The Fifth Element #2

Henry David Thoreau once wrote that "The eye is the first circle; the horizon it forms is the second." A profound observation, indeed: The horizon exists only in being perceived. Kind of like music, in fact.

But you can't take everything ol' H.D. said at face value. For instance, Thoreau also gave the famous advice "Simplify, simplify." Would it not have been simpler merely to have said "Simplify"? (Thanks, Jonah.)

Anyway, as my lead suggests, this installment of "The Fifth Element" attempts to reconcile the conflicting demands of sensation and cognition, while simplifying your life and making your stereo sound better. Peessacake. All you need is a very long piece of string, a tape measure, two bits of masking tape, a quantity of small self-adhesive removable note papers, and later, perhaps, a trip to the fabric store.

Most audiophiles know about locating early acoustical-reflection points in a listening room by moving a mirror around on the side walls: One person sits in the listening position, the other moves the mirror around. When the mirror shows the seated viewer a visual reflection of a loudspeaker, the mirror is at the point of an early acoustical reflection.

As established by Olive and Toole, Haas, and other researchers, early (ie, less than 10 milliseconds) acoustical reflections are likely to be heard by the human ear-brain system as being part of the original sound. Sensing early acoustical reflections from the playback room as part of the original sound results in the perception of the recorded sound as coming from a wider and larger source—albeit one less well-differentiated in space and time—than was the case in real life. To paraphrase famous opera critic Josef Stalin: muddle, not music.

The purpose of identifying the early acoustical-reflection points is to emplace at those points acoustically absorbent material that can reduce the sound pressure of the acoustical reflections, and therefore reduce their confusing effects. The mirror method is fine as far as it goes, but it has two drawbacks: It works only on side walls (and floor and ceiling, if you want to get picky), and it does not take time functions into account, only angles of reflection.

I am indebted to the savvy folks at Mc Squared Systems Design Group, one of the pre-eminent firms in architectural acoustical consulting, for the idea of using a long piece of string to provide a three-dimensional time-delay spectrometry measurement. (Mc's website is extremely informative; I urge you to visit it.)

Take a piece of string about 15' longer than the distance from one loudspeaker to your listening position. Tie a knot about 2" from one end to serve as an anchor, and tape that end to the loudspeaker with tape that won't leave a residue. (In deciding where to place the tape, err on the side of not harming the loudspeaker.) The top surface of a stand-mounted or floorstanding speaker should be close enough.

Run the string out to the listening position, hold it taut against a seated listener's ear or nose for measurement, and mark that point by tying a knot that won't come out, or by making a mark with a marking pen. Then, measure off an additional 132" (11', or 3.38m) and tie a knot at that point. Tape that knot to the listening position, or to someone willing to humor you a lot. (You should show your appreciation more, you know!)

You now have a string that is fixed at the acoustical "send" and "receive" points and has 11' of slack—and 11' just happens to be the distance sound travels during the 10ms arrival window for early acoustical reflections. Holding the string taut while moving it around everywhere it can go—including behind the speakers and behind the listening position—will map a three-dimensional ellipsoidal solid, the surface of which is the boundary for early-reflection propagation. What is particularly nifty about this method is that it can indicate whether the front or rear walls are contributing stronger early reflections than the side walls.

Take some removable self-adhesive note papers and place them on the side wall nearest the speaker the string is taped to, outlining the area the string hits—the more slack, the earlier the reflection. Do the same for the front and back walls and, if you can, the ceiling. Then switch the string to the other speaker and repeat the process. You now have an experimentally derived depiction of which room boundary surfaces are contributing the early reflections that are muddying things up.

This no-cost fix is to get the loudspeaker positions and the listening position all far enough away from room boundary surfaces that a reflected soundwave's forth-and-back trip is at least 11' longer than the direct acoustical path from loudspeaker to listener. That may not be possible. Even if it is possible, it's likely to result in less room-boundary bass reinforcement, which could present a problem for some speakers with limited bass.

If the no-cost fix doesn't work, the least-cost fix is to go to a fabric store and buy a polyfill quilt filler large enough to cover the problem areas, and a fabric remnant you can live with that fits. You can hire someone to sew up single-faced bordered or quilted panels, or do it yourself with iron-on binding tape. (Single guys: You could do a lot worse on a Friday night than go to a fabric store and look helpless.) You can hang the panels using hook-and-loop fasteners or Bulldog clips, depending on panel size and weight. (You might even happen upon a closeout sale of a quilt or comforter that will end up costing less than doing it yourself.)

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