There are whole books written on this subject, and also a few other instructables -- but since each project is unique it's helpful, when you're planning your own studio, to see as many different solutions as possible.
You cannot build a sound studio without first understanding some theory: rik_akashian discussed this issue. The most important part to understand is that sound proofing (blocking the sound, so others don't hear you and you don't hear them) is very different from sound treatment (making your room sound good). Since this studio was built for mixing sound and music for film and TV in a residential coop apartment building in NYC, both sound proofing and treatment had to be near perfect. It also had to look good for clients... on a very tight budget.
In this instructable rather than a tutorial on the actual construction I will discuss the design, with links to the materials I used or other resources. This is not laziness, I swear! I just think it is more useful. I assume if you are building your studio you have basic construction skills.
Step 1: Planning for Noise, Heat and Power
Not only do you need to worry about sound from outside your studio, but depending on your gear, you need to worry about the noise your equipment makes. Since our studio is a converted bedroom, we had a closet which we could easily isolate and convert into an equipment "room"-- but then heat management became an important issue. Run 3 computers in a small sealed closet and they will crash within a few hours.
Since we were doing a gut renovation we were able to put in central air, but it could not be regular AC. The air handler was placed as far away from the studio as possible, and the ducts were over-sized and had a few extra bends. The same amount of air circulates, but the since it flows more slowly we don't hear the rushing air. One vent leads to the studio, the other into the equipment closet. Another difference with regular AC is the return air. Since our room is completely sealed we had to included vents to let the air out, rather than relying on cracks around the door. Doing this with a thin aluminum flexible tube would have punched a great big hole in our soundproofing, so we used 50 feet of insulated tube instead, twisting it and turning it as much as possible: air escapes, but sound can't make it through.
There is another solution if you're not able to put in central air: a ductless system like this one is fairly quiet and relatively easy to slip in wherever you need it. You just need to have access to outdoor space for the compressor.
Don't forget to plan for power! Use dedicated lines if it's at all possible. Plan where your equipment will be and figure out how much power it will draw. Heat and power are not areas for cutting corners. While your walls are open, think of other wires too. A wireless computer network will not work well in your studio if you build it properly, so it's a good idea to put in some cat6 cables. We have a piano in the living room we knew we would be recording, so we ran a couple digital sound cables from the equipment closet to a closet next to the piano. It's great to be able to make recordings without snaking mic cables all over the place for everyone to trip over.
Another thing to think about is lighting: I don't trust fluoresents because some of them buzz, and I've been trying to eliminate all incandescent lighting (plus incandescent is hot, and there's enough heat generating equipment in a studio as it is....) The obvious answer is LED. This light can be surface mounted, which makes it preferable when it comes to soundproofing. You will want to avoid using a can which will put a big hole in the ceiling (and soundproofing).
Step 2: Soundproofing Theory
The frustrating part about soundproofing is that you won't know how good it is until the work is completed. This is because soundproofing is only as good as the weakest link. You can have a great wall with resilient channel, double stud construction and quietrock, but put a regular flimsy door on it and the whole thing will have the same lousy sound rating as the door. Bore a single 1/4 hole through that same wall and all the soundproofing is ruined. If you drill a screw all the way through a neoprene puck to the stud below then you've wasted your time and the puck.
One way to understand soundproofing is to differentiate between two types of sound: impact and airborne. To cut the transmission of airborne sound you need mass. To reduce impact sound (as in footsteps, hammering, etc) you need air, i.e. isolation. So the ideal solution is a room within a room: floating floors, walls and ceilings decoupled from the building's structure and from each other. You want small 1/4 inch gaps everywhere so sound vibrations cannot transmit from walls, to floor, to ceiling below, then you need to fill those gaps with something which will seal them completely and stay elastic, such as acoustic caulk. You want your walls, floors and ceiling to be heavy. You can either use multiple layers of sheetrock or even MDF and slather a damping glue between them such as Greenglue or buy ready-made solutions such as Quietrock.
Of course, this being sound, it gets more complicated than that. Other factors need to be considered, the most counter intuitive one being the notion of the triple leaf effect. This article explains it beautifully, but it boils down to a simple fact: a wall with two (or more) cavities will perform a lot worse than a wall with one. Most walls in apartments or homes have one cavity, so if you attach a resilient channel to an existing wall and add a layer of sheetrock you might actually be LOWERING your STC rating (of course this is simplifying things again: you might be blocking more high frequencies but the low frequencies, the ones you really want to stop, will go through more easily). Either you need to tear down one side of the wall to attach your resilient channel to the studs, or you must add layers to the existing wall without leaving any air space in between. Also, don't forget your floor and ceiling: these should be treated like walls, both for sound proofing and sound treatment. You can't just soundproof one part of your room: because of sound conduction, building a single, beautiful soundproof wall just won't work.
