Bi-amping Rules

While anecdotal indications are that there are certainly **some** cases where audiophiles have achieved fine results by bi-amping, in both passive and active configurations and by using different as well as identical amplifiers, I agree with the foregoing comments and the article that in the great majority of circumstances the corresponding funds are likely to be applied more constructively in other ways. And presumably and hopefully the designers of most high quality speakers have gone to great pains to try to make them sound as coherent as possible throughout the frequency range. Why risk undoing that by using different sounding amps?

Also, while I agree with most of what is said in the referenced article, I don’t quite agree with the following paragraph:

Ok, so what about just using two amplifiers and forgetting about the electronic crossover? Simply using two amplifiers is not true bi-amping and does not offer the same advantages; we still face the limitations of the passive crossover. What about the notion that bi-amping reduces stress on the amplifiers since they are powering only limited frequency ranges? That would be true in a true bi-amp configuration where the frequencies are split ahead of the amplifiers, but in a passive environment both amplifiers receive a full range signal from the preamp and dump that power into the speakers, regardless of whether one is connected to the tweeter or woofer inputs. The only benefit (and it marginal at best) is simply the additional power offered by the second amp.*
* There may be a bit more advantage obtained when one employs two identical amplifiers, one for each speaker – vertical bi-amping.

Passive biamping will in fact relieve the bass amplifier of having to deliver current and power above the frequency at which the low pass section of the speaker’s crossover has essentially completed its rolloff, and will relieve the mid/hi frequency amplifier of having to deliver current and power below the frequency at which the high pass section of the speaker’s crossover has essentially completed its rolloff.

HOWEVER, when it comes to passive bi-amping what seems to often not be realized is that since both amps have to output VOLTAGES corresponding to the full frequency range of the signal, using a very powerful solid state amp for the lows and a much lower powered tube amp for the mids/highs (as some audiophiles do) will probably result in much of the power capability of the higher powered amp being unusable. A much lower powered amp can be expected to generally have a much lower maximum output voltage capability than a much higher powered amp, which in a passive bi-amp arrangement (i.e., without a crossover "ahead" of the amps) means that how much of the power capability of the higher powered amp is usable will be limited by the clipping point (the maximum voltage capability) of the lower powered amp.

Good luck. Regards,
-- Al

A couple of comments and clarifications regarding today’s posts in this thread:

In the case of passive biamping, i.e., biamping without an electronic crossover "ahead" of the power amps, it is of course correct that what has to be matched in some manner is the gain of the two amps (gain being the ratio of an amplifier’s output voltage to its input voltage, for a given load impedance), not their maximum power ratings. While amplifier gain is often unspecified, if Stereophile has reviewed the product the measurements section of the review will usually indicate the gain, or it may be determined by contacting the manufacturer, or it can be calculated to a reasonably good approximation from the max power rating and sensitivity specs that are usually provided, per the methodology indicated in the second of my posts dated 3-10-2012 in this thread.

Passive biamping will greatly minimize the amount of low frequency CURRENT and POWER that is supplied by the high frequency amp, and will greatly minimize the amount of high frequency CURRENT and POWER that is supplied by the low frequency amp. However the VOLTAGE that will be supplied by each of the amps will correspond to the full frequency range of the signal. As I indicated in the last paragraph of my post earlier in this thread, a consequence of that (which would be avoided if an electronic crossover is used) is that if there is a **large** disparity in the power capabilities of the two amps, much of the power capability of the higher powered amp will not be able to be utilized without driving the lower powered amp into clipping.

Regards,
-- Al

Pani, to be sure it's clear, my comment that you quoted was not intended to imply anything inconsistent with your comments.  And personally I am in essential agreement with everything you have said above.  From my post in this thread dated 7-25-2016:

While anecdotal indications are that there are certainly **some** cases where audiophiles have achieved fine results by bi-amping, in both passive and active configurations and by using different as well as identical amplifiers, I agree with the foregoing comments and the article that in the great majority of circumstances the corresponding funds are likely to be applied more constructively in other ways. And presumably and hopefully the designers of most high quality speakers have gone to great pains to try to make them sound as coherent as possible throughout the frequency range. Why risk undoing that by using different sounding amps?

Regards,
-- Al