Do you know how a traditional Indian three-lane road works? You have a middle lane reserved for motor vehicles in both directions, plus one small lane on each side for pedestrians and bicycles. Whenever two trucks meet on the middle lane, pedestrians and cyclists are well advised to dive into the bushes for cover.
Of course, things aren’t quite so dramatic along the signal path between amplifier and loudspeaker – after all, music playback with just one cable for all frequencies works perfectly fine. Nevertheless, some say that splitting the frequency spectrum into two cables – one for the highs and mids and a separate one for the bass – can improve sound quality. Let’s find out whether bi-wiring and bi-amping actually make sense, and, if so, why.
What are we even talking about?
Bi-wiring means that each speaker is connected to the amplifier using not one, but two cables. Of course, this requires two sets of binding posts each on both the speaker and the amplifier. While speakers often have bi-wiring terminals specifically for this purpose, stereo amplifiers often have two pairs of speaker terminals to enable rudimentary multi-room setups in which two pairs of speakers supply two rooms with the same signal. The terminal pairs – usually labeled “A” and “B” – can then usually be switched via a rotary dial; in order for the double cabling to work, the “A+B” position must be selected on the amplifier. On the speaker terminal, the bi-wiring bridges must be removed to avoid short-circuiting the signal directly before the crossover.
Frequency spillover
Now that we have correctly wired our bi-wiring setup, we can of course ask ourselves what exactly we’re trying to achieve – what problem are we trying to combat? The main argument for signal separation is stray currents between the crossover paths: due to their inertia, drivers always exhibit a certain hysteresis, i.e. they overshoot at the excursion peaks and don’t immediately come to a standstill after the signal is cut off. As dynamic drivers work according to the induction principle, the voice coil reacts to these uncontrolled movements in its magnetic field like a generator and produceses a counter-EMF (electromotive force), which “bounces back” via the speaker cable towards the amplifier, distorting the signal along the way. A well-designed power amplifier should have a low internal resistance and therefore a high damping factor, i.e. it should be able to quickly dissipate this back EMF to ground before it can cause any significant damage. However, the cable resistance effectively lowers the damping factor and thus increases the risk of some of the back EMF finding its way to a neighboring frequency branch. If you now consider that a bass signal carries many times the power of an equally loud treble signal, it becomes clear that even a fraction of this energy can have a considerable negative effect on the sound.
If you connect the mid-bass and tweeter branches to their own speaker outputs, you can avoid this problem by moving the transfer point to the inputs of the frequency branches away from the crossover directly to the power amplifier output – the cross-connection between the branches is much better protected against unwanted exchange at this point, as the power amplifier can dissipate the stray currents much more quickly. Furthermore, the back EMF from the bass-midrange driver can only influence the relatively robust bass-midrange signal along the cable, but not the delicate high frequencies.
Bi-Amping
You can, of course, go even further and, instead of using separate cables, give each frequency branch its own power amplifier. As the transfer point is then shifted to the outputs of the preamp, the high frequencies can only be influenced by residuals of the unamplified line-level low frequencies. Ultimately, this also makes you independent of the damping factor of the power amplifier.
However, as bi-amping is much more expensive than bi-wiring, the cost-benefit question inevitably arises here. Basically, the higher the damping factor of an amplifier, the more effectively it can neutralize stray currents. It follows logically from this that we can expect a noticeable sonic improvement from bi-wiring, especially on amplifiers with low internal resistance. An upgrade to bi-amping should not make a big difference in these cases. For fans of small SET amplifiers, however, the situation may well end up completely reversed, with bi-wiring turning out to be relatively ineffective, but bi-amping yielding good results. Finally, it should be noted that multi-channel power amplifiers such as the Primare A35.8 (read my review here) can make bi- or even tri-amping much more cost-effective.
The theory therefore clearly says yes to bi-wiring and, in the right constellation, possibly also to bi-amping. However, whether there is an audible sonic advantage at all or whether it is worth the effort is one of the many hotly debated topics among hi-fi-enthusiasts. It is therefore advisable to form your own opinion before taking the dive: Borrow an additional set of cables, perhaps even a power amplifier, from your trusted dealer, play around for a weekend and then decide for yourself.
