Audio Q&A by Ian G. Masters (Jan. 1994)

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Collapsing Surround

Q. When I watch VHS movies recorded in surround sound, the multichannel audio collapses to the center speaker just for a moment, perhaps ten or fifteen times during a movie. All other sources work perfectly. is my problem inherent in the VHS Hi-Fi system?

A. It’s not inherent in the VHS format, but it does sound as though you have a problem with your VCR. hi-fi videocassettes al ways have the sound duplicated on a conventional linear track so that they can be played on older machines, and this second track is usually mono. Most hi-fi machines automatically switch to the linear track if the hi-fi sound is interrupted (or if it’s missing altogether), and that’s what appears to be going on in your case. Your VCR is losing its “lock” on the hi-fi sound every so often and reverting to the linear soundtrack, which, being mono, is reproduced only by the center channel. The problem may be dirt on the heads or slight mistracking; in either case you can correct things easily. Or it might indicate a wiring fault in your VCR, which will need professional attention. Or, if the problem occurs mainly on tapes you have rented, it may be caused by dropouts in the tape surface.

Equalizer Pay-Off

Q. I bought a graphic equalizer with a built-in spectrum analyzer, and I have no idea how to use it. The instructions say that the supplied condenser microphone and “pink noise” can be used to compensate for something, but I’m not sure what. How can I use this equipment to make my system perform better?

A. In the words of Earl Butz, if it ain’t broke, don’t fix it. Unless you know there is definitely something amiss with either your mom or your equipment, trying to “improve” matters by equalization will probably only make things worse. There are conditions that equalization can help tame, however: resonances or standing waves resulting from the shape or dimensions of the listening room, for instance, or anomalies in the response curve of your speakers.

In such cases, and provided you use it with a light touch, equipment like yours can be ideal:

The pink-noise generator produces a signal with equal energy in each octave of the audio spectrum, the microphone (placed at the main listening position) detects the signal as modified by your equipment and room, and the spectrum analyzer displays it in narrow frequency bands that correspond to the equalizer’s controls. Any peaks or dips can then be corrected by nudging the controls up or down. Be aware, however, that most adjust will be valid only for one listening position, and that if you have to make anything but subtle alterations to the system’s response, a more fundamental fix is probably necessary. And response measured by this means should usually roll off somewhat at high frequencies rather than be perfectly flat.

Cable Duty

Q. Although my new speakers sound fine, I was told that if I were to redo the internal wiring using heavy-duty specialty speaker cable I would achieve much better sound. Is that true? Do you recommend it?

A. Heavy cables are definitely advisable for long runs of wire, but you probably wouldn’t use more than a couple of feet inside a speaker. For that sort of length, the benefit would be negligible. Taking your speaker enclosure apart to make the modification, on the other hand, might do it irreparable damage, and you would certainly hear that.

Multiple Drivers

Q. I have difficulty understanding how a speaker with only two drivers can play as loud and as well as another with four or five drivers. Doesn’t the simple matter of the in creased radiating area of the multiple-transducer speaker make for a more dynamic output?

A. Yes, all else being equal, but no one speaker configuration has a lock on any particular aspect of audio performance.

Multiway systems do usually have better power handling, which means that they can either play louder or play at moderate volumes with lower distortion. But if the drivers in, say, a two-way system use extra-heavy magnets and are built for long voice-coil and cone, excursion, they can often equal the performance of speakers with more drivers. And the fewer the drivers, the fewer the transitions from one to the next and the simpler the crossover network. That makes it much easier to get smooth response and a reasonably uniform radiation pattern.

Road Noise

Q. My new car stereo speaker system consists of a pair of two-ways in the doors, two 6 x 9-inch speakers in the rear, and two 10-inch subwoofers. The speakers are all amplified separately. Would it be wise to add a noise-reducing component as well in order to eliminate sounds from the road?

A. Road noise can be a problem if the music you listen to contains a lot of low-level material, which might easily be over whelmed. Given the sort of system you have, however, I don’t think you spend a lot of time in the pianissimo zone, in which case ambient noise reduction is probably unnecessary.

Three Heads vs. Two

Q. I am considering buying a new cassette deck and am interested in a three-head system, which as I understand it makes better recordings than a two-head model. Is this actually true? And two of the models I have considered have total harmonic distortion specs of 1.5 and 0.8 percent, respectively. Is that a sign difference?

A. Three-head decks have a couple of advantages. One is that the record and playback heads, being separate, can each be optimized to its function—the criteria are quite different. Also, three-head machines let you monitor off the tape as you record, alerting you immediately to any problems. That’s not to suggest that there are no excellent two-head decks available—there are—but most people who do a lot of recording prefer the three-head configuration.

As for the distortion figures, the fact that one is almost double the other would seem to be fairly important. But there is little consistency in the levels used for such measurements, so they are often hard to compare.

“Ping-Pong” Stereo

Q. When! listen to some music recorded in the 1960’s and 1970’s, the separation of the instruments is so great that sometimes I find myself turning my head as ff to watch the drummer or guitarist at the extreme left or right. With more recently recorded music there seems to be very little, if any, separation. With today’s technology, why are recordings being made with less “true” stereo than twenty or twenty-five years ago?

A. The effect you describe is usually referred to, somewhat derisively, as “Ping-Pong stereo,” and it was often used in early stereo recordings just to emphasize that they were indeed stereo. Even then, most serious listeners knew that such exaggeration was far from natural—once you get more than a few rows back in most concert halls, for instance, the sound you hear from the left and right of the stage is pretty much blended together. Now that the novelty of stereo has worn off, most recording engineers go for a more realistic effect.

Source: Stereo Review (Jan. 1994) BY IAN G. MASTERS

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