Step 3: Soundproofing Case Study: Walls
Since this room is relatively small we had to make some compromises: we could not build a complete room within a room because we would not have had enough space left over for the 5.1 surround sound system. We were not overly worried about our next door neighbor because her kitchen abuts the studio. We were concerned about the elderly lady upstairs who is nearly deaf and blasts opera or Jerry Springer, and we worried that the subwoofer would disturb our downstairs neighbor. In our own apartment we have two very loud boys and a beagle to deal with.
Searching on Craigslist, I found somebody who had ordered too many sheets of Quietrock 525 so I bought his leftovers for a third of the price. This is an excellent product but its cost can add up if you have to buy it new. It is much heavier than sheet rock and is layered with built-in damping. The sheets I got have the same sound rating as 8 stacked layers of regular sheet rock (but this isn't quite as good as it seems: 8 layers of sheet rock do NOT work 8 times better than a single layer...). We laminated the existing plaster partition next to our neighbor's kitchen with the Quietrock using Greenglue, and we have not heard a single pot bang since then.
On the opposite wall we tore down one side of the plaster partition, attached resilient channels to the studs and used isoclips, again, found for a fraction of the original cost via Craigslist, to float a new Quietrock partition. We were careful to leave a small gap between this partition and the other walls, the floor and the ceiling, which we later filled with acoustic caulk. If you make this system with store-bought materials it will get very expensive. If you aren't as lucky as I was finding deals, check out this instructable for a cheaper construction method.
Inside the wall we put a layer of Ultratouch, insulation made with recycled cotton fiber. You'll need to wear a respirator when you install this, but it is still much greener, healthier and more pleasant to work with than fiberglass. It won't itch. I also think it's better for sound, but that's just my subjective opinion, I haven't seen any studies. We were careful to leave an air gap and NOT to stuff the wall full. The purpose of the insulation is not directly soundproofing, rather sound absorption. We want to prevent the cavity inside the wall from acting like an echo chamber (which would amplify sounds the same way an acoustic guitar does). Using less insulation and leaving an air gap will soundproof better than stuffing the wall full.
The window wall looks out onto a relatively quiet courtyard so we did not soundproof the brick wall itself, but we did buy a soundproof window installed inside the window frame. Because closet was in the way we were not able to treat the back wall either. Since it's a brick wall it's got a pretty good sound rating, but unfortunately we can still hear when our neighbors open and close their front doors. That kind of impact sound is almost impossible to eliminate...
Step 4: The Weekest Link: the Door
The is no point in going through all the trouble and expense of building a great wall if you ruin if by putting in a regular door. When I started researching my options I came close to despair: one quote for a measly STC of 41 (slightly better than a regular door) was over USD 1200.00 for a single door.... Another for an STC of 56 was over $6000.00, again, for a single door. Since the best way to get good results is to use a pair of doors, this was not an option for us. I decided to try my luck at building my own doors using layers of MDF and Greenglue, and special sound gaskets, but I wasn't certain of the results, and it wasn't going to be that cheap either.
That's when I really lucked out: on Craigslist I found somebody who was leaving a rental studio and dismantling all the expensive, custom fixtures. Not only did I get a pair of doors the perfect size for my space ($500 for 2 doors & frames), but I got loads of beautifully built panels for sound treatment.
If this seems like just dumb luck which you couldn't possibly have, think again. You make your luck. I was looking on Craigslist every single day for months, so when I saw it I was ready to jump. And unfortunately with this economy, plenty of sound studios are going belly up. They're glad to get a chance to get whatever they can to recoup some of their investment, but they're also usually on a very tight deadline to get out of their space -- so prices can be negotiable. Keep your eyes and ears peeled, be patient, flexible about dates and pick-up, and chances are you will have just as much luck as I had. Plus you might save great stuff from clogging up dumpsters... I heard about Sound One dismantling some studios one week after their materials were carted away to be buried on Staten Island. That was upsetting on so many levels....
Step 5: Soundproofing Case Study: Floor
The proper way to do this would have been to tear out the existing floor and the underlayment, then to use Uboat neoprene floaters such as these to float 2 by 4s on the beams. Then if I'd layered 3/8" plywood, greenglue, quietrock, followed by more greenglue and another layer of 3/8" plywood, finishing it all up with cork I would have had a superb floor. Oh well. To save money I used these simple neoprene pucks I bought from Canal Rubber on Canal Street in Manhattan, and improvised a system to float a new floor above the existing one.
