Old 07-18-2010, 06:26 AM   #1
ralfk
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Default Basement studio build: To drywall or not?

Hello. I've bought a house and I'm about to build my music room in the basement. I need some advice about how to approach covering the concrete walls to achieve, in the end, a neutral room.

I know that forums like John Sayer's are the best place for acoustic discussions. But, admittedly, I'm getting confused in my research and I'd like to ask my very basic questions in a nice, friendly forum first.

Background: The basement is not the ideal shape, but it's what I've got to work with: 30 x 8 1/2 x 6 1/2 feet. I would like to build a hobby studio in which I record rock: Mostly guitars direct, vocals, electronic drums & keys and mix. The latter is the main reason I seek acoustic neutrality. Sound isolation is much less of a concern.

The basement is surrounded on all four sides by concrete (3 external walls and one inner concrete wall that was originally an exterior wall before an addition was added in the 50s).

The basement was semi-finished: Walls: drywall -> pink insulation -> plastic membrane -> concrete wall. Floor : bare concrete.

I wanted to see what was behind the walls and, thinking that I would start from scratch, I ripped everything out (except the framing) down to the bare concrete walls. It's a good thing I did: I discovered that the three external-facing walls were in dire shape, crumbling away after decades of water infiltration and sub-standard concrete mixture. The previous owner and I have come to an agreement about replacing the walls, so I really am starting from scratch!

My question is: Given four concrete walls (once the replacement is complete), what is my best choice for achieving a neutral acoustic space:

1) pink insulation and drywall, and then additional bass traps and diffusers?

2) rockwool or rockboard and a porous cover (fabric instead of drywall) and then any additional bass trapping etc?

The real question is: Drywall or no drywall?

Thanks in advance!
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Old 07-18-2010, 09:36 AM   #2
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If I were you I'd sacrifice some of the 30ft. for a proper bass trap wall, as the dimensions are a little bit "off" indeed. But this will give you enough space for fitting (lots of) rockwool close to the exterior wall (which, I assume will be the wall behind your monitors), mount a frame and cover it with these perforated panels.
On the floor I'd use a simple carpet, and on the side walls some (tilted) flutter echo absorbers.
A problem will be the low ceiling, as I'd prefer to put some absorber tiles there as well, but it will make the room too low in height overall. No clue how I'd handle this... Anybody has done this?
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Old 07-18-2010, 10:04 AM   #3
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Yes, I'm willing to sacrifice quite a bit of the length of the room to acoustic treatment.

Living in Canada, I will have to insulate the three exterior facing concrete walls of the basement. I'm trying to make the right choice of materials. Should I frame, install mineral wool and then drywall. Or, should I skip the drywall and use breathable fabric (fire-proof, of course) like one does for bass traps (if that is even allowable by code)? Or something else?

I will be stuffing mineral wool between the joists in the ceiling.
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Old 07-18-2010, 07:26 PM   #4
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Hi ralfk,

I'm sure I don't have to tell you that concrete walls and floor are cold..... so even a thin "airspace" between the outer and inner walls will help you with this aspect. Putting a thin layer of acoustic material inside the walls will aid more in both sound and temperature proofing - "real" acoustic treatment can be applied on the inner walls as you go.

Bacause of your height restriction I suggest carpet tiles with rubber backing for the floor - they're cheap, easily fitted, replacable / moveable and they offer pretty good insulation underfoot. Some "nicer" rugs on top in certain spots will make it warmer underfoot and look prettier :-).

Do whatever you can to make the walls non-parallel - this will reduce standing waves. Then use an spectrum analyser to work out the acoustic treatment for walls / corners.

You can make some movable hanging baffles for the ceiling and place them where you need depending on what you are recording.

Mostly I'd say to do it step by step to avoid buying things that don't help your end goal.

Hope this helps.
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Old 07-18-2010, 08:47 PM   #5
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I wouldn't leave the concrete wall as is. You can put some styrofoam for insulation and the drywall over. Do you have to soundproof as well? Do you have neighbors?
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Old 07-18-2010, 08:51 PM   #6
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The plastic vapour barrier is (was) there for a reason.

Hercules is right on target: concrete floors are indeed cold, so I suggest building an insulated sub-floor to go along with your Roxul-filled drywalled stud walls. Removing the inch of useable height will be barely noticable, unless the 6.5' dimension is the height!
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Old 07-19-2010, 03:42 AM   #7
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Whatever you decide on, you need a sealed barrier between the concrete outer wall and any organic material on the inside, or you will end up with mould. If you don't have the knowledge and/or time to do this properly, hire a contractor...

