Sound Advice: Understanding Acoustics

Unfortunately, you've fallen victim to poor room acoustics and no amount of processing in the world can completely repair the empty, distant sound on your recording. While you can't fix the damage, you can avoid similar problems in the future. Let's explore what makes rooms sound the way they do and what, if anything, you can do to optimize them for audio recording.

The primary variable that determines the sonic characteristics of a room is its shape. The majority of rooms you'll encounter are either square or rectangular in shape. However, on occasion, you will find other shapes such as hexagons, octagons and even a round room from time to time. The main thing to remember is that each of these shapes affects the sound character of the room differently. A rectangular room will sound very different from one with an octagonal shape. Round rooms (such as the dome of an observatory) can be acoustically disorienting as sounds reflect and amplify, seemingly to coming from behind you, even with your back to the wall. Don't forget to factor in the ceiling, whether flat or vaulted, and any other unique architectural additions such as alcoves and nooks.

Rooms with parallel walls (the most common situation) produce standing waves of sound. This phenomenon is easily demonstrated by centering yourself between the two walls and clapping your hands. You will likely hear a quick series of echoes with each handclap. These are called "flutter echoes" and can ruin a recording if allowed to creep into your microphone. I once did some work in a large geodesic dome building and, while its architecture was awe inspiring, the room acoustics were challenging to say the least. In virtually every location, there was some sort of echo. The liveliness of the sound reminded me of a racquetball court. Needless to say, it was not designed for acoustic appeal. Pay attention to the shape of the room and listen closely to how that configuration molds the sound of your subject.

In addition to the shape of the room, its relative dimensions also play a key factor in the acoustic quality you'll hear. Acoustical engineers use principals called "golden ratios" - mathematical ratios of length, width and height - to determine room dimensions that produce a pleasing sound . Used on everything from home theaters to concert halls, these golden ratios are proven ways to create an acoustic space that works well with both natural and amplified sound. This works by minimizing the effects of another acoustic issue called "room modes." Room modes occur in the lower frequencies and often make a room sound boomy or bass-heavy. Certain room dimensions can produce problems with the distribution of sound in the room and often result in hot spots that contain a significant buildup of sound energy in certain tonal ranges.

Of course, you aren't designing the rooms you'll shoot in, but an understanding of basic design principles will increase your ability to capture good audio during the shoot.

After the shape and dimensions of a room have been established, furnishings and floor coverings also play a key element in room sound. The finish of a room's floor has more to do with its sound character than any other item. A tile or concrete floor is very hard and reflective. Consequently, sound bounces off the floor easily and will continue to reflect off every hard object in the room until it dissipates. However, a floor covered with an area rug - or better, carpet - will absorb sound to varying degrees and minimize the effects of reflected sound. As an added bonus, it will also minimize background noises from shuffling feet and moving furniture.

Furnishings also play a role in the acoustic signature of a room. A large, overstuffed couch with big pillows will absorb a great deal of reflected sound, while a hardwood dining table and chairs will reflect more of that sound. Reflection isn't all bad, though. Recording studios spend a great deal of time and money installing controlled sound reflectors or diffusers. These specialized devices scatter reflected sound in a special way that reduces the ill effects while maintaining even dispersion.