Attached Garage Home Studio Build

yet another home studio build! after humming and hawing for 4-5 months i've finally dug in and started converting my garage. I've been reading this and other forums, and Rod Gervais' book. A few primers- I live in Vancouver, BC Canada, half a block away from a major trucking route. you can feel the ground shake. I have neighbours (who are very nice and have never complained about band practice in the existing, untreated garage). And also roomates. I do a lot of different stuff- film composing, sound design, producing/recording artists and bands and playing bass and drums in a few bands myself. nothing especially loud, though. So my priorities are 1- isolation. 2- A decent sounding room to record and mix in. I've always worked out of treated bedrooms, so i'm looking forward to stepping it up a bit. I've attached a crude sketchup detailing my plans. The raw dimensions of the garage are 20' x 17.5'. The house is built on top of the garage. half of the room (east) has a kitchen above, the other half a deck. the house is a 'vancouver special'- 30 years old, cheap cheap cheap. the exterior is 1" concrete stucco with 1x8 rough lumber underneath, framed with 2x4. I have solid core doors- might add 1-2 layers of 5/8" to beef them up. I plan on building a window for the vocal booth with 3/8" + 5/16" glass. In total i hope to keep costs under 5k. What i've done so far is removed the existing drywall and placed 5/8" drywall flush against the 1x8 and sealed with acoustic caulk. I've left the garage doors, but fixed them permanently to the wall, encasing them with a 2x6" frame. then 2 layers of 5/8" and then another to seal the whole unit. oh and vapour barrier, R20 between the metal door and drywall. Next i'll be framing 2x4 walls with 2 layers 5/8" and Green glue. two leaf all the way. I'd like to float these on some kind of elastomer/rubber puck. Suggestions? HVAC wise, i plan to build a small exterior enclosure on the north side for a fan, then run ducting in between the walls on the east side. I'm hoping to tie into the furnace somehow. A/C is N/A. I have three things that remain big question marks: 1- Vocal booth. I realize this totally f's with the symmetry of the room, but with the limited space this is the best i could come up with. Am i totally crazy to hope to have decent speaker placement in a room like this? 2- Ceiling. I tore out half of the drywall on the west side which is under the deck. the other half curiously has 2 layers of half inch. My original plan was to layer the whole underside with 5/8" (flush, like the walls) and then do some kind of resilient channel with 2 layers of 5/8", green glued. But now i hesitate to tear out 2 layers of 1/2". would it be better to leave the two layers and do my channel + 2 layers on top? 3- Beam. I realize there's going to be flanking issues with the existing beam structure. I was thinking about building a 1x4 frame around these off of some kind of decoupling/resilient channel, and then hanging drywall off of this asssembly. Any suggestions?

Hi Fellow Lower Mainlander, Couple of questions to start with. Have you looked into beefing up the beam and supporting structure so that you could remove the central post? What is the ceiling height? What I would do is make the airlock a bit bigger, make the entrance to the vocal booth from the airlock, build a complimentary angled wall on the other side ( where bass trap 3 is) and use the void behind this for a nice big bass trap. This would give you better isolation between the voc booth and the control room, remove a door from the control room and give you a symmetrical room. The only real issue I see is the post in the middle of your room. Regards, Steve

Ahh.. beefing it up never occured to me, i guess i'm a bit nervous about pulling off such an engineering feat. Would I just add more 2x10s? the other thing i was considering was replacing the post with a 4" steel one you see in most garages- but this would be a purely cosmetic solution.. the ceiling is 9'3". I thought about making the airlock bigger and angling the opposite wall, i'm just weary of loosing the floor space. The only other solution i have for the vocal booth is getting rid of it and converting an adjacent bedroom on the east side.. a bit more work in the end but i get a 9x10' room out of it, plus i could put a nice big window in and this could double as a control when i'm tracking drums, for example. Thanks, Gregor

Talk to a structural engineer before doing anything with the post. It's not just a matter of the strength of the span, it is also what is carrying the load where the span rests and is there a good enough footing etc. That post is going to be a pain if you leave it for both isolation and ergonomics. If you leave it you'll have to box it in with an isolated frame and a couple of layers of drywall. I would give up a bit of square footage for symmetry and less walking routes to doorways that must be kept clear. That vocal booth was going to be fairly tight after treatment. If you could free up another room that would be even better. With the height of your ceiling you should be able to box in the beam and then hang clouds on each side of the beam. Steve

with this post, sounds like i can kiss my >5k budget goodbye! about the ceiling, do you think it would work to R-channel over the existing two layers of drywall? what do you mean by clouds? thanks, Gregor

about the ceiling, do you think it would work to R-channel over the existing two layers of drywall?