Last edited by pac-man; 07-19-2010 at 03:52 AM.
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Old 07-19-2010, 05:13 AM   #8
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Thanks for all the replies.

I have a contractor with no particular knowledge of soundproofing/acoustics who will be re-pouring the three damaged exterior-facing basement walls, giving me the opportunity to do whatever is required to achieve reasonable isolation and acoustical goodness.

What I'm hearing is:

1) Frame and fill with mineral wool (Roxul). The contractor states in the estimate that he will be using polyethylene. I think that that will seal many of the air leaks, improving isolation. So, from what I' hearing here, he is to stuff mineral wool (say, 4 inch) on top of that.

2) Add drywall. I thought that using a breathable fabric _instead_ of gypsum, like one would do when building bass traps, would deaden the room (a good thing for a long hall-like shaped room like what I've got). And then I could hang reflectors here and there to liven the room up again. But, I guess that's not how things work? So drywall it is.

3) I'll be adding mineral wool or rock board between the ceiling joists and covering with fabric. I was not going to add a drywall ceiling due to restrictive height: It's a bit over 7 ft between the joists, so adding a ceiling would bring it way down (and I'm 6 ft 2 ) . The floor above is made up of 3 or 4 layers of plywood plus a maple floor, so that mass is likely to provide some isolation.

4) I'm undecided about the floor, but I can figure that our later. I'll definitely do something.

The level of isolation does not have to be super high. Sure, I have neighbours, but not attached to the house. And, this is the big city and they can deal with a bit more noise

Thanks again for all the help. Let me know if I'm on the right track.
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Old 07-19-2010, 07:31 AM   #9
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Hi ralfk,

For what it's worth, I wouldn't put anything on the cement floor other than maybe some carpet if it's needed for acoustical reasons. The cement floor gives you a good solid, ridgid base to work with which can be pretty important when useing mics on stands sometimes.

Haveing a cold floor shouldn't be a proplem, especially if it's in a basement. My studio sits on a cement slab at ground level and I have never had a problem even when the temp gets to 10 degrees F below.

I think you've got the right idea for the ceiling considering the height. The joists might even be a plus for a little diffusion. You can always add something later if it becomes a problem.
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Old 07-19-2010, 10:43 AM   #10
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When you say: the exterior walls will be redone anyway - is there a chance to have them insulated from the outside? Why? As you can already see, there'll be humidity built up on the walls, coming from temperature differences wall/room. You can prevent this by leaving air gaps on the upper or lower edge of the drywall/absorber wall in order to get some air circulation behind the mineral wool.
An architect friend of mine insisted in this when I asked him about a similar project (which wasn't realised) because of health risks (mold etc.)!
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Old 07-20-2010, 08:53 AM   #11
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Alright, let's assume that I'm standing in this 9 x 28 x 7 ft space. I'm surrounded by concrete walls. They are moisture sealed from the interior by polyethylene foam to code. The framing is up. The ceiling is stuffed with rockwool and covered with a breathable fabric. The floor remains bare concrete.

The question for the walls remains: Do I:

A) Stuff rockwool into the framing and then drywall it all up?

B) Don't bother with the rockwool and just drywall it up.

C) Stuff rockwool into the framing and not drywall it, instead covering the walls with a breathable, fire-retardant fabric?


Note that all three options assume that additional acoustic treatments may need to be added to the room once the walls are finished. But, I'm trying to understand what my best option is for the walls themselves that will minimize the need for additional acoustic treatment.

Because the room is so damn narrow (9 ft before framing), I would like to avoid adding additional treatment. Can I integrate the treatment into the wall itself? Is the drywall necessary for a good sounding room? Or will option C work?
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Old 07-20-2010, 09:25 AM   #12
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You can integrate treatments into the framing, but it will be a process of trial and error: construct, try it out, rip it down if it doesn't sound right, repeat as necessary.
The best way in your case IMHO is to frame, stuff and drywall, then treat reflections with baffles/spot absorbers/diffusion til it sounds right and/or you eliminate measured modes to the greatest extent.

Someone on John Sayers' website stickied links to our National Research Council's acoustical testing of wall constructions for transmission loss. Make sure to read up and get enlightened if you haven't already, because what you're trying to do is absorb reflections off the concrete mass of your foundation. (You need to put an appropriate mass on the inner leaf of the system for it to work properly, as well as an appropriate depth of air between the 2 masses (drywall and concrete)). PM me if you can't find them and I'll dig around on my HD and email the pdfs to you.
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Old 07-20-2010, 09:57 AM   #13
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Quote:
Originally Posted by audioguy_on_ca View Post
(You need to put an appropriate mass on the inner leaf of the system for it to work properly, as well as an appropriate depth of air between the 2 masses (drywall and concrete)).
Thank you! I had read a bit about leaves on the John Sayer site before posting here, but I couldn't understand whether this related exclusively to sound isolation between rooms or whether the 2 leaf system also helps with flattening the acoustics response of the room. I only have one room, so I have a hard time figuring out what is applicable to me.

