Sound Attenuation in Duct Elbows
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.
Type | Width B (mm) | Octave band center frequency (Hz) | |||||
---|---|---|---|---|---|---|---|
125 | 250 | 500 | 1000 | 2000 | 4000 | ||
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
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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