋅=ξ
26 November 2014
35
Temperature and humidity
• NS/ISO 3382-1:2009
- 9.2 Test report
• NS/ISO 3382-2:2008
- 9.2 Test report
36
27-11-2014
7
37
Example – Project for a new church
P12
34
56
78
910
1112
1314
1516
P1
Odeon©1985-2013 Licensed to: Odeon A/S
0 10 20 30 40 metres
0
10
20
30 metres
P1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
P1
Odeon©1985-2013 Licensed to: Odeon A/S
38
Influence of humidity
Air absorption
10000 Solid gl
10005 Glass, l
1002 Brick, u
11057 Chairs,
80 80% abso
102 Smooth c
4048 30 mm pl
Absorption area distributed on materials
Frequency (Hz)
63 125 250 500 1000 2000 4000 8000
m² Sabin
e
655.36
573.44
491.52
409.6
327.68
245.76
163.84
81.92
Odeon©1985-2013 Licensed to: Odeon A/S
Air absorption
10000 Solid gl
10005 Glass, l
1002 Brick, u
11057 Chairs,
80 80% abso
102 Smooth c
4048 30 mm pl
Absorption area distributed on materials
Frequency (Hz)
63 125 250 500 1000 2000 4000 8000
m²
Sa
bin
e
1,310.72
1,146.88
983.04
819.2
655.36
491.52
327.68
163.84
Odeon©1985-2013 Licensed to: Odeon A/S
20°C 90% RH
“Summer”
20°C 20% RH
“Winter”
39
Lower limits of RT
4026 November 2014 Room acoustic measurements Rindel (ca. 1984)
Measurement uncertainty
26 November 2014 Room acoustic measurements 41
Calculated according to ISO 3382-2: 2008 Annex A
Survey Engineering Precision
LS positions 1 2 3
Mic positions 2 3 4
Positions 2 6 12
Room acoustic parameters
Room acoustic measurements 42
ISO 3382-1 Parameter SymbolJust noticeabledifference (JND)
Early Decay Time EDT [s] 5%
Reverberation Time (20 dB range) T20 [s] 5%
Reverberation Time (30 dB range) T30 [s] 5%
Clarity (80 ms) C80 [dB] 1 dB
Definition (50 ms) D50 0.05
Centre Time Ts [ms] 10 ms
Sound Strength G [dB] 1 dB
SupportSTEarly [dB]
STLate [dB]-
26 November 2014
27-11-2014
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Case study - Auditorium
Room acoustic measurements 43
P1
1
2
3
4
5
6789
101112131415
P1
Odeon©1985-2013 Licensed to: Odeon
Auditorium 21, Technical University of Denmark
Volume 1175 m3
T30@1000 Hz = 1.90 s
26 November 2014
Case study - Auditorium
Room acoustic measurements44
EDT at 1000 Hz
Distance
R3 a
t 4
,55 m
R2 a
t 6
,84 m
R5 a
t 8
,95 m
R1
at
10
,12 m
R4
at
12
,76 m
ED
T (
s)
2,4
2,2
2
1,8
1,6
Odeon©1985-2013 Licensed to: Odeon
T(30) at 1000 Hz
Distance
R3
at
4,5
5 m
R2
at
6,8
4 m
R5
at
8,9
5 m
R1 a
t 1
0,1
2 m
R4 a
t 1
2,7
6 m
T(3
0)
(s)
2,1
2
1,9
1,8
1,7
Odeon©1985-2013 Licensed to: OdeonSPL at 1000 Hz
Distance
R3 a
t 4
,55 m
R2 a
t 6
,84 m
R5 a
t 8
,95 m
R1
at
10
,12 m
R4
at
12
,76 m
SP
L (
dB
)
20
18
16
14
12
Odeon©1985-2013 Licensed to: Odeon
C(80) at 1000 Hz
Distance
R3 a
t 4,5
5 m
R2 a
t 6,8
4 m
R5 a
t 8,9
5 m
R1
at 1
0,1
2 m
R4
at 1
2,7
6 m
C(8
0)
(dB
)
2
1
0
-1
-2
-3
Odeon©1985-2013 Licensed to: Odeon
Measurement
Simulation
5 receiver positions
26 November 2014
Reproducibility – position7 repetitions with small changes to position
Room acoustic measurements 45
5
10
11
12
13
14
15
Odeon©1985-2013 Licensed to: Odeon
-0.1 m
0.1 m
0.3 m
-0.3 m
-0.2 m
0.2 m
P1
1
2
3
4
5
6789
101112131415
P1
Odeon©1985-2013 Licensed to: Odeon
26 November 2014
Reproducibility – positionEDT
Room acoustic measurements 46
Simulated Avr.gfedcbSimulated MingfedcbSimulated MaxgfedcbSimulated Std. dev.gfedcbMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 5,10,11,12,13,14,15
Frequency
125 250 500 1000 2000 4000
ED
T (
s)
2
