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Noise Attenuation by Changing Duct Area

Changing duct size and nosie attenuation

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Duct size change - sound attenuation

Sound attenuation when changing duct areas or dimensions:

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


dL = noise attenuation (dB)

A1 = inlet area (m2)

A2 = outlet area (m2)

Note! - valid only for sharp changes.

Example - Attenuation when changing the size of a duct

The attenuation of noise when the ratio between area before and after A1 / A2 = 5 - can be calculated as

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

    = 2.5 dB

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