Audioclinic (Feb. 1981)

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Channel Separation of Phono Cartridges

Q. Because 1 have been a professional musician for 25 years, I am sensitive to acoustic properties. Hence, I find it necessary to periodically up grade my music system.

Upgrading a system can be a series of pleasurable experiences. The limiting factor in this upgrading process, however, seems to be the relatively low channel separation in phonograph cartridges.--George Edmond, Jr., Montclair, N.J.

A. I do not think that you should be overly concerned with stereo channel separation in phonograph cartridges, or in other components for that matter. It has been proven that most listeners cannot detect any improvement in stereo imaging with channel separations greater than 12 dB. Certainly 20 to 30 dB of channel separation should not cause any degradation of stereo imaging to even the most discerning listener.

Inasmuch as you are a musician, I am sure you have noticed that sounds which are heard by one ear are, to some extent, heard by the other one.

The musicians in a combo or band are just too close to one another to have it any other way.

You can see from this simple example that channel separation in a live situation is not great; even so, the stereo effect is present, enhancing your enjoyment while you are playing.

The rather close spacing between our ears is yet another example of the fact that channel separation is not as important as one might think.

Further Notes on Multiple Speaker Systems

Q. I have had trouble obtaining multi-strand wire larger than 16-gauge, needed because I have 60 to 70 foot cable runs. Is single-strand wire just as good? Is this a case where very high amplifier damping could be a help? Aside from damping, is there any loss of speaker quality by connecting speakers in series?

-James Smith, West Palm Beach, Fla.

A. Single-strand wire will work just as well as the multi-strand wire will. It is, however, more difficult to handle--especially when attempting to connect it directly to the amplifier or to the loudspeaker terminals. It may be necessary, therefore, to splice a short length of multi-strand wire to this single, main cable. Because this stranded wire is only a short length, 16-gauge wire may be used with no degradation in performance.

Many electrical stores will sell No. 14 gauge stranded wire in the form of zip cord. It is often possible to connect such wire directly to the terminals of loudspeakers and amplifiers. If even heavier gauge wire is required, No. 12 or even No. 16 gauge solid wire can be used. As has been said, however, a short length of cable must be added to this so that the cable can be success fully connected to the terminals of the equipment.

High amounts of amplifier damping will be of little help in situations of the kind we are discussing. The d.c. resistance of the interconnecting cable, the voice-coils of the individual speakers, and of the crossover inductors will be so high as to prevent the damping in the power amplifier from having very much effect.

The decreased damping created by the hookup of loudspeakers in series can, with some loudspeaker systems, produce bass which is not "tight." In addition, the speaker cones can make very wide excursions in the presence of turntable rumble or acoustic feed back. It may be best, therefore, to use a subsonic filter when using series-connected loudspeakers.

Other than those sonic changes from reduced damping, there should be no other audible effects because of the series-parallel speaker connections we have discussed.

Equalizers and Tone Controls

Q. When an equalizer is connected to a receiver, do the tone controls on the receiver still operate?

- John Kogler, New York, N.Y.

A. We generally interpose an equalizer between the tape out jacks and the tape monitor jacks. Therefore, just as the tone control still operates when a tape machine is wired into these jacks, it also works when an equalizer is used. An amplifier does not have any way of knowing whether its pro gram source is being supplied by an equalizer, dynamic range expander, or tape machine. Therefore, all controls will operate normally regardless of what is connected to their tape monitor circuits.

Explain Your Principles, Mr. Speaker

Q. I'm interested in an explanation of how the different types of loudspeakers function: Cone speakers, panels, electrostatics and dome and horn–types.

-Carl Joachim, Brooklyn, N.Y.

A. Most speakers, whether dome, panel or cone, work in the same way, employing a voice-coil which is fed by a program source and positioned in a magnetic field. The coil is alternately attracted or repelled by this magnetic field depending on the instantaneous polarity of the voltage of the program source. The amplitude of that voltage will determine the amount of attraction or repulsion. Because this voice-coil is attached to some kind of diaphragm, dome-shaped, cone-shaped or just a flat panel, the diaphragm must move because it is driven by the moving voice-coil. The moving diaphragm is in contact with the surrounding air, causing it, in turn, to move--thereby generating sound waves.

When ceramic material is flexed, a voltage appears across its two faces.

This principle serves as the basis for the well-known ceramic phonograph pickup and for ceramic microphones.

When a voltage is impressed across the two faces of a ceramic element, the element flexes. If this flexing element is attached to a diaphragm, the result is a speaker or perhaps a head phone. Speakers operating with this principle have been used mainly as tweeter elements, especially in equipment used by musicians for live performances. The flexing of ceramic material in the presence of voltage is known as the piezoelectric effect.

The principles upon which electro static speakers operate are based on phenomena which we notice almost daily but think little about. To illustrate: Run a comb through your hair on a cold, dry day. The comb can take on an electrical charge which will en able it to attract small pieces of paper and the like. This same idea is the basis of operation of electrostatic speakers.

The "comb" on an electrostatic speaker is actually a plate with holes in it.

High voltage is impressed on this plate, which serves to attract a very thin, light diaphragm. This high volt age, however, is designed so that it will vary in accordance with the signal feeding the device. This means that the attraction of the diaphragm will vary, enabling the diaphragm to be pulled toward or away from the plate.

This is an oversimplification of the principle. Actually, there are two charged plates, with the diaphragm suspended between them. The design of the system is such that the plates are alternately charged, but in such a manner that one plate tends to repel the diaphragm while the other one at tracts it. When the polarity of the volt age reverses, the plate which once attracted the diaphragm now repels it, and the plate which once repelled the diaphragm now attracts it. This balanced approach makes for symmetrical behavior of the system.

The horn system consists of a driver coupled into the narrow opening of a horn. (This driver is generally a conventional, cone-type loudspeaker.) The horn serves as a means of coupling the cone motion to the surrounding air in a more efficient manner. The horn does not contain any electrical components.

(Source: Audio magazine, Feb. 1981; Joseph Giovanelli )

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