Soundproofing + recessed light cans - is my plan hopeless? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 18 Old 07-20-2019, 11:55 PM - Thread Starter
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Soundproofing + recessed light cans - is my plan hopeless?

Hi all. I'm trying to "soundproof" a partially below-grade room. Realistically speaking, my goal is to reduce/dampen a reasonable amount of sound transmission to/from the room above, and to the adjacent room. Not worried much about vibration.



I'd like to use new-construction recessed lighting fixtures (attach to joists via nails) for my overhead lighting. Maybe around 10x total. I know this is far from ideal, but I really prefer screw-in bulbs that I can gimbal/swivel. Not sure if I'm allowed to post links, but search "Lithonia L3" for the specified enclosure.



At minimum I'll be using Roxul/Rockwool Safe'n'Sound batt insulation in the ceiling and wall to absord a bit of sound, then if it can be justified, perhaps a second layer of 5/8" drywall separated with Green Glue. There's really not much point of using resilient channel as the recessed light can + flange creates a mechanical coupling between the drywall and joists.



I realize that the can is sabotaging my chance for success, but what I'd like to know is if it's at all worth it to add a second layer of drywall + Green Glue, or if I'll see minimal benefit because of the cans. It's really got to give a noticeable performance benefit to justify the cost. Thanks
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post #2 of 18 Old 07-21-2019, 04:23 AM
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Use clips and channel, backer boxes hung off the channel, and remodel style cans. The result is a sound isolated recessed can. I've done it too many times to count. I like the 4 inch MR16 cans that can use a variety of incandescent and LED bulbs, they have the gimbal swivel feature. Globe electric is my choice and they sell contractor 10 packs, these: https://www.amazon.com/Globe-Electri...s%2C148&sr=8-1
I spray paint the trims to blend with the ceiling.
Double layers of 5/8 drywall with Green Glue hung off of clips and channel is the Mass-Isolation-Dampening approach to sound isolation. Add isulation in ceiling and wall cavities.

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post #3 of 18 Old 07-21-2019, 04:29 AM
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You could build some backer boxes.

I would use BigmouthinDC's design, which are a much simpler/cheaper/more evolved design as what I did 10 years ago.

Two layers of 5/8" drywall +GG. The first layer of drywall was cut out while the second layer was run right over the opening with the rough location of the spot light cut out marked.
I did a double step of the inner and outer MDF box, to get some more caulking area, while Big's design has that nice big flange for that, and it also makes for an easy target for drywall screws.
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post #4 of 18 Old 07-21-2019, 04:48 AM
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Thanks Tedd, I'm having a problem with my photo files, I was looking for that picture. It comes from the Summer Fun project in my signature.
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post #5 of 18 Old 07-21-2019, 05:26 AM
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We actually were responding at the same time... You beat me to the punch by the time I dug up the photos I was looking for.
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post #6 of 18 Old 07-21-2019, 10:11 AM - Thread Starter
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Thanks guys. I was contemplating going with remodel cans, but wouldn't it suffer the same issue as the new construction cans in that you still have a dozen uninsulated cavities protruding into the ceiling? Sure, remodel cans mounted to drywall will reduce the transmission of vibrations (not so much of a concern for me) but I'm wondering by turning my ceiling into soundproofing swiss cheese if it's even worth it to use two layers of 5/8 + GG? I suppose the cans you linked are not as tall as the Lithonia one I have, so maybe I can put some insulation above it. Hmmm.
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post #7 of 18 Old 07-21-2019, 10:51 AM
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you can make the backer boxes with double layer GG construction, you can also put some insulation inside the boxes if you stick to LED bulbs. Follow our advice and your ceiling will not be swiss cheese.
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post #8 of 18 Old 07-21-2019, 11:15 AM
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I don't have much insulation above the light boxes, since my floor joists are but 7.5" tall and my backer boxes eat up almost all of that height.

The Bazz 100 in those photos of mine, are remodel cans. The single layer of drywall was also about the clips that secure the cans, as they wouldn't work with 2
layers of 5/8" drywall.

I doubt the insulation is doing much anyways, save for preventing the floor joist area from becoming a resonate cavity. (Insulation will eat up high frequencies,
but do nothing to stop long bass waves.)

Don't forget to caulk the holes where the electrical wiring comes in to seal the box.

