Noise Attenuation in Chambers

Noise attenuation in a chamber:

dL = 10 log( 1 / A_o (cos(θ) / 2 π s²  + (1 - α) / (α A)))                              (1)

where

dL = sound attenuation (dB)

A_o = outlet area (m²)

A = chamber inside surface area (m²)

θ = angle between inlet and outlet (degrees)

s = distance between inlet and outlet (m)

α = inside surface sound absorption coefficient 

Example - Attenuation in a Chamber

The attenuation in a chamber lined with mineral wool with a sound absorption coefficient α = 0.65, inside surface area A = 16 m², outlet area A_o = 0.25 m², distance between inlet and outlet s = 2 m, angle between inlet and outlet α = 45^o, can be calculated as

dL = 10 log( 1 / (0.3 m²) (cos(45^o) / 2 π (2 m)²  + (1 - 0.65) / (0.65 (16 m²))))

    = 17.3 dB