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Discussion Starter · #1 ·
I'm finishing a portion of my basement that will include a home theater. Before I learned anything about sound isolation or how far I wanted to take it, I rough framed the walls & installed and wired recessed lighting. I also installed and wired my electrical boxes and circuits. This was all done before I read about sound isolation techniques I'll want to incorporate to keep the sound from disturbing anyone (including the two dogs) who may occupy the floor above. Luckily I had time to read a bit when I had to take an unexpected break to have knee surgery. While I rehabbed, I decided I wanted to do this right the first time so I read up and learned that I'd need to decouple the already framed walls from the floor joists. I also learned that I should build a double wall to essentially decouple an existing wall enclosing my staircase into the basement. I also realized my idea to use an insulated and open slatted ceiling was out the window and that I'd likely need 2 layers of 5/8" drywall sandwiched with "green goo" to keep low frequency from transmitting. If my working knowledge is flawed, please correct me because based on what I've read (learned?), this is what I believe to be true so far.

Here are my questions;
I know I to have to decouple the top plate of my existing framed walls from the floor joists. Can I simply notch out enough room to wedge 1/2" rubber pads or rubber "U" channels at each contact point? Do the bottom plates of my existing walls need to be decoupled from the 4" poured concrete floor as well? I'm counting on that not being a problem since the concrete slab has about 12" of stone below that as well. Additionally, my foundation walls are 10" of poured concrete so once the framed walls are effectively decoupled from the joists above, will it still be necessary to use decoupling clips and or 2 layers of 5/8" drywall on the walls? Will I need outlet backer pads? What treatment is suggested to prevent heating duct work and cold air returns from transmitting sound and/or low frequency?

Lastly, will I need to build enclosure boxes for my recessed light cans? I've seen this recommended but if the ceiling and walls are already decoupled, how much is this going to affect the final isolation capabilities? Granted, the "weakest link" theory comes to mind so if this remains a critical link could I used Mass Loaded Vinyl and insulation instead of boxes? On that note, could I attach a layer of MLV (what weight?) directly to the floor joists above then use 1 sheet of drywall to achieve comparable results to 2 green goo sandwiched sheets of 5/8" drywall? Am I correct in assuming that whether I use MLV and one 5/8" sheet or 2 layers of green goo sandwiched drywall I will still need decoupling clips or a similar product for the ceiling? Lastly, what products are recommended and does anyone have suggestions as to who is the least expensive online source to purchase the recommended decoupling clips, rubber channels, green goo, MLV, etc?

I really need to get this project moving ASAP so any advice I can get from those who have conquered this ground before me, would be greatly appreciated to say the least.
Thanks in advance.
Mick
 

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That's a lot to discuss in one post. I'll get the ball rolling by calling out a few basics. Yes for best results you should decouple your walls from the ceiling joists, although I'm not sure how you would do that once your walls have been built, other than by adding a new stud wall inside the existing ones. You do not need to decouple the walls from the floor. The simplest option at this point is probably to just put a clip and channel system on all walls and ceiling, and screw the two layers of drywall with green glue to that. That will provide decoupling to all those surfaces, eliminating the need to decouple the walls from the ceiling, or to make a double stud wall. It's not quite as effective as fully decoupled framing, but it's still very good and probably the most common decoupling method.
 

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If you hang the walls 1/2" short and tie them with DC-04 clips, the only places you'll need RSIC and channel is the ceiling.

Any holes you cut in the room for cans or whatever need to be boxed. Or better yet, build soffits after the room is drywalled and put downlighting in there and uplighting in crown molding. That way you don't have any holes.

Put outlets in columns again built after the room is drywalled. Again, no holes.

Bryan
 

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Discussion Starter · #4 ·
Thanks for getting things started guys. It looks like I'll be doing some re-work with my framing because the only way to decouple the existing walls is to start pulling studs one at a time and cutting them 1/2" shorter to accomodate the clips that Bryan suggested.

Thankfully, I used screws instead of nails so it won't be too bad. I was already thinking about switching to limited wall lighting to avoid having to box every can so as suggested, I may end up going with a soffit to use some of the cans. No matter what, it looks like I'll be removing all of my lighting. I'll also have to figure out how best to run/hide my rear speaker cables and HDMI's but that shouldn't be a big deal.

I expect I'll need to use DC-04's on the framing required to isolate the heating duct and cold air return runs but do I need to do anything to isolate the steel beams and support columns which are directly coupled to the floor joists above?
Thanks again Guys.
 

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Just box around posts and beams but hang the boxing from clips/channel on the ceiling.

Cabling can also be routed in the soffits and dropped down into columns for surrounds.

