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Sound Attenuation in Duct Elbows

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

Attenuation in lined and unlined ducts at different sizes and frequencies are indicated in the table below.

Sound Attenuation in Duct Elbows (dB)
TypeWidth B
(mm)

Octave band center frequency (Hz)
125250500100020004000
Ducts Unlined 150 5 8 4
250 5 8 4 3
500 8 4 3 3
1000 5 8 4 3 3 3
Ducts Lined 150 1 7 16 18
250 1 7 16 18 16
500 1 5 16 18 16 17
1000 5 16 18 17 17 18

Example - Sound Attenuation in a Duct Elbow

The sound attenuation in an unlined 500 mm duct elbow at 500 Hz is

8 dB

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Related Topics

• Acoustics

Room acoustics and acoustic properties. decibel A, B and C calculations. Noise Rating (NR) curves. Sound transmission through walls. Calculate sound pressure, sound intensity and sound attenuation.

• Noise and Attenuation

Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.

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