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
Odeon©1985-2013 Licensed to: Odeon
26 November 2014
Reproducibility – positionSPL (strength, G)
Room acoustic measurements 47
Simulated Avr.gfedcbSimulated MingfedcbSimulated MaxgfedcbSimulated Std. dev.gfedcbMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 5,10,11,12,13,14,15
Frequency
125 250 500 1000 2000 4000
SP
L (
dB
)
18
17
16
15
14
13
12
11
10
9
8
Odeon©1985-2013 Licensed to: Odeon
26 November 2014
Reproducibility – positionC80
Room acoustic measurements 48
Simulated Avr.gfedcbSimulated MingfedcbSimulated MaxgfedcbSimulated Std. dev.gfedcbMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 5,10,11,12,13,14,15
Frequency
125 250 500 1000 2000 4000
C(8
0)
(dB
)
10
9
8
7
6
5
4
3
2
1
0
-1
Odeon©1985-2013 Licensed to: Odeon
26 November 2014
27-11-2014
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PAUSE
26 November 2014 Room acoustic measurements 49
Geilo Kulturkyrkje
Acoustical measurements 2013-09-
27
Jens Holger Rindel
0 5 10 15 20 25 30 metres
0
5
10
15
20 metres
P1
P2
1
2
3
4
5
6
7
8
9
Odeon©1985-2013 Licensed to: Odeon A/S
0 5 10 15 20 25 30 metres
0
5
10
15
20 metres
P1P2123456
7
89
Odeon©1985-2013 Licensed to: Odeon A/S
27-11-2014
10
Odeon©1985-2013 Licensed to: Odeon A/S
Reverberation time, T30
Simulated Avr.gfedcbSimulated MingfedcbSimulated MaxgfedcbSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
T(3
0)
(s)
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
Odeon©1985-2013 Licensed to: Odeon A/S
Simulated Avr.gfedcbSimulated MingfedcbSimulated MaxgfedcbSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
T(3
0)
(s)
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
Odeon©1985-2013 Licensed to: Odeon A/S
27-11-2014
11
EDT
Simulated Avr.gfedcbSimulated MingfedcSimulated MaxgfedcSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
ED
T (
s)
2,4
2,2
2
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
Odeon©1985-2013 Licensed to: Odeon A/S
Simulated Avr.gfedcbSimulated MingfedcSimulated MaxgfedcSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
ED
T (
s)
2
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
Odeon©1985-2013 Licensed to: Odeon A/S
Clarity, C80
Simulated Avr.gfedcbSimulated MingfedcSimulated MaxgfedcSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
C(8
0)
(dB
)
11
10
9
8
7
6
5
4
3
2
1
0
Odeon©1985-2013 Licensed to: Odeon A/S
Simulated Avr.gfedcbSimulated MingfedcSimulated MaxgfedcSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
C(8
0)
(dB
)
10
9
8
7
6
5
4
3
2
1
0
-1
Odeon©1985-2013 Licensed to: Odeon A/S
Sound strength, G
Simulated Avr.gfedcbSimulated MingfedcSimulated MaxgfedcSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
SP
L (
dB
)
24
22
20
18
16
14
12
10
8
6
4
2
Odeon©1985-2013 Licensed to: Odeon A/S
Simulated Avr.gfedcbSimulated MingfedcSimulated MaxgfedcSimulated Std. dev.gfedcMeasured Avr.gfedcbMeasured MingfedcbMeasured MaxgfedcbMeasured Std. dev.gfedcb
Statistics
Active receivers: 1,2,3,4,5,6,7
Frequency
63 125 250 500 1000 2000 4000 8000
SP
L (
dB
)
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
Odeon©1985-2013 Licensed to: Odeon A/S
Support, STearly and STlate
Simulated
Measured
Receiver: 8
Frequency (Hertz)
63
125
250
500
10
00
20
00
40
00
80
00
ST
(Earl
y)
(dB
)
7,68
5,12
2,56
0
-2,56
-5,12
-7,68
-10,24
-12,8
-15,36
Simulated
Measured
Receiver: 8
Frequency (Hertz)
63
125
250
500
