Many audio enthusiasts are confused about the concept of bi-amplfication and rightly so because it can be a fairly complex subject. I’ll spend some time here explaining things in the simplest terms I can. Hopefully, it will help.
The Crossover Network. Most speaker systems are designed with more than one driver. A two way system will have a low frequency driver (woofer) and a high frequency driver (tweeter.) A three way system will add a third midrange driver to the mix to handle the middle range of the frequencies of the music we hear. Multi driver speaker systems include a crossover network that divides the incoming signal from the speaker terminals into separate bands of frequencies and sends them to the appropriate driver - low frequencies to the woofer etc.
Crossover networks in passive speaker systems are themselves passive and lossy. Not only is there some inherent loss in the circuitry itself but the network usually has resistors designed to even out the different sensitivities of the drivers. This is known as padding. If the drivers don’t have the the right sensitivities relative to each other, the speaker system will have a less accurate frequency response.
Passive networks are also sensitive to the impedances of the various drivers so their own ability to separate the frequencies can depend to a degree on the frequency content of the input. They will do their job more accurately sometimes and less accurately at others.
It is fair to think of the passive crossover network in a speaker system as a necessary evil.
The Active Crossover. Many of the evils of the passive network can be resolved by using an active electronic crossover network. This is an electronic device that is installed between the preamplifier and the power amplifiers that does everything the passive crossover does in a speaker system but does it better. It is not lossy. It is not sensitive to the impedance of the drivers and even makes the speakers easier to drive. It requires no padding. It provides adjustable frequency crossover points, allowing you to adjust the way it separates the signal into the various frequency bands. It serves to isolate the various drivers from each other because of its stronger cutoff slopes and the fact that each driver has its own separate amplifier. In other words not much high frequency content reaches the woofer and not much low frequency content reaches the tweeter. The active crossover also allows you to install the most appropriate mix of amplification to the system. As an example, low frequencies require much, much more amplifier power than high frequencies so you can adjust the required amplifier mix power to the job. Think of the active crossover as a better mouse trap all the way around.
The Setup. In a biamplified system, the active crossover is not added to the existing passive crossover in the speaker systems. It replaces it. You need to go inside the speaker enclosures and disconnect the passive network from the drivers or groups of similar drivers so there is no interactivity between them. You also must add a separate amplifier for each driver or each group of similar drivers. You can’t do it with a single amplifier like you did before because you have separated the various drivers from each other completely within the speaker enclosure. A bi-amplified two way system requires two amplifers per speaker system. A tri-amplified three way system requires three, etc.
If you simply add another amplifer to your existing speaker system and connect it to your drivers through the existing passive network, you aren’t really bi-amplifying. You are bi-wiring with some added amplifier power. Bi-wiring is the practice of connecting cables to both ends of the crossover network instead of just one end. The drivers, however, are still connected to each other electrically through the crossover network so it doesn't accomplish much, if anything.
While some audiophiles value bi-wiring, I’m here to tell you that the theoretical advantages of bi-wiring have not been shown to be audible. This has been proven time and again in bias controlled objective listening tests.
Don’t get me wrong. There may be an advantage in your situation to increasing amplifier power and, if there is, you should increase it. But adding it to your system in a bi-wired scheme accomplishes nothing that adding a larger amplifer wouldn’t also accomplish. You wouldn’t get any of the other benefits of bi-amplification.
Powered Bi-Wiring. You may read about the practice of “bi-amplifying” with unused surround amplifers in a receiver by simply connecting them to the bi-wire terminals of the speaker system. Let’s look at this practice objectively. I’ll call it powered bi-wiring for lack of a better term.
Since we didn’t replace the passive crossover by adding an active crossover between the preamp and the power amps, we didn’t do anything beyond bi-wiring because we didn’t isolate the drivers from each other. Furthermore, the amplifiers we added are driven by the same power supply as the amplifiers we had connected before. If the power supply supplies enough current and voltage to handle the job then all is well. If it doesn’t then all is not well. That is the case regardless of the number of amplifiers the shared supply is driving. One amp, two amps, eight amps. It doesn’t matter. In the end we didn’t really add any amplifier power to the speakers because the limiting factor is the shared power supply, not the number of amplifiers it supplies. We did nothing at all except to add a pair of wires.
Would there be a benefit to using two external amps in the powered bi-wiring configuration? Yes, if your situation requires more amplifier power. No, if it does not. Since each amp has its own supply then we are adding real amplifier power to the system, not just wires. That, at least, can be a plus.
If you are one of those who believe that bi-wiring helps, then bi-wire. If it improves your confidence to use different amplifiers on a shared power supply to do it, then go ahead. It certainly can’t hurt anything. But don’t harbor the illusion that you are bi-amplifying your system or making any change in its performance beyond adding amplifier power in the case of separately supplied amplifers. Bi-amplifiying can make meaningful improvements to the accuracy and performance of your sound system. But understand that all bi-amplifying isn’t really bi-amplifying. Hope this helps clear up some misconceptions.
