A GUIDE TO BI-AMPING SPEAKERS

What is bi-amping?

For many years, a wide range of loudspeaker models have offered extra terminals that you can use to connect the cables from your amplifier. While many enthusiasts seek out speakers with these extra terminals, many don’t really know what they’re for, how they work or what benefits they can bring. All sorts of erroneous suggestions pop up across the Internet forums, from the ability to connect a second pair of speakers, which really isn’t advisable, to allowing two kinds of amplifier to be connected at once – a stereo amp and an AV receiver, for example – which you really mustn’t do, as it’s a surefire way of damaging your speakers and both amplifiers!

So, given that you only need one set of cables with positive and negative conductors to connect an amplifier to a speaker, what are these extra terminals for? Well, each pair of terminals connects to a specific part of the crossover within the speaker that splits the incoming signal from the amp to the different speaker drivers: often, one set is marked ‘High’ or ‘HF’ or similar, to denote the midrange and treble drivers, with the other being marked something like ‘Bass’ or ‘LF’ to feed to the speaker’s low-frequency driver(s).

However, with that link removed or disconnected, it’s possible to connect to each section of the crossover separately, enabling the speaker to be bi-wired – with two runs of cable from each amplifier channel to the speaker – or bi-amplified, or ‘bi-amped’, allowing a separate amplifier channel to drive each section of the speaker. Indeed, in some large speakers using multiple drivers, you may even find a further set of terminals, allowing ‘tri-amping’, using three runs of cable and three amplifier channels per speaker, perhaps for treble/mid, upper bass and low bass, or even treble, midrange and bass.

Designed for bi-amping

For all this to happen, a speaker designer needs to do more than just fit the extra terminals: a bi-amp-capable speaker needs a specific crossover design, in which the high-pass section for the mid/treble and the low-pass feeding the bass section are completely separated when the single-wire links are removed from the terminals ready for bi-wire/bi-amp operation. That minimises the interference between the sections of the crossover, by moving the ‘point of contact’ between the two back to the amplifier – in the case of bi-wiring – or all the way to the preamplifier when two amplifier channels per speaker are used in a bi-amping setup.

Before we get to how to bi-amplify suitable speakers, let’s look at why bi-amping works – and it’s all to do with the different demands of the various parts of a speaker, and the roles they play in delivering your music in the best possible quality. Look closely at the drivers in a speaker, and the obvious thing you’ll notice is that treble units – or tweeters – tend to be tiny, and only require movements so minute as to be imperceptible to deliver their sound, while it’s not hard to see the bass units on the speakers moving, especially if you’re playing your music at high levels. And those larger drivers take a lot more energy to move them than a tiny tweeter.

The benefits of bi-amping speakers

However, things get much clearer – literally so – when you move up to bi-amplification of speakers designed with this capability. Now not only do you have the advantage of those split cables, but the way the amplifier interacts with the speaker is completely different. Think again of the way those drivers move – tiny movements of a super-light tweeter diaphragm to produce the short soundwaves of high frequencies versus the big, relatively massive cones moving much more to shift the air needed for bass – and it’s not hard to see that the treble section of a speaker requires very little power, while the low frequencies need it to do some serious ‘heavy lifting’, and that means it’s easy for delicate treble and midrange information to get swamped when the amplifier is working hard to thunder out a rock bass-line or convey the weight of a full orchestra.

In a bi-amp setup, the amplification driving the treble, or mid/treble, section of the speaker isn’t being affected by the potential interference and noise coming back down the cable from the bass driver. Indeed, the high-frequency ‘leg’ of the crossover will be demanding much less power than those big low-frequency drivers, with their large magnetic ‘motors’, which enable the circuits of the ‘treble’ amplification – and especially its power supply section – to react much more nimbly.

Yes, all the amplifier channels will be receiving a full-range signal from the preamplifier, but the loads presented to them will be different, enabling much greater clarity.

How to bi-amp

There are a lot of theories about amplification for bi-amping speakers: some will suggest you can use a much smaller or lower-powered amp to drive the treble section, with a much more powerful power amp for the bass, while others have experimented with different brands of amplifiers in bi-amp systems, or even using valve amps to deliver what’s perceived as treble sweetness, with solid state designs for the bass weight.

Provided the gain of the amplifiers used is the same, i.e. the factor by which they increase the incoming signal from the preamplifier, that would work, at least in electrical terms. But, ‘tuning’ the sound of a speaker using different powers or types of amplifier generally isn’t recommended.

Bi-amping components and set-up

Assuming your speakers have the correct terminals for bi-amplification, you’re currently running them with a conventional single-wired connection, and you’ve assembled all the amplification and cables – the same for each section of the setup, please! – the very first thing to do is:

• Switch everything off, disconnect the speaker cables and remove the single-wire links from the speaker terminals.

• Then, with the entire system powered off, connect up the amplifiers according to the diagrams here – cabling from integrated amplifier to power amp, or preamp to power amps, or reconfiguring your AV receiver to biamp mode (you can do this last one with the receiver powered up, but with the speaker cables for the front left/right speakers disconnected, and then powered down once the setting have been made and saved).

• When you’ve done this, stop, have a cup of tea, coffee or whatever, then go back and check you’ve connected/set everything correctly.

• Run your extra speaker cables from amplification to speakers: it’s a good idea to use some masking tape and a pen to label both ends of the cables as ‘Left HF, Left LF, Right HF, Right LF’, just to make sure you haven’t (literally) got your wires crossed.

• Time for another cup and another check. Getting everything connected correctly is vital if your system isn’t to sound different, but not necessarily better, and to avoid any possible damage to your system – there are tales of even experienced bi-ampers managing to connect together the outputs of two amplifiers in error, which didn’t do either amp any good.

• Finally, when you’re sure it’s all right, power up the system and, if it’s working correctly, you can remove all those messy masking-tape labels – though you might want to use some coloured electrical tape to identify your four ‘channels’, in case you need to disconnect things in the future.