John Sayers' Recording Studio Design Forum

Hi,

For isolation purposes, I'm building a room in a room in my basement for drums/tracking. Is anything else required on my concrete foundation other than making sure it's sealed up really well? In other words, would all I have to do is frame up new walls a few inches off my concrete, fill them with insulation, and drywall the inside of my drum room?

Like this (from outside to inside of drum room):
Concrete Foundation-->air gap-->studs w/ insulation-->drywall

If so, how big of an air gap is recommended?

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http://www.sethbrand.com
http://www.offbrandproductions.com

How about this:

Concrete foundation --> Airgap filled with insulation --> Drywall (2 layers of 16mm) --> Stud frame filled with insulation --> Textile covering (--> possibly wooden slats).

See John Sayers Recording Manual http://johnlsayers.com/Recmanual/Titles/Acoustics3.htm

_________________
Brian
As you slide down the bannister of life, may the splinters never point the wrong way...

How much isolation do you need, and down to what frequency do you need it?

It's a tuned system you are building, and needs to be tuned to a frequency that is at least 50% lower than the lowest one you need to isolate. Changing the size of the air gap is one way of tuning it. The other way is to add mass. So the amount of mass and the size of the air gap can be calculated based on that "lowest frequency".

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thanks for your reply. There is so much to learn. I bought Rod's book, but still have so many questions.

Anyways, the studio is in my basement, in a nice little sub division, and I want ONE room that I will be able to record drums and other loud sources in without disturbing the neighbors, or upstairs too much. It's a room within a room design. Is there a graph or something I can reference? Right now, the back of the studs are about 3.5" off the concrete on the back wall, and about 14" off the wall on another side to accommodate a pipe. The other two sides will be back to back with other walls consisting of 2x4 framing with insulation and about a 1" air gap.

As for isolation, I just want enough that if I'm recording drums at 9pm on a Tuesday night, the neighbors won't be disturbed, and the sound level upstairs is at least bearable. I know that doesn't help you though.

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http://www.offbrandproductions.com

:) Very, very true! In fact, I think you never can stop learning about acoustics: At least for me, every time I think I'm starting to get my head around it pretty well, I come across something else that throws me, and I have to start figuring out that new thing. The learning curve is steep, but it's also fun!

Questions are good! And that's what the forum is here for: to help answer them.

Actually, it does help to a certain extent. Not with any degree of accuracy, but ball-park estimate.

So, let's estimate!

Drums are the loudest of all instruments. Drums put out a lot of energy in the low frequency end of the spectrum. Low frequencies are the hardest of all to stop, due to the very long wavelengths. Drums put out percussive sound. Percussive sound is more audible at a distance and more annoying than constant sound at the same level. So an engine idling constantly out in the street is less annoying than a guy hammering on a piece of steel at the same sound level.

So, numbers: A drum kit played loud can easily put out 115 dB. Most people consider "silence" to be around 30 dB, especially in the city, where there's always some background ambient level.

So to make "drums silent" you need 85 dB of isolation. 85 dB is MAJOR isolation. Big time. Large budget. Thick heavy walls. Floated concrete slabs on isolation springs. Etc.

To put that in perspective: A typical stud wall in a house provides around 30 dB of isolation. Each time you increase the amount of isolation by 10 dB, you are talking about stopping ten times more energy. So a wall that isolates at 40 dB must stop ten times more energy than one that isolates at 30 dB. A wall that isolates at 50 dB must stop one hundred times more than the 30 dB wall. One that isolates at 60 dB has to stop one thousand times more energy. etc. And a wall that isolates to 85 dB must stop nearly one million times more energy than your average house wall.

Fortunately, you probably do not need such extreme isolation, since air itself attenuates sound over distance, and your neighbors are a certain distance away from your walls, so that helps. Also, your local municipal regulations probably do not require that you get down to 30 dB, since that is unrealistic and not necessary. Most places seem to require around 50 during the day, and around 40 at night. So your isolation needs are probably more like 65 dB, which is still high, but do-able, and you won't need to rob Fort Knox to be able to afford it (just robbing a few local banks would be enough... )

OK, so aiming for a ball-park of 65 dB isolation, one way of getting that is with a two-leaf structure consisting of a stud frame with two layers of 5/8" drywall on one side, an 8 inch air gap, and another stud wall with another two layers of 5/8" drywall on one side, with fiberglass insulation in the cavity in between. That isolates very well, even in the low end.

To improve that even more for low frequencies, add a layer of Green Glue between the sheets of drywall. That improves performance by a few dB, and is worthwhile if you need better low frequency isolation, such as for drums.

In your case, you already have a concrete shell around you (except for the ceiling) so that's your outer leaf, and there is plenty of mass in that, so all you need to do is concentrate on your air gap and inner leaf. If you go with the "decoupled stud wall plus 2 layers of 5/8 drywall plus GG" plan for the inner leaf, then you'd be more than fine if you kept the air gap at 8 inches, and you could probably go down to 7" with no problems, or even a bit less.

Just to clarify: "air gap" refers to the total distance between the two leaves, not considering any insulation that might be in the middle. In your case, that's the distance from the concrete wall to the surface of the first layer of drywall, up against the studs. So if you say that you already have a 3-1/2" gap from the concrete to the studs, then you already have a 7" air gap, since the depth of the studs is also roughly 3-1/2". So if that stud frame is properly sealed to the floor, and fully decoupled from the walls and ceiling, then you are fine: Just add two layers of 5/8" drywall to that, with GG in between, fill the cavity with insulation, and you are fine.

