p2 presentation yvonne wattez

ACOUSTICS IN SPORTS HALLSresearch on the acoustical behaviour of perforated panels

Presentation P225/01/2012

Graduation project of Yvonne WattezStudent nr. 1360809

Building Technology | Green Building Innovation Faculty of Architecture | TU Delft

Mentor 1: Martin TenpierikMentor 2: Peter van Swieten


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Yvonne Wattez 1360809 graduation projectP2 presentation 25/01/2012

Introduction

1. Graduation so farProblem description- Legislation & standards - Parameters of acoustics in sports halls

Reverberation time - Calculations vs. measurements- Porous materials vs. perforated panels- Possible explainations for the differences

Sound absorption- Sound absorbing principles- Helmholtz resonator

2. Graduation research - Standard measuremtents- Laboratory measurements- Scale model measurements

3. Design4. Timeline


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Why?I like sports.I like acoustics.


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Problem descriptionComplaints of PE teachers: - voice problems,(- hearing problems,)- tiredness.

Mainly caused by bad acoustics of sports halls.

Teachers need to shout to make themselves heard.

Measurements show that the reverberation time is often too long.

Pictures:Protest action in Rijssen - Holten.[source: tcturbantia 27 sept 2010]


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Legislation & StandardsBased on reverberation time [RT] and backgound noise level.

Limits depend on size and volume.

[source: ISA Sport, ISA-N/A 1.1 ]

picture: sports hall in Amstelveen[source:www.sportbedrijfamstelveen.nl]

seconds, the average reverberation time will be automatically less. E.L. Nesselaar used the standard for her research, not the recommendation. In this report the newest version of the standard of ISA-Sport (NOC*NSF) will be used. Standard ISA-Sport 2005 Since 2005 the newest version of the standard: ‘Standards gymnastics and sports halls and parts of sports halls with educational use.’ is used in The Netherlands. This standard is also called: ISA-US1-BF1. The standard is still based on the reverberation time because a better option is not found yet. With the help and advice of some experts, the reverberation time is defined per volume of the hall. This is important, because a sports hall twice the size should not have twice the reverberation time. The very big sports halls may have a very long reverberation time in that case. The acoustical quality is not linear with the volume. Besides the advise to introduce the volume in the standard for reverberation time, the average absorption coefficient was advised to be at least 0,25. (Nijs 2004) The ISA-Sports standard includes: information on the location, the sports equipment, dressing rooms, and acoustics of the sports facility:

• The average absorption coefficient [α] of the materials in the sports hall has to be at least 0,25. • The reverberation time depends on volume and absorbing behaviour of the room. The average

reverberation time in frequency band of 125-4000Hz may not be higher than 1,0 seconds for a sports hall of 14 x 22 x 5.5 m.

• The reverberation time per frequency band (Tmax/fb) is calculated by Tav divided by Tmax/fb. This has to be ≥ 0,7.

• The background noise level must not be higher than 40 dB(A). This applies to external sounds like outdoor traffic and internal sound sources like installation systems.

• The noise insulation index between rooms for physical education and other residences/ classrooms should be 10 dB(A), preferably 15dB(A).

Kind of room Size [m] (w x l x h) Reverberation time [s] A.1 Gymnastics ≤ 14 x 22 x 5.5 ≤ 1,0 A.2 Gym 13 x 22 x 7 ≤ 1,1 A.3 1/3 sports hall /gym 14 x 24 x 7 ≤ 1,2 B.1 Gym 16 x 28 x 7 ≤ 1,3 B.2 Gym 22 x 28 ≤ 1,4 B.3 2/3 sports hall 32 x 28 ≤ 1,5 C.1 Sports hall 24 x 44 ≤ 1,6 C.2 Sports hall 28 x 48 x 7 ≤ 1,7 C.3 Sports hall 28 x 48 x 9 ≤ 1,9 D.1 Sports hall 28 x 88 x 7 ≤ 2,0 D.2 Sports hall 35 x 80 x 10 ≤ 2,3

Conclusion Legislation has been changed during the last years. There is more attention given to acoustics is sports facilities. This results in more and adapted standards. For example, the limit of the allowed background noise caused by installations is changed from 45 dB(A) to 40 dB(A).


