Enough Room? Page 2

And what about that ever-popular ceiling tile? Its absorption characteristics are actually quite similar to carpeting (with rather significant variations from type to type). But the closer the damping material is to the loudspeakers, generally, the better, and the floor is usually closer than the ceiling. Use of both tile and carpeting is most certainly overkill. The reason you see the combination so often in audio shops has less to do with acoustics than with the fact that it is a relatively cheap way to "drop" a too-high commercial ceiling, easily hiding pipes, ducts, and wiring while still permitting easy access to them for servicing. (I wonder if some manufacturers---operating in a similarly adapted commercial environment---might not be using both carpeting and tile in their listening rooms and thereby designing and marketing loudspeakers which sound overbright in a typical domestic situation.) Incidentally, the sprayed-on "acoustic ceiling" popular in lower-cost, modern home construction is another matter entirely. I have never seen any sound absorption curves for this treatment, and suspect it is more cosmetic than acoustic.

With regard to sloped or cathedral ceilings, they are both good and bad: good in that they spread out the room modes or standing waves due to at least two opposing surfaces (RH, a strong advocate of them, built one into his dedicated listening room); bad in that they make room modes and their effects less predictable. I suspect (though I have never seen a discussion of this elsewhere) that the lack of floor-to-ceiling modes in an otherwise well- dimensioned room might make the modes due to the other walls subjectively more prominent.

I do recommend avoiding cathedral ceilings which rise to a peak in the center of the room; they tend to focus the sound in a fashion which might cause problems. A one-way slope is likely to be better. JGH has cautioned about setting up loudspeakers in such a room in a manner which places one loudspeaker under the low end of the ceiling and the other under the high; his concern seems intuitively reasonable (symmetry again). In practice, however, RH (whose sloped ceiling is one-way) uses such an arrangement with no complaint about imaging or other soundstaging problems. As an aside, I should point out that JGH has recommended strategically placed damping material on the surfaces of a cathedral ceiling to help kill the troublesome reflections. He prefers a "deader" room than I do; my only reservations about such an approach involve possible overdamping of a room which probably already has wall-to-wall carpeting. (See again my caution about carpeting combined with acoustic tile.)

Perhaps some type of diffusors on the ceiling might work better than absorption, though they would be difficult to incorporate, physically. As to the symmetry of the front and rear walls, there are many proponents of various arrangements. Most (but not all) seem to agree that the wall behind the listener be reflective with good dispersive properties, but there is disagreement about whether the area behind the loudspeakers should be the same, or heavily absorptive. The most extreme example of the latter is the live-end, dead-end room, in which the walls, floors, and ceilings around the loudspeakers and extending out slightly in front of them are completely covered in thick acoustical foam or other similar material in an effort to soak up all random reflections from the area. Its advocates---mainly from the professional arena---are vocal (footnote 2). One thing is certain: the domestic acceptability of such an arrangement is severely limited. Domestic acceptability remains a central problem with all radical room-treatment schemes.

In general, then, the setup of a good listening room should aim for a reasonable distribution of dispersion and absorption, keeping in mind the requirements of symmetry. An additional point I haven't mentioned is the desirability of absorptive surfaces on the sidewalls just in front of the loudspeaker locations (to minimize close sidewall reflections). Some experts also recommend a similar treatment of the ceiling just in front of the loudspeakers, and while this might be more difficult to manage, it could prove useful, especially with the low ceilings common in modern construction.

While the above discussion applies to just about all listening rooms, if your room is a small one you are best advised to approach with caution loudspeakers having a strong low-frequency output. The Spica Angelus, for example, has a somewhat lightweight, though tight, low end; it does not usually overload a small room. ST, who raved about the Spicas, has a rather small, squarish listening room, which was apparently quite compatible with the Angeli. But generalizing about acoustics can be risky. GL recently fell in love with the Mirage M-3s; they put out a lot of bottom-end energy, and his listening room, though rectangular, is small. Regardless of that, the Mirages seem to work for him.

Anyone desiring to get the most out of their environment should have patience and a willingness to experiment---within the bounds of domestic tranquility. Experiment with both the positioning of room furnishings in the room and the setup of the loudspeakers. Try long-wall and short-wall placement. There is no loudspeaker, be it Class A, B, C, D, or X, which will not profit significantly from proper placement in a good room. The majority of loudspeakers, in our experience, work best when well clear of side and rear walls on good stands (unless they are designed to be floor-standing), though there are exceptions. The more flexibility you have in being able to experiment with loudspeaker placement---2-3' away from the side and rear walls at least, except for those loudspeakers specifically designed to be used closer to the wall---the better chance you'll get the loudspeaker to sound its best. That does not mean that you will need to have this clearance with every loudspeaker. It means, however, that for the majority of loudspeakers, placing them away from the walls might make the difference between rather ordinary sound and a system which "sings." (Incidentally, RL, who uses the next-to-most recent version of the Vandersteen 2Ci, reports that in his modestly sized room he gets good results---if perhaps with just a touch too much bass---by positioning them about a foot from the rear wall.)

Footnote 2: See Brian Cheney's "Dispatches from the Front" article in Vol.14 No.9, September 1991.
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