Soundproofing question

gdgross · Post by **gdgross** » Tue Aug 31, 2004 7:24 am

Hi folks, it's my first time here. I posted the following on a couple other forums and they pointed me this way.

I'm planning on converting a room in my home to a recording/mixing/rehearsal room. It'll be used for electric bands as well as acoustic & classical recording/rehearsal to give you some idea of volume. There are three exterior 2x4 walls and one shared wall with the garage. The room is 10x14 with 8' ceilings and a concrete slab floor. I want to maximize every sqaure inch of floorspace, so a room within a room is pretty much out.

I had planned on pulling down the interior drywall from the walls and adding rockwool insulation, (the walls currently have no insulation whatsoever) then doing a drywall/sheetmetal/drywall sandwich on top. But a friend recently suggested to instead fill the walls with sand.

Sonically, would sand be better than fiberglass or rockwool insulation in terms of isolation? There isn't as much trapped air, but it's a lot more dense.

Practically, I am worried about the weight of the sand on the outside stucco. (On the inside I could use 3/4" plywood underneath the drywall for extra strength.) I'm also worried about keeping moisture out and what happens if it gets in. I can run all kinds of extra counduit and junction boxes before I close up the walls, so I won't have to cut into them in the future and have sand spill all over the place.

Your thoughts are much appreciated!

Thanks,
Geoff

knightfly · Post by **knightfly** » Tue Aug 31, 2004 12:09 pm

Geoff. first off welcome to the site -

Have you had time to read the REFERENCE section at the top of the construction forum yet? There is a lot to read, I know, and it could be more concise (I've been 'way too busy to catch up on that sort of project so far) - you should at least read the "complete section" thread, there is quite a bit of theory and recommendation there.

You're right to be nervous about filling a normal wall with sand - the pressure exerted at the bottom will be the entire weight of the column of sand trapped between each pair of studs - assuming an 8 foot ceiling and 24" between studs, this works out to 3.5x22.5x96 cubic inches, divided by 1728 for cubic feet, divided by 27 for cubic yards - sand weighs between 1-1/2 and 2 tons per cubic yard, so we end up with (3.5"x22.5"x96"/1728/27)x3500, or roughly 567 pounds of pressure at the bottom of the wall...

Before you continue, I need to understand what you meant by "drywall/sheetmetal/drywall sandwich on top" - can you do a basic sketch showing the wall frame and your proposed construction, as close to scale as possible? You can post drawings directly here, just size them no larger than 800 pixels wide and file size under 150k - jpegs or gifs work best.

If you can figure out the approximate thickness of your stucco and whatever sheathing is under it for the outside mass on your studs, that will help figure out what kind of isolation you can get without losing more than an extra inch or so of inside space... Steve

gdgross · Post by **gdgross** » Wed Sep 01, 2004 1:17 am

Thanks for the response. I'd estimate the stucco on the outside of the walls to be about 1/2" - 1" thick, based a few times that I've had to cut through it since we've owned the house.

Just curious, but if my walls could hold up to the weight of the sand, would that yield better or worse isolation than rockwool insulation, which would be my second choice? If the sand is indeed better, would it be possible to beef up the stucco from the inside (I will have the inside drywall down either way), or is it just more trouble than it's worth? It's starting to sound like the latter.

Anyway, regarding the 'sandwich,' see the attachment for a cross section of what the finished walls will look like.

Thanks!

PS i will check out the reference section, too!

knightfly · Post by **knightfly** » Wed Sep 01, 2004 5:21 am

Your walls can't take the stress of sand fill, but if they could that would make your entire wall one solid mass, which is only 1/3 of the ideal design - that heavy a mass, if it were possible in this case, would yield an approximate STC of 49, with a dip down to around 30 dB at its critical frequency somewhere in the range of 125 hZ - not ideal for killing drums or bass.

Are you sure there's no panel on the outer studs except the wire and stucco? Seems kind of strange to me...

There's still not enough info to figure isolation estimates here - the sheet blok I can get close to, but when you say sheet "metal", are you meaning Lead, Steel, Pewter, or what? I could assume, but it's a waste of time since every material has its own characteristics and the vary WILDLY.

