Tri-amping speakers - Which amps


I am seriously looking at running a tri-amped system with an active crossover and 6 channels of amplification (the speakers will not use passive crossovers). The speaker designer suggested 100-200 watts for the woofers.
With that in mind an obvious choice would be a 6 channel amp from someone like ATI or others. Another alternative would be to find 3 used stereo amps. Something like the B&K ST140 would seem like a readily available possibility, but that model is fairly old and repairs may be expensive. I guess I am 'testing the waters' with this setup and do not want to spend a fortune on amplification. I can always sell the active crossover and have the passive crossovers hooked up in the speakers, but a 6 channel amp would be hard to find other than new and I don't think the demand would be great to try and sell used. Any sugggestions/
cnut
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Active speakers are VERY limiting in certain ways i.e. you are stuck with the one specific sound that the designer voiced into the amplifier / speaker interphase. They also require power to the speakers where an AC feed may neither be convenient and / or practical depending on placement.

Having said that, active speakers can have multiple technical advantages to them. Obviously, the bottom line comes down to sound. One would have to like their sound quite a bit as they come, as one can't "fine tune" the system by substituting amplfiers, cabling, etc...

There are quite a few design considerations that have to be taken into account with an active speaker, and quite honestly, i've never seen one that really caught my eye. Then again, i've never really looked at actives for several different reasons. I don't like having all of my eggs in one basket, as all the baskets i've seen aren't quite sturdy enough and / or lack versatility and / or the sonic traits that i desire : ) Sean
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Thus is the entire problem with tri-amping. How much $'s and complexity to achieve sound that often is far, far removed from the "flat" response that the manufacturer's seek.

B&W has the following on their website:

"The term crossover is a little misleading. A multi-way speaker contains a crossover network that not only divides the incoming signal into different frequency ranges, appropriate to the working range of each drive unit, but also equalises each driver's response to be flat (raw driver responses are usually anything but flat)."

They further have a very interesting article (it's short):

http://www.bwspeakers.com/index.cfm/fuseaction/local.faq/ObjectID/F5CA2EE1-3D20-11D4-A67F00D0B7473B37

There is a fair amount of confusion about passive xovers. Most people think their only function is frequency separation. Not true. In many high quality units the manufacturers have "shaped" the frequencies sent to the drivers to correct for non-linear drivers and cabinets.

Further, this huge "power loss" is somewhat a myth as well. Xovers don't really dissipate power (other than the trival internal resistant of the components). What they do is "block" frequencies unwanted for a driver.

In any event, Cnut, one way to insure you maintain the voice of your speaker systems is to passive bi-amp. That is, leave the passive components alone and use two amps. Each amp ends up with a much easier task because the impedance for each amp is just much better behaved/simplier.

My "gut feel" is people, who claim a huge improvement in sound out of tweeters, are simply sending more power to those tweeters. Yes, the sound is brighter/clearer, but the same could be done with EQ's and even tone controls.

Regards,
Jerry
Jerry mentions the 'flat response' being the speaker designer's intention (in some cases). Doesn't flat depend largely on environment. As I understand it, ideally you test a speaker outside to determine how it truly measures. Tri-amping with an outboard active crossover is the recommendation of the designer of the speakers I am considering. He has several designs of 2 way monitors (with passive crossovers) that he can match with his own designed passive sub(s). The builder has indicated to me that for the 'best' sound from his design you need to leave out the passive crossover from the monitor and go the active tri-amp route. You take measurements of the speakers output in your listening room using a Radio Shack meter and aided by pc software use the controls on the crossover to 'tailor' the sound to correct any problems with the room.
While this would take some work and time, it does seem to me to be the best way to get the most out of your equipment. This route would add some expense such as an active crossover, more cables, and more channels of amplification, but if done correctly would appear to have a lot of benefit. Yes, I know I said "if done correctly". It is common now for the more expensive subs, and some of the cheaper ones, to have a built in amp & equalizer to correct for any bass nodes in the room. Bass problems are supposed to be the most common and problematic but why not address problems at higher frequencies as well? Some speaker mfg put controls on the back of their speakers for basic adjustment particularly for the tweeter. Is this merely for personal taste or are they helping to taylor the sound to the particular room?