By RALPH HODGES
GLOSSARY OF TECHNICAL TERMS--7
Compliance is the opposite of "stiffness." A soft spring is compliant, a hard spring is stiff. At one time compliance was considered the most important specification for phono cartridges (usually appearing in the form "25 x 10-6 centi meters per dyne," for example) since it was obvious that a very compliant phono stylus would yield more readily to the forces exerted on it by the undulating record groove. (Nowadays, "minimum recommended tracking force," which takes into account several other performance factors as well as compliance, is generally considered a more meaningful figure of merit.) Compliance is not really one of those "the-more-the-better" de sign parameters: rather, an optimum value should be chosen (by the manufacturer) to complement the effective mass of the tone arms the cartridge is likely to be used with. Otherwise, the compliance of the stylus and the mass of the tone arm could interact to produce a resonance that would cause difficulty with record warps or affect frequency response. (See Julian Hirsch's article on compatibility in last month's issue.) "Compliance" may also appear in speaker advertisements: for example, "high-compliance woofer." In this con text, compliance indicates that the speaker cone is capable of large back-and-forth motions (excursions). However, compliance statements about speakers are not particularly meaningful, since they ignore a number of other factors at least as important to audible performance.
Crosstalk is the opposite of "separation." Both terms are used to indicate the amount of (undesirable) signal leak age between stereo channels. A cross talk specification of-50 dB indicates that leakage signals are 50 dB below the level of the desired signal in the channel measured. A separation specification of 50 dB says the same thing: the desired signal is 50 dB stronger than the leakage signals. A crosstalk specification of-20 dB is usually adequate for good stereo.
Crossover networks, integral parts of most multi-speaker systems, are electrical circuits that divide the drive signal from the amplifier into two or more frequency sections. In a two-way system the high frequencies are routed to the treble speaker (tweeter) and the low frequencies to the bass speaker (woofer). In three-way speaker systems, containing a mid-range driver as well, the crossover network divides the audio frequencies into three sections.
The frequencies at which crossover networks act are called the crossover points, and the sharpness with which they separate the frequencies are called the crossover slopes. There is no one "correct" set of crossover frequencies or slopes. They are selected by the designer of the speaker system, who takes into account, among other factors, the optimum frequency ranges, the efficiencies, and the power-handling capabilities of the specific drivers he has chosen. Most networks are passive devices consisting of capacitors and coils installed within the speaker enclosure. However, some manufacturers offer separate electronic crossovers that do their frequency dividing ahead of the power amplifiers. Electronic crossovers require separate power amplifiers for each frequency division they produce (as a rule, this means at least two amplifiers for a multi-speaker system). Most provide a switch-selected choice of several crossover points.
Cueing refers to the act of "zeroing in" on a desired section of a record or tape- setting the phono stylus in just the right groove (or the tape head in contact with just the right point on the tape) to bring in the first notes of the wanted selection as soon as play begins. Originally a term coined by radio-station engineers, who had to respond to the "cue" of the director to start the program for air play, cueing in audio usage now designates the lever or pushbutton control on a turntable that raises the tone arm for positioning over any part of a record.
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