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ParametersReverberation Time (RT):Sabine’s formula

Reverberation TimeThe reverberation time is defined as the time that expires before a sound pressure has decayed by 60 dB after the sound source has been swiched off.

T15 (blue), T20, T30 (black) Sabine 1

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VRT

A=

with: RT= reverberation time [s] V= volume of room [m3] A= total absorption of materials in room = ( )i iSα

with: iα = absorption coefficient of element i [-]

iS = surface of element i [m2] Sabine correction of Lau Nijs This correction is made because Sabine is based on a cube. Sports halls normally have a rectangular shape. By replacing the surface factor S by a certain part of the volume V2/3, this formula becomes more realistic.

2/3

1

6 6

VRT

Vα=

⋅

with: RT= reverberation time [s] V= volume of room [m3] α = average absorption coefficient Eyring_1 This formula of Eyring works with the mean value of all absorption coefficients.

with: RT= reverberation time [s]

V= volume of room [m3] S= total surface [m2]

α = mean value of all absorption coefficients in the room = ( )i i

i

S

S

α

[-]

Eyring_2 A different formula of Eyring that works with the total absorption coefficient.

1

1

6 ln (1 )ii

VRT

S α −=

⋅ −

with: RT= reverberation time [s]

V= volume of room [m3] iS = surface of element i [m2]

iα = absorption coefficient of element i [-]

1

1

6 ln (1 )

VRT

S α−

= ⋅ −

16 4

VRTA mV

= ⋅+

4 correction for air attenuationmV =


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Parameters

absorption coefficient a= absorbed energy/incident energy

SRC diagram: Everest 2001

Absorption coefficientAbsorption coefficient a is a measure of the efficiency of a surface or material in absorbing sound.

Reflected sound (A, B, C) rTransmitted sound (D) tAbsorbed sound (E, F, G, H, I, J, K) a

r+t+a = 1Sports hall: a= 1-r

a

i

WW

α =


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ParametersSpeech IntelligibilityDepends on: - background noise- reverberation time - shape of the room

Parameters to measure speech intelligibility:- Speech Transmission Index STI- RApid Speech Transmission Index RASTI(mostly used in Europe)

Based on a comparison of the outgoing and incoming sound.Between 0 and 1. 0.8 or higher is excellent, 0.3 is the lower limit to understand sentences.


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ParametersReflecting sound in between parallel walls.

[source: Vugts, J. (2008) LBP|SIGHT via nvbv.org][source: www.ecophon.nl]

Flutter echo

13-05-2011

3

Sporthal (48 x 28 x 9 m)Ray-tracing - variant 2 t/m 4

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

125 250 500 1000 2000 4000

f [Hz]

T15

[s]

variant 2 variant 3 variant 4 Sabine norm

Wandabsorptie boven

Wandabsorptie onder

Twee wanden geheel

1 2 3

Berekende nagalmtijd ‘Aanwezige’ geluidabsorptiecoëfficiënt

Sporthal (48 x 28 x 9 m)Ray-tracing - variant 2 t/m 4

0.0

0.1

0.2

0.3

0.4

0.5

125 250 500 1000 2000 4000

f [Hz]

α [-]

variant 2 variant 3 variant 4 Sabine norm

α ‘norm’

α ‘aanwezig’

1 2 3

Sporthal (45x25x8 m) – Norm: Tgem = 1,9 s; Tmax/fb = 2,7 s

De invloed van flutterecho’s op de nagalmtijd

Sporthal (45 x 28 x 8 m)metingen

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

125 250 500 1000 2000 4000

f [Hz]

T [s

]

EDT T10 T20 T30 T15 norm

Gemeten nagalmtijd

90 m = 2 x zaallengte

Sportzaal (32x24x7,8 m) – Norm: Tgem = 1,5 s; Tmax/fb = 2,1 s

De nagalmtijd als te berekenen parameter in het ontwerp


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Reverberation TimeCalculations vs. measurements.

