Air flow generated noise in air ducts
The air flow through ducts generates noise. The noise generated depends on the air velocity and the duct size (cross sectional area).
Generated noise can be calculated with the empirical equation
LN = 10 + 50 log (v) + 10 log (A) (1)
LN = sound power level (dB)
v = air velocity (m/s)
A = air duct cross sectional area (m2)
Example - Noise generated by Air Flow in Duct
The noise generated in a 200 mm circular duct with air flow velocity 10 m/s can be calculated as
LN = 10 + 50 log (10 m/s) + 10 log (π ((0.2 m) / 2)2)
= 45 db
The noise generated in the same 200 mm circular duct as above with air flow velocity 20 m/s can be calculated as
LN = 10 + 50 log (20 m/s) + 10 log (π ((0.2 m) / 2)2)
= 60 db
Note! - due to the noise generated by the fans - noise generated inside ducts by the air flow can in general be neglected.