Noise Attenuation - Changing Duct Area

Changing duct size and noise 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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