Return air duct idea

[Stinger]

I'm in the process of building a shop. My DC will be housed in a separate insulated and sound dampened room.
The problem I've been thinking about is how to build a return air duct that doesn't compromise all of my efforts to reduce the noise of the DC system. I've read about a number of innovative ways to do this. The attached drawing is my solution.
I'm planning on using the adjoining interior wall as ducting. I believe this will be of sufficient size (volume wise) to reduce the air flow speed (and of course any noise caused by the air movement) by half. The boxes on either side of the wall should help to block any sound transmission. The flaps inside each box are there to block any noise from the air compressor (also housed in the same room) when the DC is not on. At least I hope it will work this way.
Since this part of the construction is quite further down the road, now is time to make changes.

What do you guys think?

 

[dwdrury]

Wall As Return Duct

Wall As Return Duct

Hi, Stinger,

About your return duct scheme:

Sound transmission needs either a direct or reflected path, or a means by which to transmit the vibrations. So the inlet and outlet of your "duct" need not be so far apart. But to kill the potential for reflections, there should be some sound absorbing materials in the path, something like open cell foam or fiberglass.

I'm also concerned the barrier (drywall?) that forms the wall between your duct and shop might act as a sounding board, a drum. As an example, we have geothermal heat pumps, and I made the mistake of having the water pipes run along the outside of our utility room wall. The wall actually seems to amplify the sound of water rushing through the pipes.

So I wonder if, by removing insulation to create the flow path, you might not actually make for an easier sound transmission path.

As I recall, Jameel Abraham had good success with a simpler return scheme. In the gallery, start here There may be other examples as well, but his is the one I recall. There's also a forum thread where he discusses the design and implementation. Holler if you can't find it. In there I recall some discussion of required areas.

Regards,
DWD