Audioclinic (Jul. 1982)

"Bass Brawl" Erratum

Your statement in the Dec. 1981 issue that "two 8-inch speakers have a total combined area greater than one 12-inch speaker" is in error. The areas are respectively 2 times 42 times pi which equals 100.53 square inches, vs. 1 times 62 times pi which equals 113.10 square inches. This difference is more pronounced if we deal with actual cone diameters rather than nominal ones.

-Emerson S. Hawley; Brooklyn, N. Y.

Defining Wow and Flutter

Q. What is meant by wow and flutter?

-Daniel Walter; Brooklyn, N.Y.

A. Wow and flutter are terms which are closely related. Wow refers to relatively slow speed changes, one or two such changes per second, and applies to the motion of tape decks and turntables. Wow manifests itself aurally in changes of musical pitch, and the most striking examples can be heard during sustained notes on piano and clarinet. Flutter also indicates a speed fluctuation of a device, but at a rapid rate.

ABCs of MMs and MCs

Q. I recently purchased a new receiver which has a built-in pre-preamp for moving-coil cartridges. What is the difference between a moving-coil and a moving-magnet phono cartridge? What are the advantages of each?

-Edward J. Liney, Jr., Dresher, Pa.

A. A moving-magnet phono cartridge is the more common of the two. It is relatively simple to construct, rugged and reliable. In this cartridge is a set of coils located in the proximity of a magnet mounted on the stylus assembly. The relative motion of the magnet with respect to the stationary coils will produce a voltage in the coils which is proportional to the motion of the stylus.

The moving-coil phono cartridge is similar, except that the coils are attached to the stylus assembly, and the magnets are stationary. Such a cartridge can be made to have a very high compliance and low, effective stylus tip mass. Each coil is light, having only a very few turns. The "pigtail" wires from such coil assemblies are constantly flexed when the cartridge is used, a potential source of trouble.

While possibly better in transient response when constructed properly, moving-coil cartridges are expensive to produce. Their output voltage is low because of the relatively small number of turns wound on each coil. This means that special, low-noise preamplifiers are required if the playback equipment is to have a good signal-to-noise ratio. In addition, most such cartridges must be re-tipped at the factory.

Phasing In and Out

Q. My turntable plays records out of-phase. When I reverse the leads to one pair of speakers, the sound is in phase. I must, however, return the leads of this speaker to proper phase to play other program sources. Is there a way to change phase at the turntable to eliminate the need to change speaker connections?

-Harvey B. Wyche, Roslyn Heights, N. Y.

A. It sounds as though you have wired your cartridge out-of-phase or that there was a manufacturer's error in wiring the innards.

In any event, merely interchange the leads of one channel of your cartridge, and proper phase will once again be realized.

More Power to the Speaker

Q. What does the term "minimum power" for a speaker refer to?

-Eric Freund, Sacramento, Cal.

A. The minimum power required by a loudspeaker is that power which will fill an average listening room to a relatively loud sound level. Do not select a speaker whose minimum power requirements cannot be met by your amplifier. The amplifier should be capable of producing at least twice the minimum power required by your speaker.

Where your room is larger than average or where there is a large amount of overstuffed furniture or heavy drapery present, you will want an amplifier which can produce at least the maximum power capable of being handled by your speakers.

By maximum I refer to that level of power which, when exceeded, will either produce audible distortion or physical and electrical damage to the innards of your speaker.

There are those who will say that, by using these guidelines, there is no reserve power for transient peaks. This is a discussion which can consume a lot of space. Suffice it to say, these guidelines are at least a practical, readily understood approach to the conditions discussed here.

Do I Hear a Pre-Echo Waltz?

Q. When a very quiet groove immediately precedes a loud groove, even on the best European phonograph records, some reasonably audible portion of the loud passage is heard prematurely. Would it be reasonable to assume that during sustained, very loud passages, the information in such grooves is continuously imposing on other grooves and that such imposition could produce distortion levels exceeding the levels found in even the most modest tuners, amplifiers and speakers?

Years ago, London Records did make a few recordings with more space between grooves. Are there any such records being made today or even contemplated?

-Frank Alliegro; Washington Crossing, Pa.

A. Upon visual examination of most disc recordings, you will find that the more heavily modulated grooves are spaced further apart than the low-level portions of the same disc. This is done partly to reduce the problem under discussion--known as pre-echo--and partly to insure proper tracking during playback.

If discs were recorded with uniform, wide groove spacing, the time per side would be limited.

Pre-echo can also result from electroplating problems during the record making process. If the early stage of this process is rushed, the plating does not completely represent the modulation of the grooves. Therefore, there is a slight "smearing" of the grooves which will not add distortion, as in a tuner or speaker, but will cause the louder signal levels to be imposed on silent grooves or on the softer passages.

It would also appear that some playback styli aggravate this condition, and I suspect this has something to do with momentary deformation of the groove walls. It has been long recognized that grooves are springy and can be displaced as the playback stylus passes through them. This can momentarily shift them slightly closer to adjacent grooves, helping to produce the pre-echo, or "ghost" as it is sometimes known.

Because of the somewhat elastic nature of phonographic records, the grooves spring back to their original positions after having been played.

Let Me Count the Ways

Q. I am planning to add more speakers to my component system.

What is the difference between two and three-way speaker systems. Are three-way systems really better?

-David Holladay, Hayneville, Ala.

A. The two-way speaker system consists of a woofer and a tweeter.

The audio frequency spectrum is divided in such a way that the woofer carries low frequencies (perhaps up to 1 kHz), and the tweeter carries, or produces, high frequencies, starting from the point at which the woofer drops off in response.

The three-way system is designed to slice the frequency spectrum into three parts rather than the two we have just mentioned. Here we have a woofer to handle the lowest frequencies, a midrange to handle frequencies between, say, 200 Hz and 2 kHz, and a tweeter to handle all frequencies above the highest frequency passed by the midrange speaker.

Engineering decisions are made as to the exact frequency range covered by each speaker in the system.

I do not believe that anyone can, or should even try, to select a loudspeaker system merely on the basis of whether they are two-way or three-way systems. You must listen to the speakers and compare their sound quality, one to the other. Because the speaker system makes the largest single difference in the overall sound of your installation, its selection deserves the greatest amount of care. I believe that the matter of whether a system is a two- or three-way unit is an engineering decision only. Although one can come up with arguments for and against each of these designs, the ear is the ultimate judge.

(Audio magazine, 1982; Joseph Giovanelli )

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