Tri-amping speakers - Which amps

Jerry / Onplane: I would beg to differ as i've yet to hear even a 6 dB crossover ( a simple capacitor in series with the tweeter ) that sounds as good as a "naked" tweeter ( no capacitor ) actively crossed. This not only has to do with removing the capacitor from the high current area of the circuit, but also from the electrical changes that take place prior to the amplification stage.

My Brother made the same assumption that you did here, as he was running his system as you described for quite some time. When i finally got him to try using an antique "Pro Sound" active 3 way that i had laying around, he was flabbergasted at the difference. He couldn't believe he had wasted all those listening sessions with reduced fidelity when even a 30 year old active crossover ( $40 on Ebay ) could have provided so much better results. Bare in mind that this was using cheap plastic Radio Shack 1/4" to RCA adaptors on every cable in and out of the crossover too. Sean
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As Jerry mentioned I have considered bi-amping due to the advantages such as cost, space, & simplicity to name a few. But that would seem to be a compromise. Think I would always wonder if bi-amping was an improvement, wouldn't tri-amping be better. Have not totally discarded the idea however.
Sean, you mentioned most of the things I have had to consider if I go this route. I have thought about Class A or tubes for the tweeters and mids and bipolar amps for the woofer. Obviously you cannot have this with a multi channel amp. With 3 stereo amps you have to consider compatibility issues with the system. I am not totally familiar with an electronic crossover, but as I understand it cannot totally correct for all mismatches between power sources. Any suggestions on actual amps to consider? (I am serious about doing this but don't want to just throw money at it. I like a noticable improvement, and not to quickly reach the diminishing return category.)
In your last section you mentioned 'electrical resources'. Were you talking about available power from my wall socket? If so I think the increased efficiency of tri-amping will allow amps of about 50% the usual power requirements.
The monitors with mids and tweeters are an MTM design with 4 ohm impedance and 90 db sensitivity. The wooofer cabinets have a 10" active driver & 12" passive, 8 ohm and 84 db. The sensitivity of the woofer cabinet is low but the designer has told me that 100 quality watts should do fine.
Any more discussion would be greatly appreciated.

One can typically raise the bias of ANY amp, so long as there is adequate heatsinking and air-space available. As such, you can use a multi-channel amp and have the manufacturer adjust the bias setting to operate in Class A up to X amount of power, switching over to Class B above that point.

In my experience, depending on speaker efficiency and impedance, somewhere between 6 - 10 watts of Class A power @ 8 ohms seems to work quite well with Class B operation kicking in above that point. Due to the lower impedance of your MTM section and low efficiency of your woofer section, i would recommend going higher on the bias scale rather than lower. That is, 6 watts of Class A bias @ 8 ohms is only going to net you 3 watts of Class A @ 4 ohms. While this would still be better than most, moving up to 10 watts @ 8 ohms would give you 5 watts of Class A @ 4 ohms. By the time you switch over to Class B, your listening level is so high that any form of crossover distortion becomes negligible.

As far as the woofer section goes, 100 watts wouldn't make an 84 dB woofer flinch, even if actively crossed and bandwidth limited. Besides that, passive radiator systems generate more reflected EMF than most other designs, meaning that you need even more power to keep the driver under control. I don't know how big your room is, how loud you like to listen, etc... but i would be looking at some very high powered, high current amps for that section if i were you. That is, unless you listen to smooth jazz or chamber music at background levels.

With the above info taken into account, you might want to think about a medium to high powered ( 100 - 200 wpc @ 8 ohms ) four channel amp for the highs / mids and a very robust ( 350+ wpc @ 8 ohms ) two channel amp for the woofers. Larger amps typically have more output devices and heatsinking, which allows them to share the higher load of a richer Class A bias with out as mech thermal stress on any given part. As mentioned above, sticking with the same manufacturer would have several advantages.

Before investing in any of this, do a LOT of homework. What you are attempting to do is neither inexpensive nor simple in most cases. Obviously, it can be done using less power and in a very simple & convenient manner ( one six channel amp ), but why go to all of this trouble unless you're really trying to obtain max performance? Sean
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For all the bother, you're probably better off looking at a pair of ATC active 50's or 100's. They're triamped internally and you'll avoid all the hassle of cabling, shelf space, etc. I'll bet that the results will be very similar for less money too.

As Sean mentioned this will take a lot of 'homework' to properly think it through. That is why I asked for help on this board. I have already talked with the speaker mfg at length on a couple of occasions to get his input on amplification etc. He suggested getting a multi channel amp of my choice with a minimum of 60 watts with 100 being better. I think he was trying to lower the chance of me screwing up by removing at least one of the variables. He also said his speakers did not need mega watt amps that cost what you would pay for a new car to sound great. Howvever, he did say the better the source and amplification the better the whole system would sound. I believe the Linkwitz Orion 'package' uses a 12 channel 60 watt ATI amp. This is actually what started my interest in the active system but my wife said it looked too 'odd' for HER living room.
I had not thought of contacting the amp manufacturer to discus setting the bias higher for the mid/tweeter amps. That is a great idea.
I had thought of active speakers such as the ATC. I am hoping my project will cost less and allow more control flexibility over the sound than ATC.