Ht room isolation

ciotime · Post by **ciotime** » Mon Mar 13, 2006 3:57 am

Im presently having a house built. It has a dedicated home theater room thats still bare. No paint and no ceiling yet. The walls are all made of concrete thats 6" thick. Are my 6" concrete walls good enough for isolation? Or do I need to do some sort of double walling with insulation in between? I checked the STC rating for a 6" cement wall and its about 50-60. Ive posted this question on a number of forums already but the problem is people have different opinions. Some say its good enough and that no sound can get through 6" cement walls while others say its not good enough. Please help...

Sandersd · Post by **Sandersd** » Mon Mar 13, 2006 4:44 am

The best thing you can do is fill the cells of the blocks with sand or grout - IF your foundation beams (under the wall) will support the extra weight. You should probably consult whoever designed your foundation for verification. Don't rely on your builder.

Next best is to build new walls 6"-12" inside of the block wall, put 3" of insulation and two layers of drywall. Of course there are a thousand little details I'm sure others on this forum will be happy to point out

, but that's the short version.

Try not to get sucked up into the "perfectly isolated" acoustic universe mentality. It's just a home theater.

knightfly · Post by **knightfly** » Mon Mar 13, 2006 8:29 am

I saw nothing in your post about the walls being hollow blocks, but if they are then it's correct to fill them if you want heavy-duty isolation - but this comes down to "how loud are you gonna get", and how much do you wanna spend, etc - as to the comment about "no sound getting thru 6" concrete", bull.

If you intend to listen to action movies at 2 am while your family sleeps in the next room, then you need secondary walls that will work in tandem with the concrete to kill the low frequency sound - that's the most difficult to stop, so generally by the time you've solved THAT problem the rest of the sound spectrum isn't a problem at all.

With just 6" SOLID concrete (or sand/grout-filled blocks) outside you'll just start to hear explosions, bass drum, stuff like that when it's about 85-90 dB in the room - if you were to add an inner 2x4 frame, NOT touching the outer wall, and spaced 1" away from the wall, then fill the frame with insulation (the right kind) and put two layers of 5/8" gypsum wallboard on ONLY the inside of that frame, you would help your low end Transmission Loss by about 8 dB, so you could approach 95 dB at low frequency before it became audible outside the room - This would raise the STC from around 55 to around 75 (since STC is centered at 500 hZ) so anything BUT bass would be inaudible outside til your sound meter reads 'way over 100 dB.

Bottom line is, how expensive do you want to go and how loud do you wanna be (without anyone knowing you're even in there) - And, as sandersd pointed out, how strong is your existing construction so you know if you can beef things up at all? Steve

AVare · Post by **AVare** » Tue Mar 14, 2006 2:56 am

Meant in a helpful way, but we don't even how much you want, or your neighbours want, or how loud you will be, or quiet your neighbours are/want. More specific questions can be answered more specifically. Good luck with your house!

Andre

ciotime · Post by **ciotime** » Tue Mar 14, 2006 12:08 pm

Sorry Im not really knowledgeable re DBs...but no problem with neighbors coz they're far. My real concern is the 2 rooms right next to the front and back wall. These are the bathrooms of those 2 rooms. Loud I guess coz Im gonna be watching a lot of movies. Some people suggest I add a layer of drywall spaced a couple of inches from the cement wall and put insulation in between.

Sandersd · Post by **Sandersd** » Thu Mar 16, 2006 5:13 am

If you have a bathroom at each end of your room that's great. It'll add an extra buffer zone to isolate your room from the living areas.

The cheapest and easist solution is to build a stud wall and insulate it with 3" unfaced insulation and closed up with 2 layers of drywall. Measure in from the existing walls 1" and snap a chalk line. Put the edge of the 2x4 wall on the line and nail into the joists above. Insulate, add electrical outlets, drywall, finish, trim, paint, enjoy.

ciotime · Post by **ciotime** » Thu Mar 16, 2006 12:06 pm

Thanks Sandersd...let me summarise to see if I got it right. So the only thing holding the wood stud is the top and bottom plate? Top plate to the joist above and bottom plate to the cement floor? Is the top and bottom plate also 2x4? Also do I fill all the cavities with insulation? No more air gap needed? Can I use unfaced rigid fiberglass or rockwool? So if I look at it from the side it'll be cement wall then 1" gap then the 4" of the 2x4 then double drywall.