Looking for views on bi-amping

One of the merits of biamping that I never hear discussed involves speaker back EMF. Speakers have mechanical resonances. The energy stored in these resonances can be dissapated both thermally and electrically. Just like an electrical motor can be a generator; a speaker can behave like a microphone and feed a signal back into your amp. Because of the long decay times of these speaker resonances, this signal may have little correlation with the audio signal. Now, if all amps and their components were perfectly linear, this would not pose a problem. However, when this 'duplex' signal passes through a non-linear device, these two signals will cross-modulate. This is similar to IM distortion. If you are dealing with a push-pull output stage that has any tendancy to class AB bias, this is a very non-linear operating region. Signals also usually pass through PS electrlytics; not noted for their linear behavior.
If you have read this far, here's the punch line. If you biamp, the back EMF from the woofer will not be able to cross-modulate with the mids and the highs. Since the woofer can store alot of energy (larger mass, longer excursion) in it's resonances, I maintain this results in some audible benefits.

You're talking about passive bi-amping, right?
The extra power will result in some benefits (see above) but is very expensive for what you get.
Using an active x-over before the amps (Active biampng) or a passive one, offers much great benefits.

I have recently actively bi-amped my 2 ch system (with a custom-made tube crossover). The improvement in dynamics, clarity, frequency extensions is remarkable. I had earlier tried passive bi-amping and did not notice much difference. It has been a lot of fun trying a number of different amps for midrange/supertweeter and woofers ( I have a very accomodating local dealer). Thus far I enjoy a 45 tube SET up top and a 300B push pull on the bottom.

Equipment:
SAP J 2000 twins-horn hybid speakers
EMM lab DCC2/CDSD for digital
Nottingham Dais/ Allaert MC-B MKII for analog

sorry to intrude
what about using combination of tube and ss amps for bi-amping...with obviously different power rating...
CJ60ES and Mac MC252
thanks

If you passively bi-amp, you have the problem of differences in gain between the two amps. I have a 2 way external crossover (actually it is a combined crossover/phonostage) which allows to equalize the gain between the two amps. thus I have been able to try different amps for the highs and lows. I have yet to try a SS on the lows.

The other reason to actively bi-amp is that since each ampb is only seeing the frequencies that are directed to it, that amp can work more efficiently. For example, the amp on top is only seeing frequencies above the crossover point for my speakers. So it's "sweet spot" is only working on the supertweeter/midrange horn and not share it's "goodies" with the woofer. My speaker's crossover between the woofers and up top were designed to be easily disabled.

Reg

A few questions on this as I am still a bit confused.

How do you account for amps that have unequal gain with the active cross-over unit?

If the speakers have 4 binding posts, can I assume that the lower post is for the lows (woofer) and that the higher two are for the mid/tweeter? With an active crossover any reason to open up the speakers or do I leave the internal cross-overs in place.

Did you try both SS and tube cross-overs?

Thanks

Have heard some active and passive bi and tri amp setups, sorry to say that chances of failure are high due to the many reasons posted above (gain mismatches mostly).

The only route I would consider is horizontal bi-amp using the same amps, otherwise I feel we are swimming against the flow of a basic principle here "Less Is More".

My One and a half cent

Fernando

I purchased a C-J Primier 11 from a good friend. I found the bass a bit lacking. I called C-J, and they recommended bi-amping with a MF-2250 for the bass with the P-11 for mids and highs. My speakers have dual binding posts which made the project possible. I purchased the 2250, ran two sets of cable to each speaker, two sets of interconnects to each amp from the pre-amp, and could not be more pleased with the results. I don't think I would go out of my way to bi-amp, but in my case I did not want to sell the Premier 11!
Regards,

It's simple to passively biamp with different brands. At least, it's simple after the mistakes. On the highest gain amp, add an attenuator (up to 5 KOhm will usually suffice). The pots I tried tended to sound bloated at the crossover point and always needed adjustments. Every CD and the volume made a change. Since I changed over to an attenuator, I had to adjust from what I thought it should be and it just stayed since. Probably something about capacitance. A properly selected resistor might work but I doubt it.

You can combine the best qualities of different amp designs but you have to consider matching characters. You also have to consider the crossover point. If it's above 200 Hz, you're getting into voices and you will hear the difference in amps.