The trick to this method is that the drywall panels are hung on a pair (or more) of wooden "cleats" made from a sliced 2x4. The upper cleat on the back of the drywall is isolated from the lower cleat on the wall behind by inexpensive closed-cell foam tape. No part of the outer and inner walls touch directly. In practice, very little sound is transmitted through the foam, and the walls achieve a very high degree of soundproofing. The weight of the drywall keeps it in place so surprisingly well, that I use only two cleats: one near the top and one across the middle.
Overall, this method is fairly easy. It's not nearly as quick as using resilient channel, because it involves splitting a 2x4 lengthwise. (In either method, you will want to use foam tape to add extra soundproofing, so this extra step isn't a tradeoff, unless you choose to buy the resilient-channel pre-taped. The parts list is very small - drywall, a table saw or bandsaw, one 2x4 for every 4x8 drywall panel, nails, drywall screws, foam strips, and some pipe insulation. Surprisingly, this method requires much less precision than you would think, because some mistakes are in a sense self-correcting. Of course, the DIY version of this method does assume skill and confident use of limb-shearing power tools to do a potentially-dangerous "rip cut". If you don't have a woodworker's confidence with this step, find someone who can do it for you. A great recommended alternative is to have the lumberyard cut the wood for you upon purchase. In the section on ripping the wood, I'll tell you what to say to get the cut we want.
Since soundproofing carries with it a lot of myths and misconceptions, this Instructable will start with a little soundproofing theory before heading into the steps.
Step 1: Soundproofing Theory
First I'd like to 1. clear up some basic soundproofing theory, and 2. explain some typical alternative methods.
"Soundproofing" (as distinguished from acoustical treatment) is concerned with blocking sound.
You block sound with 1. mass, and 2. isolation.
Putting foam or other absorptive things on the inside of the wall is not soundproofing, but acoustical room treatment, which is used to reduce echoes and resonances and prevent excess sound buildup within a room. Soundproofing and room treatment are completely different things. Room treatment improves the sound within the same room. Soundproofing is about preventing sound from getting out or in. Definitely, putting foam on the walls can help keep your neighbors from calling, but it's not because of "soundproofing" -- it's because you have treated your room and in effect "turned down the volume" like they asked you to do.
Soundproofing a wall involves the principles of mass and isolation. A heavy wall will soundproof better than a lighter wall of the same construction. BUT isolation is the trick that will let you achieve the same results with a lighter wall.
A traditional wall involves panels (drywall, siding, stucco) connected to a frame, with drywall attached to the inside. There is usually fiberglass insulation inside the wall. It can typically block about 30dB of sound if constructed tightly. The way it works is mainly through the mass of the wall (drywall + frame) with some absorption by the insulation (effectively "turning down the volume") in the little "room" between the panels.
You can make a better wall by finding ways to isolate one panel from the other. In the staggered stud method, the vertical studs are staggered in depth so that the front and back panels are screwed into different sets of studs. However, they are still attached to the same top and base board of the frame, so some sound will travel straight through.
The ultimate method involves "double wall" construction. You essentially create a room inside a room with no part of the inside wall touching any part of the outside wall. Double walls can block in the range of 55-60dB of sound. A disadvantage is that the extra wall thickness can eat up a lot of space within a small room.
In between these two extremes, there is the resilient channel method, which involves attaching springy metal strips to the studs of the outside wall, then screwing drywall into a flange on the strips in such a way that the wall can flex against the resilient channel without touching the outside wall's studs. When constructed properly, these walls can block into the 50dB range. Other implements can be added to the resilient structure to get into the high 50dB range, such as foam tape and varieties of "isolation clips" that are clever ways to attach the channel to the studs without screwing directly. Of course, the cost of these adds up quickly.
My method is also in between the single and double wall construction, and it is similar to the resilient channel method in creating a "springy" wall that will flex. Unlike the standard resilient channel method in which the channels are screwed into both the stud and the drywall, in my method there is no direct mechanical path from the outside wall to the inside wall. So my performance should be most comparable in soundproofing capability to resilient channel methods with isolation clips. (Exactly how close we come remains to be verified by testing however, so stay tuned for future revisions of this instructable.) I will say, however, that it's "pretty darned good".
Of course, if you're running a commercial operation or otherwise have the funds, definitely look into a well-documented industry-standard soundproofing method like resilient channel or double-wall construction. They've been studied and measured thoroughly, and there's little mystery about why they work and how well they work. But if you're desperate and/or short on funds like many musicians, this method could be just what you need to get excellent results without a lot of investment.
For more information on soundproofing, especially technical aspects of soundproofing and studio acoustics, I recommend F. Alton Everest's books Master Handbook of Acoustics and Sound Studio Construction On a Budget. For non-technical soundproofing advice (mixed with a lot of product hype) see Soundproofing.org, (which I am compelled to point out I have no affiliation with and am generally critical of, even though, quite coincidentally, they are local to me.)
