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What is Bi-wiring and Bi-amping?

Bi-words seem to be proliferating these days (bi-coastal, bipolar, etc.), and the world of stereo and home theater loudspeakers is no exception. The terms “bi-wiring” and “bi-amping” (short for biamplification) continue to confuse lots of stereo and home theater fans.

At its root, “bi” means “two,” and it relates particularly to the Axiom M80ti and M60ti tower speakers, which are supplied with “biwiring terminals.” Biwiring in practice means running two speakers cables to each speaker (a total of four to a pair of speakers) instead of one cable per speaker.

On the M80’s rear panel (and the M60’s), there are four binding posts instead of the usual two. One pair of binding posts is linked to the woofers, and the other two are connected to the midrange and tweeter section of the crossover. When the speakers are shipped, there are gold straps that run between the two pairs of binding posts, linking them so that they function electrically as a pair.

If you remove the gold metal links, however, you can biwire your speakers, using one speaker cable for the woofers, and the other cable for the midrange and tweeters. At the other end, both cables connect to the same amplifier output terminals. The practice became popular in Britain (not unknown for its eccentric audiophiles), the thinking being that using separate cables for low and high frequencies would somehow reduce interference between the two and improve sound quality.

If you look at the amplifier as a current source, then for amplifiers and receivers that are capable of supplying lots of current into low impedances, biwiring could offer theoretical advantages, particularly to loudspeakers that are linear and smooth, like the Axiom M80ti and M60ti, by eliminating potential intermodulation distortion between the low- and high-frequency portions of the audio signal. Using biwiring, this distortion would not occur because the low-frequency part of the speaker crossover would draw the current it needs for the woofers (and they need lots of current) through one speaker cable, while the midrange tweeter section would draw less current (it doesn’t need as much) through its own speaker cable. This could prevent intermodulation distortion that may occur using one big “fire hose” or single speaker cable. (Using two cables per speaker will also lower total resistance to the audio signal — and that is well and good, although a single run of 12-gauge cable to each speaker will keep resistance to an insignificant level, well below 0.3 ohms.)

Will it sound any different if you biwire? Some users think it does, but I’ve never heard any differences, nor have any of our laboratory measurements or scientifically controlled double blind listening tests ever demonstrated there are audible differences. Axiom includes the extra terminals as a nod to those enthusiasts who believe that biwiring results in audible benefits and for the bi-ampers.

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Bi-amping, or biamplification, is used mainly in professional sound reinforcement applications, where extremely high levels of loudness are required. Here big, separate amplifiers powering the low frequencies, and smaller amps for the midrange will increase overall output. Sometimes they will use a separate outboard electronic crossover (the speaker’s internal crossover is disabled or bypassed entirely) so the operator can vary and adjust individual crossover frequencies, tailor the “slope” of the crossover to match the strengths of each set of drivers, and also adjust the relative sonic balance of bass, midrange and treble to suit the environment. This is important for huge auditoriums or outdoor events where separate arrays of treble and midrange horns are operating with big “bass bins,” but such systems have no place in domestic home theater systems in normal rooms. Additionally, it puts control of the relative smoothness and tonal balance into the hands of the sound system operator, a dangerous tool for all but the most experienced sound reinforcement experts. It also partly explains why the live sound at so many concert events (not all, mind you) is so awful.

by Alan Lofft (bio), Axiom Audio (reprinted with permission)

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