HI-FI SPECIFICATIONS

Most people don't know a damn thing about sound. It's a shame, too, because their misconceptions lead them to purchase bad hi-fi equipment. The man in the street will tell you a response from 20-20,000 cps is the test of a good set. The fact is that even the worst Japanese amplifier will advertise this rating. Frequency response merely tells the potential buyer that the unit can, under ideal conditions, reproduce all audible tones.

This Frequency or pitch is measured in cycles per second. A cycle is one complete vibration, consisting of a pressure followed by a rarefaction. Each cycle causes your ear drum to bend in, then out. Low frequencies are referred to as "bass" and high frequencies as "treble."

The very low bass--tones in the 20 to 50 cps (cycles-per-second) region--gives body, depth, and majesty to music. Such tones are produced by the biggest organ pipes and bass drums, for instance.

The very high treble--sounds above 8,000 cps--provides the timbre characteristics by which the instrument's particular qualities are distinguished. The range to which the average person's ears respond is about 25 to 15,000 cycles per second. The ability to detect ultra high tones above 15,000 cps is limited mostly to babies and dogs.

The real difference between a lousy record player and a very good component system is not frequency range (although this has some importance) but the ability to produce sounds without distortion. A system which is completely faithful to the frequencies and relative intensities of the sounds played through it is nevertheless unbearable to listen to if it produces any appreciable distortion. On the oher hand, a system on which violins sound like flutes and bass drums disappear entirely, but which is entirely free from intermodulation distortion, will be very listenable.

IM, or intermodulation distortion, is the result of two or more separate tones affecting each other in such a way as to produce a spurious, discordant, frequency. It is minute traces of this type of fault which lead to "listener fatigue," a condition characterized by a desire on the part of the listener to shut the set off, even though he doesn't quite know what is irritating him. In larger doses this is the rasping, grating effect we are used to from the majority of transistor radios, for example.

Harmonic distortion is the doubling of frequency by an amplifier or other component which cannot handle low bass. It does not irritate the ear so much as it bothers one's musical sense. When instruments start taking on new characteristics, harmonic distortion is at work.

Manufacturers' specifications have been misleading in the past because of a lack of agreement on methods for measuring performance of electronic components. The new Institute of High Fidelity Manufacturers' standardized ratings have done much to relieve the confusion, and pioneering of these methods by firms such as H. H. Scott and McIntosh Laboratory, who have used them to measure their amplifiers and tuners since their introduction, has helped start them on their way to general recognition.

When buying an amplifier, your task is simplified if the manufacturer lists IHFM "music power" ratings. This method results in a figure of a number of watts of output at a given distortion figure, and this data can be compared directly with any other IHFM rating. If IHFM ratings are not used, look at the "power response" note. The amplifier should be able to produce its full rated output (20 watts, for instance) at every frequency in the spectrum of human hearing.

"Decibels" are units of loudness, so if the rating reads "20 to 20,000 cps at full rated output within plus or minus 1 decible with less than 10% total distortion" (a very good rating, by the way) this means that the amplifier can produce every tone that is fed into it with no tone emerging more than 2 decibels (a very small difference audibly) louder than any other.

Reading specs on speakers is largely a waste of time. Since no standard methods of measurement are used and since few manufacturers include the distortion ratings that are so important, your ears remain the only guide to selecting this part of your set.

Bearing us out on this point is the policy of the KLH speaker firm whose home is here in Cambridge. KLH, in a practice rare among speaker manufacturers, publishes no response or other specifications on their speakers.

To summarize: Knowing a little about the facets of "sound" helps in listening to all music. Applying knowledge of what a home music system should be able to do in order to reproduce music correctly to your study of the specs sheets can lead to good preliminary evaluations of equipment. Remember that frequency response accuracies are useful but that low distortion is vital. Look for the lowest possible distortion in all your components (under 1% total IM and harmonic is considered good today). And above all, use your ears as the final acid test of any component, and especially when contemplating purchase of a speaker.