Garage second floor studio - request for comments

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Hi Robert, and welcome! Sounds like you have your work cut out for you! Since your primary design goal is not to disturb the neighbors, I'd suggest that you put numbers on that, to see what kind of construction you are going to need to get there. So contact your local municipality and get a copy of the ordinance that regulates noise, to see what the legal numbers are: How quiet do you have to be at the neighbor's property line / window / inside (or whatever spec the regulation happens to set)) You'll probably find it is in the region of 50-something during the day, and 40-something at night (most likely A-weighted, slow, if you are lucky.). Considering that a typical 5 piece rock band can easily put out 115 dB, and even more if they get enthusiastic, you are talking about a total reduction of 70 dB. Allowing maybe 10 for the air space losses between you and them, you still need on the order of 60 dB of isolation. (I'm just guessing here: you need to actually get the real numbers. That's a tall order for a second floor! Assuming 60 dB is your design goal, you basically have two ways of getting that kind isolation: 1) an MSM system all around ("room-in-a-room") or 2) ridiculous amounts of extremely massive walls: several inches of high density reinforced concrete, all around. There just aren't any more options, sad to say. You can only stop sound with mass or with a tuned filter (or with a vacuum: "In space, non can hear you scream"). That's it. There are no more options. Since sound is just vibration in a physical medium, it is controlled by the laws of physics. And there are no magic materials that can bypass the laws of physics. You are stuck with mass law or tuned filter (since placing a vacuum around your house is really hard to do :) ). So your only real option is the MSM option. That's the only way to get high levels of isolation across the entire audio spectrum with low mass and reasonable cost. Unfortunately, "low mass" is still an awful lot of mass (tons, literally)! Which implies serious beefing up of your garage in order to support it. I don't see that being easy to do on top of a cantilevered wood floor. The good news is that you have a decent budget: it should be do-able within that range. I'd suggest that you contact John directly, by PM or e-mail, and ask him to quote for the design, then hire a contractor to build it for you.

E.g., how do I calculate what the angles of the angled walls should be?

Answer: for a live room, it doesn't matter all that much. I noticed the comment on your diagram that the purpose of those angled walls is to "reduce problems of axial modes". Unfortunately, angling your walls wont do that, and axial modes are only 1/3 of the issue anyway. Angling your walls will not get rid of modes: it will just move them to a different frequency, and make it much harder to calculate where they will be. Angling walls helps with flutter echo, yes, can also help with comb filtering under some circumstances (if you happen to have that problem, and if it happens to annoy you), and can even help to give a room character, but it cannot get rid of modes: best case, it will alter the modal response to be a bit smoother, but predicting that is really hard: you really need FEM/FEA software to do that kind of calculation properly. And you need to know how to use it, how to set the boundary conditions validly, how to model the mesh correctly, etc. Not for the feint of heart! The good news is that it doesn't matter! Since the modes are going to be there no matter what you do, your best bet is to even try to kill them! Just design to control them. Design with basic dimensions and treatment that will take care of the big issues, then measure the room once it is built, see where your REAL problems are (which will most likely be very different from what even the best software predicted), then design treatment to deal with those problems. Rinse. Repeat. You might need to do the measure/treat cycle a couple of times to get it perfect, but if it's just a non-commercial practice space then you will probably be fine just with one round. But anyway, for that size of project its probably better to get a professional designer like John to do it, than to try to do it all yourself. My US$ 0.02. - Stuart -

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Yeah, I've seen that kind of "regulation" before, and basically it means that you are screwed! Because no matter how quiet you are, someone might consider it "annoying" or that it "disturb their quiet, comfort and repose". Bottom line: if they can hear it at all, you are up the legal creek without a paddle, since there are no numbers to back up your position! Sure, you can fight it in court, and perhaps even win since laws are supposed to be objective, not subjective, but what a hassle! And what an expense! It's kind of like setting a speed limit that says "Fast driving prohibited", without ever defining what "fast" means... There's a church here in Chile where I live that is fighting that exact battle right now, under similar regulations. The neighbors don't like the music and the singing, which apparently isn't even very loud, but there is no way for the church to prove that they are not exceeding the legal limits, since there are no legal limits! They are fighting the case on constitutional religious freedom grounds, not on the noise ordinance. That's their only hope. So that's pretty tough for you! You might want to add a few dB of isolation to your design goals, just in case. (and maybe register your studio as a religious organization! :) ) Bad news, unfortunately. - Stuart -

Very interesting topic, I've been thinking about building a studio above my garage too. Have you determined that it wouldn't be cheaper/easier to rebuild the lower level walls with something stronger to support the new level? I don't know if that's possible or if it would help, but I'm curious if you've looked into it. Sorry I can't help with your questions but others here will have some ideas. Please keep us posted!

I've begun to sketchup the basic design of the building. These cutaways show the space I'll have to work with. I'd like to upload my sketchup model but the file size is almost 30 MB. Any ideas on how to reduce the file size? Is there some way to strip out all images that might remain in there?

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My architect then said, "You tell me what STC rating to design for, and I will do the design. .. What should I do?"

Find a new architect? :) Seriously, you are totally correct: STC is NOT a good system for measuring isolation of a studio,since it does not take into account the low frequency end of the spectrum at all, and that is exactly where all your isolation problems will be.

