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Change in Duct Area and Noise Attenuation

Sound attenuation vs. change in duct size.

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

Related Topics

  • Noise and Attenuation

    Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.

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