THE ANNALS OF DUNAREA DE JOS UNIVERSITY OF GALATI [602294]

THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE XIV MECHANICAL ENGINEERING, ISSN 1224-5615
2010
37

EXPERIMENTAL RESEARCHES ON THE
SOUND ABSORPTION COMPOSITES USED
FOR PUBLIC WORKS EQUIPMENT

Assoc. Prof. Dr. Eng. Nicusor DRAGAN
MECMET – The Research Center of Machines,
Mechanic and Technological Equipments
"Dunarea de Jos" University of Galati

ABSTRACT

Decreasing of sound and vibration global level inside and/or outside
the public works equipment’s cabin as well as the reduction the noise
pollution or the pollution accounted by the vibration and mechanical
shocks on the construction site is an actual matter, especially for the
countries having become lately EU members; these countries must
harmonize their national legislations regarding the environment
pollution and the labor protection according to the EU Directives
(98/37/EC, 2000/14/EC, 89/391/EEC, 2003/10/EC, 89/656/EEC,
92/85/EEC). This study presents the problem of designing,
manufacturing and testing of some protective systems made of
composite materials which can simultaneously perform the next
requirements: noise absorption for middle and high range
frequencies (400-8000 Hz), noise insulation for low frequencies (40-
400 Hz), vibration damping in order to avoid noise transmission by
structure and finally, modularity and adaptability for using to
different types of public works equipment, also for other
technological equipment with a high level of noise, vibration and
mechanical shocks. This article presents the experimental data of
sixteen composite structures with noise absorption and insulation
features and one case study of global level noise reduction
L

inside
the cabin of a crawler excavator. The experimental research has
done with Brüel & Kjær acoustic measuring equipment at the
Vibration and Acoustic Laboratory of the Research Institute for
Construction Equipment and Technology – ICECON S.A. Bucharest,
Romania. The study case for the excavator S1021 was made in
the
Research Center of Machines, Mechanic and Technological
Equipments – MECMET from "Dunarea de Jos" University of Galati,
Engineering Faculty of Braila
.

KEYWORDS: composite structures, global noise level, sound absorber, public
works equipment

1. Introduction
The goal of using innovative composite
structures in the public work equipment is to
simultaneously decrease the global level of
noise and vibrations into cabin and to dissipate the energy of the emitted sound to the
environment. These properties can be assured if
the structure of sandwich composites is made
up of one layer of material in order to insulate
the low frequency noise, one layer of porous Generated by Foxit PDF Creator © Foxit Software
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38

material in order to absorb the medium and
frequency sound and one layer of antivibratile
material. Taking into consideration the usual
noise levels of different types of civil work
equipment and the EU Directives requests, it
can be appreciated that the acoustic
performances of soundproofing treatments of
the cabins and of the cases must be
characterized by the values from table 1.

2. Sound absorbent and insulation
modular composites
The project “Modular protective
systems from sound absorbent and sound
insulator composite materials for civil works
equipment” proposes some types of composite
materials (see table 2) in order to assure the
required values for the acoustic properties.
The significance of the layers of
composites from table 2 are:
PC10 – composite cork ≠1mm
PC30 – composite cork ≠3mm
PST5 – close cell low density PS foam ≠0.5mm
PST10 – close cell low density PS foam ≠1mm PST20 – close cell low density PS foam ≠2mm
PSTM5 – close cell low density PS foam with
Alu foil ≠0.5mm
PVC8 – high density PV foil ≠0.8mm
PVC10 – high density PV foil ≠1mm
PVC15 – cellulose background PV foil ≠1.5mm
PVCT10 – textile reinforced PV foil ≠1mm
PES20 – open cell PE foam ≠2mm
PES50 – open cell PE foam ≠5mm
MTT20 – textile reinforced latex ≠2mm
PESM40 – open cell PE foam with Alu foil
≠4mm
PESM150 – open cell PE foam with Alu foil
plus textile reinforced PV foil ≠15mm
Table 3 shows six different shapes of
modules for the composite structures, each of them in
two different sizes.

3. Experimental data
The experimental data was determined
with Kundt’s Tube Bruël&Kjær for 1/3 octave
bandwidth (acoustic standing waves method,
see [2]). Figures 1 to 4 show the comparisons
between the sound absorption coefficients


determined for the composite materials with
structures acc. to table 2. The variations of


coefficients are plotted for sound frequencies
between 50Hz and 3150 Hz (centered 1/3 octave Table 1.
Requiring acoustic performances for
the composite materials for acoustic treatments
Frequency
range [Hz]

ACOUSTIC
PROPERTY Den.

