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CHAPTER-15SOUND ATTENUATORSINDEXo Introduction,Types of Sound
Attenuators,
Dimensions of Flange
o Rectangular Sound Attenuators
o Bend Sound Attenuators
o Circular Sound Attenuators
o Engineering and Performance Data
o Recommended Design Criteria for
Various Area Functions
o Noise Criterion Curves and Noise Criteria Values
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TECNALCOSOUND ATTENUATORS
INTRODUCTION
The Sound attenuators are designed by TECNALCO to combat noise
problems. All fans / impellers used in air conditioning system
produce noise, relevant to the amount of work they do to move the
air, much of the noise is generated by the fluctuations of radiated
pressure and these pressure waves are distributed approximately
equally in all directions, causing “duct born noise” and “break
out” or “flanking noise”.
After approximately determining the sound reduction requirements
of the concerned area select suitable sound attenuator to match or
reduce noise to the target level, while selecting sound attenuator
following parameters are to be considered.
1. Insertion loss2. Airlfow regenerated noise3. Static pressure
drop4. Forward or reverse flow.
Galvanised steel outer casing of the sound attenuator is
designed to HVAC standards, perforated splitters are filled with an
odourless incombustible, vermin proof and moisture proof inorganic
sound absorbing material. Primary function of this unit is to
reduce noise, operated smoothly, efficiently and trouble free
service.
Types of Sound Attenuators:
Rectangular Sound Attenuators: are generally employed in ducted
air conditioning systems to reduce the air born fan generated noise
to a predetermined noise criteria level in the areas served by the
air handling unit.
Bend Sound Attenuators : are generally employed in air
conditioning systems where space is at a premium or where the
compact shape of the square bend unit suite the restricted duct
configuration.
Circular Sound Attenuators : are used in special cases where the
conveyance of air is through circular fans or ducts.
Dimensions of Flange
AttenuatorPerimeter(Inches)
AngleSize
(Inches)
HoleDia
(Inches)
A(Inches)
36-83 1x1x1/8 5/16 9/16
84-up 1-1/2x1-1/2x3/16 3/8 7/8
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RECTANGULAR SOUND ATTENUATORS
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TECNALCOSOUND ATTENUTORS
Product Description
Outer casing
Constructed from not less than 22 gauge galvanised steel sheet
with lock formed joints.
Splitter facings
Sound absorbent material
End connections
22 gauge perforated galvanised steel sheet. The perforated sheet
will have 3mm dia holes, with 5mm pitch. Splitter facings are aero
dynamically profiled and exits are with flat faced. All fixings
made with rivets.
Inorganic, non-hygroscopic, flame, moisture and vermin proof,
rock wool fibre of the desired density to achieve the required
acoustic results to be packed under compression to prevent the
formation of voids due to setting
M.S Steel angle secured to casing. Casing peined over flange
face. Flanges will have one coat of primer paint. We can supply
with ductmate or Mez flanges , if required by the Clients.
In moisture or grease laden environments the infill can be
enveloped in Melinex materials to facilitate cleaning. This is also
used to prevent any possibility of progressive particle migration
and so can be used in hospitals, clean rooms and food production
areas.
Special cases
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BEND SOUND ATTENUATORS
TECNALCOSOUND ATTENUTORS
4
Product Description
Outer casing
Constructed from not less than 22 gauge galvanized steel sheet
with lock formed joints.
Splitter facings
Sound absorbent material
End connections
22 gauge perforated galvanised steel sheet. The perforated sheet
will have 3 mm dia holes, with 5 mm pitch. Splitter facings are
aero dynamically profiled and exits are either aero dynamically
profiled or flat faced. All fixings made with rivets.
Inorganic, non-hygroscopic, flame, moisture and vermin proof,
rock wool fibre of the desired density to achieve the required
acoustic results to be packed under compression to prevent the
formation of voids due to settling.
M.S Steel angle secured to casing. Casing peined over flange
face. Flanges will have one coat of primer paint. We can supply
with ductmate or Mez flanges, if required by the Clients.
Where space is a limit concern, our Bend attenuators are
solutions for the requirements. Bend attenuators are either of
vertical / horizontal construction.
Special cases
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CIRCULAR SOUND ATTENUATORS
5
TECNALCOSOUND ATTENUTORS
Model: TECRModel: TECRP
Product Description
Outer casing
Inner face
Sound absorbent material
End connections
Constructed from not less than 22 gauge galvanised steel sheet
with lock formed joints.
