Audio Q&A by Ian G. Masters (Sept. 1995)

Center-Channel Hookup

Q. My center speaker can be biwired or bi amplified, and my power amplifier is a six-channel model that can be bridged to operate in three-channel, four-channel, or five-channel mode. My three front speakers are identical. So in hooking up the center speaker, is it sonically desirable to bridge the amplifier and connect the speaker straight? Or should I bridge the amp and biwire the speaker? Or bi-amplify but not bridge?

A. As a general rule, you should treat all three front channels the same, especially if the speakers are identical, as they are in your case. You don’t have enough channels of power either to bridge or to biamplify all three (unless you’re willing to add yet another amplifier for the sun channels, in which case you could do either), so I suggest skipping all of the options you mention and simply connecting each speaker to one amplifier channel. The sixth channel could be used to power a passive subwoofer if you find that the system needs a little extra oomph. As for biwiring, some swear by it and some pooh-pooh its effects try it out and see whether you hear an improvement.

Noisy Equalizer

Q. My graphic equalizer contains a spectrum analyzer and is connected between the pre -out and main-in jacks of my integrated amplifier. As soon as the equalizer is turned on, even without a signal, a notice able hiss appears in the speakers. Also, the analyzer’s display varies with the volume I set for the amplifier. When I connected the equalizer through a tape-monitor loop, the hiss occurred only at very high volume levels, and the analyzer’s display was not tied to volume. Why the differences, and which configuration is correct?

A. In an integrated amplifier, all the control functions, including overall level, are done at the preamp stage that is, prior to the pre-out jacks. The power amplifier takes whatever is fed to its main-in jacks and applies its full gain to it. Thus the small amount of hiss produced by your equalizer is being fully amplified, whereas if it were connected earlier in the chain it would usually first be attenuated somewhat by the volume control. Similarly, since the pre-out jacks are after the preamp-level control, the spectrum-analyzer display on your equalizer will show overall level changes.

The line levels used throughout most systems would produce uncomfortably high sound levels if given the full gain of the amplifier […]

Choosing a Phono Cartridge

Q. […] with that in mind, how should I go about deciding which cartridge to buy?

A. Traditionally, choosing a phono cartridge has been about as personal as choosing speakers, and there are lots of opinions and controversies out there. Generally, however, the sonic differences between good cartridges have narrowed, and top models from the main brands are all reliable and offer excellent sound. Listen to a few and pick one whose sound you like.

But as vinyl recedes into audio’s history, we can expect the amount of equipment available to play it to continue shrinking, and that suggests some strategies you should use to make sure you can play your LP’s indefinitely. The first is not to scrimp; this may be the last cartridge you’ll ever buy (or be able to), so it’s worth the money to make sure it’ll last. Also, it may be unwise to opt for a moving-coil (MC) model, regardless of what the fans of that design may say. Not only are MC cartridges usually more expensive than their moving-mag net equivalents, but they almost never have a replaceable stylus. Since the stylus is the part that’s most likely to wear out, it makes sense to insure you can replace it in the fu ture (and equal sense to buy at least one re placement now, while you can). It may also be that you don’t need a new cartridge at all, just a new stylus.

Watts, Decibels, and Levels

Q. How much of an increase in amplifier power does it take to make a sound twice as lout!? How many decibels represent a doubling of loudness? And if I have a 100- watt amplifier and want to play music at twice the volume, what size amplifier will I need?

A. If you double the output power of an amplifier, that’s a gain of 3 dB, which is about what’s necessary to achieve a clearly audible increase in volume. To achieve a subjective doubling of the volume, you need an increase of about 10 dB, which means about ten times the power out put. As for what size amplifier you need to double the volume, that’s impossible to say.

You may be able to achieve that level with the amp you have, depending on where you typically set the volume control.

Amplifiers only rarely hit their rated out put. Depending on the sensitivity of your speakers, the nature of the music, and a number of other factors, it may well be that your 100-watt amplifier is actually putting out only 1 or 2 watts most of the time. In that case you could get twice the subjective level just by turning up the volume control.

DAT for Da Road

Q. I’m planning to buy a DAT deck for re cording my friends’ CD’s and for live recording. I think the extra cost will be worth it to get perfect copies and for DAT’s CD-like track access. But most of my listening will be in my car, and I haven’t been able to find any car DAT decks. Are there any?

A. First, be aware that what you are planning is illegal. The law says you can make a digital copy of your own CD’s for use in your car, but not of your friends’ CD’s. Technically, however, you should have no difficulty connecting a portable DAT deck to any car stereo system that has line inputs (car DAT decks were available from a few car stereo manufacturers and at least one major car maker several years ago, but to the best of my knowledge they’ve all since disappeared from the market).

A portable DAT machine could be used for all three functions you mention: copying discs, making recordings in the field, and listening in the car. Except for the most critical purposes, however, I think DAT might be overkill. A MiniDisc recorder will let you do the same things with greater editing flexibility and much faster track access (DAT’s track access, by the way, is five or six times slower than CD’s). I doubt that you’d be able to hear much, if any degradation of the sound compared with the original — especially in a car.

SibilantCenter

Q. When I play my hi-fi VCR through my surround decoder, “s” sounds come across with an annoying high-pitched hiss. This doesn’t happen when I’m listening to stereo broadcasts. Is there something I can do to eliminate the problem?

A. It’s hard to know exactly what’s going on here without more details on your sys tem, but it sounds like it could be a characteristic of your center speaker, which may produce some high-frequency resonances or coloration. The effect may be noticeable because the center speaker’s output isn’t balanced with that of the main speakers, and it may be more apparent on tapes because hi-fi videocassettes often have more high-frequency energy than broadcast programs.

A few surround-sound decoders and Pro Logic receivers incorporate center-channel equalization to deal with such problems. If your decoder has such controls, experiment with them. Or it may simply be a matter of backing off a bit on the treble control for the whole system; that will affect all the channels, but the removal of the sibilance from the center might well outweigh any dulling of the main channels. I have also occasion ally dealt with similar problems by tilting the speaker up or down so that the main listening position is slightly off-axis, but that depends entirely on the dispersion characteristics of your center speaker.

If you have a question about audio, send it to Q&A, Stereo Review, 1633 Broadway, New York, NY 10019. Sorry, only questions chosen for publication can be answered.

Source: Stereo Review (09-1995)