reverberation chamber design
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Acoustics Instruments and Measurements July 2013, Caseros, Buenos Aires Province, Argentina
REVERBERANTION CHAMBER DESIGN
AGUSTÍN Y. ARIAS
1
1 Universidad Nacional de Tres de Febrero, Buenos Aires, Argentina.
agustin.arias@outlook.com
1. INTRODUCTION
A reverberation chamber is, basically, a room that
has a long reverberation time and is designed as
diffuse as possible. The construction of the room
should realize a high performance of sound insulation
from any noise that comes from outside, since the
interior of the room is used primarily for acoustics
characteristics of material testing, which requires
complete independence of any unwanted outside
sound. Furthermore, the materials on the surface of
the inner walls must be carefully chosen, for
minimum absorption of sound energy. Reducing the
sound energy absorption means to increase the
energy of the reflections, which leads to achieve a
totally diffuse field and a long reverberation time.
Thus the factors that dominate the sound attenuation
are: air absorption, which is considerable regarding
the size of the chamber, especially at high
frequencies, and the low absorption coefficient of the
room surfaces.
In this report the design of a reverberation
chamber is presented according to the requirements
of ISO-354 “Acoustics - Measurement of sound
absorption in a reverberation room” [1]. The
construction details are specified and finally the
simulation results are shown for evaluating
reverberation time within the chamber.
2. ISO 354 REQUIREMENTS
As mentioned above, the reverberant chamber
design must meet certain essential characteristics
defined in the Standard ISO-354. The most important
are:
The minimum volume of the chamber should be
approximately 200 m3.
The room should allow a large diffusion of the
sound field, for which suspended diffusers are
needed (large plates that hang from the ceiling to
improve the sound diffusion).
The relative humidity in the chamber should be
greater than 40%, and temperature above 10 º C.
The shape of the reverberation room shall be
such that the following condition is fulfilled:
(1)
Where is the length of the longest straight
line which fits within the boundary of the room
(e.g. in a rectangular room it is the major
diagonal), in meters. V is the volume of the
room, in cubic meters.
In order to achieve a uniform distribution of
natural frequencies, especially in the low-
frequency bands, no two dimensions of the room
shall be in the ratio of small whole numbers.
The equivalent sound absorption area of the
empty room, A1 determined in one-third octave
bands, shall not exceed the values given in Table
1. If the volume V of the room differs from 200
m3, the values given in Table 1 shall be
multiplied by (V/200 m3)
2/3.
Table 1. Maximum equivalent sound absorption areas for
room volume V = 200 m3
Frequency [Hz] A1 [m2] Frequency [Hz] A1 [m
2]
100 6,5 800 6,5
125 6,5 1000 7
160 6,5 1250 7,5
200 6,5 1600 8
250 6,5 2000 9,5
315 6,5 2500 10,5
400 6,5 3150 12
500 6,5 4000 13
630 6,5 5000 14
3. DESIGN
3.1. Reverberation chamber
There is no ideal way to build reverberant
chambers, but it's better to select non-uniform
asymmetrical. In this manner, the reverberant field
produced indoor will be as diffuse as possible. Figure
1 shows a 3D model of the reverberation chamber
from an external and internal view.
2
Figure 1. 3D model.
The volume of the chamber is 399.52 m3 and the
total surface is 337.37 m2. The constructive details
will be described below. From Figures 2 and 3, it is
possible to observe that the walls and ceiling of the
chamber are asymmetrical. There is a double-panel
window type “fishbowl” that communicates the
chamber interior to the control room. The access to
the chamber is through a double steel gate (Figure 4).
This gate must be carefully installed with weather-
stripping in order to minimize the external noise
transmission into the room. The size of the gate
allows access industrial machinery for measurement
of acoustic power. Figure 3 shows the front view,
plan view and cross-section view of the chamber
indicating the main dimensions. To avoid any type of
background noise and to prevent vibration
transmission within the chamber, it was located
inside of a big structure of solid brick, as it can be
observed in Figure 2. The left-side wall of the
enclosure was removed for a better understanding.
Also it can be observed the side hall conducting to
the control room behind the chamber.
Figure 2. Solid brick structure covering the chamber (left-
side wall removed).
Figure 3. Reverberation chamber views. Top: cross-section
view. Middle: plane view. Bottom: front view.
Figure 4. Double steel gate.
3
3.2. Control room
The control room is placed behind the back wall
of the reverberation chamber. A double glassed
window allows a direct vision to the interior of the
chamber. The control room is used to install the
external equipment necessary to perform the
measurements (desktop and personal computers,
power amplifiers, mixer, cables patching (XLR-TRS
¼”), etc. Figure 5 shows a 3D model of the control
room.
Figure 5. 3D model of the control room.
4. SOUND INSULATION: WALLS AND
FLOORS
As it was mentioned, besides achieving a
complete diffuse sound field within the chamber, it is
necessary a complete insulation to any external noise.
