My basement soundproofing experience!

Posted: Thu Sep 30, 2004 6:27 pm

I have completed soundproofing my basement and am amazed by the results with only 2 layers of 1/2" thick sheetrock. My goal was to have a loud rock band be able to practice at full volume and not have the neighbors located 15ft to the house hear what was going on.

Yes it was a basement (so i have concrete foundation and dirt) but there was soooooooo much air where the 1st floor met the basement wall that it was practically outside, sorta.

I will just explain how I did the walls and ceiling since the door has so many hacked seals and clamps and was constructed from scratch like the walls it would be difficult to explain. The windows were also taken out including any existing framing and boarded up with multiple layers of MDF and a foam/sheetrock layer.

I will start from the outside and work in. The walls and ceiling consisted of a basic 2x4 frame and a layer of 1/2" sheetrock attached to the inside. Everything was sealed up air tight to an insane degree. To "an insane degree" means it took twice as long to seal the layer as it did to put it up and the seals probably have a better STC rating than the wall just like a good weld is stronger than the metal.

Here's where it gets funky. I then cut 2" strips of that foam bedding stuff from walmart and glued it to the sheetrock where the 2x4 studs would be. I used 3M high strength spray adhesive. The foam strips were about 2" by 2". I then glued another layer of 1/2" thick sheetrock to the foam strips. I had to use a few screws for the ceiling. Then that layer of sheetrock was sealed up again to an insane degree of air tightness.

I think it turned out so well because of how air tight each layer was and because of the foam resilient channel. The foam resilient channel does a great job of blocking the bass without lots of mass (layers of sheetrock). It also provides for a layer of dead air that is truly isolated by the foam strips without framing the room twice with 2x4's (room within a room).

It worked very well but the 3M spray adhesive is very pricey and costs about as much as a layer of 1/2" sheetrock to attach a layer of foam strips and a layer of sheetrock.

I am very pleased with the results though and was expecting to have to add more layers of sheetrock but I think I will be OK. Just thought I would document these un scientific results since I tried something new with the foam strip resilient channel and couldn't be happier with the results considering the costs and labor.

If it isn't clear how I constructed the wall let me now and I will post a picture of the wall design. And I don't think anything I did was up to code but it's just a basement right???

Posted: Fri Oct 01, 2004 12:31 am

did you ever try the driveway goop? might be fun.

so there are no screws, just 3M spray glue and foam, holding the drywall to the walls?

Posted: Fri Oct 01, 2004 12:43 am

Hello Bonesmachine,

I was trying to read your post.
Maybe a well meant tip.

If you split those sentences over more lines (line break) it's easier to read.
This continuous text caused me to stop trying.

This really is well meant.

Posted: Fri Oct 01, 2004 8:51 am

Yeah I had trouble reading over the post last night as well but I thought it was just the booze.

Thanks for the formatting tip.

And yes it's just the 3M adhesive holding the drywall to the foam and the foam to the other wall. I did use some screws on the ceiling though.

I tested the room again in a sober state of mind and am now finding that I may have to add another layer. Maybe the driveway goop sandwiched between another layer of sheetrock?

I am also thinking of maybe adding a layer of carpet under padding and then 2 layers of roofing roll and then compressing those layers with a layer of sheetrock? So the inner wall would be a sheetrock/underpadding/roofing roll/roofing roll/sheetrock sandwich. Any thoughts?

I should have beefed up the outer wall that is directly attached to the 2x4's because adding more weight to something that is just glued may not work out so well. I may have screwed myself.

I am still amazed by how much sound is being blocked with just 2 layers of 1/2" sheetrock though. I wonder if the foam resilient channel performs better than a standard metal clip resilient channel? The foam channel is more expensive. If anyone is ever conducting a real STC test I would sure like to know how the foam channel construction performs.

Again, I should have beefed up the outer wall first!!!!

Hope this interests or helps someone out there...