Unit

400-
1000

1000-
4000

Sound absorption
coefficient % 15÷20

20÷50

Sound transmission
loss L dB 10÷20

20÷30

Table 2.
The denomination and structures of
different types of composites
Denom.

Composite structure
SCFF1

PVC10+PC30
SCFF2

PVC10+PC30+MTT20
SCFF3

PVCT10+PC30+PESMV150
SCFF4

PVC15+PC10+MTT20
SCFF5

PVC10+PC30+PES20+MTT20
SCFF6

PVC10+PC30+PES50+MTT20
SCFF7

PVC10+PC30+PESM40+MTT20
SCFF8

PVC10+PC30+PESMV150+MTT20
SCFF9

PVC15+PC10+PESM40+MTT20
SCFF10

PVCT10+PC10+PES50+MTT20
SCFF11

PVCT10+PES20+PES50+PESMV150
SCFF12

PVC15+PC10+PESMV150+MTT20
SCFF13

PVC8+PES20+PES50+MTT20
SCFF14

PVC8+PC10+PES20+PES50+MTT20
SCFF15

PVCT10+PES20+PES50+PESM40
SCFF16

PVC8+PC10+PES20+PVC10+PES50+

+MTT20

Table 3.
The geometrical shapes and sizes of
the modular composite structures
Shape Size [mm]

6.6×100
43.3×50

100×86.6
50×43.3

100×100
50×50

50×90
75×45

141.4×100
70.7×50

100×70.7
50×35.4
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI FASCICLE XIV

39

bandwidth frequencies).
According to plotted diagrams from fig.
1 to 4, certain conclusions may be drawn:
►for low and middle-low frequency bandwidth of noise (
Hz 800 f

), the sound absorption
coefficient

is smaller than 20%, no matter of
the type of composite structure;

Fig.1 Sound absorption coefficient for composite materials SCFF1, SCFF3, SCFF7, SCFF15

Fig.2 Sound absorption coefficient for composite materials SCFF2, SCFF5, SCFF9, SCFF14 Generated by Foxit PDF Creator © Foxit Software
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40

►for middle frequency bandwidth of noise
(
Hz 2000 f Hz 800


), the sound absorption
coefficient

is growing faster, with values
from 15% to 70% (with maxim values for frequencies around 1,2÷1,5kHz);
►for high frequency bandwidth of noise
(
Hz 2000 f

), the sound absorption coefficient

is growing (from 20% to 95%) for all types
Fig.3 Sound absorption coefficient for composite materials SCFF4, SCFF6, SCFF8, SCFF11
Fig.4 Sound absorption coefficient for composite materials SCFF10, SCFF12, SCFF13, SCFF16 Generated by Foxit PDF Creator © Foxit Software
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI FASCICLE XIV

41

of composite structures excepting SCFF1 (for
which the coefficient

is almost constant,
with the smallest value of 12÷13%);
►for entire frequency range domain, the thicker the composite structure is, the sound
absorption coefficient

is.
Figure 5 shows the variation of sound
absorption coefficient

related to the centered

Fig.5 Sound absorption coefficient

for base materials Generated by Foxit PDF Creator © Foxit Software
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FASCICLE XIV THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI

42

frequency of 1/3 octave bandwidth for the base
materials (acc. to §2). The values of these
coefficients were determined with Kundt’s Tube
Bruël&Kjær type 4206 (acoustic standing
waves method) for the frequency bandwidth
0÷3200Hz, with an increment pitch of 4Hz. The
experiment data were acquainted and processed
by Bruël&Kjær PULSE Platform type 7758.

4. Cabin’s phonic treatments for
public works equipment – case study
According to [1] and [4], the main
acoustic features of the self propelled public
work equipment cabins are:
-the equivalent phonic absorbent area
A
[m
2
]
-the average absorption coefficient
med


-the global sound level loss
L

[dB]
The calculus relation for the average
sound absorption coefficient
med

is



 
ii imed
SS
, (1)

where:
i
S
is the area of the surface number
i

i

– the absorption coefficient of the
surface
i
S

The calculus relation for the global
sound level reduction/loss
L

is

0
AAlg 10 L 
, (2)

where:
A
is the equivalent absorption area of
the cabin after the phonic treatment
0
A
– equivalent absorption area of the
cabin without the phonic treatment
The equivalent absorption area can be
calculated as follows:



 
n
1 ii i
S A
(3)

