Mounting Acoustic Foam
By Phil O'Keefe |
Sure you can glue it directly to the walls, but there are less permanent, and less damaging options
By Phil O'Keefe
Acoustic foam isn't a cure-all; it won't "soundproof" your room and keep you from bothering your neighbors, and it's ineffective at absorbing bass frequencies, but it does have its uses - it's excellent for eliminating mid and high frequency flutter echo, and when used appropriately and in conjunction with various other acoustic tools, it can significantly improve the sound within a room. But mounting foam can be challenging. It's limp and not self-supporting. Gluing the foam directly to the walls is a commonly-taken approach, but as anyone who has ever had to remove it can tell you, gluing it up makes it very difficult to remove the foam later (prying it up with a wide-blade putty knife and a lot of effort is your best bet), and it causes significant damage to the wall surface, making it an undesirable approach for renters.
Less Destructive Alternatives
Whether you own or rent, there are several different ways you can mount acoustic foam that won't cause anywhere near the level of damage that directly gluing the foam to the walls does. Let's take a look at a few of them.
One alternative approach is to glue the acoustic foam to a backing panel, such as a sheet of 1/8" Lauan plywood or MDF board, then hang the backing board from the wall with the anchors of your choice - nails, screws, hooks, picture wire, etc. Inexpensive wood products can go for as little as $7 for a 4' x 8' sheet, making them a cost-effective backing material. It is also easy to work with, and can be easily cut with a jigsaw. If you don't have a jigsaw or a truck big enough to carry a 4' x 8' piece of wood, many lumber and large home improvement stores will cut sheets into quarters for you, making it easier to transport, and the same general size as a piece of 2' x 4' acoustic foam. Of course, foam can also be cut, but don't try to use a jigsaw or a utility knife - it will tear. An electric carving knife is the tool of choice for cutting acoustic foam cleanly. Before mounting the foam to the wood, you may want to use some flat black paint to paint the side edges of the wood so it blends in visually with the foam.
There are a couple of ways to mount foam without using a backing material, and without gluing it directly to the wall. Do you have any "coasters" sitting around? Old CD-Rs are fast becoming a thing of the past, but if you still have some unwanted CDs that you're willing to sacrifice, they can be glued to the upper-rear corners of a sheet of acoustic foam and once dry, they can be used to hang the foam on to a pair of thumbtacks inserted into the wall, and spaced equidistant to the CD centers on the wall.
Large T-pins are sometimes suggested as an alternative to glue, and they can work well for hanging acoustic foam on walls too (like the CD approach, they're less effective for ceiling mounting), but a typical 2' x 4' sheet of foam will usually require anywhere from four to eight pins to hold it up, so there's going to be a lot of holes to patch later if the foam is removed. Still, this is far less damaging to the walls than glue is. However, I feel that when it comes to studio walls, minimizing the holes is a good idea - anything that compromises the wall integrity and air-tightness should be avoided whenever possible to help maintain the wall's STC effectiveness. If you want to use T-Pins, push a few through the valleys in the foam and into the wall just far enough that the top of the "T" presses against the foam and holds it in position.
If you're willing to make slightly larger holes in the wall, you can try using Monkey Hooks to mount your acoustic foam. Monkey Hooks (and the thicker and stronger Gorilla Hooks) are curved steel wires that you insert into the wall by hand, and that can support 35 or 50 pounds per hook, depending on the version you buy. The interesting part as far as hanging foam is the shape - once into the wall, you have a strong, upwards-facing hook that can be embedded directly into the foam. Use at least a pair of hooks, and you can secure it directly into place, with the acoustic foam hanging impaled on the hooks. Mounting the foam this way is easy - use two to four well-spaced Monkey Hooks where you want to place the foam, and then push the foam slightly downwards and into the hooks as you push it against the wall. Two hooks are usually enough for a 2' x 4' foam panel, while larger 4' x 4' foam sheets may require more hooks.