Step 2: Planning Ahead
This instructable assumes you will be soundproofing over an outside garage wall with exposed studs and insulation. Both are critical for the success of this project. If your wall is already drywalled, you'll need to remove it. If it is not insulated -- we're talking fiberglass batting or equivalent -- you will need to do that first, because it's part of the soundproofing structure.
There are 5 steps to this project:
1. Arrange to slice ("rip") the 2x4 boards longwise with a mitered cut to create a top and bottom cleat.
2. Nail the bottom cleat to the studs and staple foam across the face of the bottom cleat, then set the top cleat in the valley of the bottom cleat with foam sandwiched in between.
3. Cut the pipe insulation to set up a squishy track for the drywall to sit in.
4. Set the drywall panel in the track and screw it into the top cleats.
5. Assuming it's how you'd like it, caulk the seams.
And here are the essential parts, listed in order of use.
2x4 lumber - You will need one 8 ft length of 2x4 for every 8x4 ft panel of drywall. If you choose to use more than one cleat at the top and one cleat in the middle, plan accordingly after reading all the instructions.
Helpful Hint: If you buy the wood from a lumberyard rather than a home improvement store, you can ask them to rip the wood for you. Lowe's and Home Depot cannot do the cut required for this project.
(Optional for the DIYer)
-- Table saw or Band saw (must have miter capability.)
--Measuring tape and pencil to mark the cut line.
(Recommended "No-Power-Saw" Alternative)
-- Ask the lumberyard (not Lowe's or Home Depot) to cut it for you for a small fee. See the section on "ripping the boards", where I tell you what to say to them to get the cut we want.
Hammer and 2-1/2" Nails. You'll be nailing cleats into the studs.
Closed-cell foam tape. Does not need to be sticky. This blue roll is from Lowe's in the insulation section and was very cheap. In general closed-cell foam is identified by little closed bubbles. It does not look like a sponge. It should be about 1/4" thick. The foam tape will be cut and attached between the two cleats and along the front face of the bottom cleat.
Staple Gun. (Needed if your tape is not sticky. If your roll of foam is sticky, you won't need the staple gun.)
Scissors for cutting foam tape. If it works, use it.
Pipe insulation tube for 1/2" pipes. Your drywall panels will sit in these to isolate them from the floor. You should get the "polyethylene" tubes rather than the really squishy black ones. They need to be very resilient.
Utility Knife to slice the pipe insulation in half longways.
Drywall - thicker is better, but you can always increase the thickness later if you desire, by gluing more sheets on the face. There are many advantages to doing it this way, including being able to seal the seams very easily by overlapping them with the new sheet. I used 1/2" thick drywall.
C-Clamp (not shown) - at least 6"
Screw gun for attaching drywall to the top cleat.
Drywall screws. Pick your favorite. I ultimately used self-drilling screws.
Optional (Very helpful): A drywall prybar that helps to lift drywall at the foot.
Acoustical Caulk and Caulking Gun - Acoustical caulk is "Non-Hardening" or "50 year" caulk. An important principle in acoustical isolation is flexibility. Rigidity is an enemy.
Step 3: Be Willing to Break the Rules
For any construction heads reading this, I'll take the opportunity to warn you of some ways in which soundproofing construction methodology is different from and often the opposite of conventional methodology:
Flexible wins over solid. Sound travels easily over rigidly-braced and strongly-connected construction. We want the opposite. Instead of a strong-as-a-steel-rail metaphor, we are going towards limp-as-a-fish. Of course a fish does not make good construction material, so therein lies the challenge. We need it to be just strong enough. The inside walls don't need to support a roof and hold the building together like the outside walls do; they just need to be heavy and not move. If you don't expect people to be bashing the walls in (mine will often have cabinets in front of them) then there is absolutely no need to do more than prevent it from falling down on you. Therefore use as little traditional construction (nails, screws, bracing, etc) as you can get away with.
Walls before ceiling. In conventional construction, the ceiling comes before the walls. But in soundproofing, this would be problematic for constructing a "hanging ceiling". It's much easier to set up the walls, and then hang the ceiling to either sit atop the new wall or butt tightly up against it.
Vertical may work better. In conventional construction, drywall is usually hung sideways on the walls. That's fine when you're screwing the sheets straight into the studs and cutting the edges flush with the ceiling. But in soundproofing, it's important to get a good seal at the top and the bottom, and it's often easier to get a good seal by letting the weight of the drywall sit on a strip of foam, and to let the ceiling panels sit on the top of the walls. In my case, I will let the ceiling panels butt up against the walls, but the bottom will sit in the groove of the pipe insulation to get a good seal.