I screwed the pucks into the floor through the center, laid strips of 3/4" plywood over them and screwed the plywood into the corners of the puck, being very careful NOT to go all the way through to the floor. I was also careful not to let them touch the walls. The contractors who were helping me build this were very disturbed by the wobbly construction, and kept trying to use long screws through the neoprene to tighten the plywood onto the floor below. I got tired of explaining and arguing, so instead I'd just go in at night and replace all their screws... After the floor was built it had a nice springy feel, but it was (and still is) perfectly secure and safe.
To avoid the dreaded triple leaf effect I wanted to lay recycled rubber (shredded car tires) I'd bought on Craigslist between these strips. Unfortunately the coop board got wind of my plans and forbade me from using this material, even though my architect sister assured me it was legal. Such is life. I used sand instead, and now I have 4 barrels of shredded rubber sitting in the basement. If anybody can pick them up from Brooklyn, these would be perfect for building a platform under a drum set!
I used the rest of my Greenglue on the strips, built a plywood floor and finished it with cork -- I'll discuss that choice on step 8.
Step 6: Sound Proofing Case Study: Ceiling
This is where I have the most regrets... When I told the contractor I was thinking of using MLV (Mass Loaded Vinyl) he threatened to quit (and he was only half joking). Properly installed so that it can vibrate it will add to the STC rating of any wall, ceiling or floor -- but it is both very heavy and limp, which makes it really hard to work with, especially on the ceiling. So I gave up that idea -- I figured the Quietrock, combined with Ultratouch insulation, a dropped ceiling, resilient channels with Isoclips would be sufficient. They would be too, if it weren't for my weakest link: the AC vent.... Now we can still make out the muffled Magic Flute when the deaf old lady upstairs is in a particularly festive mood. If only I'd lined the beams with MLV we would never hear the Queen of the Night...
One small product makes a big difference, both for the ceiling and walls: quietputty is like play dough which you wrap around an electrical box. I tested both with and without, and the difference was astounding... Definitely worth the expense.
Step 7: Sound Treatment Theory
Most of what I know on this subject comes from Mitch Gallagher's Acoustic Design for the Home Studio. It goes into just the right amount of detail for a laywoman like me. Good explanations and helpful diagrams so you can understand difficult concepts without a Phd. I highly recommend reading this book before building your studio -- but if you don't, these online articles are informative, or here are a few sound tidbits (and I hope I won't mess this up... I can't find my book anymore so this is all memory... please feel free to comment if I've made mistakes):
Sound is a vibration. Waves. These sound waves have different frequencies (the length of the wave) High pitch sound has a high frequency, low pitch sounds have very long waves. Volume is determined by the height of the wave. As these sound waves travel through space they loose energy (volume). This is why low frequencies travel much longer distances and can go through walls: if the width of the wall is only a fraction of the size of the sound wave, it will loose much less energy passing through than if the sound wave is smaller than the wall. Plus an identical number of vibrations will carry the low frequency much farther than a high pitched noise.
When a sound wave hits a surface different things happen, depending on the surface (and the wave's frequency): it can either go right through (for example, with panels designed to absorb sound) and as it does some of its energy (volume) is dissipated as heat, or it bounces back (most of it, at least) if it encounters a smooth, massive obstacle, like a soundproofed wall. This is why soundproofing and sound treatment are contradictory goals: to soundproof you want to block the sound waves (which keeps them in your space till they die out), and for sound treatment you're trying to get rid of the unwanted reflections.
With all these sound waves bouncing around we run into the problems of comb filtering, nodes, room modes: depending on the size of the room and the frequency of the sound wave, as it bounces off the wall it can either cancel itself out or become amplified. I won't go into this and I chose to ignore nodes and modes completely because I had no control over the size of my room. I had enough other things to worry about. It is interesting to learn about, but unless you're building from scratch I'd advise to focus on ways you CAN improve your room.
There are two ways to tackle reflections: absorption, which diminishes the volume of the reflections, and diffusion, which scatters them. In both cases it's fairly easy to handle the mid to high frequency waves, but the low frequencies will be a problem. You also want to keep a good balance. You want to reduce reflections at all frequencies but you don't want to cut them out entirely or the room will sound dead.
Step 8: Sound Treatment Case Study
I decided to focus entirely on low frequencies -- the only thought I gave to the mid to high range frequencies was to make sure I did not absorb too many of them.