Formulas compared:Big differences found in comparison of different formulas, computer programmes and measurements.

sports hall Schijndel: perforated steel panels on walls

Schijndel

Method \ frequency Standard ISA Sport Standard ISA Sport max L.Nijs & Sabine Sabine Eyring Fitzroy ODEON T30 CATT ACOUSTIC T15 CATT ACOUSTIC T30 Measurement T20

0

0.5

1

1.5

2

2.5

3

average

Reve

rber

atio

n Ti

me

[s]

RT: methods vs. measurement

average 500Hz 2000Hz 1.6 1.6 1.62.3 2.3 2.3

2.22 1.62 2.241.84 1.34 1.851.62 1.09 1.621.64 1.36 1.631.79 1.83 1.661.77 1.86 1.642.01 2.2 1.772.14 2.64 1.82

500Hz 2000Hz Frequency [Hz]

RT: methods vs. measurementSchijndel

1.6 2.3

2.24 1.85 1.62 1.63 1.66 1.64 1.77 1.82

L.Nijs & Sabine

Sabine

Eyring

Fitzroy

ODEON T30

CATT ACOUSTIC T15

CATT ACOUSTIC T30

Measurement T20

Standard ISA Sport

Standard ISA Sport max


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Reverberation TimePorous materials vs. perforated steel panels.

The reverberation is much shorter than expected at low frequencies in a sports hall constructed with perforated panels.

The perforated panels seem to behave differently than expected from laboratory results.(Especially at low frequencies.)

SRC: LBP|SIGHT

Different halls compared:

0.0

1.0

2.0

3.0

4.0

125 250 500 1000 2000 4000

T [s

]

f [Hz]

Sporthal D1 T20

S1 S2 S3 AVERAGE

Expected and measured RT; porous materials


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So, the panels seem to behave differently in practice than in a laboratory situation.

Goal of this research:

Determine why a difference in sound absorption behaviour ofperforated steel panels exists between practical applications and lab situations.

Next, some theory...


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Sound absorbing principles

- Friction and airflow resistance through a material. Porous materials (Air) - Resonance Plate resonator Helmholtz resonator: perforated panels

friction

resonance

porous materials

sound absorptionplate resonators

Helmholtz resonators perforated panel


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Plate resonators

A mass-spring system exists of a specific oscillation value. When the mass starts moving, it will start oscillating in a specific speed; the resonant frequency.

The absorption coefficient can be calculated with the use of acoustical impedance.


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Acoustical impedance

Acoustical impedance is the ratio of the sound pressure at a boundary surface to the sound flux (flow velocity of the particles or volume velocity, times area) through the surface.

Specific acoustical impedance is the ratio of the sound pressure at a point to the sound flux through that point.

( )( )( )( )

a

s

p tZv t Sp tZv t

=⋅

=


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Helmholtz resonators, perforated panel

'1 0

' 2 ''20 1

4( )

Z ZZ Z Z

α =+ +

Absorption coefficient

For Helmholtz resonators can be calculated from: Z

0= the characteristic impedance of air

Z1= the impedance of the resonator in total = Z

R/h

ZR= Z

V+Z

M

h= the percentage perforations

ZV

= impedance of the air cavity Z

M = impedance of the air in the perforation

Z’ =Z’M+ Z’

V = the real component of the complex number of Z

R

Z1’’ =Z’’

M+ Z’’

V = the imaginary component of the complex

number of ZR

Z= impedance, a complex number (z)Z’= the real component of the impedance (a)Z’’= the imaginary component of the impedance (i*b)z= a+i*b or Z=Z’+Z’’

ZV

ZM

Z0air

Z1total

h

Z1 = ZR/hZR = ZM/ZV


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Helmholtz resonators, important factors Percentage perforation The more perforations, the higher the resonance frequency.

Thickness of facing The thicker, the higher the frequency of the maximal absorption peak.