10
00
20
00
40
00
80
00
ST
(La
te)
(dB
)
7,68
5,12
2,56
0
-2,56
-5,12
-7,68
-10,24
-12,8
-15,36
-17,92
-20,48
-23,04
Diffuse field calibration
27-11-2014
12
Speech Transmission Index
• Originally based on the MTF (Modulation Transfer Function)
• Houtgast & Steeneken (1973)
– 14 modulation frequencies
– 7 octave bands
– Very time consuming measurement
• Schroeder showed that the MTF is the Fourier transform of the squared impulse response
• Schroeder (1981)
– Very quick measurement
– Background noise can be included in the calculation of STI
(afterwards)
26 November 2014 Room acoustic measurements 67
STI measurements
• Talker and listener in same room
– Source directivity and calibration should follow the
relevant standard
• Room with sound reinforcement system or PA or
VA system
– The measuring signal can be injected directly to the sound system
– The sound level is controlled by the sound system
26 November 2014 Room acoustic measurements 68
Open plan offices – ISO 3382-3
• RT is not sufficient
– (but may be measured according to Part 2 of ISO
3382)
• New parameters include
– Spatial decay rate of speech
– Distraction distance (STI = 0.5)
– Privacy distance (STI = 0.2)
– Background noise level
26 November 2014 Room acoustic measurements 69
STI and speech intelligibility
Room acoustic measurements 7026 November 2014
ISO 9921:2003, Fig. F.1
STI: Speech transmission Index
SRT: Speech Reception Threshold
PB: Phonetically Balanced
CVC: Consonant – Vocal – Consonant
EQB: Equally Balanced Phoneme Distribution
Privacy – Distraction distance
Open-plan office example
Room acoustic measurements 7126 November 2014
Measurements in open-plan offices
26 November 2014 Room acoustic measurements 72
Simple room model is
sufficient
Only with source and receivers
Just to define distances
O
XY
Z
P11
23
45
67
P1
Odeon©1985-2013 Licensed to: Odeon A/S
27-11-2014
13
Detailed model made with SketchUp
26 November 2014 73Room acoustic measurements 26 November 2014 74Room acoustic measurements
Measured STI – spatial decay
26 November 2014 Room acoustic measurements 75
Measured STI
STI regression-line
Measured STI versus distance - distraction distance /privacy distance
rD = 11,92 metres,rP = 23,91 metres
Distance (metres)
R1
at
1,7
0 m
R2
at
6,9
0 m
R3
at
9,4
5 m
R4 a
t 1
1,2
0 m
R5 a
t 1
3,4
5 m
R6 a
t 1
7,7
0 m
R7 a
t 1
9,4
5 m
STI
0,8
0,7
0,6
0,5
0,4
0,3
Odeon©1985-2013 Licensed to: Odeon A/S
Measured spatial decay of A-weighted speech
26 November 2014 Room acoustic measurements 76
Measured SPL
D2,S curve
Free field (6dB dd)
Measured spatial decay, D2,S = 10,48 dB
Lp,A,S, 4 m = 55,02 dB,
10Log(distance)
R1 a
t 1,7
0 m
R2 a
t 6,9
0 m
R3 a
t 9,4
5 m
R4
at 11,2
0 m
R5
at 13,4
5 m
R6
at 17,7
0 m
Lp (
dB
)
66,56
61,44
56,32
51,2
46,08
40,96
35,84
30,72
Odeon©1985-2013 Licensed to: Odeon A/S
Measurement line 1
STI all receivers
0,8
5
0,6
0
0,5
0
0,46
0,3
9
0,4
1
0,4
0
MålestørrelseAnbefalt
krav
Målt verdi
DL2,S (dB) ≥ 7 10,5
Lp,AS,4m (dB) ≤ 52 55
rD (m) ≤ 11 12
STI 0,2Figur under
STI 0,6 0,9
Measured
26 November 2014 77Room acoustic measurements
Conclusion
• Measurement of room acoustic parameters has
become easy and fast
• Using the sine sweep technique offers high
quality measurements
• However, be aware of possible erroneous
measurements
• Inspection of the measured decay curve is highly
advisable
26 November 2014 Room acoustic measurements 78