A Story of Look-Alikes
If you have looked carefully enough at the two cassettes pictured above (and shown in color on our cover), you will see that the packages are not identical-not quite. One is a TDK product, the other is from KDK, a new competitor in the tape market. It seems obvious that KDK has taken great pains to make the visual resemblance between its product and that of TDK very close-a move that we find confusing, if not downright deceptive.
Beyond superficial features the resemblance is not great at all. The TDK cassette shell is the more rigid of the two by a good margin. The TDK's tape is visibly duller, suggesting poor surface polish, less intimate tape-to-head contact, and poor dropout count. When we dubbed sections of a disc onto both cassettes, the TDK (which, be it noted, is not one of its premium formulations) gave an audibly greater output and a cleaner, brighter top end. Also, when unrecorded sections of each tape were played back, the KDK produced significantly more low-frequency noise.
At first glance, then, the look-alike is no match for the TDK. We'll have more on the subject of cassette construction in our tape issue next month.
A Full-Range Heil at Last
ESS, Inc., of Sacramento, California, has introduced the Transar/ATD (Air Transformation Device), a new loud speaker system in which the now familiar Heil Air Motion Transformer is mated with a Heil low-frequency driver. The driver, developed after three years of research by both ESS and Dr. Heil, is significantly different from conventional designs and operates on principles similar to those of the Air Motion Transformer.
The new transducer consists of five vertically stacked Lexan diaphragms interconnected by sets of four carbon-fiber drive rods, with a final set of rods connected to a driving coil at one end of the array. The driving force is thus distributed over the surface of each diaphragm in a manner intended to eliminate breakup and resonances. Carbon fiber is the stiffest known material and has a very high sound-propagation velocity, so all of the diaphragms are driven in phase. Due to the way in which the diaphragms interact with the static sections of the system, air is squeezed rather than pushed, and the vertical stacking contributes to wide dispersion of upper bass frequencies. Like the Air Motion Transformer, the low-frequency transducer operates as a dipole, radiating equally (but in opposite phase) forward and backward.
Since most conventional dynamic drivers have resonances that tend to influence the way in which they respond to a driving signal, conventional amplifiers (using voltage feedback) are designed with very low output impedances in order to damp these resonances. (That is what damping factor is all about.) Lacking such resonances, the Heil low-frequency driver can be "trusted" by its amplifier without such damping. ESS has found, there fore, that the Heil woofer works best with an amplifier that uses current feedback and has a high output impedance (low damping factor). That way the current (which is, after all, what provides the driving force in any dynamic driver) is kept an accurate replica of the input signal regardless of variations in the driver impedance.
We have had the opportunity to hear a Transar/ATD sys tem in prototype and were favorably impressed by it. The sound (like the general dimensions) reminds one of a full-range electrostatic speaker with an extremely large dynamic range. But Transar, which ESS indicates will be fairly expensive, really does not imitate the sound of other systems. As should be expected of a high-quality speaker, it has very little sound other than the music it plays.
FYI: The FYF System
If what you always needed but were afraid to ask for is an other quadriphonic system, FYF Studios of Athens, Georgia, is ready to provide satisfaction. The new system eschews such artifices as surround sound and places all four speakers in front of the listener-two on the floor, two at the ceiling. Tie record producer is thus enabled to "place the sounds of musical instruments in their proper physical location. That is . . . bass drum sounds are heard from near the floor, snare drum sounds from two feet above that, guitar sounds from the right or left, vocals about five feet above the floor, etc.. . ." One subject under investigation is which of the three current systems--CD-4, QS, or SQ--will work best with FYF-system recordings. Single inventory, anyone?
BSO Adds QS
The Boston Symphony Trust has decided once again to record its syndicated programs in the Sansui QS quadriphonic-matrix format as well as in the SQ format. Re-introduction of QS was partly due to subscriber demand, notably that of WFMT in Chicago, which has been receiving QS four-channel tapes for several months. Indications from Sansui are that other prestigious broadcasters are interested in switching to QS, which is widely used in "all-quad" FM to simulate quadriphony with two-channel pro grams as well.
Microphone Cluster "Hears" Four Channels
A new microphone system capable of picking up surround sound or program-plus-ambience from a single location has been developed by the CBS Technology Center. Still in prototype, it contains four pickup elements and a special matrix, and produces an SQ-encoded two-channel output.
The Ghent microphone system, as the new development has been called after the city in which it was conceived, al lows live orchestral broadcasting and recording without the conventional "forest" of microphones and without mixing. It also allows speakers or dramatic performers, miked from a single location, to move about freely.
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(High Fidelity, Jan. 1977)
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