Noise attenuation in duct elbows are caused 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.
|Octave band center frequency (Hz)|
Example - Sound Attenuation in a Duct Elbow
The sound attenuation in an unlined 500 mm duct elbow at 500 Hz is