Pod constructed from 22 gauge galvanized steel sheet with
conical facing and flat ends. Inner face with 22 gauge perforated
steel sheet. The perforated steel sheet will have 3mm dia holes
with 5mm pitch.
Inorganic, non-hygroscopic, flame , moisture and vermin proof,
rock wool fibre of the desired density to achieve the required
acoustic results to be packed under compression to prevent the
formation of voids due to settling.
Tapped end ring inserts are standard, alternative connections
would be spigots of required dia will be provided at both ends for
connecting to the equipment or duct.
In moisture or grease laden environments the infill can be
enveloped in Melinex materials to facilitate cleaning. This is also
used to prevent any possibility of progressive particle migration
and so can be used in hospitals, clean rooms and food production
areas.
Circular attenuators without a centre pod model is TECR Circular
attenuators with a centre pod model is TEC RP. TECR 400/2 indicates
that 400mm is dia of the circular attenuator and 800mm is the
length.
Special cases
Note:
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ENGINEERING AND PERFORMANCE DATA
TECNALCOSOUND ATTENUTORS
6
Insertion loss: The difference between two sound power levels
when measured at the same point before and after the sound
attenuator is installed.
Aerodynamic noise: Also called generated noise. it is caused by
air flow through elbows, dampers, branch wyes, pressure reduction
devices.
Dynamic insertion loss: The dynamic insertion loss of a sound
attenuator, duct lining or other attenuating device is the
performance measured, when handling the rated air flow. It is the
reduction in sound pressure level expressed in decibels.
Static pressure drop: The air flow pressure loss.
Sound pressure level (Lp): This is the noise level in a room
which is percieved by the human ear having been radiated from a
sound source and subjected to room dispersion and attenuation.
Expressed on a decibel scale refers to a reference sound pressure
of 2x10-5 Pa or 0.0002 microbar.
Sound power level (Lw): This represents the total sound energy
transmitted by the device (fan etc.) and is independent of the
characteristics of the room into which the sound is radiated. Sound
power level can not be measured directly. It must be calculated
from sound pressure level measurements. The sound power level of
source (Lw) is the ratio expressed in decibels of its sound power
divided by the reference sound power which is 10-12 watts.
1/1 Octave band : A range of frequencies where the highest
frequency of the band is double the lowest frequency in the band.
The band is specified by the centre frequency.
Frequency:The number of vibration or waves or cycles of any
periodic phenomenon per second.
Decibel (dB): The unit “bel” is used in the telecomminication
engineering as a dimensionless unit for the logarithmic ratio of
two power quanitites. The decibel is one-tenth of a bel. Therefore
L= 10log 10 (sound power / Reference power)The reference power for
sound power level is 10-12watts.
Test results from ETLThe tests were conducted by the Intertek
Testing Services on the selected sizes of the Sound attenuators,
the test results include insertion loss in dB, face velocity,
static pressure drop and generated sound power level (Lw) dB re
10-12 watts.
Test method: The sound attenuators were tested for insertion
loss with and without airflow and air flow generated sound testing
were conducted in accordance with ASTM standard E477-96 ,
entitled
"Standard Method of Testing Duct Liner materials and
Prefabricated Silencer for Acoustical and air flow
performance"” Sound Pressure level data was obtained using a
Bruel and Kjaer digital Frequency Analyzer Type 2131. The ITS
reverberation room is qualified in accordance with ANSI S12.31 and
S12.32 for sound measurement from 100 to 10,000 Hertz.
Note: For Complete details refers test report no: J20024293 -
002.
