I'm certainly not in any sense defending passive crossovers as the end-all to music reproduction. Indeed, I believe active crossovers are a better choice. However, that said, there are some things that young Winslow Burhoe failed to mention about running speakers out to their limits — namely nonlinearity. Normally, you want to take the section of the speakers performance curve where it is the flattest, and truncate the parts near their resonant frequency and their naturally occurring breakup. With one capacitor, you can, using the inductance and inherent resistance of one of the voice coils, create an RLC circuit using that one capacitor that will attenuate frequencies below a certain point. With only one capacitor, I don't know how you keep the speakers in phase, unless he means "one capacitor per speaker set". Before I changed the crossover in my Minimus 7's, it was essentially a capacitor and inductor on the tweeter.
It should sound like it isn't there!
There is a difference between hearing and listening...
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Carver: C-4000 & C-1 preamps, PSC-60 preamp/tuner, TX-11a tuner, M-400 (2), C-500, M-500, M-500t, M-500t Mk.II, A-500x, AL-III loudspeakers (2 pr.)
Sunfire:Theater Grand III processor, Ultimate Receiver, Cinema Grand Signature 400 ~ seven, True Subwoofer Mk. II, D-10 Subwoofer