Dust Collector - Rumble

[ChrisConley]

We have a dust collector installation (~10,000 cfm against 8" e.s.p.). The unit is ducted return back to the space, with a 5' silencer on the return.

The problem is that the system has a low frequency rumble that literally shakes the whole room, you can feel it deep in your chest.

Anyone out there have any advice on retrofits that could be tried to reduce the low frequency rumble? The sound rating on the unit (w/silencer) is 77dBA, but A-scale weighing largely ignores low frequency sound.

Typical fan noise charts show >100dB in the first couple of octave bands.

 

[lilliput1]

Find out if the rumble is caused by: the building structure resonating with the fan; or the ductwork or panels of the dust collector. If it is caused by the building structure, the vibrating equipment would have to be isolated from the structure using vibration isolators. ASHRAE Applications handbook has a table showing recommended static deflection of vibration isolators and base types for various floor spans and vibrating equipment. If the vibration is from ductwork, see SMACNA for recommended ductwork reinforcements at the applicable - inches wg duct pressure service. Hold a long screwdriver tip on the suspected vibration path & hold the handle to your ear to listen or feel for the vibration.

 

[SAK9]

Faced this problem with a huge supply air duct which had a few sharp 90 degree turns afew years ago.The turning vanes did not help much.Finally ended up cladding the ducts with a few layers of gypsum board(around 50mm or more)which solved the problem.

Low frequency noise is very hard to attenuate.So the silencer would not be of much help.

 

[atrebbe]

Why not try The Spiral Fan? A fan with low noise and very high efficiency