Foam, Panels, Hooks and Space
What about spacing the foam away from the walls as you'll sometimes hear being recommended for compressed fiberglass-based acoustic panels? Yes, there are ways to move the acoustic foam away from the wall a bit if you want to, and doing so offers similar benefits to spacing a fiberglass panel out a bit. The reason you may want to mount the absorptive material a few inches from the wall is because you'll get increased absorption at lower frequencies than if you mount the absorptive material directly to the wall. How far should you space it? A good starting point is the thickness of the material. If it's 2" foam, try spacing it 2" from the wall. You can space it further away if you have enough room, and 4" away is going to be even better at absorbing lower frequencies than 2" is. Of course, using even thicker fiberglass or foam and greater spacing distance only increases the absorption at lower frequencies, and that's almost always a "good thing" in small rooms; where mid and high frequencies are much easier to absorb and control, and low frequency absorption is almost always insufficient, so if you have the space for 4" thick sheets of foam spaced 4" away from the walls, that's usually going to be even better still.
A flat backing board is fine for mounting the foam directly against the wall, but for panels that you wish to space a few inches away from the wall, a solid backing is not recommended - both sides of the absorptive material should be open to the sound, so it passes through it both as it enters, and again as it reflects off the wall behind it. Instead of using a solid panel as a backing, cut out sections of the plywood or MDF craft board so that it creates an open-back on most of the panel.
A jigsaw was used to cut out large sections of the panel backing while leaving enough to glue to the recycled acoustic foam
Two smaller pieces of foam can be glued together (I used 3M High-Strength 90 spray adhesive) to form a spacer, and then the spacers can be glued directly to the back of the panel, so that when the panel is hung from the wall, the foam spacers hold the panel and main foam sheets out a few inches away from the wall.
In the panels pictured below, I used 2 x 2" lumber, wood screws, and Liquid Nails adhesive to pair two 2' x 4' MDF backing panels together, and then I glued Auralex 2" Studiofoam recycled from a previous glued-to-the-wall installation to the front. I used eye hooks screwed directly into the 2 x 2 as mounting hooks to hang the resulting 4' x 4' panel from two Monkey Hooks embedded into the wall. A dab of caulk at the base of each Monkey Hook keeps the wall airtight.
Foam in the Corner?
What about mounting foam across the room's corners? You can use it for that too, but as with fiberglass, the thicker the foam for this application, the better - especially if you're trying to absorb below 200Hz. Four-inch thick foam is the minimum I'd recommend for use in the corners. Building the corner frame is similar to the flat panel frames. You'll want to use a jigsaw to remove much of the center of the backing panel as you can while still leaving enough to attach the foam to. As before, 2 x 2 lumber glued and screwed across the top and bottom provide a bit more structural strength while also serving as the anchor for the mounting hardware - which in this case consists of a couple of eye bolts - one inserted into the center of the top 2 x 2, and another in the wall's corner. A couple of extra-long (14") nylon zip ties chained together, looped through the bolts and pulled tight is all that's needed to support the panel, while a few foam-filled vinyl pads (felt pads work just as well) applied to the ends of the wood provide protection to keep the wood from scratching the walls. Again, you can put a dab of caulk around the base of the wall-mounted eye bolt to keep things airtight.
Eye bolts and zip ties will easily hold a 4" thick 2' x 4' acoustic foam panel in place in the corner...
Well, there's some suggestions for mounting foam in a way that does far less less damage to your walls, increases the foam's acoustic effectiveness, and that allows you to quickly and easily take your acoustic foam panels with you and reuse them again if you ever relocate. I'm sure you can think of more ways to mount and utilize acoustic foam, and if you do, please stop in at the Studio Trenches forum (http://www.harmonycentral.com/t5/Phil-O-Keefe-In-The-Studio/bd-p/acapella-57) and tell us about them. And stay tuned for my next Technique article, which will cover where specifically in the room to place your foam panels for the best results.
Phil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.