If pressed, what would you name as the most important ele ment of a high-quality audio system? The speakers? Or perhaps the A/V receiver or preamplifier that processes the sound? Do you place special emphasis on the wires and intercon-nect cables that transmit the audio signal from place to place? Or is the source component—the Blu-ray player, CD player, or music server from which the audio signal originates—your pri-mary concern? Would it surprise you to discover that the right answer is: “none of the above”?

Let there be no doubt selecting the right gear for your room is a crucially important endeavor, but if you didn’t name the room itself as the most important element of all, you’re selling the rest of your system short, no matter its cost. According to Dr. Radomir Bozovic, president of TacT Audio (manufacturer of perhaps the finest room-correction equipment available), “Your room is doing a great deal more than passively setting the stage for quality home entertain-ment. It is a measurable fact that acoustic room interactions contribute 30 to 40 percent of the sound that actually reaches your ears, regardless of how good your system is.”

Even the most fundamental properties of your room contribute to these detrimental room interactions. The height, depth, and width of your room, for example, determine how long it takes for a wave of sound to move from one end of the room to the other. This is important because as low-frequency waves from bass and low mid-range sounds reflect back and forth between the parallel surfaces in your room, their interactions result in what’s known as standing waves, which cause your bass to be greatly reinforced (louder) at cer-tain points in the room and canceled (quieter) at others. If you walk around the room listening to bass-heavy music, it may sound as if someone is constantly adjusting your receiver’s volume knob.
The dimensions of your room also cause the entire space to resonate at specific frequencies, which is why the pictures on your wall may rat-tle in response to certain mid-to-low frequencies, but, contrary to intuition, not as a result of the lower frequencies.

A Typical Two-Channel Frequency Response	This graph, provided by Dr. Radomir Bozovic, president of TacT Audio, demonstrates that the signal from stereo speakers is boosted and cut at different frequencies as a result of room dimensions and the materials within the room. Note the most severe volume fluctuations occur in the lowest frequencies—the bass region. In the crucial mid-range frequencies, where sound starts to become more directional, the difference in response from each speaker at the listening position becomes significant. In the higher frequencies, even the smallest variation from speaker to speaker results in timing errors such as smearing and loss of directionality.
Before the advent of the powerful digital signal processing chips found in virtually all of today’s A/V receivers and preamplifiers, the solutions to these problems were straightforward—although not entirely effective. Modifying the room itself is, of course, the most obvious stopgap, and many acoustical room treatments have been developed over the years to do just that. Devices known as bass traps, for example, capture sound waves at certain frequencies and, through friction, con vert those sound frequencies into heat. Absorptive and diffusive acoustical panels placed at the front and rear of the room can also serve to absorb or scatter high-fre quency sounds, to tone down echoes, reverbera tion, and the like. But striking the right balance of reflection, absorption, and diffusion is no easy task. Too little reflection is just as detrimental as too much, resulting in a dead, lifeless-sounding room. Your chances of eliminating all of the frequency and timing errors in your room with acoustical treatments alone are next to nil. And let’s face it: How many of us are willing to cover the walls of our dens or living rooms with acoustical fabric, anyway? In the 1970s, equalizers arose as a partial solution, allowing audio professionals and adventurous do-it-yourselfers to boost or cut the volume of specific frequencies in an attempt to com pensate for the peaks and valleys in room response. Take one look at the graph on the previous page, though—the sheer number of peaks and valleys that need to be smoothed out and you’ll understand why manual equalization was a daunting, and ultimately insufficient, solution. And so, to fully and prop erly address the myriad problems that arise from placing loudspeakers in an imperfect room, Dr. Bozovic developed the world’s first commercial digital room-correction system in the mid-1990s, when microprocessors finally achieved the neces sary number-crunching power. It was a 5.1-channel system with six analog audio inputs and six analog outputs, distributed by Snell as the RCS-1000. The cost? A cool $18,000.
Dr. Radomir Bozovic, TacT Audio president	Digital room correction in the home has come a long way since then. Even many A/V receivers in the sub-$500 range have some form of room correction. Perhaps the best-known developer of room-correction software, Audyssey, licenses its technology to Denon, Onkyo, Integra, Marantz, and NAD for use in their receivers and preamps. Manufacturers ranging from retail stal warts such as Sony to niche audiophile favorites like Anthem continue to develop their own proprietary systems for measuring and correcting room anomalies. And although each different system tackles the job in slightly different ways, the goals of any room-correction system are the same: to measure the response of specific audio test signals in your room, determine exactly how the room is distorting those signals, and then to apply the inverse of those distortions to the audio signal before it leaves your speakers. The end result—hopefully—is that distortions cancel each other out and the sound that eventually reaches your ears after bouncing off all of your room’s irregular surfaces sounds as close to the original signal as possible.