Bryan
 

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Discussion Starter · #6 ·
First, a belated thanks to Bryan for his last post. That being said, I've spent the past couple of weeks or so looking into decoupling clips for the ceiling and was hoping for a few expert opinions to either backup or debunk my findings. It looks like the Pliteq GenieClip and Green Glue's Whisper Clip are both good options. Does anyone have experience with either? The GenieClip looks to have a better design to me but they have almost identical STC ratings. I'd like to keep as much low frequency as possible in the basement so is either one better than the other in that regard or should I be looking at another product altogether? As always, any help is greatly appreciated.
 

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Ted White at the Soundproofing company told me if he were to build a home theater again he would use the cheap IB-1 clips because they are cheap and the difference between them and any other clip is hardly noticeable. I don't know how much the more expensive ones are but IB-1s are $2 each. The fact that I had just spent a third of my budget on moving my furnace and ducts surely entered into my decision, but generally when Ted speaks, it's best to listen.
 

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Discussion Starter · #9 ·
Lots of good info on HTS so processing it all is a chore but it sounds like a floating joist system will give me the most low frequency transmission loss and at a lower cost than resilient clips and channel. I've looked all over for a video, sketches or a step by step instructions on how to construct a floating joists system. Anyone know of a good source where I can see detailed pics, videos, instructions, etc?
 

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Separate joists can work well. To really get the benefit totally, you would want to isolate the walls from the joists using something like the DC-04 clips. Whether or not you can actually do it depends on orientation of floor joists, any beams in the way, HVAC, plumbing, and electrical in the joist cavities that might cause an issue, etc.

If none of those are problems, you simply set new joists on top of your walls between the other ones and bracket them into place. They do not need to be as thick since they are carrying a dead load rather than a live one that the floor above would have to. Still, you want to watch the span rating.

Bryan
 

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Discussion Starter · #11 ·
Separate joists can work well. To really get the benefit totally, you would want to isolate the walls from the joists using something like the DC-04 clips. Whether or not you can actually do it depends on orientation of floor joists, any beams in the way, HVAC, plumbing, and electrical in the joist cavities that might cause an issue, etc.

If none of those are problems, you simply set new joists on top of your walls between the other ones and bracket them into place. They do not need to be as thick since they are carrying a dead load rather than a live one that the floor above would have to. Still, you want to watch the span rating.

Bryan
I have a lot going on in this area. Heating runs, cold air returns, Gas lines and steel support beam. I need to see if I can work all around all of these obstacles.
 

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Discussion Starter · #12 ·
After reading some of your posts, my construction plans have evolved a bit. Here's where I'm at:
If I hadn't mentioned it before, my room is approximately 27' x 17'. I framed all of my walls and wired all of my outlets and light cans before discovering the world of soundproofing. It was a blessing in disguise when I had to put construction on hold for the last year because it allowed me to educate myself. I've learned quite a bit since that time thanks to many of you here at the HTS. Now I need to find out if the experts who have been kind enough share their knowledge with me feel that I'm ready to start buying supplies or whether I need to tweak my plans further.

Up until a few days ago I considered using resilient clips and channel to hang the drywall from the existing floor joists but when it came to my attention that this may not be the best option for subwoofer low frequencies, I wanted to address that. Some of your suggestions and other information I came across suggested that using the rwar and floating joists combo is not only far less expensive but much more effective for low frequency which is my main concern. That being said, I'm now considering rwar and floating ceiling joists to decouple and maximize my ability to isolate the lowest frequencies from the living area directly above the home theater. It was suggested that I need not double the two walls in front of the 10" poured concrete walls as long as I use IB3 or similar isolation clips every 4 feet to decouple these single walls from the floor joists. Because it will require far less clips (and contact points) than it would to hang resilient clips and channel, I'm thinking less is better here.

I have the lion's share of my HVAC runs in this area. Should I wrap them with an acoustic mat or MLV product before enclosing them? I know I'll need boxes for my light cans which can also be mounted with IB3's and I'll use putty pads for the outlet boxes. I'll insulate between the ceiling joists and walls. I understand that 2 layers of 5/8 gypsum and green glue is typically used but with the use of floating joists is there really much additional gain using a 2nd layer of 5/8" or 1/2" sandwiched with green glue?

Lastly, I happen to have some full sheets of 1/2 OSB on hand and was wondering if they are better or worse than gypsum for sound transmission? I was thinking of using them on the backside of a few walls facing into the unfinished part of the basement instead of gypsum just to use them up. Any thoughts?

