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by Joseph Giovanelli CD-4 Disc Playing Time Q. What are the recent developments concerning CD-4 albums in regard to playing time? It is well known that one of the original drawbacks of discrete discs was the shorter amount of time they would play on each side relative to conventional stereo discs. Recently, however, I purchased some CD-4 albums, which I already owned in the stereo version. The CD-4 versions apparently took up less of the disc side than the stereo counterparts. Is this due to the improvements in the CD-4 process or is bass information being severely compressed? -Walter C. McKinnon, Ft. Worth, Texas A. Any conventional LP disc tends to suffer from distortion when playing the inner grooves, and the nature of this distortion is such that the carrier on CD-4 discs will not reproduce properly if the diameter of the groove is too small. It has, therefore, been the practice, when cutting CD-4 records, to close out the side at a diameter larger than is usually called for with a regular stereo disc. Early on, the way this was done was to cut the CD-4 disc with either reduced bass information (for narrower grooves) or to use shorter material time. However, so much attention has been paid to this problem over the past few years that it is now possible for the CD-4 recording engineers to put the same information onto a disc with larger inner diameter than is standard practice with stereo discs. Judging from your letter, I would say that what you see on your CD-4 discs is a case of the record cutting engineer being as careful as possible to have a large inner diameter, rather than limiting the bass. Eight-Ohm Speaker Wire? Q. While working in my fix-it shop, somebody asked me for "eight-Ohm wire" so he could hook up some speakers to his receiver. I offered him 16-gauge zip cord, saying that it would do the job, but he insisted on "eight-Ohm wire," explaining that television receivers needed 300 Ohm lead-in to interconnect the antenna to the input terminals of the tuner. Does wire actually have an impedance? Is there "eight-Ohm wire?" If so, why doesn't anyone talk about it? Or is TV lead-in only 300 Ohms at TV frequencies as a result of capacitive properties, but not at audio frequencies? -John Shelton, Chagrin Falls, Ohio A. Problems encountered at radio frequencies in terms of requirements of the interconnecting cables between the antenna and the tuner input are quite different from those problems at audio frequencies with speaker connection wire. In radio frequency work, it is essential to have an impedance match between the antenna and the transmission line, as well as between the transmission line and the input of the equipment being fed. When considering the electrical properties of wire, it does not have just d.c. resistance; it also possesses inductance and, in the case of a pair of wires, capacitance. At audio frequencies the inductance and capacitance of speaker wire are of too small a value to be much of a factor in the performance of the system. At radio frequencies, however, these properties, together with the d.c. resistance of the wire, combine to make up an impedance which must be taken into account. Transmitting audio power from an amplifier to a loudspeaker should be done with as little a loss of power as possible. The interconnecting cable, therefore, must have as low a d.c. resistance as possible, and thus you were right in offering a fairly heavy wire, such as 16 gauge.
(Audio magazine, Apr. 1976, JOSEPH GIOVANELLI) Also see: = = = = |
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