Fine Tunes #3

So where did we leave off? I think you were wandering around the listening room clapping your hands. You were, I hope, listening to the slap echo and noting how it changed as you meandered about. That's probably just when someone near and dear bumped suddenly into the room and gave you that peculiar look we audiophiles know so well. Try to explain what you're doing.

When that fails and you're once again alone, play some strong, bass-heavy material and get thee hence deep into the corners behind the speakers. That's right, stick that head of yours right into the corner. Notice how strongly the bass loads up there, how exaggerated and out of control it sounds.

Now back up maybe halfway between the rear wall and the speakers and take a good look at that back wall. Start smacking the flesh again. Think of the air in the room as water, and "watch" as the sound waves are excited by the dropped pebbles of your handclaps. Continuing to clap, move back to the two speaker positions and step between them. Still pounding the flesh, back up to the listening position. If this excessive whackage disturbs you, The XLO/Reference Recordings Test & Burn-in CD actually provides a "Clap Track" that you can set on repeat. (Your line: "What claptrap!" Thank you.)

The sound reflects off of the side and back walls, the in-phase and out-of-phase interference creating sound-pressure peaks and nulls. At the ceiling/wall juncture behind the speakers a ruckus of sound travels along toward the rear corners, then slaps out to meet again in the middle. Don't forget the sound reflected from ceiling and floor.

What to do? Acoustic damping, me bucko. Absorb or diffract the reflection points to kill their effect at the listening position. Here's how to do it. Have a friend (or, better yet, your Significant Other) hold a flat mirror up against both side walls around tweeter height. Sit in the listening position and ask your friend/SO to move the mirror about until you see the tweeter of the near speaker reflected there. Mark that position and, for better results, ask your assistant to move back until you can see the tweeter of the other speaker in the mirror. Mark that point, then consider checking the ceiling in front of the speakers the same way.

Unless you have sufficiently high ceilings, as we do in our loft, tacking acoustic tiles or foam to all these points can be of great help. You'll be amazed at how minimizing these first and second reflections cleans up and liberates the sound at the listening position. Then you can hear the dramatic results of moving the speakers back and forth, closer and farther apart, even from quite small-scale movements. It's the same with the listening chair. Futz and ye shall find.

Another method of voicing the listening room was told to me by the magazine's erstwhile equipment reports editor Wes Phillips. His e-mail: "I forget where I first heard this one, but it was at least 10 years ago: Since resonant modes are nondirectional (ie, they exist at both listening and speaker positions), you can put a single speaker in your listening spot and walk around the room marking where the sound changes significantly. This gives you a grid of bass-rich and bass-shy areas, and shows you the ranges of boundary effects and such. It's surprisingly effective at giving general placement info." I haven't tried it yet with the big JMlab Utopias, but it sounds like a great idea.

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