I need to get back to the construction phase ASAP but want to make sure I'm not missing anything before I begin. I have a second chance to get it right because nothing I've already done is too difficult to rework. I won't have that luxury again so please weigh in with your thoughts.
Thank you.
 

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It was suggested that I need not double the two walls in front of the 10" poured concrete walls as long as I use IB3 or similar isolation clips every 4 feet to decouple these single walls from the floor joists.
I understand that 2 layers of 5/8 gypsum and green glue is typically used but with the use of floating joists is there really much additional gain using a 2nd layer of 5/8" or 1/2" sandwiched with green glue?
There are four elements of soundproofing: Decoupling, Absorption, Mass and Damping. Clips or floating joists for the ceiling, and IB3 clips on exterior walls introduces decoupling. Two layers of drywall and green glue introduce mass and damping. Take a look at this for the ceiling and this for the foundation walls.

What the foundation walls article doesn't talk about is a "compromise solution" which I worked with Ted to come up with to avoid adding cost and width to my foundation walls. I'm going to be using a soffit to plug the gap behind the drywall on the foundation walls like this:


Lastly, I happen to have some full sheets of 1/2 OSB on hand and was wondering if they are better or worse than gypsum for sound transmission? I was thinking of using them on the backside of a few walls facing into the unfinished part of the basement instead of gypsum just to use them up. Any thoughts?
A lot of people use OSB as their first layer, behind the drywall. ALMFamily will likely chime in here, he did the first layer in his entire room with OSB. The one thing to keep in mind though is that you won't be able to use 1/2" OSB and 5/8" drywall side by side. You'll either need to do the first layer of an entire wall or ceiling in OSB, or use 1/2" drywall beside it.
 

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A lot of people use OSB as their first layer, behind the drywall. ALMFamily will likely chime in here, he did the first layer in his entire room with OSB. The one thing to keep in mind though is that you won't be able to use 1/2" OSB and 5/8" drywall side by side. You'll either need to do the first layer of an entire wall or ceiling in OSB, or use 1/2" drywall beside it.
After talking with John at TSC, he suggested OSB or drywall would work fine for the first layer as they have pretty much the same STC rating. I chose OSB since I knew I would be screwing furring strips to the walls to allow for acoustic treatment on the wall covered by cloth and the OSB would hold much better than the drywall. Plus, should I chose to put anything else on the walls, I know I do not have to use anchors as I have the OSB back there to hold up.

That said, I would not use 1/2" OSB if you choose to do it. Using 5/8" OSB and drywall will provide much more mass and damping than the 1/2". You can always use the 1/2" to contruct the inner framing of your columns if you wanted.
 

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Discussion Starter · #17 ·
There are four elements of soundproofing: Decoupling, Absorption, Mass and Damping. Clips or floating joists for the ceiling, and IB3 clips on exterior walls introduces decoupling. Two layers of drywall and green glue introduce mass and damping. Take a look at this for the ceiling and this for the foundation walls.
Thanks for the reply. I have looked at the Soundproofing Company website and read their tutorials. The information on the site is great but doesn't answer all of my questions. I was especially hoping someone could reply as to whether I need to apply MLV over the HVAC runs before I drywall.
Any thoughts?
 

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Discussion Starter · #19 ·
I assume you are enclosing them with a soffit stuffed with insulation and wrapped with double layer? Also, are they swapped over to flex duct?

If so, you should be good to go - that is how I did mine and I do not hear a peep from them.
I'm still in the planning and supply ordering stage so I haven't done anything with the ducts yet. I was just thinking about swapping out the rigid for flex but I'll lose the damper doors if I do. Probably not a big deal as the two that would be lost are open all the way. Yes there will be an insulated soffit. Did you swap out just the round branch ducts for flex or the main trunk too? I don't want to get into swapping out the main trunk. What did you mean when you said you wrapped with double layer? Double layer of insulation on the duct work? Did you use any MLV at all?
 

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I'm still in the planning and supply ordering stage so I haven't done anything with the ducts yet. I was just thinking about swapping out the rigid for flex but I'll lose the damper doors if I do. Probably not a big deal as the two that would be lost are open all the way. Yes there will be an insulated soffit. Did you swap out just the round branch ducts for flex or the main trunk too? I don't want to get into swapping out the main trunk. What did you mean when you said you wrapped with double layer? Double layer of insulation on the duct work? Did you use any MLV at all?
I just swapped out the branch ducts that ran through the room. I started the swap where it branched from the main trunk.

Apologies - I meant I put an OSB and drywall layer on the soffits that enclose the HVAC. The only MLV I used was over the false soffits to make them useable for low end absorption and the rear wall to keep the surrounds lively.
 
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