Return grating sound requirement
Return air grilles should be selected for static pressure. This pressure will provide the required rating NC and match the return system performance characteristics. Fan sound power is transmitted through the return air system, as well as supply. Fan silencer may be necessary or desirable in the opposite direction. This is especially true if silence is considered on the supply side.
Transmission gratings of ventilation in the ceiling Plenum should be remote from the Plenum of the source of the noise. Use lined sheet metal elbow can reduce the transmitted sound. Lined elbows on the ventilation grills and lined General ducts of the return channel gratings can minimize cross talk between private offices...
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