Movable isolators are used to baffle instruments such as drum kits during multitrack recording sessions. Without them, bleed can be a major problem for recording most musicians. Below, I’ve compiled a theoretical to-do list for building such an isolator on a budget, as a DIY project. As of this post, a lengthy explanation of what to get and why to get it is at hand. The step by step instructions are to come.
What to get and why to get it.
A. Decide what you want to do.
1. For general purpose isolators in studios, 4’ high absorbers block out most lateral bleed from drums and amps at the frequencies that really matter.
2. To absorb anything effectively, a barrier that surrounds the subject to be isolated needs to be made so that no gaps (small enough to fit a paper through) are open between the four corners. To achieve this, I suggest making the sides of the isolators fit together with soft, durable materials, then lock with something like a well placed gate latch. Its time consuming but without such locking, it might not work half as well.
3. If the barrier isn’t going to be permanently in one location, weight and mobility will be an issue, so wheels should be designed into the end product. Wheels open a new can of worms with the issue of ground clearance leaving space for sound leakage between the floor and the bottom of the barrier. This is easily solved by cutting sheets of fiberglass and/or plywood that fit into this space after the barriers are moved into place.
4. 4 separate isolators will be needed to make an adequate barrier in a square shape around the subject unless the subject is put in a corner (then you’d only need two). Each one should be exactly the same and should be wide enough to encapsulate a drummer and all his drums, since that will likely be the largest space you’ll need to isolate during a normal session.
1. 703 or equivalent density (about 3 lbs/square foot) fiberglass panels
a. Height should be 4’ or greater, Width should be 4 to 8’.
b. To absorb down to 125 Hz, 4” depth is needed but you can pile sheets together to get depth. 2 sets of 4” depth will be needed to sandwich the isolating materials with absorption. This means that for every isolator, 8” x 4’ x 4 to 8’ of fiberglass 703 will be necessary. If your absorbers only need to go down to 250 Hz, the thickness of 703 needed is halved to 2” depth per side.
c. 703 by spec is yellow but Western MacArthur Co. has carried black and they sell 703 in quantities large enough for this project.
d. One standard sheet of fiberglass is 4’ x 8’ so just get as close to 4” depth as possible. If you want shorter, standard cuts are usually 4’ or 6’ long (which is an easier length to ship, as well).
e. All-Rite carries fiberglass that might fit the bill and isn’t filing for bankruptcy (like Western MacArthur)! Contact info:
All-Rite California
1500 Shelton Drive
Hollister, CA 95023
(800) 642-9988
Western MacArthur Co.’s contact info (if they’re still around):
2855 Mandela Pkwy, Oakland, CA
(800) 992-7374, (510)251-2102
2. Sheetrock panels to match height and width of 703
a. Sheetrock (also called drywall) is used in most modern houses and is just as good an isolator of sound as lead when used in the same surface density.
b. For our purposes, the standard thickness of about ½” is fine.
c. Available at Home Depot, OSH, ACE, etc.
3. Plywood panels to match 703 and Sheetrock
a. Plywood makes an excellent complement to Sheetrock for isolation since it’s more durable and doesn’t give off a tinny sound, and it isn’t as heavy as another slab of rock.
b. ½” total thickness along with the rock is enough to isolate against most trouble frequencies and is practically impenetrable to high frequencies.
4. Frame materials
a. The frame will need to encompass 9 inches of materials. Many things can be used to frame the material sandwich we’re about to create. A nice smooth, durable wood (around ½” thick) will be an easy solution. As I’m writing this, I see on the Home Depot website that “Millstead 1 In. x 10 In. x 10 Ft. Whitewood Board (Model 914916)” is less than $12.00 per board. When all is said and done, three boards of length 8′ 3” or greater for each isolator will be necessary.
5. Casters for mobility
a. Casters are small self contained wheels which need only to be bolted to the underside of a surface. They’re typically more expensive in the sizes needed for a project of this weight but its still well worth it when it comes to setting up the barriers before a session in a hurry.
b. Since all things touching the ground together will resonate together, better insulation is achieved through thick rubber casters which vibrate less than plastic-rubber alternatives.
c. “Shepherd® Hardware Swivel Plate Caster (9277)” - a 3” swivel caster with a locking mechanism (Very Useful!) sells for about $18.00 a piece. Four will be needed per isolator (or just one with a lock, three without). I found this one on ACE’s website.
6. Glue and fasteners to hold it together
a. The kits for many casters come with screws and this is fine but bolts will hold far into the future and aren’t expensive. They just take an extra few minutes of measuring, drilling, and wrenching to put on correctly. The size of the bolt should closely match the size of the holes in the casters and washers should always be used over the holes through the bolts. Nuts of course will be needed to fit to every bolt on the other side of the hole.
b. Drywall screws come by the 100 and are perfect for fitting the plywood to the sheetrock after the two are glued together. Always remember when using drywall screws laterally in materials like plywood, where the wood has been pressed together, to drill a pilot hole first! A pilot hole is a small hole drilled with a drill bit before the screw is drilled into the same place. Pilot holes help maintain the integrity of the wood and without them, the wood may split, ruining both expensive wood and a partially finished project.
c. Construction glue of any variety will be used to plaster the Sheet Rock to the Plywood before attaching the 703 or the frame. These glues come in caulk tubes to be used in caulking guns - so you’ll need a caulking gun too. Most real men have a good long caulk tube and a gun.
d. There are special glues for fitting sound absorption materials together but from what I’ve heard, they’re only marginally more useful than standard construction caulk.
Building an isolator: To be continued…