In order to simulate the reduction of the
global noise level inside the cabin of the
excavator S1201, the next dimensional and
acoustic features are to be considered:
►
2
1
m 1 . 5 S
– glass surface area
►
2
2
m 2 . 1 S
– uncoated steel sheet surface
area
►
2
3
m 8 . 3 S
– phonic treated surface area
with composite structures SCFF1→SCFF16
►
33 . 0
1
 
– organic glass sound absorption
coefficient (average value)
►
08 . 0
2
 
– steel sound absorption
coefficient (1mm thickness sheet).
Fig.6 Global sound level reduction
L

for S1201 excavator’s cabin
Comparison between phonic treatments with SCFF1, SCFF3, SCFF7, SCFF15 Generated by Foxit PDF Creator © Foxit Software
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43

With the considered values, we can
calculate for the S1201 cabin:
ștotal surface area
23 2 1 i
m 1 . 10 S S S S S    


șequivalent absorption area without phonic
treatment

Fig.8 Global sound level reduction
L

for S1201 excavator’s cabin
Comparison between phonic treatments with SCFF4, SCFF6, SCFF8, SCFF11

Fig.7 Global sound level reduction
L

for S1201 excavator’s cabin
Comparison between phonic treatments with SCFF2, SCFF5, SCFF9, SCFF14 Generated by Foxit PDF Creator © Foxit Software
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FASCICLE XIV THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI

44

 
23 2 2 1 1 i i 0
m 083 . 2 S S S S A       


șaverage sound absorption coefficient without
phonic treatment
206 . 01 . 10083 . 2
SS
ii imed
  



Figures 6 to 9 show the global level of
sound
L

inside the cabin of the Romanian
crawler excavator S1201 using the phonic
treatments with composite materials tested in
the lab (SCFF1 to SCFF16).
Analyzing the diagrams which show the
reduction of the global sound level inside the
cabin of the excavator S1201, we can conclude:
♦the shapes of curves which show the variations
of global sound level reduction
L

(fig. 6, fig.
7, fig. 8 and fig. 9) are similar to the shapes of
curves of variation of sound absorption
coefficients (fig. 1, fig. 2, fig. 3 and fig. 4);
♦for low and middle-low frequencies
(
Hz 800 f

), the reduction is 0.5÷1.5dB(A) no
matter the type of composite structure; for high
frequencies (
kHz 2 f

), the reduction is
1.5÷5dB(A).

5. Conclusions
Regarding the noise assessment in
construction [3], a reduction of 2dB(A) is good
enough for some types of public work
equipment: excavators, frontal loaders, asphalt
stations, aso. For other types of construction machines and equipment (vibrating compactors,
boards and rammers, pneumatic hammers, some
hand-tools), a reduction of 3÷5dB(A) is
desirable.
From the diagrams which show the
variation of sound absorption coefficient, we
can say that the materials with “high” specific
density (like Polyvinyl) have good property of
absorption for middle frequencies and the thick
materials with open cell foam macrostructure
(like Polyurethane, Polyester) have good sound
absorption properties especially for high
frequencies. The materials type cork based
(natural cork, macro composite cork) have good
properties for vibration damping and structural
noise attenuation.

6. References
[1] Anghelache, D. , Acoustic absorption coefficient variation of
sound absorbing structures and materials , The Annals of “Dunarea
de Jos” University of Galati, Fascicle XIV Mechanical
Engineering, 2008
[2] Bratu, P. , Noise reduction in case of mobile machinery cabins ,
Proceedings of 10
th
International Conference on the Theory of
Machines and Mechanisms IFTOMM, Prague, 2008
[3] Dragan, N. , Assessing and controlling the noise in
construction. Romanian and EU legislation , The Annals of
“Dunarea de Jos” University of Galati, Fascicle XIV Mechanical
Engineering, 2008
[4] Vasile, O., Dragan, N. , Innovative Sound Insulation and
Absorption Modular Systems for Public Works Equipment ,
Proceedings of the 5
th
International Vilnius Conference
“Knowledge-based technologies and OR methodologies for
strategic decisions of sustainable development” KORSD-2009, Ed.
“Technika”, Vilnius, ISBN 978-9955-28-482-6

Fig.9 Global sound level reduction
L

for S1201 excavator’s cabin
Comparison between phonic treatments with SCFF10, SCFF12, SCFF13, SCFF16 Generated by Foxit PDF Creator © Foxit Software
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