Transcribed - Part 3
A common radio-phonograph distortion is the echo or poor definition that occurs when weak speaker magnets permit cones to resonate after the signal has stopped. A three-to-five-pound magnet will grip the tone tightly and preserve each tone's separate identity. Lighter magnets simply may not have the strength to damp the "hangover." In poorly designed cabinets echoes are created when sound bounces off front panels and reverberates behind the cone. These echoes can be damped by lining the chamber with sound-absorbing material or by using similar material to seal off the space behind the cone. A solidly built cabinet will forestall vibrations and resonance with the speaker.
The phonograph's headaches
The phonograph, like the radio, faces its own problems in the realm of fidelity. In making records, the microphone imparts its shivers to a needle that cuts them into a revolving disk. Though the process is mechanical, the fine equipment used manages to avoid creating noise. But this does not hold true for the playback. Home phonographs rarely compare in precision with professional studio equipment. The needle vibrates. So does the turntable. In addition other vibrations are created by the needle's movement across the disk's surface. ( The filler content of ordinary records acts as an abrasive to shape the steel needle point to fit the grooves: it is also responsible for considerable noise. New Vinylite disks, being abrasive-free, are quieter but require lightweight pickups to avoid excessive wear. ) These frequencies are non-musical and, when caught by the pickup, manifest themselves as noise. Most noise vibrations occur in the region above 5,000 cycles. For broadcast purposes, records and transcriptions with ceilings that go as high as 12,000 cycles are made. For the retail trade, however, recording engineers usually cut off all the frequencies above 8,000, feeling that above this level their cutting equipment will add its bit and make the total amount of noise intolerable.
The less expensive phonographs, however, do not approach even this restricted level. Furthermore their greater rattle and scratch mean more noise over a wider range. To eliminate as much of it as possible, pickups like Zenith's highly touted Cobra Arm achieve freedom from noise by ignoring frequencies higher than 4,000 to 5,000 cycles. In doing so, they beg the question of high fidelity. Where speakers with ranges above 5,000 cycles are available, only extremely light, jewel-pointed pickups will go to 10,000 or 12,000 cycles, and they alone will do the speakers — and fine records — justice.
Generally pickups fall into four classes. In each, the mechanical vibrations developed by the needle in tracking create or vary a current. In one they generate current by wiggling a crystal; in another the needle moves a coil or a bit of iron in a magnetic field; in a third the needle twists and untwists a wire, changing its resistance; in the fourth, the electronic type, the needle modulates amplifier tube current by more or less direct contact. Though pickups vary greatly in performance — depending on their weight on the record, on how closely they follow the groove, and on their sensitivity to a wide frequency range — the type, in and of itself, makes little difference.
Trying to improve quality, recording engineers sometimes purposely introduce distortions of their own. They compensate for the tendency of cheap speakers to exaggerate or understate bass and treble tones. But records so made, when played through superior speakers, are a nuisance: the lows are weak, the highs are shrill, and tone controls must be adjusted differently for every side that is played. Another kind of deliberate distortion, called pre-emphasis, is wholly beneficial — in fact, it can raise the effective record ceiling by several thousand cycles. Pre-emphasis goes beyond mere compensation. High-frequency tones are recorded at exaggerated loudness. In playback, or de-emphasizing, the highs are brought back to normal volume relationship, and surface noise is eliminated with the volume cut out in de-emphasizing. Because de-emphasizing units would add appreciably to the cost of the radio-phonograph, pre-emphasized records are used almost entirely for broadcasting.
Even with the best equipment, absolute or perfect fidelity obviously can never be reached. Perfect fidelity would mean that the radio-phonograph transported the listener to a point near the actual sound source — say, eighth row center Carnegie Hall. Even assuming that transmitter, receiver, and speaker functioned to perfection, the volume of the live orchestra would not be necessary in the home. Nor could any living room handle it acoustically. To approach absolute fidelity you may have to redecorate your home a little, removing unwanted resonance and providing a proper acoustical setting for the speaker. But the point is that absolute fidelity is by no means necessary for superb musical reproduction and its consequent pleasures. High fidelity — say the delivery of 8,000 to 10,000 cycles without any of the avoidable distortions — provides reproduction of breathtaking clarity and richness. Yet there are those, including many devout musicophiles, who do not want it. Before the buyer looks over the new radio-phonograph combinations he should hear the arguments on both sides.
Golden ears
Thomas R. Kennedy Jr. of New York is a radio engineer whose avocation is fine music well performed. A "golden ear" of the richest sheen, he is one of that small band who have dedicated a good part of their lives to extending the range of reproduced sounds to the limits of human hearing. Merely reproducing the highs and lows to which most prewar instruments are deaf will not satisfy Tom Kennedy or any other golden ear. A purest, he insists that the tones be noise-free and undistorted, sharp, clear, and full from treble to bass. The only damper his enthusiasm seems to know — so far not very effective — is the fact that when fidelity even approaches the degree achieved in his laboratory, the cost graph rises like a helicopter.
Kennedy has gone to fantastic lengths. His receiver is well designed and, of course, has an FM circuit. His main amplifier was built at the Bell Telephone Laboratories. His speaker has three units. To forestall phonograph vibration, the motor is mounted separately, while a dental-machine belt carries the rotary motion to a turntable anchored in 600 pounds of sand. The pickup arm sports a feather-light sapphire needle, kept at even temperature and humidity in an airtight container until just before it is used. Kennedy makes his own superior recordings of broadcast music. As a result, his parlor concerts are unsurpassed for fidelity. He has been accused of making a fetish of it, of listening to tone rather than to music. "Listen!" he says. "Compare music from my equipment with what the average combination gives. You'll go home and throw rocks at your set."
Tin ears
On the other side of the argument are many radio-phonograph manufacturers, whose standards of fidelity are years behind practicable levels. They are known as "tin ears" in high-fidelity circles. Their position is understandable enough — if not exactly admirable. They have heavy investments in plants, patents, and franchises. High fidelity threatens the value of many of these commitments. Cagily, they have moved out of the defensive position with an attack on what they term "unreasonable" high fidelity. Their thesis is simple: the public neither wants nor likes wide-range reception or wide-range instruments.
They will admit that in a concert hall most listeners enjoy the wide range. But, they add, there is a reason. The "live" orchestra, spread across the stage, is a diffuse sound source. The listener has a chance to use his ears as a kind of quality control, turning them toward pleasant sounds and away from the raucous. In the parlor, while the listener may not be aware of it, the situation is different. Here the source is concentrated in the loudspeaker, and no amount of twisting will avoid unpleasant tones. The tin ears make much of this fact, pointing out that extreme highs and lows can inflict positive pain on sensitive auditory nerves. Indeed, they go so far as to claim that, by restricting the ranges the transmitter and receiver are capable of handling, they are actually doing the listening public a favor.
The tin-ear documentation is extensive. In one test, ( Tonal-Range and Sound-Intensity Preferences of Broadcast Listeners, by Howard A. Chinn and Philip Eisenberg of the Columbia Broadcasting System ), audiences chose standard broadcasts ( up to 5,000 cycles ) over wide-range programs ( up to 10,000 ) by more than two to one. Broken down, the figures are even more plausible. Owners of FM sets, presumably with highly developed tastes, rejected the wider ranges by more than four to one. Professional musicians, surprisingly, voted fifteen to one against wide ranges and thus, apparently, against high fidelity.