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ENGINEERING AND PERFORMANCE DATA
7
TECNALCOSOUND ATTENUTORS
Velocity (M/sec) TEC1 TEC2 TEC2 TEC4 TEC5 TEC6
1.001.101.201.301.401.501.601.701.801.902.002.102.202.302.402.502.602.702.802.903.003.103.203.303.403.503.603.703.803.904.004.104.204.304.404.504.604.704.804.905.00
56789
101112131415161820222426283032343638404244475053565760636669727579838791
112233445566778899
1010111112131415161718192021222324252627293132
111112222233445566778999910101111121213141516171819202122
9101214161922242730333739424752576166717681859095103109115121128134142148155162169
223344455668910111112131415161718202224262728293032333435373940414345
11112222333444555567789101112121316161717171818192021222223
Attenuator Pressure Drop for Rectangular Type
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ENGINEERING AND PERFORMANCE DATA
TECNALCOSOUND ATTENUTORS
8
Attenuator Pressure Drop for Rectangular Type
Velocity (M/sec) TEC1 TEC2 TEC2 TEC4 TEC5 TEC6
5.105.205.305.405.505.605.705.805.906.006.106.206.306.406.506.606.706.806.907.007.107.207.307.407.507.607.707.807.908.008.108.208.308.408.508.608.708.508.909.00
9599
103107111115119124129134
343537384041434547495153565759616365676972757881848791
23242425262728293031323334353637394142434446484951525354555960626466
485054586061626364656769737781869193959799102
232424252627282930313233343536373840424346485051515253545455555657585964646566
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ENGINEERING AND PERFORMANCE DATA
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TECNALCOSOUND ATTENUTORS
Note: The Sound Attenuator type ‘ TECR ’ does not present any
obstruction to the air stream and hasa negligible pressure
drop.
Attenuator Pressure Drop for Circular type TEC RP
Pressure drop
Pa
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.3
0.45
0.54
0.63
0.71
0.78
0.84
0.9
0.97
1.01
1.06
1.11
1.16
1.2
1.25
1.29
1.33
1.37
1.41
1.45
0.5
0.72
0.88
1.02
1.17
1.27
1.37
1.47
1.57
1.63
1.71
1.79
1.87
1.93
2.02
2.08
2.15
2.21
2.27
2.34
0.82
1.17
1.43
1.66
1.86
2.04
2.19
2.34
2.53
2.63
2.76
2.89
3.02
3.12
3.25
3.35
3.45
3.55
3.66
3.76
1.29
1.84
2.25
2.62
2.92
3.2
3.46
3.7
3.93
4.14
4.35
4.54
4.73
4.91
5.08
5.25
5.41
5.57
5.72
5.87
2.09
2.98
3.62
4.2
4.71
5.16
5.55
5.93
6.38
6.64
6.96
7.28
7.6
7.86
8.18
8.43
8.69
8.94
9.2
9.45
3.35
4.78
5.81
6.73
7.55
8.26
8.87
9.49
10.21
10.82
11.13
11.65
12.16
12.57
13.08
13.48
13.9
14.31
14.72
15.12
5.43
7.74
9.4
11.01
12.2
13.37
14.36
15.36
16.51
17.17
18.01
18.84
19.65
20.33
21.14
21.8
22.46
23.13
23.79
24.45
TECRP300 TECRP400 TECRP500 TECRP600 TECRP800 TECRP1000
TECRP1250
Model - Airflow m3/s
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ENGINEERING AND PERFORMANCE DATA
TECNALCOSOUND ATTENUTORS
10
Recommended Design Criteria For Various Area Functions
a. Range Of Indoor Design Goals.
Type of AreaRange ofA -Soundlevels,Decibels
Range ofNC CriteriaCurves
Range ofA -Soundlevels,Decibels
Range ofNC CriteriaCurves
Type of Area
RESIDENCESPrivate homes(rural and suburban)Private homes
(urban)Apartment houses, 2- and 3-family units
Individual rooms or suitesBallrooms, banquet roomsHalls and
corridors, lobbiesGaragesKitchens and laundries
HOTELS
25-3530-4035-45
20-3025-3530-40
40-5040-5540-5545-55
35-4535-5035-5040-50
35-45
40-5045-55
40-5040-5540-5045-55
40-50
45-55
45-55
35-4540-5040-5045-60
35-4540-55
30-4035-50
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NOISE CRITERION CURVES AND NOISE CRITERIA VALUES
Noise Criterion Curves
Noise Criteria Values
Octave BandPreferred Frequency Hz
NC - 20NC - 25NC - 30NC - 35NC - 40NC - 45NC - 50NC - 55NC -
60NC - 65NC - 70
1635054576064677074778084
4044485255596367717579
3337424650545863677175
2731364045495458636872
2227313641465055606570
1924293439444954596469
1722273238434853586368
1621263137424752576267
2125
3250
4500
51K
62K
74K
88K
OCTAVE BAND CENTRE FREQUENCY- Hz
OC
TAVE
BA
ND
SOUN
D PR
ESSU
RE L
EVEL
dB
TECNALCOSOUND ATTENUTORS
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