Communities Car Audio Blog Sound Absorber Option

5. Sound absorption. The use of sound-absorbing linings and piece volumetric structures to reduce noise

For
reflected sound reduction is applied
protective devices with large
absorption coefficient values, k
These include, for example, porous and
resonant absorbers (felt, cotton wool,
foam, pumice).

Decrease
noise in sound-absorbing
barriers
due to the transition of the vibrational
energy into heat due to the internal
friction in sound-absorbing materials.

sound-absorbing
structures (suspended ceilings, cladding
walls, rocker and piece absorbers)
should be used to reduce levels
noise at workplaces and in areas
permanent residence of people in
industrial and public buildings.
The area of ​​sound-absorbing linings and
number of piece absorbers
determined by calculation.

piece
absorbers should be used if
linings are not enough to get
required noise reduction, and instead of
sound-absorbing false ceiling,
when his device is not possible or
ineffective (high
production premises, availability
overhead cranes, light and aeration
lanterns).

acoustic
cladding is done for
decrease in the intensity of the incident and
reflected sound waves in order to reduce
noise level in the room. When reflected
sound wave from the barrier part of the sound
energy lost: converted to heat
or passes through a barrier.

Along
with porous materials for sound absorption
apply
special mastics that cover
partitions and separate parts of machines.

V
as a sound absorbing material
using ultra-thin fiberglass,
kapron fiber, mineral wool,
wood fiber and mineral wool
plates, porous polyvinyl chloride, etc.
The thickness of the facings is 20–200 mm.
In low rooms, they only veneer
ceiling, as the walls in them are practically
do not affect sound reflection, and in high
and elongated rooms - veneered
both walls and ceiling. For some
manufacturing processes (eg.
riveting, trimming, stamping, cleaning)
difficult or impossible to effectively reduce
noise with sound absorption.

Need
and the feasibility of using acoustic
noise reduction cladding
revealed by acoustic calculation.
Sound-absorbing structures should
apply when required reduction
sound pressure level Δ
L_tr,
dB, in the reflected field does not exceed 3 dB
less than three octave bands or
exceeds 5 dB in at least one of the octaves
stripes. At the calculated points selected on
workplaces, required reduction
sound pressure level should
exceed 1 dB and 3 dB, respectively.

sound-absorbing
facings are usually placed on
the ceiling of the room and on the upper parts
walls. To achieve maximum
possible absorption recommended
veneer at least 60%. total area
enclosing surfaces.
Placement of acoustic cladding on
the ceiling of the room is most rational
with a room height of not more than 6–8 m.
narrow and very high rooms
it is advisable to place an acoustic
lining on the walls, leaving only
the lower parts of the walls (2 m high) unlined.

If
the walls of the room and the ceiling are designed
translucent materials and area
few free surfaces, recommended
additionally use piece
(volumetric) sound absorbers of various
structures. Piece sound absorbers
can be used for acoustic
processing of premises and as
independent sound absorbers.

Efficiency
applications of acoustic cladding in
noisy environments depends on the acoustic
characteristics of the selected structures,
ways and place of their placement, sizes
premises and locations of settlement
points. The calculation should be made for
each of the eight octave bands with
geometric mean frequencies 63,
125, 250, 500, 1000, 2000, 4000, 8000 Hz.

V
industrial premises with sources
noise high intensity sound absorbing
facings and piece sound absorbers,
usually used in combination with
other notable events
noise reduction (soundproofing
casings, enclosures, screens, etc.), since
maximum noise reduction in
zone of the reflected field (at a sufficient
distance from the source of noise) at
acoustic treatment of rooms
usually does not exceed 8 - 10 dBv
low frequency region and 10-12 dBv
areas of maximum values
sound absorption coefficients.

Acoustic characteristics of sound-absorbing materials

Thickness sound-absorbing material, mm	Air clearance, mm	Reverb sound absorption coefficient geometric mean frequencies octave bands, Hz
63	125	250	500	1000	2000	4000	8000
PA/O boards mineral wool acoustic, size 500x500 mm
20 20	50	0,02 0,02	0,03 0,03	0,17 0,42	0,68 0,93	0,98 0,90	0,86 0,79	0,45 0,45	0,20 0,20
Plates "Akmigran" mineral wool size 300x300 mm
20 20	50	0,01 0,03	0,04 0,25	0,30 0,66	0,59 0,91	1 0,93	0,93 1	0,81 0,90	0,70 0,80
Super thin mats fibers
50	0,1	0,4	0,85	0,98	1	0,93	0,97	1
super thin fiberglass sheathed fiber and coated with gypsum board thickness 7 mm perforated
100	0,9	0,66	1	1	1	0,96	0,7	0,5
Waste kapron fiber, mesh fiberglass grade SE, coated with perforated metal sheet
100	0,02	0,15	0,46	0,82	0,92	0,83	0,93	0,93
Plates "Silakpore" dimensions 450x450 mm
45	0,10	0,25	0,45	0,60	0,70	0,80	0,90	0,95
"Vinipor" semi-rigid
35	—	—	0,07	0,12	0,19	0,45	0,89	0,89
heat insulating material
25	50	0,10 0,11	0,12 0,16	0,21 0,40	0,44 0,83	0,77 0,94	0,90 0,82	0,92 0,92	0,90 0,80
Plates PP - 80, PPM, PMM sound-absorbing semi-rigid
30 50	50 50	— — — —	0.08 0,21 0,14 0,20	0,30 0,40 0,52 0,61	0,64 0,72 0,92 0,90	0,89 0,98 0,99 0,94	0,95 0,79 0,42 0,92	0,83 0,75 0,82 0,78	0,73 0,75 0,78 0,76

where:

B
– room constant before installation in
sound-absorbing cladding, m2;
is determined in the same way as in formula (1);

B₁
– room constant after installation
it has sound-absorbing structures,
m2;
its definition is discussed below;

 and ₁
- coefficients determined according to the schedule
in fig. 3, respectively before and after
installation of sound-absorbing structures.

Permanent premises
B₁
should be determined by the formula

where:

– equivalent
sound absorption area of ​​surfaces
not occupied by sound-absorbing lining,
m2;

 - average
room sound absorption coefficient
before installation of sound-absorbing lining;
is determined by the formula

;
where S_ogre
- total area of ​​enclosing surfaces
premises, m2;

S_region
- the area of ​​sound-absorbing facings,
m2;

A
- the amount of additional sound absorption,
introduced by the sound-absorbing structure
cladding, m2;
is determined by the formula

,
where _region
- reverberation coefficient
sound absorption of the selected design
facings in the octave band;
determined according to the table. eight.

₁
– average sound absorption coefficient
rooms with sound absorbing
structures, determined by the formula

Selected sound absorbing
cladding will provide the necessary
noise reduction in octave bands
frequencies in the event that as a result
calculations received
.