Wood panels: these were another find. A vendor at one of the big exhibits at the Javit's center had these mahogany panels custom built for the show, then needed to get rid of them quickly. I got them from him for one twentieth of the original cost. They were hollow, so I removed the back, rewired them (they plug in to the outlet on the wall, then I use their built-in outlets), filled them up with Ultratouch and then stapled fabric on to keep the insulation in place (the fabric came from the trash: a church down the street was throwing a away a huge bolt of perfectly clean, perfectly good fabric which I didn't need but couldn't pass up. After sitting in my closet for a couple years I finally put it to great use here!). The wood on the back was also mahogany veneer, so I used it to build the desk you can see in the studio shots. These panels work really well as bass traps. The wood reflects the higher frequencies, and since the panels are placed at a slight angle, not only does it improve the bass performance (the farther removed from the wall, the better), but it prevents the reflected sound waves to return to the mixer's sweet spot.
Absorption panels. As I mentioned in step 4, I found these on Craigslist for much less than it would have cost to buy or build them new. However if you can't find any second hand, this instructable will teach you how to build your own. Placement is important. Each corner is a bass trap opportunity -- including the corners between the walls and ceiling. Normally you will try to place panels on the spot of first reflection. Sit at the mixing spot, and move a mirror on the wall till you see your monitor: that's where you want the panel. However since we already had our wall/bass trap there, and it was placed at an angle we didn't need to bother with that one. Don't forget your ceiling! It's like another wall. Instead of putting the panels right up against the wall or ceiling, leave as much air space in between as you can spare. This will help for the lower frequencies.
Diffusion. Once again through Craigslist I found 4 skyline diffusors. They were pretty beat-up and ugly, plus they would also get horribly dusty, so I mounted them on the rear wall with a frame which I covered with the identical acoustically transparent fabric used on the absorption panels.
Floor. Avoid using carpet for 2 reasons: First, it will put your room off balance. Carpet will only absorb high to mid frequencies. If you have enough bass traps (which will absorb high frequencies too) you don't need that. Second, our ears are accustomed to hearing with a "live" reflective floor. Your recording or mix might sound OK when you're in the room, because your ears and brain will be compensating, but when you leave your space it probably won't sound as good as you thought it was. I used cork because it was cheaper and thinner than hardwood. This is not the same cork as the stuff used for absorption in walls and as underlayment. It is denser, and with the polyurethane coat it is reflective, so it feels and sounds good.
After all was said and done, and I'd spent many hours contorted in the closet hooking up all the equipment, we tested the room. Our frequency response chart came out beautifully flat, with a dip at a single low frequency: that was from the room size which we could not control, and since it's just a single frequency it's easy to fix with software EQ.
Speaking of hours spent contorted in an equipment closet: a very useful tip I can share is to hang a mirror on the wall behind your computers. When the space is so tight you can only fit your arm behind the equipment it is VERY helpful to be able to see where you are plugging all the cables.
If you'd like to hear some of the music composed and mixed in this space, go to www.johnmdavis.com In addition to John Davis' music and filmography you will be able to watch two very rare (and wacky) silent films.
Step 9: Summary of What's Green for the Benefit of the Contest Moderator
Since all the little green elements are hidden within the text (or in some cases, not even mentioned because they felt irrelevant), I thought I'd summarize them here, in no particular order:
Lighting: choice of LED. Less energy consumed directly, but also saving on AC use since this does not heat the room like incandescent lights. Also, no mercury.
Floor: use of cork. This decision was both financial and ecological. It's cheaper, AND it's greener than hardwood because it's renewable and does not destroy the tree it comes from.
Insulation: Ultratouch costs more than regular fiberglass insulation, but it's manufacture consumes a lot less energy. It's made of entirely recycled cotton, which is treated with a fire retardant. It is also much healthier, to work with and to live with. The green points make the cost worthwhile.
Second hand materials: the energy cost to produce these (for the second user) is zero, the only energy cost is transportation, and since that was all local and mostly public transportation, these all had a pretty low carbon footprint. Second hand materials I mentioned: sound absorption panels, soundproof doors, wood wall panels, quietrock, isoclips (although the last 2 were left-overs, they weren't really second use). One I neglected to mention: The plywood I used for the floor was left over from a film shoot.
Dumpster diving: all the green benefits of second hand use, plus the joy of using stuff which was clearly destined to be wasted. Free, too. Huge bold of fabric from the church down the street. The absorption foam in the equipment closet was also from that same church's garbage. The bookcase I built came from scaps found in my basement. The Barcelona chair was broken and on its way to the trash when I rescued it from a very un-handy friend.
Using leftovers/no waste: since I didn't need the back on the wood panels, I used them to make the desk.
Now come on, if this isn't a project with a green twist, what is?