P2 presentation Yvonne Wattez

ACOUSTICS IN SPORTS HALLS
research on the acoustical behaviour of perforated panels

Presentation P2
25/01/2012

Graduation project of Yvonne Wattez
Student nr. 1360809

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

Mentor 1: Martin Tenpierik
Mentor 2: Peter van Swieten

ACOUSTICS IN SPORTS HALLS Yvonne Wattez 1360809 graduation project
research on the acoustical behaviour of perforated panels P2 presentation 25/01/2012

Introduction

1. Graduation so far
Problem 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. Design
4. Timeline

2


Why?
I like sports.
I like acoustics.

3


Problem description
Complaints 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]

4

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. Yvonne Wattez 1360809 graduation project
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 Legislation &
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
Standards
average absorption coefficient was advised to be at least 0,25. (Nijs 2004)
Based on reverberation time [RT]
The ISA-Sports standard includes: information on the location, the sports equipment, dressing rooms, and backgound noise level.
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
Limits depend on size and volume.
reverberation time in frequency band of 125-4000Hz may not be higher than 1,0 seconds for a [source: ISA Sport, ISA-N/A 1.1 ]
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 picture: sports hall in Amstelveen
D.2 Sports hall 35 x 80 x 10 ≤ 2,3 [source:www.sportbedrijfamstelveen.nl]

5
Conclusion


Reverberation Time Parameters
The reverberation time is defined as the time that expires before a sound pressure Reverberation Time (RT):
has decayed by 60 dB after the sound source has been swiched off. Sabine’s formula

T15 (blue), T20, T30 (black) Sabine 1 V
1 VRT= ⋅
RT =
6A
6 A + 4mV
with: RT= reverberation time [s]
V= volume of room [m3]
A= total absorption of materials in room =  (α S )
i i

with: αi = absorption coefficient of element i [-]
Si = surface of element i [m2]
4mV = correction for air attenuation
Sabine correction of Lau Nijs
This correction is made because Sabine is based on a cube. Sports halls
shape. By replacing the surface factor S by a certain part of the volume
realistic.
1 V
RT =
6 α ⋅ 6V 2/3

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 coe
1 V
RT =
6 S ⋅ ln (1 − α )−1  6
 


Absorption coefficient Parameters
Absorption coefficient a is a measure of the efficiency of a surface or material in Wa
absorbing sound. α=
Wi
Reflected sound (A, B, C) r
Transmitted sound (D) t absorption coefficient a=
Absorbed sound (E, F, G, H, I, J, K) a absorbed energy/incident energy

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

SRC diagram: Everest 2001

7


Speech Intelligibility Parameters
Depends 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.

8

– Norm: Tgem = 1,9 s; Tmax/fb = 2,7 s EDT T10 T20 T30 T15 norm


Flutter echo Parameters
De nagalmtijd als te berekenen parameter in between
Reflecting sound
in het ontwerp parallel walls.
90 m = 2 x zaallengte

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

3

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

9


Formulas compared: Reverberation Time
Big differences found in comparison of different formulas,
computer programmes and measurements.
Schijndel
Calculations vs. measurements.
Method frequency average 500Hz 2000Hz
Standard ISA Sport 1.6 1.6 1.6
Standard ISA Sport max 2.3 2.3 2.3
L.Nijs & Sabine 2.22 1.62 2.24
Sabine 1.84 1.34 1.85
Eyring 1.62 1.09 1.62
Fitzroy 1.64 1.36 1.63
ODEON T30 1.79 1.83 1.66
CATT ACOUSTIC T15 1.77 1.86 1.64
CATT ACOUSTIC T30 2.01 2.2 1.77
Measurement T20 2.14 2.64 1.82

RT: methods vs. measurement
Schijndel
3

2.5 L.Nijs & Sabine
Sabine
Reverberation Time [s]

2 Eyring
Fitzroy
1.5
ODEON T30

1 CATT ACOUSTIC T15
CATT ACOUSTIC T30
0.5 Measurement T20
Standard ISA Sport
0
Standard ISA Sport max
average 500Hz 2000Hz
Frequency [Hz]
sports hall Schijndel: perforated
steel panels on walls

10


Different halls D1 T20
Sporthal compared: Reverberation Time
4.0
Porous materials vs. perforated steel
panels.

The reverberation is much shorter
3.0
than expected at low frequencies
in a sports hall constructed with
perforated panels.

The perforated panels seem to
T [s]

2.0
behave differently than expected
from laboratory results.
(Especially at low frequencies.)
1.0

0.0
125 250 500 1000 2000 4000

f [Hz]

S1 S2 S3 AVERAGE

Expected and measured RT; porous
materials
SRC: LBP|SIGHT

11


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 of
perforated steel panels exists between practical applications and lab situations.

Next, some theory...

12


Sound absorbing principles
- Friction and airflow resistance through a material.
Porous materials
(Air)

- Resonance
Plate resonator
Helmholtz resonator: perforated panels

friction porous materials

sound absorption
plate resonators
resonance
Helmholtz resonators perforated panel

13


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.

