Help with bi-amping

There are several methods of biamping.

Horizontal biamping - This uses two different types of amplifiers one to drive the upper speakers of both channels the other to drive the woofer section of both speakers. Many folks use a solid state for the bottom and a tube amplifier for the top end so they get a tube sound on top coupled with better defined lower frequencies. This is a form of "passive biamping."

Vertical biamping - Uses two of the same amplifiers to drive both channels. You may either dedicate an amplifier to the top end on both speakers and an amplifier to the bottom end on both speakers or, as you suggest, dedicate an amplifier to each speaker. This is another form of "passive biamping."

Active biamping - This uses an active crossover to split the signal and only send the high frequencies to the channel which will be reproducing them, likewise for the low frequencies. This is the best form of biamping, but also the most costly, since not only are two amplifiers required but also an active crossover.

Horizontal and vertical biamping will have some sonic benefits, but I would test with your system to see how large they are. You can view an extensive thread on the topic at: http://audiogo5.iserver.net/cgi-bin/fr.pl?aamps&990003839
There are some wonderful and concise comments in this thread.
Another link which might interest you is:

http://sound.westhost.com/bi-amp.htm

although I personally think that the benefits of vertical and horizontal biamping are greater than the author of this does. (I use vertical biamping and it makes a big difference in my system).

The amp does not have to be biampable. For vertical and horizontal biamping, it is easier if there are two preamp outs for each channel, but I don't think very many preamps suport this so, the easy solution is to use a Y cord out of the preamp and run one leg to each channel you will use. I use a Sunfire Cinema Grand, which has two inputs to each channel, and the manufacturer recommends running into one input and then out the other input into the other channel. For active biamping, there will be two outputs from the active crossover for each channel, so you just connect a cord to each.
My experiences with the biwiring and vertical biamping are that the definition and range of the speaker improved with each change, that is, biwiring was better than single wire, verrtical biamping was better than biwirng. I also found that my speakers frequency response improved with vertical biamping. Every system is different though, so you should experiment.

Regards,
Greg

Thanks!

It's sort of an interesting set of tradeoffs comparing the two. The two single amplifiers mean that the high and low frequencies are not intermodulating, which will produce a better sound. This is the opinion I have seen most often from "experts." The single amplifier on the other hand will better divy up the power between the upper and lower frequencies, which will probably let you drive the speakers to a higher SPL. There is also a consideration in that the quality of components used by manufacturers tends to improve with the power of the amplifier, so I don't think that a real world comparison of two 100 watt amplifiers to 1 200 watt amplifier would be an apples to apples comparison.

If that wasn't too clear, when you have two amplifiers connected independently you run out of steam whenever either one reaches it's power limit. On my system the passive crossover crosses over at about 120 Hz. I have seen 240-340 Hz mentioned as the point at which most music contains an equal amount of energy above and below. I can't confirm this, but it seems about right, and for the purposes of this discussion, the exact point really doesn't matter, just that it exists.

Putting these two things together, I think I would run out of power and start clipping on the top end before I ran out of power on the bottom end. Of course, the approach I used is to have more power available on both the top and bottom ends than my speakers can handle, so it really doesn't matter. :-)

Another factor to consider is that with the passive bi-amp system, you are well on the road to having active bi-amping and I have never seen anyone try to claim active bi-amping wasn't better with two 100 watt amps than a single 200 watt amp since this argument would ultimately reduce to the contention that passive crosovers are superior to active crossovers which would be a pretty tough proposition to sell. That is, assuming of course, that the amplifiers used were of the same quality.

Regards,
Greg

pmwoodward - Could you provide a link to the information from Martin Logan? All I could find on their web site was the following paragraph under the ESL Tech technology brief.

"Common low and high pass filter crossovers and the inherent problem of crossing over at higher frequencies produce phase shift and amplitude fluctuation problems when the music signal is recombined. This is because high frequency signals have shorter wavelengths, and changing the distance from the sound source to the ear can present a 180 degree phase shift, and this translates as silence to the human ear".

First, I believe that this statement refers to passive crossovers, not active crossovers. As you noted they do state that they incorporate a crossover in their ESL speakers. One way or the other the thrust of what I saw on their web site seemed to be that no crossover was better than a crossover, not that a passive crossover is better than an active crossover.

That's probably true, but I don't know enough about their technology to comment one way or another. Since we are discussing bi-amping and you can't bi-amp without a crossover of some sort, passive or active, I don't think it applies to this particular discussion thread.

Regards,
Greg