Bi-amping: Using twins

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While writing on the subject of bi-amping, bi-wiring and all things esoteric with connecting amps to speakers, I have run into plenty of advice from far and near. The good Dr. King, BHK, suggests perhaps we could use three terms instead: bi-amping as I described it–two amps one input, bi-wiring as described–one amp, two speaker cables, and bi-channeling–two amps, fed from a low level electronic crossover. However we describe these connections, the idea behind bi-amping is the same: load sharing. We can use a stereo amplifier per speaker–left channel feeding the tweeter, right channel the woofer. Or, as is more common, one stereo amp for the bass, another for the treble. And best is when we use dissimilar amplifiers optimized for each task: small and sweet for the top end, big and brutish for the bottom. But conventional wisdom suggests it's always best to use identical amplification channels for each task. I don't agree. The idea behind identical amp channels feeding both top and bottom frequency drivers is simple. Sharing the load. But what modern amplifier today has such poor performance it cannot handle the requirements of a loudspeaker? In days past this made much more sense. Tube amplifiers, in particular, were (and still are) quite poor at driving woofers. Their transformer coupled outputs can't handle impedance swings of loudspeakers–so splitting their duties made sense. Well designed solid state amplifiers shouldn't have issues driving both tweeters and woofers if they are of sufficient power to match the speaker. But there is a problem with that. Increasingly, there is a polarization amongst speaker designers, similar to the American political system. More designers are heading to opposite ends of the spectrum: some towards higher efficiency horns, others towards lower efficiency perfect measuring speakers. Each extreme has its problems, but the one I am concerned with most is the trend to lower efficiency designs. Speakers with 83dB to 87dB efficiency border on the power hungry–and many add insult to injury with wildly varying impedance dips. In these cases, breaking up amplification duties makes good sense. But, for normal loudspeakers, defined as middle of the road in terms of efficiency, 87dB and above, I see little advantage in bi-amping with identical amplifier channels. Tomorrow, we'll look at bi-channeling.
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Paul McGowan

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