This requirement leads to the design of the surface
structure. The walls of this structure are designed as
indicated in Figure 6 [2]. In addition to this structure
design, it may be added a metal mesh in the air gap
between the walls to avoid electromagnetic
interferences (Faraday Cage).
The Acoustic Reduction Index for that partition is
shown in Figure 7. The Acoustic Reduction Index
weighted is Rw = 57 dBA.
Regarding the construction of the reverberation
chamber, a double wall was designed. In addition, a
floating floor is required to avoid any type of
vibrations transmitted to the chamber interior. Figure
8 shows the wall structure of the chamber.
The Acoustic Reduction Index for that partition is
shown in Figure 9. The Acoustic Reduction Index
weighted is Rw = 47 dBA.
Figure 10 shows the floating floor of the chamber
and the walls design. Finally, the ceiling of the
reverberation chamber is made of a reinforced
concrete slab of 140 mm thickness. The space
between the cover structure and the chamber is
coated with glass wool “ISOVER” PV 40 mm
thickness.
Figure 6. Side walls of the cover structure.
Table 2. Side walls materials of the cover structure.
Item Wall
structure Material
Thickness [mm]
Weight [k/m
2]
4a Plasterboard
lining Plasterboard 10 8.0
4 Panel
“ISOVER” Calibel
Fiberglass 25 1.7
3 Air chamber - 20 -
2 Gripping
paste - - 4.0
1 Solid brick partition
Ceramic 120 180
Total 175 194
Figure 7. Acoustic Reduction Index of the cover structure
partition. (- - -) without acoustic treatment. (---) with Panel “ISOVER” Calibel.
R [
dB
]
Frequency [Hz]
4
Figure 8. Side walls of the reverberation chamber.
Table 3. Side walls materials of the reverberation chamber.
Item Wall
structure Material
Thickness [mm]
Weight [k/m2]
4 Double
hollow brick wall
Ceramic 80 -
3 Panel
“ISOVER” PV Glass wool 40 -
2 Simple
hollow brick Ceramic 35 -
1 Laying of plaster
Plaster 10 -
Total 165 140
Figure 9. Acoustic Reduction Index of the reverberation
chamber walls.
Figure 10. Reverberation chamber walls and floor
construction.
5. INDOOR ENVIRONMENT OF THE
REVERBERATION CHAMBER
As shown in Figure 10, the indoor surfaces of the
chamber consist of tile walls, and terrazzo floor.
These materials were chosen because of their low
sound absorption coefficient, which are detailed in
Figures 11 and 12. To improve sound diffusion inside
the chamber and thus increase the reverberation time
especially at high frequencies, the installation of
fixed and removable diffusing surfaces is
recommended. For example, fixed diffusing surfaces
may be convex wooden plates MDF (medium-density
fiberboard) as seen in Figure 13.
Figure 11. Absorption values of Tile
Figure 12. Absorption values of Terrazzo
Double wall Terrazo Tile
Concrete
Felting “ISOVER” FF
12mm
Reinforced
concrete 100mm
R [
dB
]
Frequency [Hz]
5
Figure 13. MDF convex board.
The absorption coefficients of the double-panel
window and the steel gate are shown in Figures 14
and 15 respectively.
Figure 14. Absorption values of double-panel window
Figure 15. Absorption values of steel gate.
6. SIMULATION
The reverberant chamber was modeled on EASE
to predict the reverberation time with the surface
absorptions mentioned above. The reverberation time
was calculated according to Sabine’s equation.
V: volume of the chamber [m3]
Atot: total absorption of the chamber [m2]
m: attenuation sound constant in air
Figure 16. Chamber model in EASE.
The results obtained are shown in Figure 17. It is
observed the high influence of the air attenuation at
high frequencies, so the diffuser installation is highly
recommend. At low frequencies the reverberation
time remains above 10 s, which indicates an excellent
performance of the chamber in those frequencies
bands.
Figure 17. Reverberation time obtained according to
Sabine’s equation.
7. BUILDING
In addition to the reverberant chamber and the
control room, the building has two administrative
rooms, a bathroom and a dining room, as shown in
Figure 18. The total terrain area is 227.27 m2. The
principal dimensions are: width 9.38m, 24.23m long
and 6.34 m height. These dimensions were adjusted
to the urban planning code of Buenos Aires [3]. In
addition, the urban planning code establishes that the
dividing wall between two adjacent buildings must be
at least 150 mm thickness.
6
Figure 18. Building rooms.
8. REFERENCES
[1]ISO-354 “Acoustics - Measurement of sound
absorption in a reverberation room
[2]ISOVER “Manual de Aislamiento”.
[3]Ley 449. BOCBA N° 1044. Buenos
Aires.Argentina. 2000.
Administrative rooms
Dinning room
Bathroom
Reverberation
chamber
Steel gate
Control room
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