Nope! that would leave a very thin air gap between the old and new drywall, which would give you a really high MSM resonant frequency, and your isolation would be lousy. You need an air gap of at least four inches (10 cm) to have any hope of a reasonably low MSM resonance. Take off the existing drywall, and even use that to beef up the other side, between the studs / joists. Then RC plus new drywall. That will give you enough mass and enough depth for reasonable isolation. - Stuart -

Nope! that would leave a very thin air gap between the old and new drywall, which would give you a really high MSM resonant frequency, and your isolation would be lousy.

I had a feeling this would be the case. Anyone with any suggestions on how to remove drywall intact?

Ok, so I've modified my plans a bit, I'm close to finalizing my HVAC and starting to look down the road towards treatment options. I've decided to go with inside-out walls for the sides of the main room with wooden slats covering the cavities. I plan on using that handy helmholtz calculator to determine width and spacing- I'm unsure as to what i should put in the cavities though. Should i seal off compartments within the 24"x9' cavity to avoid resonance issues? I've detailed bass trap plans in my sketchup- will this be enough or should i increase their size/#? I'd like to build some sort of ceiling cloud above the mixing position (in front of the glass, next to the post) but have no idea where to begin. any suggestions? I'd also like to incorporate some diffusion into my plans, especially on the back wall. Any ideas?

I'm curious about the layout that you are planning for that room, since I can't see how you are going to arrange your speakers / desk / mix position / treatment in there, without the parts interfering with one another. Perhaps you can show what you have in mind for your room layout and geometry? I'm also curious about that really wide air gap on the right side of the room: why does it need to be so big? Also, what is that "deep bass trap" thing at the front right corner of the room, and how is it going to be built?

I plan on using that handy helmholtz calculator to determine width and spacing- I'm unsure as to what i should put in the cavities though.

It would probably be much easier to just go with John's "standard" design, which works well in most rooms. He's already figured out all of the dimensions for you, and has provided detailed construction plans. Follow those, and you'll be fine.

Should i seal off compartments within the 24"x9' cavity to avoid resonance issues?

I'm not sure I understand what you mean by that. Could you explain that in greater detail, or better yet post a SketchUp model of what you have in mind?

I've detailed bass trap plans in my sketchup- will this be enough or should i increase their size/#?

Personally,m I think you'll need MUCH more bass trapping! All I see on your diagram is a deep broadband slot wall on the right hand side wall (which is not a bass trap) plus a small vertical box labeled "deep bass trap" in the front right corner, but without any details on design principle. I would suspect that such a device would damage the room symmetry, too. It would probably be a lot easier to go with tried and test bass trapping techniques, such as superchunks in the four vertical corners and at least a couple of the other eight corners.

I'd like to build some sort of ceiling cloud above the mixing position (in front of the glass, next to the post) but have no idea where to begin. any suggestions?

Make a large frame that covers the entire first reflection area on the ceiling, plus a generous extra margin, and fill it with 4" thick absorption (mineral wool, fiberglass, etc.). Hang it on chains or something similar. Cover it with acoustic cloth. Done! But first search the forum for clouds, to see how others have done it. You might want to also put a hard back on the top of your cloud and angle it, to help treat flutter echo and vertical modes.

I'd also like to incorporate some diffusion into my plans, especially on the back wall.

The room isn't really big enough to benefit from diffusers. I'd go with deep absorption on the rear wall. You'll be getting some diffusion form the slot walls anyway. Another comment: that beam down the middle with the post supporting it is goig to be a real problem. Have you figured out how to deal with that yet? - Stuart -

Thanks, Stuart. To clarify, I've revised the sketchup with a crude positioning of console/monitors. sorry for the pdf, the file was too big.

I'm also curious about that really wide air gap on the right side of the room: why does it need to be so big?