It's good that you can remove the inner wallboard; once we find out everything about your wall, that will make things easier to improve where necessary.

More details please... Steve

gdgross · Post by **gdgross** » Wed Sep 01, 2004 6:57 am

Thanks!

You've convinced me about the sand! It would be a royal pain to get inside the walls anyway.

I am 98% sure there is nothing beneath the stucco except the wire mesh and tar paper. This house was built in the 50s, and there is NO insulation whatsoever in any of the walls. Everywhere else I've opened walls up this has been the case. (I live in Los Angeles.) I suppose back then folks thought that energy was cheap and would be cheap forever?

As far as the sheet metal, it doesn't necessarily need to be anything in particular, I had just heard of people doing this. I would be open to any suggestions. I'm not even really sure what's available to use

It also doens't necessarily even need to be metal if there is a better alternative. Perhaps there is a commercial product similar to the auralex sheetblock? Maybe some kind of rubber or vinyl product? Covering a room with sheetblock will get expensive quickly.

Thanks again!

knightfly · Post by **knightfly** » Wed Sep 01, 2004 7:08 am

Cool, I'm glad you decided against wanting your walls to explode

Now, we need to discuss budget, a way of deciding just how much isolation you NEED, ceiling/roof construction, ditto for floor, doors, windows - sound proofing is pretty much an all or nothing proposition, since the stuff likes to find the easiest ways to get in/out... Steve

gdgross · Post by **gdgross** » Thu Sep 02, 2004 1:18 am

Thanks, man! I really appreciate your time and effort here!

I'm kind of planning this project in a few phases. First is all the constrtuction. i.e, tearing down the old wallboard, insulating, putting up new dryall, floating floors, ceilings, etc. At this point I'm not worried about acoustic treatments inside the room or equipment, etc. I'll cross that bridge when I come to it.

I was hoping to try and keep costs for construction materials under $1000-$1500, not counting the windows. Is that reasonable? I will be doing all the work myself, except possibly the window installation, but that will come out of a separate budget, when we replace the windows in the rest of the house. All of the room treatment stuff except the windows is coming out of my gig money.

The room is 10x14 with an 8' ceiling.

Regarding windows, there's two in this room (well, three actually, but I'll be closing one off when I tear down the wallboard.) Right now they are single-paned aluiminum frame, so they pretty much will negate any soundproofing I do to the rest of the room, until they get replaced. I may decide to seal another small one off. If that's the case, i'll be left with one fairly large (4'x3') window on the long axis of the room.

Any suggestions for window brands? I can't frame my own, since at least one of the windows does need to be able to open/close. We have a sliding glass door by Anlin in the house, and it seems to be pretty good in terms of sound transmission, at least as far as non-specialized windows go. It's double-paned with about 1" of gas between the panes. I emailed Anlin yesterday to ask about STC and NRC specs, but I haven't got a response yet, and I didn't see any info other than thermal data on their website. I did take a look at the milgard windows, but these are 2x4 walls, and the milgard looked like it was 5 or 6" deep!

There's no HVAC in this room, and I don't think there is enough space in the attic to install one. I'm in Los Angeles, so there aren't real temperature extremes like in other parts of the country.

The attic is fairly shallow because the room is small. It's shallow enough that I can't really crawl around up there. I could probably make it through the crawl hole, but I don't think I'd be able to move around much. The ceiling is 2x6 construction. I believe the roof also has 2x6 rafters. There are three exterior walls and one shared wall with the garage. The floor is a concrete slab. (Carpeted right now, but that may change.) I assume it's poured right up next to the garage, as this room was an addition and not part of the original house. I don't really care too much if sound leaks into the garage, but I do want it to stay there if possible.

As far as how much isolation I need, I'm not really sure. I guess I figure I want the best I can get given a modest budget, and reasonable time and effort on my part. I do want to be able to have a reasonably-volumed electric band in there (space is tight, I know!) and not piss the neighbors off. It'd be nice to be able to practice the drums without everyone listening to me, too. This space is mostly a rehearsal studio, but I will be doing some PC-based recording in the future, as well.

Thanks!!!!

