Sound Attenuation in Duct Elbows
Noise attenuation in duct elbows by reflected sound.
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
