Tri-amping speakers - Which amps

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.

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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