Dust collector exhaust noise

[Roy Petersen]

Exhaust noise from the DC; a topic that led me to signing up here, since so many searches found the place. I was hoping that maybe I've missed something in what I looked for and have done that might help.

Used to have my DC (ancient 2HP Grizzly) in a semi enclosed cabinet off the back of the main shop (back room, where non-dusty work was done). Since it was so removed I never bothered replacing the original bags, depending on distance and being boxed in it's own closet (escape for air in that was filtered before entering that room) to manage the fine stuff. I hadn't piped it very well (4" PVC with sharp turns, into a can with a "poor man's cyclone" of elbows in the lid) and it was not very good at it's job.

Not long ago I unexpectedly sold something for enough to afford a real system overhaul, and went with the Dust Deputy (5" inlet) and 5" metal 24ga ducting to replace the former setup. Took the DC apart, moved it into the attic and piped it into the shop in one corner. Dust Deputy directly below it, flex hose down to the can that holds the bulk of what's spun out. Took the exhaust and shot that through the wall into that back room (7' of straight 5" pipe off the DC, pair of wide radius elbows to get it into the filter), now into a fine pleated canister filter that allegedly has a muffler in it (again from Oneida-air). I say allegedly, because it pretty much screams while in use. That's not going to work for me.

I've tried isolating the exhaust pipe with a Fernco slip fitting, and it had no effect. My fairly inaccurate sound meter on my phone has this at 75-80 db or so, but I suspect it's somewhat louder than that in reality. It's loud. Very loud. Since there are times one of us is working in there while it's running, I'd like to quiet it. The former closet around the original DC had been removed, so it's open to the room currently.

I've read about mufflers (home made and paid, little change in volume), baffle boxes (slows movement which hurts performance), insulated flexible pipe with curves (don't recall the downside of that one, but I have mice galore up there) and so on, but can't seem to find something that will quiet it significantly and not require lots of maintenance, since the attic is hard to work in.
Have I hit on the main ones, and that's about all there is to try aside from moving it outside (not really an option here) to upset the neighbors?

[John K Jordan]

Can you somehow build another closet? I use the 5hp ClearVue cyclone and it is certainly deafening in that you would soon go deaf working with it in the same room without hearing protection. I built a closet for it and a 5hp air compressor. Now I can actually hear a whisper outside the closet. I can't possibly go in the closet when it's running without over-the-ear hearing protectors, the kind used for shooting.

I used a staggered stud wall, staggered 2x4 studs to make a 6" wall, insulation snaked between the studs, 1/2 plywood on either side (since that's what I paneled the entire shop with.

staggered_studs_IMG_2013071.jpg

I put insulation in the ceiling too, above the closet and around the return duct.

I exhaust through dual Wynn filters and return the air to the shop through a baffled duct I built in the attic between the trusses using plywood. Almost no sound gets through the return duct. When the thing is running the loudest thing in the shop is the air rushing into the pickups.

If you haven't looked there yet, try the ClearVue forum for discussions on reducing sound. When I was planning my shop I found a lot of info there. Some people did report good results from an exhaust muffler.

JKJ

[Roy Petersen]

Thanks, John. I was hoping to avoid using up a lot of space in that back room, but that may be the lesser evil here. Had you tried something more dense than (I'm assuming) fiberglass insulation in the walls, like rock wool? Faced or exposed to the airstream?

[John K Jordan]

Thanks, John. I was hoping to avoid using up a lot of space in that back room, but that may be the lesser evil here. Had you tried something more dense than (I'm assuming) fiberglass insulation in the walls, like rock wool? Faced or exposed to the airstream?

I used fiberglass insulation (pulled off the facing) but some people recommend an insulation made for sound. I can't remember what it is but a search will tell you if someone else doesn't say.

A number of things should work. Some people build a conventional wall and use insulating panels inside and special insulation inside the wall. Perhaps look up staggered stud wall construction. This isolates the inside of the wall from the outside so sound can't be picked up by one wall and transmitted through the studs. Worked very well for me, even without using special sound insulation materials. I suspect a staggered stud wall with special sound insulation would be the ultimate.

I built my closet 4'x8' with insulated double doors for easy access and big enough for the cyclone and big compressor but some have made a much smaller space with removable panels for access.

Don't forget other sound paths. Fastening a cyclone to a wall will transmit some sound and vibration through the wall. I mounted mine on a exterior wall; some people use vibration dampers. Sound can go through the ceiling or floor and then back into the shop. One thing that might help - build an insulated closet AND put a muffler on the cyclone exhaust (before the filters or dumping it outside.)

JKJ

[Roy Petersen]

The sound appears to mainly be the whine from the exhaust pipe itself, not wall vibration and the like. If I hang a heavy moving blanket in front of it there's a noticeable drop, so I think I'm on the right track of where to fiddle with this. I think I'll start with a simple open wood plenum (square, 12" across, 30" long) just after the fan port, with offset openings and interior padding. Shouldn't restrict the air flow appreciably, but may bounce/absorb the sound enough to make some difference. If that has little to no effect, it's going to be enclosing it, and deadening with insulation.
Thanks again.

Did check the Clearvue forum, and like most things of this nature, widely varied techniques with some claims of great and others total fail with similar options. Trial by fire, kinda.

[Jim Becker]

In addition to the techniques that John described, I also put 1/4" pegboard as the inside walls of my DC closet with the rough side showing. This allowed the insulation to be more of a bass trap and also cut down on reflective noise. That, combined with an indirect return path for air to the shop keeps things to a reasonable sound level. The only time the DC noise increases appreciably is when I'm running the J/P and that's the nature of the tool...it seems to amplify things. But I'm wearing hearing protection at that point, anyway.

[Bill Dufour]

Any one know anything about active noise cancellation? I wonder if the cheap headphones could be used to drive bigger speakers? I would think a constant noise like from a dc would be easier to cancel out. Of course you would probably need multiple speakers to cover the frequeny range needed.
Bill

[Rod Sheridan]

Any one know anything about active noise cancellation? I wonder if the cheap headphones could be used to drive bigger speakers? I would think a constant noise like from a dc would be easier to cancel out. Of course you would probably need multiple speakers to cover the frequeny range needed.
Bill

Bill, that works best where both sources are a known distance from your ears to make sure that they are 180 degrees out of phase.

If I put a loudspeaker in the room, at certain points it would be 180 degrees out of phase, at other points it would be in phase and add to the noise.

Regards, Rod.