Sound Transmission through Duct Walls

Calculate sound pressure level in a room based on sound transmission from ducts to surrounding rooms using the formula: Lp = LN - TL - 10 log(A F / 4 Ad)

Duct Sheet Thickness (mm)	125 Hz	250 Hz	500 Hz	1000 Hz
1.25	17	22	25	29
1	15	20	23	27
0.75	14	19	22	26
0.65	12	17	20	24

Calculator

Inputs

Sound Power Level in Duct (LN) (dB)

Transmission Loss through Duct Wall (TL) (dB)

Room Absorption (A) (m² Sabine)

Cross Section Area of Duct (F) (m²)

Surface Area of Duct (Ad) (m²)

Results

Sound Pressure Level in Room (Lp)-- dB

Formula

Lp = LN - TL - 10 log(A F / 4 Ad)

Where:

Lp = Sound pressure level in room (dB)
LN = Sound power level in the duct (dB)
TL = Transmission loss through duct wall (dB)
A = Room absorption (m² Sabine)
F = Cross section area of duct (m²)
Ad = Surface area of duct (m²)

Notes

The acoustic performance of round and oval ducts is superior to rectangular ducts since their curved surfaces allow less breakout noise. Low-frequency sound is better contained in round ducts.