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by Robert Long Unfettered FM I own four FM receivers, three from Europe and one from the U.S. The Europe an receivers-and European FM trans missions-have a frequency response and dynamic range that are immediately identifiable as superior to what's available here. Is there something about FCC regulations that limits the quality of U.S. broadcasting? -J.R. Frame, Cecilia, Ky. No. I suspect that what you are perceiving is an unfortunate by-product of the largely commercial nature of U.S. broadcasting. FM stations in Europe are mostly noncommercial government operations, designed to deliver a network signal to a relatively small area. The "reach" of the individual transmitters is generally less important (be cause there are so many of them carrying the same programming) than the quality of the signal being transmitted. In the U.S., the number of listeners that can be corralled into listening is important for both commercial stations (to attract sponsors) and publicly supported ones (to attract donors). Thus broad dynamic range becomes intolerable, because it allows the quietest passages to drop "into the mud" and alienate listeners who can't get really quiet reception. This puts a premium on the use of various signal processing equipment to "grab" listeners-even if that means compressing (and compromising) the sound. There are very few stations with the guts to forego such devices and the greater listenership they generate. The FCC has contributed to this dilemma by choosing a noisier stereo broadcast method than it might have. But in the competitive world of FM-commercial and otherwise--"punch" out pulls quality. ---------- Help! I wonder whether readers can help me find those large white plastic clips that the 3M Company used to make to hold in place the ends of open-reel tapes? The smaller red and orange ones I find now don't seem to do the job, and I have a collection of more than 100 tapes that I want to keep in first-rate condition. -Sid Rosen, Toronto, Ont., Canada. Frankly, I prefer those little "bricks" of sponge rubber (at least that's what it feels like) that Memorex used on its short-lived open-reel tape line. You could make some thing like that for yourself, cutting a springy sponge material (its actual composition is immaterial, as long as it has good resiliency and grip) a little thicker than the distance between the insides of the reel flanges, so the block will wedge in place. Maybe some of our readers have even better suggestions. ---------------- Sound in Space I've been advised that some speakers should be better suited to creating the Carver holographic image than others, but several of the recommended models sound "boxy" to me. I have heard the Dahlquist DQ-10s with a Dahlquist subwoofer. The effect with the Carver device is quite pleasant, but a dealer tells me the Dahlquist/Carver combination is redundant. Who's right? -Ken Lausa, Lima, Ohio. You are: Ultimately it is a question of your own aural judgments--whatever I or your dealer may say. For holography, it's theoretically desirable to have all drivers in a speaker system aligned vertically, whereas the DQ-10 design takes care to align them in the same acoustic plane, but not necessarily in a vertical line. The Carver holographic effect and the coplanar drivers of the DQ-10s are not identical in intent, however, and therefore not redundant. Dahlquist seeks to prevent what has been called "time smear" in reproducing whatever signal is fed to the speakers that is, to keep the signals from the various drives in step with each other-and to reduce diffraction. The Carver device's compensatory circuits correct for acoustic anomalies that occur once the signals are sent out into the room, which are caused by room interactions and by the geometric relationships between a pair of speakers and a pair of listening ears. -------------- A Thin Line I recently came across a TDK D C-180 tape. The tape looked extremely thin and hardly capable of high-quality reproduction. What are your opinions on it? -S. Docie, Trenton, N.J. TDK's D (for Dynamic) formulation is its least expensive, but is capable of very good results in appropriate recorders-at least with the C-90 and shorter lengths recommended for music. I've even used C-120s with good results, though I don't know a single cassette-deck manufacturer who's willing to recommend the length-in any brand. The C-180, however, is another story--as TDK itself is the first to admit. With such thin backing, mechanical strength is reduced and print-through increased. And the magnetic coating also is much thinner, even by comparison to C-120s. The result is poorer performance, particularly in the bass. TDK evidently makes C-180s expressly for users to whom maximum possible recording time is an overriding necessity--for speeches, for example-but the company doesn't recommend them for music. Nor would I. ------------- Proportions I am considering modifying a garage measuring 24 by 18 feet for use as a stereo listening room. Can you recommend physical changes so the room will pro vide the best possible acoustical environment? -Linda E. Bailey, Dothan, Ala. Perhaps. First, these proportions sound worrisome. When the distances between parallel walls have a common denominator (in your case, six feet) standing waves will be created at common frequencies. Many acousticians try to avoid parallel walls altogether when planning a listening environment. But it's obvious that, without major and very expensive alterations, you're stuck with the current dimensions of your space. What you can control more readily is the relative "liveness" (reflectiveness) or "deadness" (absorptivity) of the materials on and between the walls. It's fundamental that live and dead materials should be intermixed to break up the sound. A growing number of designers favor making the area behind the speakers as dead as possible and the listening end of the room relatively live. (A really dead wall will also prevent serious standing waves, even if a live wall is parallel to it.) This is a very complex subject, however, and if you need detailed help you should seek out a builder or other professional with practical experience in creating home listening environments. ----------- We regret that the volume of reader mail is too great for us to answer all questions individually. Also see: |