Active crossovers

There are serveral good active cross overs. Bryston 10B and the Marchand are the two that both reasonably priced and sound very good. They are both solid state. I bought the Bryston--at the time Marchand did not make a balanced cross-over. I'm pretty sure they do now. As to tube cross-overs, I can't really comment. I know of a few, but have not heard them. As to your "Stupid Question", it's really not a stupid question. If your speakers are designed to be actively crossed over then their response and impedance curves should be reasonable enough that it will not cause a significant change at various levels. However, if the two amps are not reasonably well matched in terms of sensitivity and possibly more importantly their current delivery (depending on the speaker), then you could wind up with a problem. I have not experienced this problem, but my differential between high and low end is only 1 dB. The Bryston only allows a +/- 5 dB, and this may be the reason why--if it were more you could run into some non-linear problems as you suggested.

To add to the post above, most amps are pretty linear in what is called their "gain curve". This means that what you put in is amplified at the same level regardless of how much drive is applied. To put things into generic numbers to make things easy to follow, putting .1 volts into the amp would give you 10 volts out. Putting 1 volt into the amp would give you 10 volts out. Putting 10 volts in would give you 100 volts out. In other words, it SHOULD remain a consistent LINEAR ratio.

If that were not the case, momentary peaks would be REAL loud and quiet passages would be REALLY quiet if you adjusted your listening level by the average output. Obviously, linear amplification can take place so long as the amplifier is not driven beyond its' capacity and there is enough signal to begin with to drive the amp. I have seen situations where there was enough signal to drive the amp, but not enough to drive it to full output. This tends to sound "flat" due to the reduction in dynamic range and "squashed peaks" that occur in such a situation.

With that in mind, setting the drive levels for each amplifier at the crossover SHOULD produce relatively even output through-out the various frequency ranges. This should take place regardless of volume adjustments at the preamp. Obviously, something to check before buying a crossover would be the amount of adjustability in output from band to band that the crossover would allow. It is possible to use amps with varying levels of gain so long as one could gain match them to begin with. The fact that the individual amps may be being driven harder or easier than one another to achieve initial equal output should not come into play so long as they are TRULY "linear" in amplification and have enough headroom to linearly amplify the signal presented to them.

If the amps were NOT linear in amplification, another factor that would need to be factored into the equation is that the impedance that each amp sees at the output would also vary. As such, power potential for each individual amp would change too. It is quite possible that one could be using two identical amps to actively bi-amp with and still have two different wattage potentials. This is due to the differences in impedances that the amp sees in each frequency range.

For instance, a speaker using a single tweeter and dual mid-woofers ( like a D'Appolito or MTM array ) might present an 8 ohm load for the tweeter and a 4 ohm load for the mid-woofers. While some of this would have been addressed in the passive crossover components, one could not make adjustments for this at the amp or active crossover other than to initially make sure that the output levels were balanced. After that, it would simply be a matter of each amp having enough power potential to work within the volume demands that the end user dialed up.

Keep in mind that when multi-amping, it is possible to "clip", "overdrive" or "saturate" one amp and not the other being used in a different frequency range. This explains why one can TYPICALLY get away with using a smaller amp on tweeters than one would use with woofers. Different frequency ranges put different levels of power / current demand with low frequencies requiring the most "juice" to operate properly. While some e-stat's present a VERY TOUGH load at high freq's, there usually isn't enough musical content up that high to make it overtly demanding. That is, unless you expect high volume levels out of such a design. Sean
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Gentlemen,
thank you for the excellent responses.

The speakers in question are von Schweikert VR4's; I've learned they have an impedance low of 3.8 ohms at 25 Hz and a high 0f 19 ohms at kHz. Crossover between mids/highs and woofers is at 150Hz. High/mids and woofers are physically separate (stacking design).

I would be using Rogue Magnum's for the high/mids, bass amp(s) not yet determined. The Rogue amps have an input resistance of 200k ohms.

Hiram