When Arnie Nudell first proposed the idea of Genesis loudspeakers he said something I'll never forget. "A speaker line is based on the tweeter. Everything else follows from there." Every amazing loudspeaker traces its routes back to its tweeter. Tweeters reproduce the higher frequencies, typically from 1 kHz through 20 kHz. They come in every shape, size and technology: domes, ribbons, folded, horns, planars, electrostats, even massless devices like the "blue flame" Ionovac or Hill Pasmatronics. What most have in common is their need to be limited in what they reproduce. High frequencies. The tweeter frequency dividing network, called a crossover, can range from the simple to the complex. Generally, they are simple. Many tweeter crossovers, from the uber-expensive four-figure beasts to the $100 a pair variety, rely on a single element to restrict what they play. A capacitor. Capacitors are simple devices. They consist of layers of conductive material sandwiched between insulating materials. They work somewhat the opposite of the coil we discussed yesterday. A coil passes DC (battery voltage) and low frequencies without restriction. A capacitor passes no DC, and signal begins to flow only as frequency rises. The most common tweeter crossover circuit is a single capacitor inserted between the power amplifier and the tweeter. The point at which music starts to play depends on the tweeter and the size of the capacitor. The bigger the cap, the lower the frequency that passes. And here's an area where quality matters. Cheap speakers use cheap capacitors. Expensive speakers use expensive caps if they are to sound good.
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