Today, I'm going to talk to you about bi-amplification. I would like to do it in a straight-forward, easy to write, easy to read, fun and exciting manner. That's not possible. But here goes.
First, Let's Clear Up Some Confusion
An active subwoofer being sourced by a receiver's sub out is a basic form of bi-amp'ing.
Now that you're less confused, let's move on...
Without bi- and tri-amp'ing that insane amount of power would be exponentially greater. This is because in multi-amp'ed systems passive crossovers are used and passive crossovers suck up an amazing amount of power and turn it into heat. Couple that with the need for concert audio systems to be somewhat modular to adjust for differences in hall and arena sizes (not to mention outdoor gigs), and the only feasible way to make an act sound decent without shutting down the local power grid is to tri-amp or bi-amp the audio.
This is accomplished through the use of active crossovers and people who know how to set them. Active crossovers are placed between the source and the amplifier and are individually adjusted for the speakers that make up the lows, mids and highs (think about the link between the amplifier and your CD player at home or the digital file reproducing your favorite artist's vocals while she dances and pretends to sing at that concert you just spent a fortune on).
If you are not using an active crossover between the source and the amplifier, you are not actually bi-amp'ing anything, but to make you feel better the audio gods have coined the term "passive bi-amp'ing." To truly bi-amp your home system, you will have to remove the passive crossovers from the speaker cabinets and use a line-level active crossover in the signal chain above the amps. But if you've spent a fortune on a good pair of speakers with well-designed passive crossovers, it seems kind of dumb to pull the crossovers out in order to save a few watts of power or reduce some theoretical intermodulation distortion (IM).
Also, keep this in mind: Unless you are pulling out the passive crossovers and replacing them with a well-tuned and highly stable active crossover network, and then tuning that active crossover properly with the proper test equipment, the power benefits you are gaining will probably not be worth the extra money.
In terms of intermodulation distortion, you are basically replacing one circuit that may or may not cause IM with another circuit that may or may not cause IM. If you've bought a decent pair of speakers with a well-designed passive crossover network you may not realize any noticeable gains, and in fact, unless you know how to set an active crossover, you are more than likely causing more harm to your overall sound quality than if you had just left your system alone.
What About Power?
Of course, then you have to concern yourself with matching the volume of the HF with the volume of the LF so you can listen to your music as it was intended to be listened to. This factor is often overlooked, but to my ears it's a pretty major thing.
Also, if you are not splitting the frequencies before the power amp you are not reducing the stress of frequency-related loading within the amplifier circuit and power supply as the amps are receiving the full frequency range. This means that the amp is producing the full frequency range and presenting it to the speakers regardless of what you want it to do.
Horizontal And Vertical Bi-Amp'ing
In a horizontally bi-amp'ed system, one stereo amp powers both (L & R) bass drivers and one stereo amp powers both (L & R) MF/HF drivers.
In a vertically bi-amp'ed system, one stereo amp is used for the MF/HF and LF (L channel) and another stereo amp is used for the MF/HF and LF (R channel).
In both cases, you can think of it in terms of having four separate amplifiers.
Theoretically, a vertical system will be more efficient because the heavier loading of the lower frequencies is split between two amps (and subsequently two power supplies). Meanwhile, some people like the horizontal system because they can use one type of amp that may work better with high frequencies (like a nice low-power tube amp) and one type of amp that works better with low frequencies (like a meatier high-power solid state amp). Unfortunately, like most things in life, this sounds really neat on paper but in the real world there are unintended consequences that may cause you more aural grief than sonic joy.
So once again, if you are considering bi-amp'ing your system, tread carefully and do as much research as you possibly can before taking the plunge. You may be better off spending your money on a really good, clean, 250 Watts per channel amp, than buying two 125 Watts per channel amps.
There are still benefits to bi-amp'ing (if all of the above is taken into consideration). Those benefits are:
Caution! Opinion Below
Can you benefit somewhat from even a passively bi-amp'ed system? To an extent, but the return on your investment isn't enough to convince me you shouldn't just spend your money upfront on a decent to really good multi-amp'ed system.
Another thing to consider: Our engineers spend an enormous amount of time and money getting our passive crossovers set precisely for the cabinet volume and driver configuration of our speakers so you don't have to.
There will be some who swear I am dead wrong here, but that's okay. A lot of this comes down to what we think we hear and there is nothing wrong with that, but what you've got now are the technical reasons for going one way or the other.
Take note here that monoblock systems are not bi-amp'ed systems and aren't covered by this article.
The opinions expressed in this article are the author's own and do not necessarily reflect those of KEF or its employees.
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