Sound Attenuators

Sound attenuators(silencers) are devices that reduce the noise produced by air conditioning and air transfer systems. Noise decrease is accomplished by converting sound energy to heat energy with the help of acoustic media. These devices are consist of some baffles filled with sound-absorbing materials and ductwork. Moreover, baffles’ width and length are designed and determined according to the sound intensity at different frequencies. All audible frequencies can be controlled through variable baffle length and width if there is enough space at the installation location.

Silencers are consist of:

  • Perforated sheet on baffles
  • Sound absorbing materials inside the baffles, which are mostly made of insulating wool such as rock wool.
  • The ductwork, which has usually two flanges and is made of a metal sheet(usually galvanized sheet).
  • Splitter stuffing coating, which can be used in high-velocity applications to prevent particle scattering.
  • Baffle nose and tail are designed based on air velocity and produced sound by the silencer

In addition, these products are produced both in rectangular and circular shapes. While designing these sound attenuators factors such as inlet sound level, air volume, maximum sound level after silencer, duct dimensions, pressure drop, and regenerated sound.

Application

  • Decrease of noise produced by ventilation and exhaust fans
  • Railway industries and subway
  • Noise reduction of air duct equipment in industrial projects
  • Lower the noise of air handling units
  • Control the sound level in generator rooms and diesel generators
  • Ship and aircraft ventilation systems

Installation

Sound attenuators’ dimensions and lengths must be considered when installing.  Additionally, two flanged silencers are connected to ducts or ventilation facilities through flanges. The following must be intended:

  • Any equipment like air dampers, fans, duct elbows must be installed at a suitable distance before or after the sound attenuators.
  • Baffles must be placed vertically when silencers are mounted in front of centrifugal fans.
  • To prevent sound transmission in cases that the silencer is mounted in the wall and there is a gap between the wall and the silencer it is recommended to use an additional concrete coating.

Technical Information

R Description Material Thickness Action Finishing Note
1 Perforated Plate Aluminum Profile 1 Fixed - -
2 Baffle Holder Galvanized Sheet 1 Fixed - -
3 Baffle Galvanized Sheet 1 Moving - -
3 Sound Insulation Coated Rockwool Various Fixed - -

*Quadrangle Sound Attenuator

R Description Material Thickness Action Finishing Note
1 Perforated Plate Aluminum Profile 1 Fixed - -
2 Bafflet Galvanized Sheet 1-2 Moving - -
3 Sound Insulation Coated Rockwool Various Fixed - -

*Circle Sound Attenuator

Design Information

Length Airway Width Octave Band f3[Hz] Vs(m/s)
63 125 250 500 1000 2000 4000 8000 6 10 14
500 50 4 9 10 11 19 25 21 16 10 29 56
500 100 3 4 5 8 13 15 11 8 8 23 45
1000 50 5 11 18 20 28 34 28 23 13 37 72
1000 80 4 8 12 16 23 25 19 15 10 28 55
1000 100 4 7 9 1 21 21 15 11 9 26 51
1500 50 6 14 26 29 37 42 36 29 16 44 87
1500 80 5 11 18 22 32 32 24 19 12 32 63
1500 100 4 9 14 19 29 28 19 13 10 29 56
2000 50 7 17 34 38 46 >50 44 36 19 52 102
2000 80 6 14 24 29 40 40 29 23 13 36 70
2000 100 5 12 19 24 37 34 22 16 11 32 62
2500 50 8 20 42 47 >50 >50 >50 43 22 60 118
2500 80 7 16 30 35 48 47 34 27 14 40 78
2500 100 6 15 24 30 44 41 26 19 12 34 67
3000 50 9 22 50 >50 >50 >50 >50 50 24 68 133
3000 80 8 19 35 42 >50 >50 39 31 16 44 85
3000 100 7 17 28 35 >50 47 30 22 13 37 73

*Insertion loss and differential pressure for 10cm baffles

Length Airway Width Octave Band f3[Hz] Vs(m/s)
63 125 250 500 1000 2000 4000 8000 6 10 14
500 50 4 6 18 21 24 18 15 13 21 58 114
500 100 2 4 12 13 15 12 10 8 11 31 61
1000 50 6 13 29 34 39 29 20 17 24 67 131
1000 80 5 11 24 26 29 22 16 13 15 43 84
1000 100 4 9 21 22 24 19 13 11 13 35 69
1500 50 8 20 41 46 >50 41 26 21 27 75 147
1500 80 6 16 33 36 40 30 20 16 17 48 94
1500 100 5 14 30 32 34 25 17 14 14 40 78
2000 50 10 28 >50 >50 >50 >50 31 26 30 83 164
2000 80 8 22 43 47 >50 39 24 19 19 53
2000 100 7 20 38 41 43 32 21 17 16 44 86
2000 200 3 12 23 22 18 12 10 7 9 25 50
2500 50 13 35 >50 >50 >50 >50 37 30 33 92 180
2500 80 10 28 >50 >50 >50 47 28 23 21 59 115
2500 100 8 25 47 50 >50 39 28 19 17 48 94
2500 200 4 14 29 28 22 14 11 8 10 28 54
3000 50 15 42 >50 >50 >50 >50 42 34 36 100 197
3000 80 11 34 >50 >50 >50 >50 33 26 23 64 126
3000 100 10 30 >50 >50 >50 46 28 22 19 53 103
3000 200 5 17 35 34 26 16 13 10 11 30 59

*Insertion loss and differential pressure for 20cm baffles

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