Audioclinic (Q and A) (May 1970)

Power Line Considerations

Q. I am a foreign student. I am about to buy an FM stereo receiver. Because the household power in my country is 220 volts, 50 Hz, I would like to know if the use of a step-down transformer will in any way affect the performance of the receiver.

Is it O.K. to use the same step-down transformer to power the receiver and the turntable? Going a bit further, is it O.K. to use the same transformer to power my audio equipment and my household appliances? In other words, is it O.K. to use one big transformer for all my needs or is it better to use several smaller ones?

-E. de Weerth, Albany, Cal.

A. There is no reason why you cannot use a step-down transformer to obtain the voltage and current required to operate your equipment. Further, all devices you plan to use can operate from this same transformer. However, when doing this, the physical size of the transformer becomes quite large. Remember that the transformer must be capable of handling the total power used by all the devices which you plan to drive with this unit. For instance, household appliances, such as refrigerators and irons, consume quite a bit of power.

You must remember one more item. The receiver is designed for 117-volt operation, but at a frequency of 60 Hz. It will operate at 50 Hz, but the power transformer will become warmer than when operated at 60 Hz. Therefore, you need to be certain that the power transformer can withstand this added heat.

Phonograph and tape recorder motors are something else again. Their speed is not determined by the voltage applied to them, but is determined by the frequency of the power source. Hence, a motor designed for 60-Hz operation will run slower when supplied with 50-Hz energy than it will when it is operated at its design frequency of 60 Hz. Therefore, you will need either a new motor or you will need some kind of pulley adaptors which will result in correct operation of the equipment. Many tape recorders and phonographs are so arranged that they can accommodate such pulleys.

Hence, you see that there is no problem about the use of the step-down transformer. Whether you use one large one or several smaller transformers will be a matter of what you can obtain rather than other considerations. Remember that motors which must operate at precise speeds will have to be modified in order to compensate for the frequency difference between 60 and 50 Hz.

Electrostatic Speakers

Q. I am considering the purchase of a full-range electrostatic speaker. I am most anxious to have the following questions answered.

1. Do electrostatic speakers "wear out?"

2. Does weather affect the operation of these speakers or cause deterioration of them?

3. Do the high-voltage transformers used with these speakers fail?

4. Do these speakers require any type of maintenance?

5. Any other information regarding electrostatic speakers.

-Don R. Parman, La Canada, Cal.

A.

1. Any speaker can fail after a period of operation. Electrostatic speakers are quite delicate. If they are fed with too much power, there is danger that the diaphragm will come into contact with the outside screens. This will result in an arc which will ruin the diaphragm. Also, if the diaphragm material was not pre stretched, it could gradually sag and be attracted toward the screens and thus be ruined by arcing. However, I have heard from people who own these speakers that they just continue to operate very well over the years.

2. I have heard of a few instances where high humidity has caused some arcing and unexplained sounds emanating from the speakers. However, this does not appear to be a common problem.

3. I have never heard of these speakers failing because of high-voltage-transformer breakdown.

4. There is nothing that the owner of an electrostatic speaker can do in the way of preventive maintenance. It is unlikely that you can make the necessary repairs in the event of a failure any more than you can make such repairs with a conventional speaker.

5. The one drawback which I have noticed about electrostatic speakers is that they cannot handle large sound levels. You might have to add an additional speaker to each channel to get the kind of volume that you want. If you are not interested in really loud sound, you have no problem at all. If the sound was loud enough for you, when you heard the electrostatic speakers for the first time, you should be able to buy them with assurance that you will enjoy them.

I would imagine that if you heard these speakers in the typical dealer's showroom, that this room is larger than your living room. Thus, if the sound was sufficiently loud for you under these conditions, you should be happy with them in your smaller living room.

Stereo Cassette Player Problem

Q. I installed a stereo cassette player in my car which requires 3.2-ohm speakers. My problem arises, I think, from the two 8-ohm speakers that I mounted in the car doors. I was getting some distortion with this arrangement. High-pitched instruments sound unclear. An alto sax, for instance, sounded as if it needed to "clear its throat." Incidentally, the same tapes played on a home cassette unit sound fine.

I tried to compensate for this mismatch by adding a set of 8-ohm, four-inch speakers in parallel with the original set. These were mounted in the kick-panels. I believe this has eliminated the distortion. Now the sound is so shrill that with some recordings it is almost unbearable, even with the treble completely attenuated by the tone control.

Should an upward mismatch of 3.2 to 8 ohms produce distortion? What would you suggest as a remedy other than the obvious substitution of a pair of 3.2-ohm speakers for the original 8-ohm units?

-David H. Sexton, M.D., Knoxville, Tennessee

A. Possibly you are now getting the shrill sound because the two additional speakers are more efficient than the original 8-ohm speakers you were using. Because these speakers are smaller, they will reproduce treble frequencies more efficiently than the original speakers. This would result in the shrillness. I am guessing, of course, that the original speakers are physically larger than those you added more recently. Otherwise it just might be that the added speakers are just "brighter" and more efficient all around than the original ones.

With the 8-ohm speakers running by themselves, it is likely that the amplifier simply cannot supply sufficient power to fill the car without producing distortion.

Naturally, the mismatch of impedances results in somewhat less power being transferred to the speakers than would otherwise be the case. Further, if these speakers are relatively inefficient, this would add to your troubles. The obvious cure for the problem is to use speakers having the proper impedance, obtaining units which are as efficient as you can find. The only other solution is to use larger, more efficient 8-ohm speakers than you added. This will give you more overall sound in the car and might in the end provide better sound than could have been produced merely by changing your original speakers to 3.2-ohm units. I realize that adding larger speakers is not always easy because of the limitations imposed on you by the physical layout of the automobile.

If it should happen that one set of speakers is more efficient than the other, as is apparently the fact now, you should consider using a T-pad at the more efficient speakers so as to equalize the volume between the speaker sets. Ideally you should use the same kind of speakers that you now are using as the original. At least this will eliminate all problems arising from differing efficiencies.

(Audio magazine, May 1970)

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