soundproofing basement, 3 external block walls

Posted: Wed Aug 08, 2007 11:53 am

Hi everybody.

What a wonderful forum.

I'm an electric guitar player that likes to record and compose a bit. I'm shopping for my next house around greater Cleveland, Ohio.

I think I've got a house picked out but need to check some assumptions.

My concerns: I am far more concerned with sound getting out than getting in. This is a reasonably remote house so I'm not terribly concerned with sound coming in or out of the house itself. BUT I want to be able to play an 18 watt guitar amp, and maybe a drum kit, in my basement while my beloved family and noise-sensitive wife is sleeping. If I was going to be seriously recording for the evening no one would be running around above.

In fact, the layout of the house is such that there isn't much directly above the studio area to be concerned about! The bedrooms are at the far end of the house, and there is a large masonry fireplace structure for fireplaces in the basement and 1st floor between the basement studio and the first floor bedrooms!

I'm a recovering audiophile so I really want to keep thought about the eventual acoustic treatments to a minimum until I understand soundproofing better. I'll get the dimensions and non-parallel walls and all that jazz figured out later, IF this is going to be as easy to soundproof as I think.

So, we'll push the priority of silencing my guitar amps from the rest of the family as far as possible until I get a feel for a budget. I'm a hardcore DIYer with enough tools and time to be dangerous. Budget is a function of time, the longer it takes, the more money I'll probably have to put towards it and vice versa Smile

But I'm the kind of person that expects to be able to save a lot of money by being clever and about the cleverest thing I can do at this point is ask for help.

I do realize I will probably end up with a separate booth inside the main room for mic'ing really loud amps or vocals. But I really want to be able to just relax and play with a buddy or two in the evenings without much at all being heard in the rest of the house.

the overall structure is a single-story 1700 sq ft "ranch" style house with a 1700 sq ft block basement built in the 1960s. The area in question is shown in the attached drawings. I need to build one new wall to wall off a 15 x 20ish area of the basement, with a soundproof door. That studio door will be behind another door in the basement. At the top of the stairs is another door, and at the first floor hallway to the bedrooms is another door and at each bedroom is another door. Let's assume I'll have the ducting and other air-born sound details tamed for now, although I'm all ears on any issues. There is a boiler at the other end of the basement with baseboard radiators all around the basement and first floor, and also central AC which has no critical ducts going through this space.

So I have three 8' walls (slab to bottom of joist) of external block and a basement slab floor. I'm willing to go all out on the ceiling and the fourth wall since I'm assuming the three walls up against the block won't be terribly expensive.

attached is a lame drawing of my understanding of how to get started.

My questions are:

For the new ceiling layers, should I try to span new joists on top of the new inside walls? If so, how do avoid the "three leaf" syndrome? I've only got 8' from slab to joist so I'll begrudge any headroom loss but isolation is the highest priority. Cost would be a close third priority. If spanning is gonna kill my headroom too much, what's a good thinner plan for the ceiling? I'm thinking RSIC or those Kinetics springy hangers. I need to support new cross-members hanging below the existing joists to put a few layers of drywall on, correct? But no third layer of drywall in between the floor on the first floor and ceiling layer of drywall in the studio?

Should I put in some kind of floor? What sort of frequencies are going to move through this earth-bound slab into the earth-bound walls to be heard at any other point in the structure? Seriously, should I worry about the floor assuming the rest of the new "room within a room" structure is ideal?

If I do put in a floating floor, should I stand the walls on top of it? Will it hurt or help if I decide to add to the floor later, and have the floor constructed as a caulked-in plug inside the walls that are essentially standing on the slab?

Assuming I can get away with not doing anything to the floor, how do I decouple the walls from the slab? Should I stand them on felt or neoprene? Specific product recommendations appreciated.

I can't quite get my head around the "three leaf" issue with regards to the new walls being contructed right next to the existing block exterior walls. Should I just put up a new steel studded wall with only layers of drywall (and green glue?) on the inside only?

For my my crucial fourth wall that is separating the studio from the rest of the basement, it's only gonna be like 16 wide x 8 tall so a few extra layers of RC or drywall or whatever would be totally practical if it's gonna help, what would the ultimate construction be? I'm thinking the two rows of steel studs, with at least a double layer of 5/8" drywall (with green glue) on both inside and outside, and I can see doing a layer of RC in there somewhere too. Remember, I'm far more concerned with sound getting OUT than in. So I would probably put the RC on the inside of the inside studs, and hang some drywall/glue layers from that? Should I do many layers of drywall/glue, or at what point is my door going to make it irrelevant?

I have a 36" VERY heavy solid core door I snagged off some construction demolition. I plan on buying a real acoustic seal set and automatic threshold (any ideas?). I'm thinking a second door would be beneficial. Don't really understand how to frame in the two doors on top of each other. I'd imagine the frames need to be isolated from each other. I can only see having one door on one leaf and the other door on the other leaf. What do I put between the two door frames?

Posted: Wed Aug 08, 2007 12:10 pm

Are my pics ok? I thought I had them resized to 700 pixels across but now I'm not so sure...

Posted: Wed Aug 08, 2007 4:33 pm

if you build the new "wall" with 2 steel stud walls (separated by 2-3") and 3 layers of 5/8" drywall on the outside of each, R19 insulation inside of each, you'll get pretty decent isolation. for the ceiling, if you can add 3 layers of 5/8" drywall inbetween the existing joists (be sure to calc load...) and then put in an ceiling with rc2 spanning across the joists and another 3 layers of 5/8", you'll be able to keep the ceiling height and probably have the isolation you need. again, doing this would depend on the span and load calcs for the existing flooring.
on the inside of the 3 block walls, i'd put up slat resonator walls to treat the space - with some angles to keep flutter echos down and add some trapping to the space.

Posted: Wed Aug 08, 2007 4:40 pm

Thanks for the ideas!

How do I calculate what the existing beams can handle? Is that a city by city thing or would be according to the Ohio code or is it more of a reality rather than legal thing?

If I wanted to hang a significant weight from the existing joists would I probably just end up doubling up a few of them?

Posted: Wed Aug 08, 2007 9:48 pm

You need to invest a couple of hundred dollars and have a structural engineer make an assessment of your current loading to make that determination.

Rod

Posted: Thu Aug 09, 2007 11:07 am

Ok so the option of spanning or attaching to existing joists will be up in the air for now.

What about the implications of starting with 3 exterior block walls and slab floor? Is it a dream come true or am I missing something?

Also it's a classic "three leaf" situation, right? If I build internal walls next to these three block walls, the block walls are already leaf number one, correct?

Anyone else think I can get away with not even building these 3 walls?

Posted: Thu Aug 09, 2007 7:42 pm

if you're only building a single wall within the block walls, its (maybe) a two leaf system. if you were put drywall on each side of the new interior wall you might suffer some loss of isolation. you probably should make some measurements inside and outside to determine how much sound is getting out and try to determine the paths it is taking to escape. armed with that info, you can decide what you need to do to isolate the space. get yourself a sound level meter and play some drums and bass while you measure around.

if you're not aware of it, Rod Gervais (moderator on this forum) has a book available on home studio construction. one of the main benefits (imho) of the book is his pragmatic approach to solving sound isolation issues using cost effective materials and techniques as well as keeping it all to code (not very common in how-to books). the hvac section is an excellent and rare resource as well.

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