You knew it was possible to tune an instrument, and you’ve certainly fine-tuned graphics and audio plug-ins, maybe even tuned up a car, but did you know you could tune a room?
For whatever reason, audio is often one of the last considerations in a video production. Even more neglected is the topic of room acoustics. Every room has a characteristic sound which affects your recordings and mix decisions. Whether you need to temporarily tune up a room for a shoot or you’re creating a better space to mix your productions, a little acoustics knowledge goes a long way.
The acoustic properties of any room are the sum of several parts. First are the room dimensions. Height, width and length each determine a part of the equation. In fact, architects and other designers sometimes use a magic formula called the “Golden Ratio” that defines dimensions in an “ideal” room. Another critical element is construction materials. If you’re working in a concrete bunker, it will sound dramatically different from a carpeted room filled with overstuffed furniture. This brings us to the third component – items in the room. Draperies and cushions provide sound absorption, while wood, drywall and ceramics reflect sound.
Reflections present themselves as a combination of echoes and reverb in an acoustic space. While these are desirable in a concert hall, they are tougher to deal with in a smaller space like your edit suite. As a test, stand in the middle of any room and clap your hands. Listen closely and evaluate the sound of the room. Is it bright and bouncy, dead and lifeless or somewhere in between? What you’re defining is the timbre of the space. Independent of pitch or loudness, timbre is the acoustic character of the room. Try the clapping test in different locations, noting the differences in sound. Throughout your test, you will probably notice harsh echoes bouncing between walls. These are called slap echoes, and they create confusion in a listening environment. They’re just plain annoying during a shoot.
A subtler problem is the effect of standing waves. Standing waves occur when specific frequencies bounce back and forth against themselves in a room. This may cause an increase or reduction of that frequency at that location, creating an uneven picture of the sound. Standing waves typically happen in the lower frequencies, due to the limited size of typical rooms. Finally, there is the boundary effect. This is the effect of ceilings, walls and floors on the placement of a sound source. This problem is easy to spot with speaker placement. Here’s another test: set your playback speakers against a wall and listen. Then, try them in the corners and out in the open. You’ll notice a dramatic difference in the bass region. Make a mental note for later.
Time for a Tune-up
Whether you’re shooting a project or mixing in your edit suite, there are ways to combat the effects of less-than-ideal room acoustics. In the studio, you have more control over the methods and treatments applied to tune your room. The first place most people start is the application of sound-absorbing foam on the walls. There are dozens of types of sound foam, ranging in price from reasonable to home-equity-loan territory. Depending on your vendor, you’ll find several different colors and designs. Don’t forget safety – sound-absorbing foam comes with a fire-retardant rating, the higher the better. You can mount the foam in small squares, rectangles or full sheets, using permanent or temporary methods. Of course, foam isn’t the only option. Several companies offer pre-made panels, built with a combination of wood, fiberglass insulation and other materials. For a more decorative touch, consider thick draperies or even oriental rugs. While these items aren’t specifically designed for sound treatment, they will work with variable results. Whatever material you use, wall-mounted absorption will reduce or eliminate those nasty slap echoes that can cloud your mixing judgment.
Remember our speaker placement test? The bass got bigger in the corner, didn’t it? That’s because lower frequencies tend to ball up in corners and wall intersections. Auralex and other manufacturers have addressed this problem with corner-specific solutions. Made of foam or fiberglass, these bass traps will tame the low-frequency problems in most smaller spaces. But absorbing and trapping aren’t the only techniques in tuning a room; sound diffusion and controlled reflections also play a part. If you completely deaden a room, it sounds unnatural. That’s why studio designers include diffusion in their projects. There are several consumer options for sound diffusion, usually offered by the same companies that make absorption materials. Materials are often wood, fiberglass and even rigid foam. Diffusion material is usually placed on the back wall and/or ceiling of the mixing space. Placement depends on several factors, including speaker and listening locations.
Out and About
In the field, your only course of action is to temporarily minimize room reflections. Sound-absorbing blankets are a great place to start. Starting around $20 each, these blankets are easy to afford, handle, transport and store. Setup is simple if you have a couple of unused light stands. Clamp a piece of pipe or a boom arm horizontally at the top of the stand, and either drape a blanket or hang it using clamps. If you have enough on hand, place a blanket at either side of the scene and maybe a couple just behind the camera. For extreme acoustic environments, you may need one or two suspended over the scene. This gets tricky, due to lighting and audio equipment, but sometimes it’s the perfect way to eliminate a nasty echo. If you need to be a bit more creative, consider using thick blankets or comforters instead. It’s easy to hang lighter materials from suspended ceiling grids. You can block an open doorway using whatever blanket you have on hand and some gaffer’s tape. Be creative and have fun with new solutions to tune up your audio.
If all this seems a little vague, that’s because each situation is different, and there is no one-size-fits-all solution. If you’re serious about tuning your mixing space, several suppliers and manufacturers offer free design suggestions based on the measurements of your room. Alternatively, there are also sound treatment kits that include most of the basic tools you need to cover a standard room. For remote applications, grab some sound-absorbing blankets, stands and clamps. Setup will require some experimentation, but, after a few tries, you’ll have a better idea of what’s required. Don’t forget to check the resources in the sidebar, and happy room tuning!
Contributing Editor Hal Robertson is a digital media producer and technology consultant.
Sidebar: Acoustic Treatment Resources on the Web
www.auralex.com/news.: Auralex has a great free download called Acoustics 101
Acoustical Society of America: http://acousticalsociety.org/
www.audioscientific.com/news.: Visit the Acoustic Treatment Materials link