Ducts - Noise Generation
Air flow and noise generated in ducts
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When air flows through ducts noise are generated. The noise can be calculated with the empirical equation below:
Lw = 10 + 50 log( v ) + 10 log( A ) (1)
where
Lw = sound power level (dB)
v = air velocity (m/s)
A = duct cross sectional area (m2)
Example - Noise generated in Ducts
The noise generated in a 200 mm circular duct with airflow 10 m/s can be calculated as
Lw = 10 + 50 log( 10 m/s ) + 10 log( π ((0.2 m) / 2)2 )
= 45 db
The noise generated in a 200 mm circular duct with airflow 20 m/s can be calculated as
Lw = 10 + 50 log( 20 m/s ) + 10 log( π ((0.2 m) / 2)2 )
= 65 db
Note! - the noise is generated inside the duct. Compared to the noise from the fans - the noise generated by the duct can in general be neglected.
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