He showed me products in the binders used for soundproofing, including "SelectSound™ Black Acoustic Board Fiber glass" which is "designed to provide excellent acoustical performance for multiplex theaters, sound studios and performing arts center." Two inches thick of the stuff promises an ATSM C423 absorption coefficient of 0.18 at 125 Hz. 2 inches of the "SelectSound™ Black Acoustic Blanket Fiber Glass" has a coefficient of 0.27 at 125 Hz.

Ummm.... sorry, but that has NOTHING AT ALL to do with isolation! Your architect seems to be a little confused! Isolation is what you do to all six sides of the boundaries of the room to attenuate sound coming in and out, and is related mostly to mass, not absorption. Treatment is what you do to the room once the basic shell is finished, to give it the acoustic characteristics that you need for a studio, in terms of controlling modal issues, flutter echo, first reflections, overall response, RT60, etc., and is related mostly to absorption, not mass. These are two entirely different and diametrically opposed things. You CANNOT isolate a room by putting "Black Acoustic Blanket Fiber Glass" on the walls! The coefficient of absorption of fiberglass has precious little to do with isolation, but is very important for treatment. If he is trying to sell you on a TREATMENT product for your ISOLATION, then go back and read my first comment: "Find a new architect.".

I was hesitant to give him a number, because I didn't know the technical definition of STC and strongly suspected, from the types of materials he was proposing, that STC was a voices and loud televisions sort of standard and not something used by acousticians in designing isolative spaces.

Exactly! Spot on! You seem to know more about it then he does...

What should I tell him? What specification do I need to have him design for?

This goes back to my first response to you, in my original post: "Since your primary design goal is not to disturb the neighbors, I'd suggest that you put numbers on that, to see what kind of construction you are going to need to get there."In other words, you have to measure real levels with a real sound level meter, then decide on what NC profile curve you want for your room, which will dictate the amount of TL you want (Note: TL, not STC), then based on those numbers, you can decide what kind of construction you would like to use to get there.

He was also not keen on the idea of cutting thin strips of sheetrock to mount them between studs, saying this would be too labor intensiveand that after a while of cutting sheet rock, the builder would want to turn his knife on me....

Then maybe you need to be talking to the builder, not the architect? He's the guy who knows how much work will be involved, and how homicidal that is likely to make him... :) Your other alternative is to take the siding off the outside of the wall and add the mass there... But either way, you DO need to put more mass on the outer leaf if you hope to achieve the kind of isolation that you say you need. I'm surprised that your architect didn't mention the issue of structural integrity: If he really does know how to design for very high STC levels, then he must know the huge amounts of mass that are required to do that, and he must also know that you cannot support that kind of mass on the type of cantilevered floor you have! We are talking about many thousands of pounds of mass, here... I would have thought that a good architect would mention this, since beefing up the structure is going to be a MUCH more "labor intensive" (and also expensive) part of the entire build than cutting a few strips of drywall. He seems to have his priorities a bit mixed up...

Two inches thick of the stuff promises an ATSM C423 absorption coefficient of 0.18 at 125 Hz. 2 inches of the "SelectSound™ Black Acoustic Blanket Fiber Glass" has a coefficient of 0.27 at 125 Hz.

Seeing that he's the one talking about ASTM C423, you might want to ask him if he actaully understands what that standard is all about, and how it applies to isolating your room, because in reality it has nothing at all to do with isolation... Take a look here, and read what it says: http://www.astm.org/Standards/C423.htm Not much about isolation in there, is there?

2 inches of the "SelectSound™ Black Acoustic Blanket Fiber Glass" has a coefficient of 0.27 at 125 Hz.

So what? Two inches of plain old 703 when properly mounted (E-405) has a coefficient of 0.84 at 125 Hz., and four inches of 703 has a coefficient of 0.65 at 125 Hz, and a surprising overall NRC of 1.15 (ie, above 100%)! But none of that has anything to do with ISOLATION. That is only important for TREATMENT. There is a huge difference between the two. Seriously, you might want to consider hiring someone who knows what they are talking about for this design! You have the budget to do that, so why not e-mail John directly? - Stuart -

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So its just a live room? No control room? In other words, just a rehearsal space with no recording facility? - Stuart -

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OK, makes sense! One other question: What is the purpose of the small room in between, on the other side from the stairs? Is that an iso booth? - Stuart -

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"So your only real option is the MSM option. That's the only way to get high levels of isolation across the entire audio spectrum with low mass and reasonable cost." In an elevated wooden structure I would ask first from whoever is to be involved in this project to produce some real figures as it pertains to isolation. The suspect that mass spring mass will work in an elevated wooden structure has been overstated as it applies to the methods used in a concrete earth damped type environment. Which by the way the numbers don't even come from that but from a testing facility...mostly of concrete, and the attempt to extrapolate how that operates and the division that exists between it and a wooden structure is enormous. It is enormous because why? Flanking can be predicted or at least anticipated in an experiment with learned people and known values. To pre-suppose that this will work (M/S/M) in an environment that has a thin and far less dense substrate than concrete, a flanking problem with the entire building is to spend someones money that is not yours and have no regrets :) Back to the basics...prove it.:)

i think Brien is making the point that a second floor framed floor is not going to provide the same degree of isolation as a concrete on earth floor. however, it would be possible to use some tactics to help reduce direct transmission through the floor structure and presumably your garage is unoccupied so that air space can be beneficial in your isolation goals. here's some interesting reading on floor isolation. http://www.craftsmanspace.com/free-book ... entry.html (a classic) http://www.nrc-cnrc.gc.ca/obj/irc/doc/p ... /rr103.pdf (helps understand why this is a challenge)

Thanks! Where in the 1875 text is the isolation material?