I would wager your door leaking sound will be an issue long before properly sealed backer boxes ever will. They are simple to make, inexpensive (Big's version far
more mine), and work well. I will double down with Big's design next home theater build, when I retire and relocate. Kind of hard to argue with good, cheap,
and effective.
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post #9 of 18 Old 07-21-2019, 11:55 AM - Thread Starter
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Ok, I think I have a pretty good idea of the best performance construction, but in the spirit of saving cost and time, could you rate the performance (1 to 10, with 10 being perfect) for the follow concepts?


Concept 1. Acoustic mineral wool between joists. Two layers 5/8" with GG mounted directly to joists. Remodel cans, no backer box.
Concept 2. Acoustic mineral wool between joists. One layer 5/8" on resilient channel. Remodel cans, no backer box.
Concept 3. Acoustic mineral wool between joists. One layer 5/8" on resilient channel. New construction cans in backer box.


Have to look for clips + channel. I know I can source resilient channel fairly easily.



Appreciate the help.
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post #10 of 18 Old 07-21-2019, 12:18 PM
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I don't understand the choice of options as they are all flawed in some manner, if sound isolation and noise containment are a design goal.

Unless of course, resilient channel is what you can source. What not clips and hat channel? Is this a cost consideration?
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post #11 of 18 Old 07-21-2019, 12:40 PM - Thread Starter
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It's just a matter of finding a compromise. If I can find an option that gets me 75% to the perfect solution, then I prefer to go with that over something that costs 2x as much as takes twice the time to complete. For example, backer boxes would be amazing, but building those for a dozen lights sounds like a nightmare with my skillset. I could do it, but it would take me a long time. If I can get the same performance with double drywall, then that would be a lot quicker for me to install.



I realize that I may come across as wanting "half-assed" soundproofing, but my use-case doesn't demand perfection. 90% of the time I'm the only one in the house, and even then I don't tend to listen to music loudly.


So in the end, looking for the best value solution. I just need your help figuring out which one that is.
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post #12 of 18 Old 07-21-2019, 01:33 PM
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There is no real compromise position. You either have it or you don't. That 75% position is just wasted money, when you think about flanking noise.

Backer boxes are simple to build, and assemble. No handy friends with a chop saw? You could start with MDF shelving, and likely eliminate a height cut.
I'm maybe the one missing the boat here... But you are going to hang drywall but can't assemble a dozen small boxes? Drywalling is a far more demanding skill.

My vote would be double drywall (which doesn't eliminate impact noise from above) and backer boxes.
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post #13 of 18 Old 07-21-2019, 01:42 PM
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you can get A237 clips on Ebay, then the 7/8 furring (hat) channel is at just about every drywall building supply house that stocks metal studs. You can actually get it on Ebay but it is shorter and more expensive pieces than you can usually pick up locally. Don't walk into Home Depot and expect to find these items.
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post #14 of 18 Old 07-21-2019, 01:49 PM - Thread Starter
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I have a miter saw and table saw, so I have the tools to get the job done. Admittedly I haven't done much carpentry. I'm coming from an electrical background. Suppose it's time I learn.


Would I mount the backer box directly to the joists if I don't use res channel? Maybe it wouldn't matter since the drywall would be coupled to the joists anyways.


Thoughts on using plywood instead of MDF?
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post #15 of 18 Old 07-21-2019, 02:21 PM
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Great, you have all the harder to acquire skills. Now you can work on the easy simple stuff.


The double layer of drywall could support the backer box. That flange is a nice wide target for several beads of silicone and drywall screws.

Plywood should work if you have that on hand. I simply went with unfinished MDF shelving, on sale, rather cheap and very effective.
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post #16 of 18 Old 07-23-2019, 06:32 PM
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Same approach for ceiling speakers in an Atmos setup? Backer boxes secured to the decoupled hat channel and drywall? I haven't searched for a thread for that yet, but I stumbled on this one and figured I'd ask ...

It appears my hypocrisy knows no bounds.

Brian
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post #17 of 18 Old 07-23-2019, 06:37 PM
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same concept and approach
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post #18 of 18 Old 07-23-2019, 06:43 PM
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Thank you, Jeff.

Now back to the previously started thread about light cans ...

It appears my hypocrisy knows no bounds.

Brian
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