Fill Soffits with Insulation? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 13 Old 04-26-2019, 11:05 AM - Thread Starter
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Fill Soffits with Insulation?

I have two large soffits, 1 in the front and 1 in the back, and then 3 false soffits with lights in them. I plan on putting R19 in the ceiling joists, as this is in a basement, but am not sure if I should fill the soffits.

From doing some initial searching on these forums, it sounds like the general consensus is to lightly fill them with fiberglass. Is this true? I assume this is to help with acoustics some? Would there be any concerns with fiberglass around the lighting, its LED lighting so I wouldn't think heat would be much of an issue?
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post #2 of 13 Old 04-26-2019, 11:46 AM
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Any cavity adjacent to or included inside a theater space is prone to resonating due to the sound energy in the the theater which will excite the resonant frequencies. You don't want to hear that shh it. Fill er up. Being in contact with LED fixtures should not be a problem.
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post #3 of 13 Old 04-26-2019, 06:10 PM
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Light fixtures are rated IC for insulation contact, or non-IC rated. Non-IC fixtures are supposed to have the insulation kept a few inches or more away from the fixture.

If they're LED fixtures then they are probably IC. Should be indicated on the packaging.

Either way you can and should insulate the soffits to they don't resonate, like Jeff pointed out.

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post #4 of 13 Old 04-27-2019, 04:11 PM
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I put body pillows in mine from Walmart.
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post #5 of 13 Old 04-28-2019, 05:42 AM - Thread Starter
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Quote:
Originally Posted by bluer101 View Post
I put body pillows in mine from Walmart.
Interesting. That'd certainly be easier ... I wonder if there's much of a cost difference either way?
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post #6 of 13 Old 04-28-2019, 06:02 AM
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The pillows were $8.27 a piece. I decided to use pillows so I can accesss my soffits in the future without itching. It was really easy to do.

https://www.walmart.com/ip/Mainstays...hite/168674724


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post #7 of 13 Old 04-28-2019, 06:48 PM
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If the soffits are built inside the soundproofed theater envelope, another consideration is whether to intentionally leave parts of them open to serve as low frequency absorption. They are in room corners after all. Openings can be covered with fabric to disguise.
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post #8 of 13 Old 04-28-2019, 07:42 PM
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If the soffits are built inside the soundproofed theater envelope, another consideration is whether to intentionally leave parts of them open to serve as low frequency absorption. They are in room corners after all. Openings can be covered with fabric to disguise.
That is what I did. Drilled 4 inch holes at irregular distances and covered the panels in black acoustic fabric. Ofc also filled the soffits with Rockwool covered in blow through sheer fabric to minimize dust in the room.

This makes it work like a huge basstrap in corners and all along the wall/ceiling "corner".
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post #9 of 13 Old 04-29-2019, 04:28 AM - Thread Starter
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Interesting idea. So how many holes you talking here ... just one every couple of feet at varying places or making it look like swiss cheese?

Can you share any photos, if you have them, of the fabric?
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post #10 of 13 Old 04-29-2019, 08:04 AM
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There are plenty of examples scattered throughout build threads but I don't have them catalogued in that way. The fabric type doesn't really matter, they are all transparent enough at low frequencies.

How to do the holes is a little more complicated but practically speaking more and larger is better. A few smaller holes along the wall will turn the soffit into a tuned Helmholtz resonant absorber... very effective over a narrow frequency band. Figuring out what frequency of absorption you'll get with a certain soffit and hole combination isn't trivial, and you (probably) don't want to attack just a narrow frequency band anyway. If you were really determined you could theoretically internally divide the soffit into a few segments along its length and tune each to attack a specific measured in room problem nodal frequency. But if the holes become large and numerous enough the whole soffit becomes a broadband absorber, which isn't as effective as the resonant absorber at those tuned frequencies, but remains moderately and uniformly effective over a wide frequency band.

Carrying that idea to its end, you can just leave one or both faces of the soffit (horizontal, vertical) open framed and use cloth instead of drywall to "close it in" visually, trimmed appropriately. That has been done many times.

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post #11 of 13 Old 04-29-2019, 08:05 AM
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Keep in mind though that this assumes the soffit is built inside of a soundproofed shell. If it carries piping or ducting and has to serve as part of that envelope/shell, then it needs to be constructed the same as the walls (clips, channel, double drywall, greenglue most commonly).
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post #12 of 13 Old 04-29-2019, 08:26 AM - Thread Starter
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So the entire front and back of the room soffits will be built as apart of the shell, but then there will be soffits around the side of the rooms, and another in the front, for lights that will tie into the other soffits and theses will be built inside the shell.
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post #13 of 13 Old 04-29-2019, 08:09 PM
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My soffit fronts are fabric covered frames to act as absorbers too, just not in the photos above.
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