So, I'm getting it now: Walls built with 2 leaves of appropriate mass, etc. will tame the low freqs of the room somewhat. The remaining fine-tuning can then be addressed with bass traps and diffusers.

I will look up those NRC tests.

thanks again.

Last edited by ralfk; 07-20-2010 at 09:58 AM. Reason: grammar
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Old 07-20-2010, 02:13 PM   #14
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Quote:
Alright, let's assume that I'm standing in this 9 x 28 x 7 ft space. I'm surrounded by concrete walls. They are moisture sealed from the interior by polyethylene foam to code. The framing is up. The ceiling is stuffed with rockwool and covered with a breathable fabric. The floor remains bare concrete.
Hi ralfk,

The way it looks to me you're already somewhat compromised because of the dimensions. You say the walls will be "moisture sealed from the interior by polyethylene foam to code" and I'm assumeing this foam is somehow glued on.

Most foams have an absorption quality to them so if it was me I'd forget about frameing the wall because you've already got a start on the absorption. What I'd do is go from the foam and start adding absorption baffles and diffusion, your basically going to need them anyway.

Absortion baffles or panels can be easily made in different ways depending on the absorption material you use. I've always used 701 semirigid insulation but there might be better materials now days, this was a few years ago. Basically I made frames out of 1X4s, stuffed them with 4 inches of the 701 and covered them with various fabrics.

As far as diffusion goes there is a lot of info on the net that might show you how to make them or where you can purchase them in a cost effective manner.

I've done a few studio constructs and learned the hard way to take it a step at a time. Heh heh, of course I couldn't quite afford an acoustical engineer and I had all the tools along with the building experience so I just did it all myself.

Just some suggestions in case money is a consideration.

Tod
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Old 07-21-2010, 09:30 AM   #15
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Wood sounds good. Instead of drywall, use 7/16 "chipboard", in 4x8' sheets,then cover with fabric, and a decorative pattern of wooden moulding.

The chipboard is often cheaper per sheet than drywall. I did this in my 24x28x10 live room and it looks good and sounds fantastic...
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Old 07-21-2010, 12:13 PM   #16
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Quote:
Originally Posted by ralfk View Post
Thank you! I had read a bit about leaves on the John Sayer site before posting here, but I couldn't understand whether this related exclusively to sound isolation between rooms or whether the 2 leaf system also helps with flattening the acoustics response of the room. I only have one room, so I have a hard time figuring out what is applicable to me.

So, I'm getting it now: Walls built with 2 leaves of appropriate mass, etc. will tame the low freqs of the room somewhat. The remaining fine-tuning can then be addressed with bass traps and diffusers.

I will look up those NRC tests.

thanks again.
You're welcome.
for your inner leaf (leaves) think 5/8" or 3/4" thickness drywall. you should only have to do 2 leaves rather than 3 or more of the standard 1/2" stuff...and don't forget the adhesive between leaves(green glue)...and acoustical sealant...otherwise, all is for naught.
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Last edited by audioguy_on_ca; 07-21-2010 at 12:14 PM. Reason: grammar correction
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Old 07-21-2010, 10:08 PM   #17
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I don't see the point in drywall if it's a basement? If anything you risk ending up with the classic "drywall-dimensions boxy" sound, and a smaller room?
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Old 07-22-2010, 01:46 PM   #18
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Quote:
Originally Posted by chip mcdonald View Post
I don't see the point in drywall if it's a basement? If anything you risk ending up with the classic "drywall-dimensions boxy" sound, and a smaller room?
I agree, the cement walls already have the mass you need. I would think adding a wall to this would lower the mass and possibly create some sympithetic vibrations, especially on the lower end. Heh heh, you've only got 9 feet to work with on the width...
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Old 07-22-2010, 02:43 PM   #19
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Ok, so then I won't drywall.

I'll still frame, stuff the framing with rockwool and cover with breathable fabric. Of course, the room will probably end up too dead. I suppose I could drywall bits or hang boards here and there to inject some life back in the room?
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Old 07-23-2010, 07:05 PM   #20
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Quote:
Originally Posted by ralfk View Post
the room will probably end up too dead. I suppose I could drywall bits or hang boards here and there to inject some life back in the room?
I don't buy the "you don't want it too dead" line if you're talking about a small room. The less of a signature the better IMO.
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