83

Chapter 12

Fig,2. Absorption coefficient versus frequency graphs for a perforated faced sound absorber system for different percentage perforations of the facing. (Davern 1977)

Fig,3. Absorption coefficient versus frequency graphs for a perforated faced sound absorber system using different thickness of facing with the same percentage perforations. (Davern 1977)


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Helmholtz resonators, important factors Density of the porous backing material The denser, the broader the tuning of the system.

Air space between the facing and backing material Gives an overall decrease of absorbing properties of the system.

85

Chapter 12

Fig,4. Absorption coefficient versus frequency graphs for a perforated faced sound absorber system using porous backing materials of different densities. (Davern 1977)

Fig,5. Absorption coefficient versus frequency graphs for a perforated faced sound absorber system with and without an air space between facing and porous backing with the same facing perforations but different facing thickness. (Davern 1977)


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Helmholtz resonators, important factors Impervious layer between the facing and backing material Gives a huge overall decrease of absorbing properties of the system.

87

Chapter 12

Fig,6. Absorption coefficient versus frequency graphs for a perforated faced sound absorber system with and without an impervious layer between facing and porous backing with the same facing perforations but different facing thickness. (Davern 1977)

Fig,7. As in figure 13. but with different facing perforations and the same facing thickness. (Davern 1977)


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Research to do

Test method: scale model

Test method: laboratory measurement

Fundamental data: standard measurements in sports halls: RT and background noise.

Testing hypothese:A perforated steel panel behaves differently in practice than in a laboratorysituation on absorption coefficient because the shape of the panels causes a better sound absorption of parallel striking sound than on sound with a normal incidence, based on a phase shift principle. This principle increases the absorption coefficient results of the measurement in practice since there is more specific parallel striking sound than in a reverberation room (like the laboratory).

A perforated steel panel behaves differently in practice than in a laboratory situation on absorption coefficient because the different placement of the panel in the laboratory than in practice has influence on the result.

S R

S R

S R

a

b


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Research to do

Test method: scale model

Test method: laboratory measurement

Results and design:When the shape of the panels and so the phase shift seems to have good influence on the sound absorbing behaviour, the design could adapt on this result by using panels with other dimensions.

When the height / different placement of the panels in the laboratory gives different sound absorbing results, the design of the backing construction could be adapted in a way that the sound absorbing behaviour is optimized. S R

S R

S R

a

b


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Timeline:Week 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27Presentaons P2 P3 P4 P5Date 12-Dec 19-Dec 26-Dec 02-Jan 09-Jan 16-Dec 23-Dec 30-Jan 06-Feb 13-Feb 20-Feb 27-Feb 05-Mar 12-Mar 19-Mar 26-Mar 02-Apr 09-Apr 16-Apr 23-Apr 30-Apr 07-May 14-May 21-May 28-May 04-Jun 11-Jun 18-Jun 25-Jun 02-Jul

geen onderwijs afwezigMondayTuesdayWednesdayThursdayFriday aanvraag P4 aanvraag P5Weekend

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Timeline version 19-01-2012


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Questions?


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13-05-2011

2

Achtergrond huidige norm (2) • Goede

spraakverstaanbaarheid

• Signaal-ruisverhouding: – Direct geluid (nuttig) – Diffuus geluid (storend)

• De verhouding tussen ‘signaal’ en ‘ruis’ wordt bepaald door de hoeveelheid

geluidabsorptie

Sporthal (48 x 28 x 9 m)Afname geluidniveau

-20

-10

0

10

20

30

1 2 4 8 16 32

afstand bron-ontvanger [m]

G [d

B]

Totaal Direct Diffuus S/N

diffuusdir

tot

mfpr

GGNSAr

QG

/

)1(44

log1031/

2

S/N = 0

Achtergrond huidige norm (3) • De hoeveelheid geluidabsorptie in een sportzaal is bepalend

voor het ‘akoestisch comfort’ • Uitgedrukt in de gemiddelde absorptiecoëfficiëntα.

