Calculating weighted noise reduction (DnTw) from reduction Rw (Sound insulation)
Equations
For lightweight walls, you can calculate this using the following equation:
$R_\text{w} = D_{\text{nTw}} - 10 \log_{10} d + 14$
For heavyweight walls, use:
$R_\text{w} = D_{\text{nTw}} - 10 \log_{10} d + 11$
Only the value at thee end of these changes.
Look up table
For general floor and wall partitions, use the following look-up table:
| Depth perpendicular to partition | 2.5 m | 3 m | 4 m | 5 m | 6 m | 7 m | 8 m |
|---|---|---|---|---|---|---|---|
| DnTw – Rw (Light) | 10 | 9 | 8 | 7 | 6 | 6 | 5 |
| DnTw – Rw (Heavy) | 7 | 6 | 5 | 4 | 3 | 3 | 2 |
Floors
If we are considering floors, the we frequently have a ceiling height of between 2.5 and 3 m. If this is the case, then we can calculate a simple subtraction value to convert:
| Ceiling height | Difference lightweight | Difference masonry |
|---|---|---|
| 2.5 m | 10 dB | 7 dB |
| 3.0 m | 9 dB | 6 dB |
To obtain the required Rw value from the DnTw value, simply subtract the value in the table above. For example, for a lightweight ceiling with a height of 2.5 m with an Rw of 50 dB, the DnTw value will be 40 dB DnTw.
How we use this
DnT,w is the sound insulation metric reported in sound insulation testing for Approved Document E compliance. Rw is the laboratory-measured equivalent quoted on manufacturers’ datasheets. The conversions above let you specify a partition build-up against an Rw target on the datasheet, predict the on-site DnT,w you should achieve, and prepare for testing.
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