The goal of the room is for it to be multi-purpose, not purely a mixing room.. so the air gap is a trade off to shift the whole room slightly to the left, this improves the overall ratio and offsets the beam to not make it so awkward for room setups. there is also an existing furnace duct to the upstairs that drops from the ceiling 9" in this area, sorry i should have detailed that in the sketchup.

Also, what is that "deep bass trap" thing at the front right corner of the room, and how is it going to be built?

This is a sealed cavity (double 5/8"+GG). I'm open to suggestions here, but i was under the impression the deeper the better for bass traps. I was thinking of 2" of 703 covering the opening. better ideas?

Personally, I think you'll need MUCH more bass trapping!

Point taken. The plan here was to do the corners with plywood/1" 703/ 3.5" sealed air cavity, A la Ethan Winer. But if super chunks are the way to go, then.. Regarding the Helmholtz slat walls, I've been looking at this: http://www.sae.edu/reference_material/audio/pages/Low%20Mid%20Frequencies.htm#helm Which i now realize is not the same thing. I'll stick with your advice and do as john says. One thing, though.. John's inside out plan calls for 75mm polyester between studs, would pink fluffy eg.R12 work for this?

that beam down the middle with the post supporting it is goig to be a real problem. Have you figured out how to deal with that yet?

That beam is my nemesis. Unfortunately doing away with it is beyond the scope of the project. Current plans are to box around it with double 5/8"+GG. I was thinking of replacing the post with a standard metal garage pole, and boxing around it to reduce the profile. Thanks again for the feedback, Gregor

so the air gap is a trade off to shift the whole room slightly to the left, this improves the overall ratio and offsets the beam to not make it so awkward for room setups.

The problem I see is that you won't have symmetrical acoustics, since the depth of your slots on the right is very much greater than on the left, so they will be tuned to entirely different frequencies. You could fix that by building a leaf behind that, at the same distance as for the left wall, but then you might be running into three-leaf problems...

.. improves the overall ratio ...

Actually, the way you have drawn it, it doesn't change the ratio at all! A slot wall is treatment, not isolation, so it doesn't really change the acoustic width of the room. To change the ratio, you have to build a proper sealed, massive leaf.

sorry i should have detailed that in the sketchup.

Yup! That would help! And anything else that might be missing!

This is a sealed cavity (double 5/8"+GG). I'm open to suggestions here, but i was under the impression the deeper the better for bass traps. I was thinking of 2" of 703 covering the opening. better ideas?

So it just a box sealed on three sides with drywall, and open to the room, but with a single layer of 703 covering the front? Is that it? If so, I'm not really sure what that would do, but I don't think it would be an effective bass trap.

The plan here was to do the corners with plywood/1" 703/ 3.5" sealed air cavity, A la Ethan Winer.

Do you have a link to that? Sounds like a membrane trap, but can't be sure. Ethan has a lot of stuff on his sites, so a link to the specific one you are talking about would be great. "plywood/1" 703/ 3.5" sealed air cavity": Why do you think you are going to have an issue with 100 Hz.? Wouldn't it be better to wait until the basic room is built, then measure the real response, then decide if you are going to need some kind of tuned device like that?

Which i now realize is not the same thing.

Actually, if I'm not wrong, John wrote that too! It's just a more generic version, showing the principle of operation and the equations. But with his slot wall, he has fully designed something that works as a broadband device for most rooms, so it saves you doing the math yourself. But it's the same basic principle.

One thing, though.. John's inside out plan calls for 75mm polyester between studs, would pink fluffy eg.R12 work for this?

Yup. No problem. It will work fine. It's only purpose is to damp the resonance in the cavity, so anything that accomplishes that will work.

That beam is my nemesis. Unfortunately doing away with it is beyond the scope of the project. Current plans are to box around it with double 5/8"+GG

That probably is the only realistic solution. The problem will be to build that box all around the beam, such that is does not touch the beam at all, or the post. It will need some careful workmanship, especially at the junctions where the beam meets the front and rear walls, but not impossible. - Stuart -

Stuart,

the depth of your slots on the right is very much greater than on the left

Apologies again for my sketchy sketchup. Both slat walls are identical in construction, 2x4 framed inside-out, double 5/8"+ GG.

