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How to mount silencer boxes for room in a room?
Old 4 weeks ago
  #1
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How to mount silencer boxes for room in a room?

Hey guys. I'm going to build a room in a room with the overriding purpose to keep drum noise from escaping during practice. I've read about building silencer boxes, but I'm a little unclear on how to mount them.

In my case, my plan is to draw treated air in from an adjacent room and then expel it back to the same room. From an isolation perspective it would seem that I would want a silencer box mounted to the inner leaf and outer leaf for both the ingest and expel paths, so 4 boxes. Is that right? If so, how do people go about mounting the boxes to the inner room when the air gap is on the order of 6-7" only? Would I mount it on the interior of the room, so I'd have two big bumps using up space, or is there another alternative? If I mount it outside the outer layer, I think I will have compromised the isolation, either with a structural path or an air gap.

Thanks for any clarification.
Old 4 weeks ago
  #2
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Quote:
Originally Posted by Mastiff View Post
... my plan is to draw treated air in from an adjacent room and then expel it back to the same room...
You should check what is legal in AZ. I am in Europe and when I wanted to do something similar because our winter temperatures go down to around -20°F the HVAC installation company told me it was not possible because of local laws. In my case I had to pull in fresh air and pump stale air to the outside world. AZ may have different laws.

Quote:
Originally Posted by Mastiff View Post
From an isolation perspective it would seem that I would want a silencer box mounted to the inner leaf and outer leaf for both the ingest and expel paths, so 4 boxes. Is that right? If so, how do people go about mounting the boxes to the inner room when the air gap is on the order of 6-7" only? Would I mount it on the interior of the room, so I'd have two big bumps using up space, or is there another alternative?
Yes, that's right, 4 boxes, one on the inner leaf and one on the outer for each direction of airflow. And yes, they use up space from your inner room's volume.
Old 4 weeks ago
  #3
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Quote:
In my case, my plan is to draw treated air in from an adjacent room and then expel it back to the same room.
As Starlight said, that probably isn't allowed by code. Most places do not permit using one habitable space as the source or destination of the entire airflow from another habitable space. The reason for that is simple: the O2 levels in the "other" room will already be low, and the CO2 levels high, just from it having people in it. You would then be dumping air back into that space that has even lower O2 levels, and even higher CO2 levels.... the sucking that air straight back into your room, and repeating the cycle. I think you can see why this is not a good idea.

Quote:
If so, how do people go about mounting the boxes to the inner room when the air gap is on the order of 6-7" only? Would I mount it on the interior of the room,
If the silencer won't fit in the wall cavity, or the ceiling cavity, then you have no choice: it will have to go inside the room, as you realized. The way to decide how big to make your boxes, is to first do all the math to figure out your room volume, air flow rate, and air flow velocity, and that allows you to figure out your duct size. Based on that, you can figure out the internal cross-sectional area of the silencer boxes. Take into account the thickness of the duct liner, and the thickness of the walls of the box that is needed to keep the overall mass of the leaf consistent, and that will lead you to the outer dimensions of the box.

Quote:
If I mount it outside the outer layer, I think I will have compromised the isolation, either with a structural path or an air gap.
It's a drum room, and you need high isolation, so you need one box on the outer leaf, and one on the inner leaf, for EACH path. If you don't have enough space to put those inside the cavity between the leaves, then one will have to go outside the outer leaf, and the other inside the room. So you will have two boxes outside the outer leaf, and two boxes inside the room. Each pair of boxes will be linked across the cavity with flex duct.

Quote:
If I mount it outside the outer layer, I think I will have compromised the isolation, either with a structural path or an air gap.
Each box becomes part of the leaf that it penetrates. So the box on the outer leaf IS the outer leaf, and the one on the inner-leaf IS the inner leaf. That said, it's still a good idea to decouple them if you can. Make the hole where the sleeve of each silencer box penetrates the wall a bit bigger than the sleeve itself, then fill that gap with backer rod and abundant high-flexibility caulk.


- Stuart -
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