Bi-amping: Mix and match

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Loudspeakers generally have crossovers to separate the amplifier signals: high frequencies to the tweeter, lower frequencies to the woofer. Many loudspeakers feed these crossover components from two sets of inputs, each with their own binding posts–and there is usually a jumper tying them together. Here's a picture of such an arrangement. Polk back 2 The top set feed the tweeter crossover, the bottom the woofer. The shiny copper straps tie them together so a single set of speaker cables feeds both. Remove the strap, and now we can connect two separate amplifiers, each fed the identical input signal. This is what we call bi-amping. But that's not the only way. We can also eliminate the need for the speaker's internal crossover by using an electronic version before the two amplifiers; their outputs fed directly to the speaker driver. But this is not the norm, because few loudspeakers haven't a crossover built inside. Traditional Bi-amping is what I had previously described. So, what are the advantages? Amps, like people, are happiest when they're doing as little as possible. Divide the workload between two amplifiers and you'll likely improve the system's performance. But the benefits are minimal–depending on the amplifier's capabilities. There's another reason we might think of bi-amping; mixing and matching. Not all power amplifiers excel at everything. Some have better bass, others, a sweeter top end. Few are great at everything, until you get into the top crop, like a BHK, D'agostino, or Constellation. So one clear advantage is to mix and match: spend good money on the top end amplifier; perhaps a tube, and a brute for the bass. But here's the trick. You have to make sure the two amps are gain matched. Most amplifiers do not have the same gains. In my view, this is a reasonable and meritorious approach to system amplification–one you can get great results without selling the farm to pay for it. Tomorrow, we'll look at using identical amps.
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Paul McGowan

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