Unlined Sheet-Metal Ducts - Sound Attenuation

Noise attenuation in unlined sheet-metal ducts at different frequencies.

Unlined Sheet-Metal Ducts - Sound Attenuation

Attenuation of sound in unlined sheet metal ducts at different frequencies. The table below shows attenuation values in dB/m for various duct types and octave band center frequencies.

Note: 1 in = 25.4 mm

Duct Type	63.5 Hz	125 Hz	250 Hz	500 Hz	1000 Hz	2000+ Hz
Round 100-300 mm	0.1	0.1	0.1	0	0	0
Round > 300 mm	0	0	0	0	0	0
Rectangular 150 x 150 mm	0.65	0.65	0.5	0.35	0.35	0.35
Rectangular 600 x 600 mm	0.65	0.65	0.35	0.15	0.15	0.15
Rectangular 1800 x 1800 mm	0.35	0.35	0.15	0.03	0.03	0.03

Calculator

Inputs

Duct Length (m)

Attenuation Rate (dB/m)

Results

Total Sound Attenuation-- dB

Example Calculation

For a rectangular 600 x 600 mm unlined duct with an attenuation rate of 0.35 dB/m at 250 Hz frequency, the total sound attenuation over a 10 m duct length is:

(10 m) × (0.35 dB/m) = 3.5 dB

Unlined Sheet-Metal Ducts - Sound Attenuation | MEPKit Engineering Tools | MEPKit