Air Return Plenum for Dust Collector Closet

[Tom Bender]

Agree with you and Jim, you are in a very good place re noise thru the duct.

How are you with transmission thru the walls and ceiling? Is this a basement shop, garage shop or stand alone shop?

If the compressors are loud you might focus on that by putting duct board on the wall adjacent, soft side out, to prevent that patch of reflected noise.

[Michael Zerance]

Thanks for your thoughts on this, fellas. I'm going to fabricate the duct with rounded corners and no baffles.

To answer your question, Tom, the shop is standalone. I built the equipment room with soundproofing in mind so I believe the sound transmission should be low. The framing is isolated from the rest of the structure, the penetrations are well sealed, everything has been insulated, the door is solid-core 1-3/4" with weatherstripping and a bottom sweep, and we used 5/8 drywall.

[Jack Frederick]

I understand what you are trying to do here, but wonder if turning vanes in the sweeps would help quiet the air flow. I know you want turbulence for absorption by the glass but there is a balance in there somewhere.

[Michael Zerance]

I understand what you are trying to do here, but wonder if turning vanes in the sweeps would help quiet the air flow. I know you want turbulence for absorption by the glass but there is a balance in there somewhere.

I think the noise of the airflow in the duct will be inconsequential because the noise of the air flowing into the tool pickups and through the dust collection ducts inside the shop will be louder than the return air. It's more important for me to block the sound of the equipment in the closet from coming through the return duct. I found a comprehensive duct attenuation calculator spreadsheet and, when I input the specs for my duct, there is an average of 75 db attenuation with rectangular elbows versus 65 db for rectangular elbows with turning vanes. The spreadsheet doesn't have an option for a three piece elbow so I'm going to just assume that the three piece elbow would be somewhere in the middle around 70db (those calculation don't include the sound generated by the turbulence or velocity of the airflow in the duct; it is just the attenuation of sound through the duct from one end to other).

[Michael Zerance]

Quick update. I got the duct sections fabricated and ready to be installed.

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[Aaron Inami]

that actually looks super cool!

[Jim Becker]

That looks really great, Michael!! It's got a lot of area inside to keep from adding back pressure but is compact when it's "up there" so it doesn't take away much from the space. Great solution!

[Michael Burnside]

What the hell Michael? Is this art school or a shop project?

Looks excellent!

[Ole Anderson]

Uh, might be overthinking the issue. I just routed mine out through a joist space lined with mineral wool.

[Michael Zerance]

Uh, might be overthinking the issue. I just routed mine out through a joist space lined with mineral wool.

Haha, without a doubt I overthought this one. While installing it I came to the realization that it was ridiculous and overkill. I overthink and am obsessive about everything I do.

[Michael Zerance]

Installed:

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[Jim Becker]

I see no issue with "having nice things" and that's really a great installation to fulfill the purpose. Clearly, you have the ceiling height available so that it has little impact on usability of the space below, too.

[Alan Lightstone]

Nice installation. Really impressive. What are you doing to insulate the door leading into the room with the cyclone? I've found that even with a solid door, that's an area that needs attention to attenuate the sound.

[Michael Zerance]

Nice installation. Really impressive. What are you doing to insulate the door leading into the room with the cyclone? I've found that even with a solid door, that's an area that needs attention to attenuate the sound.

You're right about the door needing attention. I put a weatherstripped 1-3/4” solid core door on the bathroom and it does not block anywhere near the amount of sound I thought it would.

So, this is my plan for the equipment room: The door will be a 1-3/4” solid core door to which I will laminate a piece of 1/2” or 3/4” mdf to the inside face (I already purchased a set of wide-throw heavy duty hinges to allow for the extra thickness and weight). I plan on installing weatherstripping on the two sides and top as well as a sweep for the bottom. The door is an inswing so that any back pressure in the room from the dust collector will push the door tight into the weatherstripping. Also, rather than boring a hole though the door for a knob, I plan on installing push/pull plates and utilizing a magnetic catch. The wall that the door is going into is double stud construction so I plan on splitting the jamb between the two wall sections and using an acoustical caulking to seal the joint.

Thoughts?

[Alan Lightstone]

Thoughts?

In my dust collection closet, I hung a curtain rod and hung a moving blanket that had eyelets in it from the rod covering the door. It's amazingly effective. I'd have to look up what my readings were, but as I recall it cut down the noise in the workshop by 3-5dB.