### Strutt Help

Regenerated Noise from Duct Termination/Grille
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**Strutt|Mechanical Services|Regenerated Noise|End/Grille** predicts the regenerated noise from a duct termination (e.g. grille, diffuser). Note that the method is not intended for very high aspect ratio grilles e.g. slot diffusers.

The sound power level in the peak octave band (which occurs at a frequency `f_(peak)=160u`) is as follows:

`L_("W(Peak)")=10+10log(A)+30log(Delta p)`

where:
`u` is the flow velocity upstream of the diffuser (m/s)

`A` is the diffuser area (mē)

`Delta p` is the diffuser pressure drop (Pa)

Regenerated noise levels in other frequency bands are calculated from the peak band value using the following spectrum shapes:

- Below `f_(peak)` -3 dB/octave slope
- Above `f_(peak)` -5 dB/octave slope

Reference: CIBSE Guide B (2005) Section 5.A2.5

Comments or suggestions to
strutt@arup.com