Another DC Closet? Doubting Myself Again

[Ken Deckelman]

I am reading what you are writing Ole-but it's not sinking in yet...getting closer though. Thank you for your patience.

Edit: Here are two pictures with the foam board removed.

[Steve Schoene]

I used 1/4 peg board installed rough side out on the inside of my DC closet. It served to break up some of the sound waves, rather than bouncing them and also helped decrease the higher frequencies with the perfs allowing some direct absorption by the fiberglas insulation in the wall cavities. I faced the shop side of the closet with Homasote and then 1/4" bead board. BTW, use R15 rather than R13 in the wall...denser material. Same thickness.

I don't understand why avoiding bouncing sound wave--on the noise side of the barrier is a problem. The goal is to absorb or dissipate the energy of the sound before it can be transmitted to the quiet side. Each time it bounces from a heavy surface some of the energy should be used up (turned to heat I suppose). I don't think giving it a free pass to the space, with sound deadening insulation in it or not, closest to the quiet side is a benefit. I'd think I'd want to make it work just to get to the insulation. It probably helps make the sound levels inside the DC closet lower--which is why acoustical ceiling tiles are perforated, but that 's not the goal here. We aren't trying to reduce the sound levels in the space where the sound is being generated.

My recommendation would be to use heavy drywall, attached to studs with resiliant clips. Causing the panel on the side of the sound to vibrate is one of the standard methods of reducing sound transmission through walls.

Of course, for sound isolation there would be no air return into the shop and sealing all possible routes for air transmission would be undertaken.. The more sealed the better. But, and it is a big but, sealling the DC closet from air has a huge impact on heating and cooling make up. The return air should have to pass through a baffled opening so there is no straight shot for sound waves. I suspect that the design of the baffled air return would be critical to achieving a quiet shop even with the DC running.

[Jim Becker]

If you choose to direct the return air from the upper space of your closet, and not by utilizing a vertical duct bringing it up from the floor, you really need to form some sort of return air duct with a circuitous path or else you will have a direct path for the sound to exit the closet. In effect you need to build a muffler. Two joists and the floor above provide 3 sides of the duct and putting a limited amount of shop ceiling near the door in the shop will provide the bottom of the "duct". Now think in terms of making that 4 sided duct (actually two ducts by utilizing two joist spaces) into a muffler by turning it into a glass-pack muffler. One advantage to this design is that you are not trapping motor heat. Although with 600-900 cfm exiting the filter that may not happen.

Exactly...and that's how I did it.

[Ken Deckelman]

Exactly...and that's how I did it.

Perfect, thank you. A picture is indeed worth 1000 words.

[Joe Angrisani]

Perfect, thank you. A picture is indeed worth 1000 words.

+1 on that. Thanks Jim. I had been overcomplicating things in my head for some reason, but I now plan to incorporate a similar folded design inside my "cyclone room" soundbox since my ceiling height allows for it.

[Ken Deckelman]

Another though Jim/Ole: What are thoughts on me using the foam board I already have to build the duct like Jim pictured?

Locating the Roxul in my area is a no go-special order everywhere I call. So I am thinking of just using the pink R13 that I have and using PVC lattice to hold it in place. I'd really like to get this completed this week.

[Joe Angrisani]

.....and using PVC lattice to hold it in place.....

Chicken wire?

[Phil Maddox]

The Pink board is not a good choice for sound control. The Rockwool you are talking about is one of the best products for this use. The staggered stud wall is really good also but overkill as the return air hole you have will negate it to some degree.

The best way (within reason) is:

stud walls - steel or wood on caulking or sill sealer - staggered is great but overkill
fiberglass or rockwool insultation in stud cavity
5/8" drywall both sides - mudded and taped
make the return air take some turns. 3 - 90 degree turns would be good.
lining the interior of the closet with rigid insulation will help if the noise is high pitched - My 3hp Gorilla is lower pitched - never heard a CV.
lining the return air path will soak up a lot of sound also.
aim the return air opening away from you or up.

good luck.

[Justin Freund]

Roxul can be special ordered at Home Depot regardless of what they tell you. It comes through PrimeSource, the distributor they get their nails and screws from. It took some doing when I ordered some for myself because nobody expected that they would be the distributor for the the Roxul. It took calling Roxul, then calling HD corporate, then finally ordering from PrimeSource.

[Gary Radice]

I used Roxul on my closet, obtained from the local 84 Lumber. I left it exposed on the inside of the closet but to avoid dinging it up I covered some of it with drywall where I was likely to bang into it (when moving the bin in and out of the closet) and the rest I covered with a layer of garden blanket stapled to the studs. I also double-drywalled the outside using green glue as an additional damper.

[Ken Deckelman]

Roxul can be special ordered at Home Depot regardless of what they tell you. It comes through PrimeSource, the distributor they get their nails and screws from. It took some doing when I ordered some for myself because nobody expected that they would be the distributor for the the Roxul. It took calling Roxul, then calling HD corporate, then finally ordering from PrimeSource.

Thank you! With your help I got it ordered today at HD. Me and the guy had a little go-round for a few minutes..."I have been behind this counter for 6 years and never heard of it" he said, then he goes and looks on the shelf with all the books on it and what do you know-a Roxul binder was there! $32.95 a bundle, minimum order of 3 bundles.

[Ole Anderson]

I also double-drywalled the outside using green glue as an additional damper.

Good move. I have seen plans for demising walls between cinema theaters that use as much as 5 layers of drywall on each side of staggered studs. And you can still hear the thunder from the adjacent movie.

[Ken Deckelman]

Update: I got the "folded plenum" built thanks to Jim's picture, added a muffler, and Roxul. No final numbers yet since the door is still off for painting.

Here are some pictures: https://picasaweb.google.com/kdeckster/DC#

[Phil Maddox]

No one seems to want to hear this but these extreme measures - double drywall, staggered studs, blue jeans insulation, etc. are darn near a waste of time for this application. Stop visiting Home Theater websites.

If you need to vent the exhaust back into the shop (not venting outside) this is BY FAR the greatest source of the noise coming back into your shop. All these other things, which by the way, I have on my dedicated home theater, are a waste of time. The second biggest culprit is your door.

Build simple walls - 2x4 is fine. 5/8 drywall on the outside (mass is your friend, to a point), Roxul insulation in the wall. Leave it open on the inside if you want to save a couple of bucks. Make the return air route back to the shop 5 or 6 times the surface area of the duct going to the DC. Make the air take a couple of turns on the way back. Line the path with rigid fiberglass insulation. Solid core 1 3/4" door. exterior weather stripping on the door with a sill. Done.

This will make a dramatic improvement - it won't get it all, you need to exhaust outside to do that.

Good luck.

PM

[Paul Wunder]

Phil,

Good advice. It almost mirrors the video that Ed Morgano of ClearVue prepared on how to build a closet. He achieved a better than 20db reduction in noise by constructing the walls as you advise. He went a bit simpler on the baffle (your baffle advice is more thorough). The video can be seen at the ClearVue website.

Paul