14


Acoustical impedance
p (t )
Acoustical impedance is the ratio of the sound pressure at a boundary surface to the sound Za =
flux (flow velocity of the particles or volume velocity, times area) through the surface.
v(t ) ⋅ S
Specific acoustical impedance is the ratio of the sound pressure at a point to the sound flux p (t )
through that point. Zs =
v(t )

15


Helmholtz resonators, perforated panel
Z 1 Z1 = ZR/h
Absorption coefficient total
ZR = ZM/ZV

4 Z1' Z 0 ZV
α= '
( Z + Z 0 ) 2 + Z1''2 ZM

For Helmholtz resonators can be calculated from: Z 0
air
Z0= the characteristic impedance of air
Z1= the impedance of the resonator in total = ZR/h
ZR= ZV+ZM h
h= the percentage perforations
ZV = impedance of the air cavity
ZM = impedance of the air in the perforation
Z’ =Z’M+ Z’V = the real component of the complex number of ZR
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’’

16


83
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.

Fig,2. Absorption coefficient versus frequency graphs Fig,3. Absorption coefficient versus frequency graphs for
for a perforated faced sound absorber system for different a perforated faced sound absorber system using different
percentage perforations of the facing. (Davern 1977) thickness of facing with the same percentage perforations.
(Davern 1977)

17


Helmholtz resonators, important factors 85

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.

Fig,4. Absorption coefficient versus frequency graphs for Fig,5. Absorption coefficient versus frequency graphs for
a perforated faced sound absorber system using porous a perforated faced sound absorber system with and without
backing materials of different densities. (Davern 1977) an air space between facing and porous backing with the
same facing perforations but different facing thickness.
(Davern 1977)

18


Helmholtz resonators, important factors 87

Impervious layer between the facing and
backing material
Gives a huge overall decrease of
absorbing properties of the system.

Fig,6. Absorption coefficient versus frequency graphs for Fig,7. As in figure 13. but with different facing perforations
a perforated faced sound absorber system with and without and the same facing thickness. (Davern 1977)
an impervious layer between facing and porous backing with
the same facing perforations but different facing thickness.
(Davern 1977)

19


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

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

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

b

20


Results and design: Research to do
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
Test method: scale model
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

Test method: laboratory
measurement

a

b

21

Date
Week

Friday

Acvity
Tuesday
Monday

Deadline
Thursday

Weekend
Wednesday
Presentaons
Literature, theory

12-Dec
50
Thursday: Zalen bekend (materiaal bekend) fabrikant benaderen Literature, theory, organize material

19-Dec
51
Timeline:
Literature, theory

26-Dec
52

geen onderwijs
Second mentor known
02-Jan
1

Prepare tests, prepare P2
09-Jan
2
Timeline version 19-01-2012

16-Dec
3
P2

23-Dec
4

afwezig

Report (not a lot)
30-Jan
5

Tests scale model
06-Feb
6

Marterial available Tests scale model
13-Feb
7

Tests sports halls done Tests scale model
20-Feb
8

Tests sports hall
27-Feb
9
research on the acoustical behaviour of perforated panels

P3

Tests sports hall
05-Mar
10

Tests laboratory
12-Mar
11

aanvraag P4

Tests laboratory done Tests laboratory
19-Mar
12

Tests laboratory
26-Mar
13

Report
02-Apr
14

In situ measurements done Report
09-Apr
15

Design
16-Apr
16

Design
23-Apr
17

Design, Presentaon
18
P4

Presentaon
30-Apr 07-May
19

Presentaon
14-May
20

Presentaon
21-May
21

aanvraag P5

Most conclusions ﬁnished
28-May
22

Report
04-Jun
23

Report
11-Jun
24

Report, Prepare presentaon
18-Jun
25

Prepare presentaon
25-Jun
26
P2 presentation 25/01/2012
Yvonne Wattez 1360809 graduation project

P5

22
02-Jul

Prepare presentaon
27


Questions?

23

2.5

ACOUSTICS IN SPORTS HALLS 2.0
Yvonne Wattez 1360809 graduation project
1.5

RT [s]
1.0

0.5
Example RT to a
Nagalmtijd 0.0
125 250 500 1000

Gymzaal (21 x 12 x 6 m) f [Hz]
Meting vs berek ening Gymzaal (21x12x6 m)
T20-meting T-Sabine
– Norm: Tgem = 1,0 s; Tmax/fb = 1,4 s
2.5

2.0

Tgem = 1,6 s
1.5
RT [s]

Tgem = 1,0 s
1.0

0.5 Tgem = 0,8 s

0.0
125 250 500 1000 2000 4000
f [Hz]

T20-meting T-Sabine norm
‘Berekende’ geluidabsorptiecoëfficiënt De nagalmtijd in relatie tot de v
Gymzaal (21 x 12 x 6 m)
van de geluidabsorptie
Meting vs berek ening
Sporthal (48x28x9 m)
0.6
α ‘aanwezig’ - Norm: Tgem = 1,9 s; Tmax/fb = 2,7 s
0.5

0.4

α ‘norm’
α [-]

0.3

0.2
α ‘gemeten’

De nagalmtijd in relatie tot de verdeling 0.1

van de geluidabsorptie 0.0
125 250 500 1000 2000 4000 3 varianten met gelijke hoeveelheid geluidabsorptie
Sporthal (48x28x9 m) f [Hz] • Variant 1: Wandabsorptie rondom bovenste vlakken
• Variant 2: Wandabsorptie rondom onderste vlakken
- Norm: Tgem = 1,9 s; Tmax/fb = 2,7 s T20-meting T-Sabine norm
• Variant 3: Wandabsorptie twee hele wanden

24


absorption coefficient calculation porous
materials
Zs,material= specific impedance of the material Z 1 Z1 = ZR/h
total
ZR = ZM/ZV

α= 1−
(1 − Z / Z 0 s , material ) ZV

(1 + Z / Z )
2 ZM

0 s , material
Z 0
air

h

25

P2 presentation Yvonne Wattez

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