Post by **Aaronw** » Thu Sep 02, 2004 3:02 am

I was hoping to try and keep costs for construction materials under $1000-$1500

A floating floor alone will cost this much. Mine was about $1200-$1300.

gdgross · Post by **gdgross** » Thu Sep 02, 2004 8:38 am

Aaronw wrote:A floating floor alone will cost this much. Mine was about $1200-$1300.

Yikes!

I knew this stuff was expensive, but I thought I could get by for at least under 2 grand.

For the floor, I had planned on simply using 3/4" plywood on top of 2x2s (I want to keep as much height as possible) on top of auralex uboats or something similar (and cheaper). Filling the area underneath the plywood with fiberblass or something thin, since it's only 2" high.

What is wrong with that picture? What am I not including that makes it add up to $1000? The room is only 10x14.

Post by **Aaronw** » Fri Sep 03, 2004 12:33 am

For that size a room, it probably won't be nearly that much. Mine was roughly 16'x17'. I used 3/4" T&G OSB (2 layers). At the time I bought it, it was about $24 a sheet. Then it shot up just after that to $30, but I noticed it's dropping back down again. Right now, materials are more or less at a record high or close to it.

I also ran conduits for electrical and low voltage cabling. That added a couple hundred bucks there.

http://www.johnlsayers.com/phpBB2/viewt ... &start=131

giles117 · Post by **giles117** » Fri Sep 03, 2004 3:12 am

Yeah the sheeting material changes the cost. All my floated floors were floated using particle board at 8.99 a sheet

My small room only costs me about $150 to float. (13x11)

Electrical depending upon how complex or simple you go varies accordingly.

gdgross · Post by **gdgross** » Fri Sep 03, 2004 6:39 am

Aaronw wrote:I used 3/4" T&G OSB (2 layers).

I'm slightly embarrased to ask, but what's OSB?

Post by **Aaronw** » Fri Sep 03, 2004 6:45 am

Orient Strand Board

http://www.osbguide.com/osb.html

gdgross · Post by **gdgross** » Tue Sep 07, 2004 11:08 am

Is Orient Strand Board like particle board or MDF?

I assume this is better than plywood because it doesn't have a consistent grain structure, so it'll vibrate less?

I think I've got a pretty good idea about what I need to do, and I have a rough plan. The only things I'm not sure about are:

HVAC: There isn't any in this room right now. Does someone make a very small A/C & heater unit that could fit in a shallow (2') attic? (humidifier/dehumidifier would be nice, too...) If so, how would I go about keeping the room relatively airtight and soundproof with the unit installed.

Windows: I think the milgard windows are too thick for my 2x4 walls. Any recommendations on other brands?

Door: Is is possible to fit a double-door in a normal door frame? (this is a normal 36" door/frame) Obviously I would need to figure something out with the door handles, and probably install the doors so the hinges are on opposite sides of the doorjam. Also, how do I go about getting the drywall flush with the doorjam? Up until now I had just thought I'd get it about 1/4" apart and caulk the gap.

Thanks again! You folks have a wonderfully helpful forum here.

knightfly · Post by **knightfly** » Tue Sep 07, 2004 3:12 pm

Here's a good page on OSB -

http://www.umass.edu/bmatwt/publication ... ywood.html

HVAC - I'm pretty much an idiot on this, but Rod Gervais (a member here, and a fellow mod on another site) is VERY knowledgeable on this - you could try PM-ing him and posing your questions on AC, etc -

Windows - one option could be to leave your windows in place, and either add storm windows or these -

http://www.soundproofwindows.com/index.html

In order for this to work as good as possible, the original windows would need to be sealed and possibly re-installed, checking all aluminum extrusions for voids - these would need to be fully caulked to keep the frame from being the weak link.

Most other windows these days are double glass, and will NOT improve at all in the low end by adding a third pane (the double glass window is your first TWO panes)

Door - have you checked the REFERENCE section's door thread yet? It's not much, but gives SOME insight - and, getting the drywall within 1/4" and caulking well before replacing the molding is fine - if you have a metal threshold it will need to come off and get filled with either plumber's putty or caulk, so it's not hollow... Steve