The first time I can remember anyone paying attention to room treatment was back in the mid 1970′s when the local manager of our Pacific Stereo store added a brick surface to the wall behind his loudspeakers, a pair of Bose 901 Direct Reflectors, in an effort to provide a “perfect” reflective surface for the Bose. The system screeched like a wounded owl and required either a lot of alcohol or a quick exit from the room to enjoy the results.
The industry and knowledge base has come a long way in the many years after this first encounter: due mostly I would imagine to the high-end borrowing from the recording and pro folks who have used some form of room treatment for decades before anyone in the high-end figured it out.
There are two main schools of thought when it comes to treating a room: absorbing or diffusing or a bit of both. Many devices created for this task have both a reflective and an absorptive surface that can be employed in the service of making the room a friendlier environment for our stereo systems.
Absorbing the sound is a near impossible task because you pretty much can’t absorb all frequencies. Absorbing the higher frequencies is rather easy but as the frequency of the music gets lower and lower it becomes increasingly difficult to absorb and eliminate the sound. Furthermore, it seems to me to be the wrong idea if we’re considering the room as our friend we want to include it in the system instead of fighting it at every turn. I think diffusing the sound is by far the best way to go.
Diffusing the sound scatters the sound in such a way as to allow your ear/brain mechanism to pay less attention to it than the directly received sound. This allows us to ignore (or reduce our awareness) of the scattered sound in favor of paying attention to the more direct sound – kind of like what we want to achieve with absorbing without having to use such brute force measures as are required with any absorber type of system.
One of the first tasks we’re going to start with is to try and eliminate the point of first reflection from the sidewall. This is the classic area to start with assuming you’ve placed a throw rug or some type of absorbing material on the floor in front of the speakers (diffusing on the floor is nearly impossible from a practical standpoint) and the ceiling is pretty far away. If the ceiling is as close to the speaker as is the sidewall you may wish to explore the idea of repeating the process we’re going to next suggest – on the ceiling.
For this exercise you’ll need the help of an accomplice holding a small mirror that isn’t overly concerned with looking a little goofy. First, remove the grilles on your loudspeakers. While you’re seated in your listening position, which was set in the procedure we detailed in yesterday’s post, have your cohort stand with his/her back touching the sidewall in front of the speaker, perhaps halfway between the speaker and your seating position, holding the mirror directly in front of them and parallel to the sidewall behind them.
You want to look at the image in the mirror and have them move toward or away from the speaker until you see the speaker’s tweeter in the center of the mirror. This is the point of first reflection where the sound from the tweeter and midrange first strike the wall and then point towards your ears. Because the distance traveled from the loudspeaker to your wall and then to you is greater than the direct sound, you hear a slightly delayed version which confuses the image. So it is at this very spot you need to diffuse the sound so no longer is your ear/brain confused. The improvements in imaging can be significant.
A good diffusor is important but almost anything will be better than a bare wall.
Tomorrow I’ll discuss what I use and recommend for diffusors.
Paul McGowan – PS Audio, Intl.