To bi-amp or not to bi-amp?

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I actually have this dilema myself... I mean, I _HAVE_ the extra channels, so I could take advantage. I even have the appropriate Y-cables and speaker wire lying around, so it's no added cost... (Just picked up a Rotel 1077)


However, at some point I'll want to move from 5.1 to 7.1, so if I get used to the sound from bi-amping, maybe I'll be less happy with single amping.


Of course, my dealer may be happy as I might feel the need to get a stereo amp (;

To reword what Kal said, but int more authoritative terms, it is a fact that there is no benefit to merely hooking up two amps to the passive crossover of a speaker. The amp still has to swing the full voltage load, its just that the peak current the amp sees (and thus the peak power) it sees will be less. This only solves the problem of having a power amp with a weak power supply. Getting a superior amp would solve this problem with considerably more simplicity.


The benefits to biamping primarily come from filtering the signal in active components at line level so you can have predictably flat response. Also, eliminating passive components between the amps and the drivers allows the amps to have better control over the drivers.


Most of these hifi companies only add two sets of terminals for marketing value, not an actual engineering reason to do it. The sales they could potentially lose from ignorant audiophiles demanding to (incorrectly) biamp, or even worse, biwire the speakers far exceeds the value of the terminal itself. It may be good business practice to add two pairs of terminals, but its not good audio practice to attempt to make use of them.

Its voltage rails. Even with NOTHING connected to the speaker terminals (i.e. no current drawn, an open circuit) a power amp can not swing a voltage greater than its rails. If your amp has 35V rails, it can't put out a signal beyond (or even near that, really), without significant distortion. Regardless of the current draw, the voltage fed to the input times the voltage gain of the amp will result in the voltage it wants to swing to. If it can't reach it, you've got clipping (or at least some sort of nasty distortion). If you take one amp that can swing a max of about 25V (80 watts into 8 ohms assuming unlimited current supply) and then passively biamp with another identical amp, your headroom is still only 25V at instantaneous point in time. Say you had a signal that was a 100hz sinewave and a 10khz sine wave summed together. Each sine wave has a peak of 15V before summing. When you add the signals together, the new amplitude of the signal is 30V. If you fed this into two "25V" power amps separately, they both see a 30V signal even if they may be supplying no current at all. The signal will be clipped and you will have distortion. This is why passive biamping doesn't work.


The reason active biamping DOES work is because the signal is filtered before it gets to the power amp. Take a 100hz 15V sine wave and a 10khz 15V sine wave, add them together, separate them again in a crossover, and one amp will get a 100hz 15V sine wave and a greatly attenuated 10khz sinewave (you can calculate exactly how much based on the rolloff of the crossver). So individually, each amp might only see a 15.1V peak instead of a 30V peak. They will also have, just like in the passive biamping situation, more current output by way of TWO transformers rather than only one.


Active biamping A) increases the amps control over the driver because there are no longer any passive components in there, B) reduces intermodulation distortion (the narrower the bandwidth, the less intermodulation distortion there is), and C) also increases the total amount of potential power.


Passive biamping doesn't accomplish A) because you still have passive components in the signal path. It doesn't accomplish B) because both amps still have to amplify a full range signal. It doesn't "really" accomplish C) because you're still limited to the voltage rails of each amp. In short, passive biamping does nothing.

And at the possibility of looking like a doofus posting three times (I don't like editing posts unless its a mistake I catch immediately after posting it), I'll ALSO say that Anthem's overall conclusion is pretty much the truth.


Replacing a passive crossover with an active one requires more knowledge than most end users have. The "correct" way to biamp is to design a proper circuit, actively, to fix the shortcomings of the driver. This is not possible with an off the shelf black box. I converted my speakers to active biamping, but I also had the schematic for the factory-biamped version of the speaker to go off of. While it is not in good business sense to recommend against a course of action that would sell more amps (i.e. "Don't biamp at all if you can't do it right"), the reality is that unhooking the passive crossover and hooking up the wrong active crossover is worse than just leaving it as is. Passive biamping will sell more amps, but is pretty much pointless for the end user.

Ethan -


In my experience bi-amping DOES work. I ran my Aerials off 2 channels of the 5125 and it did fine... then I bi-amped them with 4 channels off the 5125 and the improvement was immense.


I would however recommend that you buy a higher current capable amp than relying on bi-amping with lesser amps. For example - I then replaced my 4 channels of 5125 power with 2 channels from a Levinson 336. You want to talk about night and day....


I guess what I'm trying to say is buy the best amp that you can... more channels of amplification isn't always better - but if you bi-amp with the same power then it will most certainly be better than not.


Sorry if that's confusing. BTW... I'm going to keep the 5125 (to bi-amp my center channel and drive a pair of surrounds).


What's your budget - just curious? You can score some great deals on used gear.


Jim