Drywall also absorbs bass. The main role of drywall in soundproofing is as a high-mass-barrier. But drywall construction also plays a huge role in room treatment as a bass absorber. Of course, the drywall itself is not very absorptive; but the wall construction definitely is. You've surely experienced that hitting a wall with your fist is like banging a huge bass drum. Banging that drum takes energy. Sound within the room is constantly beating on the big bass drum created by the wall, and thus is losing energy in the bass region. The effect is a lot greater when there is insulation to absorb the sound within the big drum.
This is relevant to the way you construct the walls. Adding more mass in the form of studs or bracing will add to the mass-barrier effect, but depending on how it is done, extra bracing may decrease desirable bass absorption within the room. For example, decreasing the distance between studs to add more bracing has the same effect as shortening the length of a vibrating string: the resonating pitch goes up. You can easily determine the resonant frequency of the wall after-the-fact by banging on it lightly and listening for the tone. Is it higher or lower than you want? Does it seem more broadband (like hitting a normal wall) or more tuned-to-a-note (like a tom-tom). A great advantage of my design is that you can easily remove the wall to adjust the tuning! (preferably before you've caulked it :) In the case of my own walls, the construction of which I am describing in the Instructable, they seem to be tuned in a very broadband way around approximately 60hz vs. my normal house walls which seem to be tuned more tightly around 100hz or so.
Flexible caulking NOT Mud Along the lines of the flexibility principle, we want to use acoustical caulk which is commonly available as "50-year" or "non-hardening" caulk. The seals need to be flexible, because the panels need to flex. Therefore, absolutely no "drywall mud". We use only acoustical caulk to seal the seams.
No short-circuits! Resilient-channel methods are commonly defeated by sloppy or unknowledgeable installation that allows the outside wall to touch the inside wall via a screw or a nail that wasn't tightened all the way in or some other tiny missed detail that allows a direct path from the outside wall to the inside. It is a mechanical "short circuit". My wall is less prone to this, but you must be vigilantly aware of the possibility. The weak points in my design will be the staples and foam, so I will warn again when we get to that step.
Step 4: Step 1: Buy and Rip the Boards.
After buying your 2x4s (one 8ft board per 4x8 drywall panel)...
You'll first need to arrange a way to slice (rip) a mitered cut longways through an 8ft length of 2x4.
Recommended Easy and Completely Non-Dangerous Way: Go to your local lumber yard and ask them to cut the boards for you. If you buy the wood there too, you can get it all done in one shot for just a small fee. (note: Lowe's and Home Depot cannot do this cut)
What to tell them: "I want to rip each these boards once down the center, mitered at 25 degrees." Show them with your hands how it should be cut, and ask them how much they would charge.
As they cut the boards, set them aside as matched pairs. Tape or tie them together.
If you have to be DIY about it:
Here are the essential steps of the board-ripping stage:
1) Set your power saw to miter at about 25 degrees.
2) Adjust your cutting line so that the mitered cut will rip the board in half evenly.
. . . (For 25 degrees, that works out to be 2" from the right)
3) Rip the board longways, leaving two trapezoidal pieces.
4) Set aside the boards as a matched pair.
Remember that you'll be using matched halves of wood that won't even be touching each other directly, so don't fuss too much about accuracy.
If all of this seems obvious and easy to you, ie. "you know what you're doing", go for it. Since this instructable is not a power saw lesson, if anything about setting up and using the power saw is unclear to you, I highly recommend getting acquainted with the staff at the local lumberyard.
Step 5: Step 2: Prepare the Bottom Cleat
Once the cleats are cut from the 2x4s, we need to nail the bottom cleat to the wall and place foam tape across the front and on the top where it meets the studs. Once prepared, we simply lay the top cleat across the foam and move to securing the drywall.
1. Nail the bottom cleats to the wall horizontally. Starting with one 8 foot 2x4 pair, choose one of the halves to be the bottom cleat. Orient it on the wall according to the pictures. (The top surface should slant upwards towards you.) If you've cut them unevenly, I suggest saving whichever one of the pair has the larger small-side to be the top cleat. (The reason is that you will be screwing the drywall to the top cleat's small-side blindly, so you may as well use the one with the larger surface.)
The only real variable here is location. The drywall will be supported against the wall at three locations: the floor, at the middle, and near the top. You interpret where that means for your garage. I chose the middle to be well above the cross members of the framing system, in order to reduce the risk of accidentally shorting out the soundproofing. I chose the top to be about 2 inches below the ceiling, since that would assure that I have room to raise and detach the drywall if I need to adjust something.
Nail the cleat to the studs. I don't believe it's necessary to nail it in more than about 3 times - at the middle and both ends. I recommend using a level, but it's not a big deal if you don't. In any case be sure to line up the next 8-footer with the first.
