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Engineering ToolBox > Sound Attenuation due to End Reflection
The attenuation due to the end reflection at some typical duct dimensions and different frequencies, are indicated in the table and diagram below:
| Attenuation ( dB) | ||||||
| Duct Dimension1) (mm) | Octave Band Center Frequency (Hz) | |||||
| 63.5 | 125 | 250 | 500 | 1000 | 2000 and higher | |
| 125 | 17 | 12 | 8 | 4 | 1 | 0 |
| 250 | 12 | 8 | 4 | 1 | 0 | 0 |
| 500 | 8 | 4 | 1 | 0 | 0 | 0 |
| 1000 | 4 | 1 | 0 | 0 | 0 | 0 |
| 2000 | 1 | 0 | 0 | 0 | 0 | 0 |
1)The duct dimension is the diameter of round ducts - or square root of area of rectangular duct.
