Reduced Dust Collector Noise 10 dB

[Robert Strasser]

After a couple of years of putting up with noise generated by my dust collector, I decided to do something about it. It cost me around $300 and reduced the noise level by 10 dB. I did this in three steps.

First step was to build sound absorbing panels and installing them around my dust collector. This is very helpful in my case because my dust collector is set in a corner. Corners tend to project noise out into the room. I used the Home Depot Select Pine 1 by 4s, Roxul Safe and Sound insulation, and a canvas drop cloth. This step alone reduced the noise by 4 dB.

The second step was to build a muffler around the exhaust filter. I purchased an 18-inch snap-lock pipe for this. I then used 3M 77 spray glue to attach some 1/2 foam rubber to the pipe inside walls. Use some plastic gloves when working with that glue. I purchased the foam rubber (Open Cell Foam Lux-HQ) from the Foam Factory. They had reasonable prices and excellent service. You do not need to buy some kind of acoustic foam in my opinion. The muffler sits on a short stand and is not touching the dust collector. I first tried having a hole in the stand to allow air flow out the bottom. This is not a good idea. The sound flows out the bottom and bounces off the floor. But if you like those super loud bass systems that some people put in their cars, well you might like it. Anyway, I put a solid top on the stand which really made a huge difference. This step reduced the noise by an additional 5 dB.

The third step was to apply sound dampening material where I thought it would do the most good. The material I used (RAAMmat and Ensolite) came from RAAM Audio. It is similar to Dynamat, FatMat and other products used in automobiles. I first installed sound dampening to the short stand. The solid top of the stand was now acting like a drum. I applied RAAMmat BXT II on the bottom of the stand and Ensolite on top. You could substitute some thin foam rubber for the Ensolite. Next, I applied dampening material to the dust collector exhaust fitting and around the fan housing. This third step only gave me an additional 1 dB improvement.

The noise reduction of 10 dB does not tell the whole story. The sound meter does not respond to all frequencies. So there is a qualitative nature to the improvement that I cannot measure. But I am very pleased with the results.

I got the most improvement from the muffler and the wall panels. Sound dampening, especially with the automotive-type products, did not produce results that I could measure, but it definitely seemed to help. I would not change anything if I did it again.

[Enrico Caruso]

Hi Robert,
Congrats, reducing noise is very important for your long term hearing protection. As a mechanical engineer, I worked on reducing noise in a newly refurbished automotive engine manufacturing plant in Cleveland to less than 80dBa in the entire factory. What final level have you achieved? Electric motor noise is directly related to the speed of the motor, so if motor speeds are reduced from 3600rpm, or 2400rpm to say 1800rpm or 1200rpm more noise reduction improvement can be obtained. Also motor mount isolaters are important. Good luck with further improvents.
Enrico Caruso

[Allan Speers]

As Enrico wrote, mechanical isolation is critical. Most shops have concrete floors, so there's no problem there, but one must make sure that it the beast is attached to the ceiling or walls, that they use resilient mounts.


Nice job, Robert! This is why I always tell folks to build mufflers on the output side.

One thing, though. It's never a good idea, cost-wise, to use any commercially pre-fabricated products like that automotive stuff. HUGE waste of money. (though it IS convenient.) Low frequencies are stopped by density and / or air space, nothing else. MDF is your best friend here, or lead sheets if you really need massive sabine isolation.

The panels you put on the wall are not a bad idea, but realize that they are only soaking up a few sabines, and probably at about 250 hz and up. Mid (125 hz & up) & high frequencies are absorbed perfectly by 4" of 3 lbs per cubic foot mineral wool. ( 4 or 5 lb soaks up a little more near the bottom of those frequencies, which might be better for DC noise.)
Mineral Wool batts are dirt cheap & available at any commercial builders' supply house. This is also what I recommend inside the mufflers. You don't even have to cover it with fabric, as you do with stiff fiberglass. (Owens 703, etc) - I would, but you can get away with leaving it raw.

Still, I applaud your efforts and results !

[ian maybury]

Hi Robert. Good going. Another here that's posted before about getting a sizeable (subjective - not measured) noise reduction by double soft mounting a (DIY to Bill Pentz's drawings) dust system fan, fitting an exhaust muffler and isolating the ductwork from the fan using a couple of flexible joints.

For anybody reading this thread - it's important if noise is a concern to stop fan vibration feeding into surrounding structures, as even solid seeming materials like a masonry/concrete black wall or a timber loft floor can often vibrate like hell, and create significant amounts of noise. A concrete floor resting on the ground should be fine. Part of the issue is that it's normally not obvious to your hearing that much of the noise is in fact coming from the surrounding structures - it seems to be coming from the fan.

It's so much easier to sort this stuff out during the initial install...

Even using materials that come to hand these sorts of measures normally work really well, although in theory full optimisation might require selecting exactly the right stiffness of mounting. The original eye-opener for me back in the early 90s was encountering and building competition aerobatic model aircraft using soft rubber isolators in the engine mounts - it was quite incredible how they dropped the sound in that case (by reducing the vibration being fed into the airframe) from a harsh scream to a pleasant hum. Also around the building of competition cars where noise levels typically go crazy when they are stripped out. An extra pay off on my dust system was that these measures removed the harshness from the sound too, so that the residual noise is a quite pleasant rumble.

It's quite possible that you might get some more improvement by installing length of flexible hose between your ductwork and the fan inlet Robert. Maybe also between the fan and the filter housing - but much less likely there since your lagging is keeping that from vibrating...

[Robert Strasser]

Allan is correct about the automotive products. The Dynamat is the most known and by far the most costly. That is why I did not use Dynamat. I just wanted to experiment with one of the automotive products to see what the hype is all about. I still do not know since I could not measure sound at various frequencies. The rock wool (or stone wool, or mineral wool) is the most cost effective approach I have found for sound proofing. the Roxul safe and sound is a stone wool made from basalt and slag. I do not know how many sabins my panels soaked up, but they made a big difference. Especially since the collector was in the corner. I have used mineral wool insulation in bathroom walls of my house. It works great. I also used fiberglass and it was a waste of money.

[Ole Anderson]

That is quite an improvement without enclosing the unit. Good job. I only picked up 7 dBa with a full enclosure. https://www.youtube.com/watch?v=8X8qwMqm3Ek Probably a lot more, the 7 dBa was just door open/door shut, I did not do a measurement before the enclosure as the enclosure was done with the initial install.

Please tell me about your bin alarm and device holding your bags in place.

[Robert Strasser]

The bin alarm is sold by Oneida Air Systems. They call it the Dust Sentry. Cost is $148. It uses an infrared sensor installed in the bin lid. Oneida also sells a Drum Liner Bag Holder Kit for $48. It is a sheet of plastic you form into a cylinder.