2. Add foam across the front face. I cut my foam (with scissors) longwise down the middle to make it an appropriate width, and then cut it into 8" or so lengths and stapled them across the face. You don't need to attach them contiguously -- it's better to leave space between them so that the foam can expand sideways. After stapling with as few staples as possible (just one in the middle works fine) hammer each staple all the way in with one blow to make sure it is well below the surface of the foam. Avoid hammering away the bubbles as much as you can.
Upgrade Hint: If you have the patience to use glue for the foam, then you eliminate all stapling issues. I found gluing to be frustrating, but maybe you can find a good way to do it.
3. Apply foam to prevent the top cleat from contacting either the studs or the bottom cleat. Next cut some smaller strips, about 4 inches, and staple the strips vertically to the studs about 2 inches above the cleat. See the photo. Again, hammer the staples all the way in so that they don't short out the whole thing. You can avoid this issue by stapling well above the height of the top cleat.
4. Once you've got everything padded like the photo, simply lay the top cleat in there snugly and move the next step.
Step 6: Step 3: Cut the Resilient Track
This step is pretty easy. Using a utility knife, slice a 1/2" (inner diameter) pipe insulation tube in half longways. Here is what I did:
1. One side is pre-sliced. Open it by ripping through with the butt of a utility knife, as in the photo.
2. Clamp the insulation tube lightly in the portable benches, just to keep it straight.
3. Score the other side with a utility knife and rip it open with the butt end.
Once cut, lay each half down as a track for the drywall.
Step 7: Step 4: Secure the Drywall to the Top Cleat
1. Set the drywall panel in the track. This may be the most frustrating part, as the lightweight pipe insulation wants to move under it. Do the best you can before you clamp it. Make the bottom of the wall the same distance from the wall as at the middle cleat.
2. Clamp the drywall to the bottom cleat.See photo. The clamp makes everything so much easier. Since the panel is somewhat flexible, use the opportunity make final adjustments to the track. I found a drywall pry very helpful at this point.
3. Sound Check: Now is a good time to check your acoustical construction. Press your ear up to the drywall and scratch on the top cleat. Compare the volume of that sound to the sound of scratching on the studs behind. There should be a huge difference - scratching on the stud should sound very far away in another room. If the difference is not so great, backtrack to the previous steps and search for signs of short-circuiting, through a staple, nail, or a point where the drywall is actually touching the bottom cleat. Remember that the wall should should flex -- if it's not flexing, there may be a problem in that location. Once the sound check is satisfactory...
4. Double-check the top cleat: Make sure it's snug in the "trench" before you screw it in place. Check again that there are no signs of short-circuiting -- when you wiggle it around in there, it should never feel like you're hitting something.
5. Screw the drywall sheet into each top cleat. Again, for soundproofing reasons don't get carried away with screws. I used just three at each level. Since this is a blind maneuver, you'll find it helpful to pre-mark where you are going to drill, based on the level of the top cleat at the sides of the drywall panel.
6. Check again! Before you caulk it up, it's a good time to check to whole operation. Is the resonant frequency as you'd like it? Is it as sturdy as you require? Is anything too crooked for your tastes?
Step 8: Step 5: Caulk the Seams
The last step is simple:
Load your caulking gun with some acoustical caulking, a.k.a. "non-hardening" or "50 year" caulk. Apply it liberally to the seams and over the screw holes.
Step 9: What Now?
Are we done?
We'll we're done with one step of a long project. You should now have a pretty solid acoustical wall that both soundproofs very well and absorbs deep bass from within the room. Unlike a resilient-channel wall, which you should NOT screw into since there's nothing solid behind it to block the sound that will come through the screw hole, with my wall, you could even use the top cleats as a way to secure supports for shelving, tools, or acoustical devices. If you try this, I would advise drilling the hole, then filling it with caulk before adding the screw.
But are we really done?
Chances are, like me, you need to soundproof your ceiling, doors, and even floor also to really notice the full difference. It's amazing how much sound will leak through small cracks and seams -- those small cracks can make the whole project seem pointless until you deal with them. I will cover ceiling and doors and floors in future Instructables when I actually get to those projects. I have more nifty ideas for saving money on all of these.
For me, the most pressing problem is the garage door ("solid" plywood-over-frame), which I wish to remain openable, yet completely sealable. The edges around the lever mechanism are a profound soundproofing issue, because the pseudo-scissors-action of the door relative to the wall make it impossible to seal it ilke a normal door, and the lever-mechanism is totally in the way of any plan I might have. I also don't know how to create anything resembling a resilient channel or double-wall construction on a moving door without making it impossibly heavy to lift. Not to mention all the bolts and truss rods and bracing that are in the way. Any ideas?