Posted: Fri Oct 01, 2004 3:02 pm

i'd test a little strip before sandwiching anything between sheets without a good idea of what it will do. if the goop didn't yield any internal damping, and if it stiffened the panel, you may have wasted your time. (lowered coincidence dip, etc.)

i'm amazed that spray adhesive is holding 2 layers of drywall, i think it's very cool that you got great results. i don't think adhesive-only meets code in ND.

take it easy

Posted: Fri Oct 01, 2004 7:48 pm

I never tried the driveway sealer stuff. I think it dries pretty hard so I decided against it. I think it would almost be like adding a thin layer of hard plastic, not much help...

The 3M adhesive is great stuff and makes a bond that is stronger than the foam itself. I glued a test strip to a 2x4 and it took allot of force to rip it off and the foam is what finally gave not the bond. On sheetrock the paper layer is what gave.

I would like to get a little feedback on what I am thinking of doing for the last inner layer. The layer is currently just 1 layer of sheetrock. I am thinking of adding a layer of foam carpet under padding and then one more layer of sheetrock. I hear that just adding another layer of sheetrock to sheetrock won't yield great results.

The idea would be that the sheetrock/foam/sheetrock sandwich would isolate each layer of sheetrock to some degree to get the best bang for my buck. The foam padding of course would not provide any damping or soundproofing value by itself but would just isolate layers of sheetrock. I do know that isolating vibration is a very good way to soundproof things. Has anyone tried this before?

I already have rolls and rolls of the foam padding from my last dumpster diving adventure at a carpet store which I plan to later use in my gorilla style treatment of the acoustics in the room.

Thanks in advance for any help or feedback about the sheetrock/foam/sheetrock layer.

Breaking up the sentences is great for readability!!! Who knows, maybe I'll even start including numbered lists???

Posted: Sat Oct 02, 2004 2:10 am

well, ...

always remember that any isolator, be it resilient channel, a layer of foam, springs under a floor, or an air cavity, comes with a catch. every layer of isolation will have a resonance region

at the resonance, it will make things WORSE, for about an octave or so

below the resonance it won't do anything (in theory same as rigid connections)

so here's why i'd not put anything resilient between those layers:

you will either use 1) full-area foam or 2) partial-area foam (like small squares) creating a small air cavity between layers

1) is likely to yield a high or highish resonance point
2) is guaranteed to yield a high or highish resonance point

also, at times adding more mass to a resiliently mounted wall can have considerable effec - by lowering said resonance, which all resilient anythings (or even all panels, for that matter) must have.

my largest concern if it was my wall would be structural strength (no screws in the wall). i know you're not concerned, but i'm paranoiac about that stuff, lol

Posted: Sat Oct 02, 2004 2:59 am

Have a look at the Acoustics FAQ, second in the list on his Articles page:

www.ethanwiner.com/articles.html

It also refers to the Author's site (5 discrete links) where one can find much more useful info.

Posted: Sat Oct 02, 2004 9:23 am

OK thanks...

Maybe I'll just have a layer of vacuum as the isolator. A layer of vacuum wouldn't have a resonance region, right? Just kidding.

I am still not sure what to do but will figure it out. I may just stick with this idea and see if it helps enough to say that I am done with soundproofing. If some frequencies resonate their way out, I guess it will just have to be that way.

Posted: Sat Oct 02, 2004 12:13 pm

Actually I think I'm going to keep things the way they are. I just did some more testing and found that the only sound that I could hear from outside was coming from the windows or rather where the windows used to be.

This is very good news for me because I can easily add more layers to the windows. Thanks for convincing me not to do anything insane and waste my time and money.

I may be back with room acoustic problems in a few days after I give it a go with the foam and carpet. It's just a practice room though so I should be fine.

Thanks again!

Posted: Sat Oct 02, 2004 10:08 pm

hey bones,

i should clarify a couple of things.

most would recommend a wall with an air cavity, right? but if you read this forum, very bad opinion about having TWO air cavities. (the dreaded triple leaf system)

every air cavity comes with a resonance, including that first one. the reason the second air cavity is so bad is now you have two.

so i wasn't trying to say your resilient mounts were bad, just offering that ANOTHER SET of resilient mounts might not be what you need.

also, sometimes adding a bit of mass to a resilient/decoupled wall can ahve a big effect.

so all i was trying to say is that if it were me, i'd skip the additional layer of foam/spring/bouncy stuff.

good luck!

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