Unlined Sheet-Metal Ducts - Sound Attenuation

Noise attenuation in unlined sheet-metal ducts.

Attenuation (dB/m duct) Load Calculator!
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

The sound attenuation in a rectangular 600 x 600 mm unlined duct is 0.35 dB/m for frequency 250 Hz. The sound attenuation in 10 m duct is

(10 m) (0.35 dB/m) = 3.5 dB

Lined Sheet-Metal Ducts - Sound Attenuation - Noise attenuation in rectangular straight, lined, sheet metal ducts.
Sound Attenuation - Duct split to Terminals - Estimating sound attenuation where ducts splits to terminals.
Sound Attenuation in Duct Elbows - Noise attenuation in duct elbows by reflected sound.
Sound Attenuation in Ducts due to End Reflection - Low frequency noise transferred from main duct to end terminals is reflected back to main duct.
Sound Transmission through Duct Walls - Sound transmission from ducts to surrounding rooms.
Sound Transmission through Flanking Paths - Sound transmitted through duct walls, floors and ceilings.
Ventilation Systems - Acoustic Calculation Procedure - Acoustic noise calculation procedure HVAC systems.
Ventilation Systems - Classification of Noise Reduction Silencers - Noise in a ventilation system can be reduced by reactive, diffuser type, active and/or dissipative silencers.

Attenuation (dB/m duct) Load Calculator!
Duct	Octave band center frequency (Hz)
Duct	63.5	125	250	500	1000	2000 and higher
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