Noise Attenuation - Changing Duct Area

Changing duct size and noise attenuation

duct size change sound attenuation

Sound attenuation when changing the duct area or dimension can be calculated as

dL = 10 log( ( 1 + A1 / A2 )2 / 4 (A1 / A2) )          (1)

where

dL = noise attenuation (dB)

A1 = inlet area (m2)

A2 = outlet area (m2)

Note - only for sharp changes.

Example - Attenuation when changing size of ducts

Noise attenuation when the ratio  A1 / A2 = 5 can be calculated as

dL = 10 log( ( 1 + 5 )2 / 4 5 )

    = 2.5 dB

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