I own a Pioneer SG-9500 equalizer and Infinity Monitor Jr. speakers. The Pioneer's frequency response is rated up to 70 kHz and the Infinity’s are rated up to 22 kHz. Am I endangering my speakers if I turn up the highest frequency control on the equalizer?
-Gerald Brown, Willmar, Minn.
There is always some risk to loudspeakers when they are in use, especially if high sound pressure levels are involved. A deep scratch on a record can pop tweeters-even with a fairly modest power amp. Raising the amount of power received by the tweeter for a given listening level (as by use of an equalizer) could make this possibility more likely.
Judicious boost (a dB or two) can probably be used without much danger, but remember that a boost of 3 dB doubles the power in that band. It has been observed, incidentally, that most listeners find an audio system most natural-sounding when the highs beyond 6 to 9 kHz are rolled off at about 3 dB per octave.
Recently I began having difficulty with my Kenwood KR-5340 two-four receiver. When it's in the phono mode, crosstalk is picked up from the AM section. No matter where the tuner is set on the AM band, I pick up a local radio station that broadcasts on 1,400 kHz.
Interference with the magnetic cartridge on my turntable seems rather unlikely since the radio station is at least two miles away. I have the local TV cable attached to the FM antenna terminals through an adapter for the FM broadcast. When I disconnect the FM cable, the crosstalk is noticeably diminished. A local repair shop wants to replace the entire AM section of the receiver. Am I right in feeling that this is a case of using the "shotgun" technique to cure a problem?-Bruce P. Rose, Fort Walton Beach, Fla.
Since the tuning of the AM section does not affect the spurious signal that you receive, and since disconnecting the FM cable ameliorates the problem, we suspect that the AM section is not at fault at all, but that some other section of the system-perhaps the phono leads-is receiving and detecting a very strong local AM signal. (Such interference is not at all ruled out by a two-mile separation from the transmitter.) First, we would suggest that you ask the repairman why he thinks he has made the correct recommendation. Second, try removing the cartridge and replacing it with a shorting plug; if the interference goes away, a new cartridge with less RF sensitivity may be the answer. If it does not, it may pay to experiment with the orientation of the turntable and receiver and to try audio cables with braided (rather than wrapped) shields. Finally, you may want to try shielded speaker leads.
My older records, which were originally played on a less than high fidelity rig, have a curious kind of distortion that increases with modulation level and gets worse near the center of the disc. I have cleaned the records with a Watts Manual Parastat, soap and water, and even a simple felt pad, with no results. Is this kind of distortion commonplace? As best as I can describe it, it's the sonic equivalent of the feel of sandpaper.
-Jim Larsen, Springfield, Mo.
We suspect that the distortion you hear from your older discs is an irremediable result of their having been played with a worn stylus or low-quality pickup in a poor arm. It is possible that a cartridge with a Shibata or similar stylus, which has a larger area of groove contact than spherical or elliptical types, might extract the goodies and leave some of the distortion behind.
Recently I was stationed overseas and am planning to have my stereo shipped over. My turntable pitch control is calibrated for 60 and 50 Hz, but not my Wollensak 4765 tape deck. I suspect that the tapes I recorded in the States with a 60-Hz line frequency will run slow when played using the 50-Hz line frequency used here in Europe, and the tapes I record over here will run fast when I return to the States. Is there any way to "recalibrate" the motor speed?
-Mark L. Strand, APO New York.
A conversion kit (part number 81-01854890-9) for 50-Hz power is available from Wollensak. The swap, however, is a job for a qualified technician.
I have a pair of large Advent speakers driven by an Onkyo 4500 receiver, to which I pro pose to add one or two center speakers. Since I find the sound of the Advents slightly "distant," I am considering small EPI, Bose, Ohm, or KLH speakers, all of which strike me as more "forward," for the center pair. But all of these seem to be more efficient than the Advents and would require some means of controlling their levels if hooked up in parallel with them. I have heard that individual controls can be incorporated into the speaker leads. Can you tell me what these are called and how to use them? Also I have read that a single center speaker is preferable in an arrangement such as this, but I cannot see how to connect just one. Is this true, and if so, how can I make the connection?
-L. J. Korden, Sandusky, Ohio.
The control you want is an L-pad. (Actually, a 100-ohm, 10-watt potentiometer wired in series with the hot lead to the speaker will work about as well.) But quite frankly, we are not overly fond of the idea of controlling speakers by means of pads or resistive net works between the amplifier and the speakers, especially if critical listening is contemplated (and your concern about the "forwardness" of the center pair certainly suggests critical listening). This is because speakers thus controlled are not damped by the amplifier--i.e., they are driven from a source impedance comparable to or higher than their own, which is definitely not what their designer had in mind.
A far better approach would be to purchase a small integrated amp (15 to 20 watts per channel very likely will do), connect the new speakers to that, and plug it into the tape output of the Onkyo. Should you wish to use a single center speaker, you can switch the amp to mono and leave one channel unused. Levels then would be no problem, since the amp has a volume control.
The lights in the room in which my stereo sys tem is set up are controlled by a dimmer switch. Whenever the lights are on, a buzz is transmitted into the unit when it is in the phono or aux mode. Is there some way to shield either the stereo or the dimmer switch to prevent the buzzing?
-John P. Blumberg, Long Beach, Calif.
What you have is radio-frequency interference caused by the switching action of the dimmer circuit. This is best suppressed in side the dimmer itself, so one possibility would be to look for a brand of dimmer with better RF suppression. The buzz may also be coupling to your equipment via the power line, in which case it could be ameliorated by choosing an AC outlet that is not on the same circuit breaker or fuse circuit as the dimmer.
Alternatively, you could listen with the lights off or go back to a regular light switch. Other remedies exist in theory, but they tend to be only spottily effective and require connection of filters directly to the power line. This is ex pensive with properly designed commercial equipment and otherwise risky (perhaps illegal, depending on the local building code).
Living in an apartment, I think it prudent to consider my neighbors. Is there a way of effectively isolating the bass vibrations from my floor-standing speakers and preventing direct transmission to the floor (and my neighbors' ceiling)? Would an extra piece or two of carpeting be effective to any degree? Would special "foot mounts" for use with turntables be of value when used to isolate speakers?
-A. Francis, Downsview, Ont.
Such vibrations can be attenuated but not eliminated entirely. The Audio-Technica Acoustic Insulators are a possibility, as are Acousti-Mount Speaker Pods by Netronics.
You can of course try the extra carpeting first to see if it works.
I just demagnetized the heads on my Teac 450, only to discover that I had forgotten to remove all my precious tapes from the area. I had the tool on one-and-a-half to two minutes and had four tapes in the cassette well on top of the deck. Others were in a closed drawer of a desk on which my equipment sits.
I played several tapes to check the damage and was surprised to hear that even the tapes that were within inches of the demagnetizer sounded no different. Was I lucky or will these tapes eventually develop dropouts or noise? (I only use the best tapes.)
-Christopher Mazzarella, Perry, N.Y.
Kiss your rabbit's foot--you were lucky. The field from a head demagnetizer is easily strong enough to do in tapes. Provided you don't repeat your folly, the tapes should be all right.
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(High Fidelity, Oct. 1977)
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