Provided that you do all the other walls, and the ceiling, and the door(s) and the window(s) (if any), and the HVAC system, and the electrical system, to the same level, then you should be able to meet your goal.

Those will not give you the level you want. You are going to have to beef up the drywall on those, and create a bigger gap.

What I outlined above will do that for you, if you build it right!

But all of this is based on ball-park assumptions: To make sure that this is what you REALLY need, you should get a sound level meter and do some real-world tests in YOUR room, with YOUR drums, and YOUR neighbors, to find out what your actual needs are, in terms of real, objective decibels.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thanks Stuart! You are awesome!

It "sounds" like I'm on the right track. By 1" air gap, I actually meant the distance between studs...so it would really be about an 8" air gap between my walls on two of the sides, a 7" air gap between my walls and the concrete another side, and a 14" air gap on the final side between wall and concrete. Should be plenty I'm hoping.

I was only planning on one layer of drywall on the outsides of walls, but I'm thinking I probably should double up just to be sure as all my research is telling me to.

I am now to the point of trying to figure out how to properly seal everything. I'm thinking that some acoustic caulk of some kind run along the floor/wall seal, the ceiling wall seal, all 4 corners adjoining wall seals, any screws, around light fixtures and outlets, etc...

As for doors, I'm thinking of going with sliding glass doors on one wall (so actually I'd buy two sliding glass doors and place them back to back, one in each wall). I would think some decent sliding glass doors from Lowes or something should seal pretty good for the most part. Am I wrong?

Lastly, how about sealing around ceiling light fixtures, light switches, outlets, etc.? Do I just caulk around all that stuff? Is that safe?

_________________
http://www.sethbrand.com
http://www.offbrandproductions.com

Thanks again Stuart. I'm trying to find a good sliding glass door that will work (2 of them actually) and don't want to screw everything up by getting something that is going to allow sound to pass through easily. Would something like this be ok do you think?

http://www.lowes.com/pd_391799-94705-10 ... facetInfo=

If not, is there anything you'd recommend? Also, what would be the best way to seal around these types of doors?

Thanks again!

_________________
http://www.sethbrand.com
http://www.offbrandproductions.com

The normal method is to run three beads of caulk along the floor BEFORE you put your sole plate down for the stud frame: one down the center line of the stud, then and one about an inch to each side. Then as you hang each layer of drywall, you put a thin shim under it to keep it off the floor, take out the shim after the panel is nailed in place, put in a piece of backer rod, then caulk the gap. Do the same for the second layer. That gives seven seals on a two-leaf wall, which might seem like over-kill but is actually very necessary.

So the same where the new walls meet each other, and where they meet the new ceiling.

But, since your frame are already in place, the best you can do is to carefully clean the edges on each side, where the meet the floor, and caulk along there, trying to make sure that the caulk goes into the crack really well, as deep as possible. Then follow the same plan for the layers of drywall.

Sealing is important. More than important, it is critical. If you don't have a good seal, then you don't have isolation. It's that simple. Even tiny cracks will allow a LOT of sound through, so everything must be sealed, and that includes the existing outer leaf! That must also be sealed, very carefully. The concrete walls, for example, should be painted with something that seals the surface, since concrete is porous. Also the existing outer-leaf ceiling must also be sealed, air-tight: All tiny cracks and gaps must be filled.

You don't need to seal around them, because the new ones you install will not be the normal type that penetrate through the drywall! You CANNOT cut holes in the drywall: That is your isolation. Any holes in it will severely damage, or even totally destroy your isolation. So you can't cut a hole every place you need a switch or outlet, or places where you need to pass cables through. Instead, all your wiring must be done with surface-mount fixtures. They sit on top of the drywall, instead of poking through it. And you use plastic "raceway" ducts to run the wires..

NOTHING AT ALL can pass through the drywall, if you want isolation. There is only one place where that happens, where the main power feed comes into the room, and there's a method for dealing with that to keep it sealed.


Sliding glass doors are an option, yes. But! .... they need to be the right type, with the right glass.

The glass in windows and doors is part of the isolation wall around your room. Since the entire wall must have the correct air gap AND CORRECT MASS to provide the isolation you need, that means the glass must also comply. Glass is about three times the density of drywall (depending on type of glass), so in order to get the same mass it needs to be about one third as thick as the total amount of drywall. If you have two layers of 5/8" drywall, then you need glass roughly 3/8" to 1/2" thick in your doors, in order to maintain the same surface density. Plus, that glass needs to be laminated glass, not ordinary window glass.

The same applies to the frames for the sliding doors, of course; they must also be dense enough to maintain the same amount of mass per unit area around the entire room. And then you have to consider the seals: You need at least three independent seals around all of the edges of the doors, in order to keep things air-tight.

The type of cheap door sliding-glass door you find Lowes or Home Depot just isn't up to those specs. Normally they use thin glass, or even worse, double-glazed panels. Those are great for thermal insulation, but lousy for studio isolation.

You can get sliding glass doors that meet those specs, but they don't come cheap! Think upwards of a thousand dollars per door.

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Can't wait to see this come to life as i'm planning a similar project in my basement/garage/workshop. The problem with England is that we're so tightly packed in that you're never more than a few metres from someone else! Wish i was in USA or Australia etc!!! Luckly i've got 14" thick stone walls all around me (built in about 1840!) but unfortunately not much money as i'm buying my brothers half of the house. Good thing is i'm always in there with the angle grinder going (i own a few rusty lancia deltas!) and never had a complaint! Will have to start doing my homework, just incase i can ever afford a project like this. I'm sick of my practice pads now and haven't played a real kit for about a year and a half, its killing me!

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