Sound Thinking

Some signposts to help guide the interested listener through the bewildering abundance of modern hi fi equipment.

Twenty years ago music came out of a big brown box called a hi-fi console. You could stick it in a corner, shut your eyes, and pretend you were sitting in a concert hall.

You were only fooling yourself.

Instead of a big brown box you now can buy the kind of equipment audio engineers didn’t even dream of in the 1950s—tuners that bring in stereo radio broadcasts, speakers that catch almost every nuance of the actual performance, and amplifiers that bring a 100-piece orchestra or a ten-piece rock group in­to your lap. There are still brown boxes around, infinitely better than their an­cestors; and there are “compact hi-fi systems” and “portable phonographs.” But the best way to get concert-hall quality high fidelity is to assemble a series of components. The components include loudspeakers (two for stereo, four for quadraphonic sound), an ampli­fier with or without a built-in AM-FM tuner, a record player, and perhaps a tape player.

The myriad technical specifications associated with a true high-fidelity sys­tem are directed toward a few simple goals. First and foremost, a good sound system must be capable of reproducing all the tones or frequencies contained in the original program source at their correct relative intensities—what the audio world calls “flat frequency response.” Since the limits of human hear­ing are generally considered to extend from twenty vibrations per second to about 20,000 vibrations per second, ideally all the components of a high- fidelity system should be responsive to that range of frequencies. All-in-one console units must generally restrict fre­quency response, particularly at the low bass extremes, since the vibration from their built-in loudspeakers would other­wise induce vibration into the phono pick-up system and could cause a loud, howling “feedback” sound. So, the first requirement in a good sound system is that the loudspeakers be physically sep­arated from the other components. This requirement is also necessary for proper stereophonic dimensional effect.

In addition to reproducing all musical frequencies at the proper loudness, the components should not introduce un­wanted electronic tones or noise not present in the original program. Noise, whether it be in the form of a steady hum (usually generated from sources related to your home power line) or as a random “hiss” (often associated with weak radio signals, poor-quality tape re­cordings, or discs containing a high level of surface noise), detracts from musical enjoyment.

The system, finally, must have dy­namic range—the ability to reproduce faithfully the very loudest as well as the very softest passages of a musical pro­gram. A loudspeaker which cannot ac­cept powerful electrical signals fed to it without introducing distortion is as undesirable as an amplifier or receiver that introduces high orders of distortion to the electrical signals before they ever reach the speakers. In short, each com­ponent of the system must be compati­ble with each other component, and each should be of a high enough quality within the owner’s budget so as not to denigrate the performance of the others.

The two most popular music sources are records and FM radio. Unlike AM radio, which is generally limited in the range of sound it can transmit and is plagued with static and other interfer­ence problems, FM radio can be re­ceived with noise-free quality and is transmitted with fidelity extending al­most to the limits of human hearing. In addition, more than half of all U.S. FM stations transmit all or part of their programming in stereo, with left and right channel signals transmitted over a single station but separable into two signals by home stereo tuners or re­ceivers. The unit of a hi-fi system which picks up and amplifies these signals is called an FM stereo tuner and may be a separate component or part of a single component known as a receiver.

A receiver consists of three elements which can be combined or acquired separately. The tuner picks up the high-frequency radio signals and converts them to much lower frequency audio signals; the pre-amplifier amplifies pro­gram signals and allows their signal and tone to be stepped up; the power ampli­fier further steps up the signals and converts them to the energy necessary to activate loudspeakers so the signals can be heard.

A rec ord player consists of three ele­ments: the turntable, the tone-arm which contains the pickup or cartridge with its stylus (“needle” was the name used in pre-hi-fi days). The turntable rotates at a constant speed with as little induced vibration as possible. These seemingly simple requirements, if not met, can lead to distortion. The tone arm should move freely and position the cartridge so that the stylus can trace the complex undulations inscribed in a rec­ord groove with a minimum of down­ward force (tracking force). The car­tridge should respond uniformly to all audio frequencies and translate physical motions generated by the record grooves into accurate electrical signals. The bet­ter cartridges employ magnetic or elec­tro-magnetic principles instead of the ceramic or crystal elements in lower quality cartridges. Diamond styli are al­most invariably used these days since they retain their precision-ground shape up to 1000 hours of record play and are less apt to damage the grooves of rec­ords. The quality of a cartridge, which is often purchased as a separate item, is, in part, governed by the quality of the turntable system chosen. Inexpensive record changers may not be able to ac­commodate

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