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# Noise Attenuation in Chambers

Noise attenuation in a chamber:

dL = 10 log( 1 / Ao (cosθ / 2 π s2  + (1 - α) / (α A)) )                                         (1)

where

dL = sound attenuation (dB)

Ao = 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 Ao = 0.25 m2, distance between inlet and outlet s = 2 m, angle between inlet and outlet α = 45o, can be calculated as

dL = 10 log( 1 / (0.3 m2) (cos45o / 2 π (2 m)2  + (1 - 0.65)/(0.65 (16 m2))) )

= 17.3 dB

## Related Topics

### • Noise and Attenuation

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

## Related Documents

### Change in Duct Area and Noise Attenuation

Sound attenuation vs. change in duct size.

### Sound - Attenuation and Speed vs. Sound Frequency and Air Humidity

The speed and attenuation of sound in moist air varies with sound frequency and air humidity.

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