Sound Attenuation in Ducts due to End Reflection

Low frequency noise transferred from main duct to end terminals is reflected back to main duct. This tool provides sound attenuation values for typical duct dimensions with sharp ends at different octave band center frequencies.

Duct Dimension (mm)	125 Hz (dB)	250 Hz (dB)	500 Hz (dB)	1000 Hz (dB)	2000+ Hz (dB)
125	17	12	8	4	1
250	12	8	4	1	0
500	8	4	1	0	0
1000	4	1	0	0	0
2000	1	0	0	0	0