• De in de norm gestelde eis aan de nagalmtijd is dus een indirecte eis aan de hoeveelheid geluidabsorptie!

totAVT

6

ii

n

itot SA

1

tot

tot

SA

Gymzaal (21x12x6 m) – Norm: Tgem = 1,0 s; Tmax/fb = 1,4 s

De nagalmtijd als indicator voor de hoeveelheid geluidabsorptie

Gymzaal (21 x 12 x 6 m)Meting vs berekening

0.0

0.5

1.0

1.5

2.0

2.5

125 250 500 1000 2000 4000

f [Hz]

RT [s

]

T20-meting T-Sabine norm

Tgem = 1,0 s

Tgem = 1,6 s

Tgem = 0,8 s

Nagalmtijd


0.0

0.1

0.2

0.3

0.4

0.5

0.6

125 250 500 1000 2000 4000

f [Hz]

α [-]


α ‘norm’

α ‘aanwezig’

α ‘gemeten’

‘Berekende’ geluidabsorptiecoëfficiënt De nagalmtijd in relatie tot de verdeling van de geluidabsorptie Sporthal (48x28x9 m) - Norm: Tgem = 1,9 s; Tmax/fb = 2,7 s

3 varianten met gelijke hoeveelheid geluidabsorptie • Variant 1: Wandabsorptie rondom bovenste vlakken • Variant 2: Wandabsorptie rondom onderste vlakken • Variant 3: Wandabsorptie twee hele wanden

13-05-2011

2

Achtergrond huidige norm (2) • Goede

spraakverstaanbaarheid

• Signaal-ruisverhouding: – Direct geluid (nuttig) – Diffuus geluid (storend)

• De verhouding tussen ‘signaal’ en ‘ruis’ wordt bepaald door de hoeveelheid

geluidabsorptie

Sporthal (48 x 28 x 9 m)Afname geluidniveau

-20

-10

0

10

20

30

1 2 4 8 16 32

afstand bron-ontvanger [m]

G [d

B]

Totaal Direct Diffuus S/N

diffuusdir

tot

mfpr

GGNSAr

QG

/

)1(44

log1031/

2

S/N = 0

Achtergrond huidige norm (3) • De hoeveelheid geluidabsorptie in een sportzaal is bepalend

voor het ‘akoestisch comfort’ • Uitgedrukt in de gemiddelde absorptiecoëfficiëntα.

• De in de norm gestelde eis aan de nagalmtijd is dus een indirecte eis aan de hoeveelheid geluidabsorptie!

totAVT

6

ii

n

itot SA

1

tot

tot

SA

Gymzaal (21x12x6 m) – Norm: Tgem = 1,0 s; Tmax/fb = 1,4 s

De nagalmtijd als indicator voor de hoeveelheid geluidabsorptie


0.0

0.5

1.0

1.5

2.0

2.5

125 250 500 1000 2000 4000

f [Hz]

RT [s

]


Tgem = 1,0 s

Tgem = 1,6 s

Tgem = 0,8 s

Nagalmtijd


0.0

0.1

0.2

0.3

0.4

0.5

0.6

125 250 500 1000 2000 4000

f [Hz]

α [-]


α ‘norm’

α ‘aanwezig’

α ‘gemeten’

‘Berekende’ geluidabsorptiecoëfficiënt De nagalmtijd in relatie tot de verdeling van de geluidabsorptie Sporthal (48x28x9 m) - Norm: Tgem = 1,9 s; Tmax/fb = 2,7 s

3 varianten met gelijke hoeveelheid geluidabsorptie • Variant 1: Wandabsorptie rondom bovenste vlakken • Variant 2: Wandabsorptie rondom onderste vlakken • Variant 3: Wandabsorptie twee hele wanden

Example RT to a


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ZV

ZM

Z0air

Z1total

h

Z1 = ZR/hZR = ZM/ZV

( )( )

0 ,2

0 ,

1 /1

1 /s material

s material

Z Z

Z Zα

−= −

+

absorption coefficient calculation porous materialsZs,material= specific impedance of the material