Unlined Sheet-Metal Ducts - Sound Attenuation
Noise attenuation in unlined sheet-metal ducts.
Attenuation of sound in unlined sheet metal ducts at different frequencies are indicated below:
| Duct | Attenuation (dB/m duct) | |||||
|---|---|---|---|---|---|---|
| Octave band center frequency (Hz) | ||||||
| 63.5 | 125 | 250 | 500 | 1000 | 2000 and higher | |
| Round 100 - 300 mm | 0.1 | 0.1 | 0.1 | 0 | 0 | 0 |
| Round > 300 mm | 0 | 0 | 0 | 0 | 0 | 0 |
| Rectangular 150 x 150 mm | 0.65 | 0.65 | 0.5 | 0.35 | 0.35 | 0.35 |
| Rectangular 600 x 600 mm | 0.65 | 0.65 | 0.35 | 0.15 | 0.15 | 0.15 |
| Rectangular 1800 x 1800 mm | 0.35 | 0.35 | 0.15 | 0.03 | 0.03 | 0.03 |
- 1 in = 25.4 mm
Example - Sound Attenuation in an Unlined Duct
The sound attenuation in a rectangular 600 x 600 mm unlined duct is 0.35 dB/m for frequency 250 Hz. The sound attenuation in 10 m duct is
(10 m) (0.35 dB/m) = 3.5 dB
