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Regenerated Noise from Duct Termination/Grille    1/1, 1/3

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 (m²)
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