PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Architectural acoustic design using absorption materials: the casestudy ”Snooze Panel”
Livio MAZZARELLA1; Maria CAIROLI2
1

Politecnico di Milano, Italy

2

Politecnico di Milano, Italy

ABSTRACTThe Snooze ® sound-absorbing panel is the result of the necessity to characterize an architectural space suchas offices, corridors, classrooms, hospitals while guaranteeing the required acoustic characteristics using
renewable materials. An experimental case study is proposed showing how different chooses in panel
assembly arrangement are affecting its acoustic performance. The proposed procedure allows evaluating theacoustic properties of a panel assembly, specifically the rating of sound absorption according to the EN ISO
11654 i.e. the weighted sound absorption coefficient aw, considering the intrinsic panel characteristics and thedifferent types of installation with variable distance from the wall surface behind the panel. While thematerial characteristics can be assessed in laboratory using appropriate instruments as explained, the acoustic
behavior of the panel due to the geometry and installation solutions are evaluated in actual assembly inreverberation chamber according to the standard EN ISO 354.
Keywords: absorption, insulation, measurements

1. INTRODUCTION
An architectural space is intrinsically sonorous; it is characterized by its own musicality andresonance depending on volumes, materials and shapes that define it.
The Snooze® panel can be an architectural element that satisfies aesthetic requirements while
guaranteeing the required acoustic characteristics of the space. It can be successfully used most of thetimes, when solutions to improve the space acoustic quality are taken into consideration and proposed
only in the executive phase of the project and not together with the architectural design.
The proposed procedure allows evaluating the acoustic properties of a panel assembly, specificallythe rating of sound absorption according to the EN ISO 11654 (1) i.e. the weighted sound absorption
coefficient, α w, considering the intrinsic panel characteristics and the different types of installation
with variable distance from the wall surface behind the panel.
The material characteristics are assessed in laboratory using appropriate instruments following
different standards (2), (3), the acoustic behavior of the panel due to the geometry and installation
solutions are evaluated in actual assembly in reverberation chamber according to the standard EN ISO
354 (4).

2. MATERIALS AND METHODThe Snooze® panel is made of hot-moulded polyester fibre, the absorbing material. The shape issquare 630 x 630 mm with rounded corners (Figures 1 and 2). The absorbing material is then coveredwith a synthetic lining.
This work aims to report about an assessment procedure for a panel assembly that can help todesign an assembly able to reach the absorption class A as defined by the ISO 11654, showing theinfluence of different design parameters as the material density, the mounting and the use of a liner.
The single-number rating specified in this International Standard can be used to formulaterequirements and to describe acoustical properties of sound-absorbing products to be used for
applications in offices, corridors, classrooms, hospitals, etc.
123474livio.mazzarella@polimi.it
Maria.cairoli@polimi.itFigure 1: panel without lining

Figure 2: panels with the lining on the reverberant chamber floor
The rating is not appropriate when the products are to be used in environments requiring special
careful acoustical design. In such cases, only complete sound absorption data as a function offrequency are satisfactory.
As the rating curve in this International Standard has as a lower limit the 250 Hz octave band,the rating is not appropriate below this frequency. If such low frequencies are of interest, reference
must be made to the complete sound absorption curve.
In this paper, much attention is given to the absorption class, but the measured absorption curveis also reported.
In particular, to improve the abortion properties different solutions are considered and combined
together, without changing the assembly panel shape and dimensions as defined by the Architects;
these potential improvements are:- an higher density of the polyester fiber instead of a low density polyester;- the increasing of the air gap behind the panel;- a lining improving the sound absorption properties of the panel
As explained in the literature, improving the density of an absorption material, the soundabsorption coefficient grows up at low frequencies and decrease slightly at higher frequencies (Figure3).
The influence on the acoustic absorption coefficient of the panel assembly has been investigate
comparing two equally shaped panel assemblies made with different densities (40 kg/m3 and 80 kg/k 3).

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Figure 3: the density effects in a porous panel (fibreboard thickness 40 mm)
Regarding the air gap behind the panel, if a thin porous absorber is positioned such that it has anairspace behind it, the composite impedance at the surface of the material, and thus the absorption
coefficient  is influenced by the backing. This influence has been analysed in a comparative way
assessing the acoustic performance of a pane assembly without and with a specified air gap behind.
The lining can have different characteristics. It can be transparent to the sound, i.e. the sound goes
through without any absorption, or it can be characterized by a specific flow resistance, according tothe EN 29053 (5), which can contribute to improve the overall sound absorption. To assess theinfluence of the usual liner covering such kind of absorber, measurements on the same assembly withand without the liner have been carried out.

3. Results and Discussion
3.1 Reverberant chamber measurements
Description of test environment in the reverberant room follows in Table 1:
Table 1: test environment
Room volume V
Room surface S 0
Diffusers surface St
Sound source positions:
Reference test area = 11,1 m2

191 m3244 m235 m2
411,1 m2

Five different configurations are tested:- n° 30 panels, density 80 Kg/m3, on the floor, without lining- n° 30 panels, density 80 Kg/m3, on the floor, with lining- n° 30 panels , density 40 Kg/m3, on the floor with lining- n° 30 panels with lining and 200 mm air gap behind, with lining 40Kg/m3- n° 30 panels with lining and 200 mm air gap behind, with lining 80Kg/m3
The results follow in Table 2 and in Figures 4-6:3476

Hz

100
125
160
250
315
400
500
630
800
1.000
1.250
1.600
2.000
2.500
3.150
4.000
5.000