A slot wall is treatment, not isolation

I was under the impression that John's inside out wall accomplishes both of these, with its double layer of drywall being the first 'M' in 'MSM'? The SAE plan does not have the layer of mass behind the slats- ie. slats/insulation/air/mass, as opposed to slats/insulation/mass/air/mass. So they are different. I've attached the two plans to clarify. Ethan's Bass Trap plans: http://www.ethanwiner.com/BTPlans.gif It appears that his plans all incorporate a sealed cavity with different arrangements of 703 covering it, which is what my 'deep bass trap' plan is, in essence. But if you think this will be ineffective, i'm sure there's other things i could do to make such a space an effective trap.. ideas?

Why do you think you are going to have an issue with 100 Hz.? Wouldn't it be better to wait until the basic room is built, then measure the real response, then decide if you are going to need some kind of tuned device like that?

yes, you're right- i'll determine the specifics once i measure the room. I just want to have the location of the traps firm at this stage. To sum up, it sounds like i need to incorporate more bass trapping. Am i right in assuming you would recommend going with superchunks in all corners? would that be enough?

Apologies again for my sketchy sketchup. Both slat walls are identical in construction, 2x4 framed inside-out, double 5/8"+ GG.

Ahhh! OK, that's better. But since it appears as just a slot wall with no leaf behind it on your diagram, that was confusing!

I was under the impression that John's inside out wall accomplishes both of these, with its double layer of drywall being the first 'M' in 'MSM'?

Yes, but they are still two SEPARATE things, acoustically, even though John's design places them on the same structure, to save space. I think I cans see where your confusion is coming from...

The SAE plan does not have the layer of mass behind the slats- ie. slats/insulation/air/mass, as opposed to slats/insulation/mass/air/mass. So they are different. I've attached the two plans to clarify.

Actually, they aren't different acoustically. A slot resonator consists of an open gap between two slats of wood over a sealed air cavity, with insulation in the cavity. Nothing more. Both diagrams show that. One of the diagrams ALSO shows the SECOND leaf of the MSM wall, which is not part of the slot resonator at all! It is part of the wall. So the only difference between those two diagrams is that one shows both leaves of the MSM wall, while the other side shows only one leaf of the MSM wall. In fact, you don't even need an MSM wall at all to make a slot resonator work: a slot resonator will work over any sealed cavity, regardless of what is on the other side of that cavity. You could build it up against the rock face of a cliff, and it would work just fine. The only thing that matters to the slot resonator is the dimensions of the air gap between the slats, the slats themselves, and the depth of the cavity. Whatever else might be around has no bearing on the resonator. (OK, before some perfectionist jumps on me; yes, other things do matter, like air temperature, pressure, humidity, porosity, sealing, etc., but I'm trying to simplify!). So both of those drawing are equivalent, except that one shows the complete wall (both leaves, plus even the floor), while the other shows only a section of the inner leaf, which is the one that matters for the slots.

Ethan's Bass Trap plans: http://www.ethanwiner.com/BTPlans.gif It appears that his plans all incorporate a sealed cavity with different arrangements of 703 covering it,

Yep, that a panel trap all right... but it is a TUNED trap. It is designed to operate over a narrow band of problematic frequencies. You tune that type of trap by changing the surface density of the plywood front panel (thickness) and/or the depth of the cavity. But that's not what you need for your room, initially! What you want for your room is basic broadband bass trapping. Once that is done, you then measure the room response to see what problems are remaining, and in that case you might well then want to make a trap like Ethan's, tuned to the specific problem that you see in your analysis. But you probably wouldn't start out with one, unless you foresee a major problem due to your room ratio. I'd suggest that you would be better off starting out with superchunks in all four vertical corners, and maybe some of the horizontal ones as well, then measure the room and see what still needs to be done.

I just want to have the location of the traps firm at this stage.

Unfortunately, you can't really do that successfully at this stage either! It might turn out that the problematic frequency you are trying to deal with just doesn't have an anti-node at the location in the room that you set aside for your tuned trap, in which case it will not be effective there: you'd have to move it to one of the anti-nodes (or nodes, depending on the type of trap...).

To sum up, it sounds like i need to incorporate more bass trapping. Am i right in assuming you would recommend going with superchunks in all corners? would that be enough?

Yup! Good starting point! :) - Stuart -

Ok, now it all makes sense.. thanks so much for clarifying! -Gregor