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Engineering ToolBox > Sound Attenuation in Unlined Sheet-Metal Ducts
The attenuation of sound in some common unlined sheet metal ducts at different frequencies can be taken from the table below:
| Attenuation (dB/m duct) | Octave band center frequency (Hz) | |||||
| Duct | 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 150x150 mm | 0.65 | 0.65 | 0.5 | 0.35 | 0.35 | 0.35 |
| Rectangular 600x600 mm | 0.65 | 0.65 | 0.35 | 0.15 | 0.15 | 0.15 |
| Rectangular 1800x1800 mm | 0.35 | 0.35 | 0.15 | 0.03 | 0.03 | 0.03 |