Table 2: Sound absorption coefficient () in third octave bend
panel,panel,
panel ,
panel withdensity 80
density 80
densitylining andKg/m3 , on
Kg/m3 , on
40Kg/m3 , on 200 mm air
the floor,
the floor,
the floor
gap behind,
without
with lining
with lining
40Kg/m3
lining 
w 0.70
w 0.80
w 0.80
w 0.90Class CClass BClass BClass A
0,05
0,11
0,08
0,15
0,04
0,05
0,05
0,1
0,08
0,15
0,14
0,23
0,36
0,5
0,47
0,59
0,54
0,73
0,7
0,78
0,74
0,98
0,93
0,91
0,86
1,13
1,04
0,95
1,03
1,21
1,08
0,95
1,12
1,2
1,14
1,03
1,14
1,18
1,09
1,111,11
1,11
1,06
1,11
1,08
1,07
1,02
1,14
1,06
1,06
1,01
1,14
1,02
1,05
1,02
1,15
1,03
1,07
1
1,13
1,02
1,02
0,96
1,1
0,97
10,92
1,04

panel withlining and200 mm air
gap behind,
80Kg/m3
w 0.95
Class A
0,160,13
0,25
0,67
0,9
0,99
1,06
0,99
1,07
1,14
1,14
1,17
1,18
1,19
1,21
1,18
1,133477

abFigure 4: panel, density 80 Kg/m3, on the floor: (a) without lining, w 0.70; (b) with lining w 0.80

Figure 5: panel on the floor with lining , density 40Kg/m3, w 0.803478

abFigure 6: panel with lining and 200 mm air gap behind, (a) 40Kg/m3 w 0.90, (b) 80Kg/m3 w 0.95
At first, the lining properties are investigated comparing the absorption coefficients of the same
panel assembly with and without lining, density 80 Kg/m3 . The deviation of the absorption coefficientis defined as it follows:
𝐷 = (𝛼 − 𝛼 )/𝛼(1) is related to the panel without lining and to the panel with lining

Figure 7: absorption coefficient deviation due to the lining
The lining increases the absorption coefficient in all the considered range of frequencies. At lowerfrequencies, the contribution is much more significant but also up to 250 Hz and, at central frequency,

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there is an improvement that can be considered useful to improve the absorption Class of the panel.
The second consideration is about the material density.
The absorption coefficient deviation of the panel assembly on the floor is studied. In this case, isrelated to the panel without lining, density 40Kg/m3, and to the panel with lining, density 80Kg/m3.

Deviation
40,00%
35,00%
30,00%
25,00%
20,00%
15,00%
10,00%
5,00%
0,00%

Deviation
Log. (Deviation)

Figure 8: absorption coefficient deviation due to the material density
The highest absorption coefficient increasing due to the density improvement is at low frequencies
while up to 250 Hz the phenomenon is present but does not increase the absorption class of the panel.
The third study is the deviation due to the air gap for both the panels with a density 40Kg/m3 and 80
Kg/m3 ( in comparison with the same panels on the floor (.

Figure 9: absorption coefficient deviation due to the air gap, density panel 40 kg/m3

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Deviation
200,00%150,00%100,00%Deviation

50,00%

Log. (Deviation)

0,00%-50,00%Figure 10: absorption coefficient deviation due to the air gap, density panel 80 kg/m3
The air gap does not improve the absorption coefficient at central frequencies between 400 and
1500 Hz, but, because the absorption coefficient increases outside this range especially at lowfrequencies, the sound absorption coefficient, αw increases in both cases.

4. CONCLUSIONSThe lining proposed at first by the architects, for aesthetic reasons, is considered to increase theabsorption coefficient and it is introduced in any possible configuration.
The panel with 40 kg/m³ allows performances between class B and class A where it is progressively
distanced up to 20 cm from the wall (for example for ceiling applications). Moreover, its absorption
spectrum on the typical frequencies of the word (from 250 to 4000 Hz) is always higher than 0.5, withabsorption at the central frequencies of the speech close to 100%, obtaining great effectiveness on theintelligibility of the phonemes and therefore of the language.
The panel with density equal to 80 kg/m³, applied to the wall, allows performance close to class A.
In particular where it is progressively distanced up to 20 cm (ceiling application), class A is widelyachieved. The minimum absorption at the medium-low frequencies (250 Hz) is higher than 67%, whileon the higher frequencies it is always maximum (100%), resulting in the maximum efficiency in termsof speech intelligibility.
For a high acoustic performance space, it is then reasonable to propose the standard weight panel
with a density of 80 kg/m3 with the standard liner, which gives an A class as result, even if mountedvery close to the surface.

ACKNOWLEDGEMENTS
We thank dot. Moretti CEO of Biobyte s.r.l. to have shared with us the Snooze Panel tests in thereverberant chamber

REFERENCES
1. CEN-ISO. EN ISO 11654:1997,” Acoustics - Sound absorbers for use in buildings - Rating of soundabsorption (ISO 11654:1997)”, CEN, 1997.
2. CEN-ISO. EN ISO 10534-1:2001 “Acoustics - Determination of sound absorption coefficient andimpedance in impedances tubes - Part 1: Method using standing wave ratio (ISO 10534-1:1996)”, CEN,
2001
3. CEN-ISO. EN ISO 10534-2:“Acoustics - Determination of sound absorption coefficient and impedance
in impedances tubes - Part 2: Transfer-function method (ISO 10534-2:1998)”, CEN, 2001
4. CEN-ISO. EN ISO 354:2003 “Acoustics - Measurement of sound absorption in a reverberation room
(ISO 354:2003)”, CEN, 2003.
5. CEN. EN 29053:1993 “Acoustics - Materials for acoustical applications - Determination of airflowresistance”, CEN, 1993.

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