Sound Attenuation in Duct Elbows

Noise attenuation in a duct elbow is caused by reflected sound. It is only in larger ducts and at higher frequencies the attenuation is considerable

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Sound power level attenuation in an elbow is based on sound reflection. It is only in larger ducts and at higher frequencies the attenuation is considerable.

sound attenuation elbows

Attenuation in ducts at different sizes and at different frequencies for some common configurations are indicated in the table below.

Attenuation(dB)
Type Width B
(mm)		 Octave band center frequency (Hz)
125 250 500 1000 2000 4000 8000
Duct without insulation 125 0 0 0 6 8 4 3
250 0 0 6 8 4 3 3
500 0 6 8 4 3 3 3
1000 6 8 4 3 3 3 3
Insulation in front of elbow 125 0 0 0 6 8 6 8
250 0 0 6 8 6 8 11
500 0 6 8 6 8 11 11
1000 6 8 6 8 11 11 11
Insulation after the elbow 125 0 0 0 7 11 10 10
250 0 0 7 11 10 10 10
500 0 7 11 10 10 10 10
1000 7 11 10 10 10 10 10
Insulation in front and after the elbow 125 0 0 0 7 12 14 16
250 0 0 7 12 14 16 18
500 0 7 12 14 16 18 18
1000 7 12 14 16 18 18 18

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Related Topics

  • Acoustics - Room acoustics, acoustic properties - decibel A, B and C - Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity, attenuation and more ..
  • Noise and Attenuation - Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems

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