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All depends on the crossovers, how the all thing is put togheter, but i think you should not run your amps the way you're describing. Much better would be if you run your amps as mono for lows and highs, if you connect one chanel for lows and the other for highs, don't forget there is crosstalk on each stereo unit, power supply and other factors. Question about impedance would be best resolved by contacting manufacturer of the speakers.
as far as what ohms your amps will be seeing, i'd tink ya have to contact the speaker mfr. as to the crossover construction.
as far as vertically biamping your speakers, ie: using one stereo amp per side & having the left channel drive the tweet while the right channel drives the bass/mids, many folks have done this w/good results. the possible cross-talk between channels (bass-treble) in this set-up may be less than the cross-talk between left-right channels in a conventional *horizontal* biamped set-up.
but, there's one thing i'm confused about - ewe say yure using an outboard x-over *before* the amps, then the signal gets routed thru the speakers' x-over? this i definitely wood not do. if ya wanna experiment w/active x-overs, that's fine (tho, again, i'd recommend contacting the speaker mfr as to their recommendations for x-over point/slope/etc). but if ya do this, then ewe should hook up the speaker cable directly to the drivers, & disable the speakers' built-in passive x-over.
good luck, doug
Sedond is right about the active cross-over. Only use this if the internal cross-over has been disabled (bipassed). I'm using an active cross-over, but my speakers were designed to use an active cross-over--in fact, if bi-amped they must use an active cross-over.
Using one stereo amp for left and right is not a bad idea at all. There is less cross talk in this set-up because one amp is seeing the left channel--rather than two different channels. There will be differences due to the high pass vs low pass, but they will be harmonious and I would not see cross talk as being much of an issue--if any. I presume you are doing this to get each amp very close to the speaker and run as short a speaker cable as possible--if that's the case--good choice.
Lastly, ohm rating. I'm going to go out on a limb here and guess you have a nominal impedance speaker (4 ohms), but I'm guessing you are asking this question because it has a tendancy to go very low in impedance, and you think bi-amping will help this problem. As previously posted, only the manufacturer of the speaker can give you this information. It will be different for the high end and low end. I have a pair of Martin Logan Monolith IIs. They have very low impedance from the panel. The bass has a reasonable impedance--4 ohms and probably doesn't dip much below that, but the problem with single amps on this speaker is the impedance drops from the panel, then a bass drum kicks in and there's no umpf left in the amp (umpf is a technical term). By bi-amping you isolate the demands of the woofer vs the low imedance from the panel. I don't know if you own MLs or other speakers with similar characteristics--but I said I was going on on a limb here. If this is the issue you are trying to address--it should work very well--it did for me.
Good suggestions, I will check to see if my speakers really require an active crossover or not, but I don't think they do. The reason why I want to use one BEFORE the amp is that I want to reduce the load on the amp by getting rid of the frequencies that the speakers will not produce. I am sure you have seen my other questions relating to bi-amping a pair of Infinity Kappa 9's Putting all the suggestions together I have come up with the following set-up. Almost all of my components are higher-end Yamaha (sort of mid-fi I guess) I have a Yamaha CX-1000 pre-amp with two sets of outputs. One is being run to a Infinity SSW-210 sub (250 watts, 2 10" drivers) The other set I plan on running to a Paradigm X-30 sub crossover. This is due to my Kappa 9's having a 80hz crossover for bi-amping/bi-wire configurations. And the x-30 has 80hz as it's middle high-pass setting. According to reviews and tests the high pass is actually about 75hz. So I figure if I run the high pass out to one of my two Yamaha MX-1000 amps and then to the Kappa 9 crossover I should have a seamless connection with the K9 crossover throwing out just 75-80hz. I will also run the low-pass a bit above 80hz with the same results on the low end. That way the amps are only producing the frequencies that are required. I think it will all work fine. My Ohms??? question is because the Kappa 9's are rated at 4 ohms, but that drops to less than 1 ohm over part of the frequency range. And this is a bit too much for one MX-1000 sometimes. (my second MX is on it's way) I am hoping that by bi-amping I will solve that. Less paths for the power to travel equal more resistance right? I know, I know I really want to get a Sunfire Signature and bi-wire it for a much better result than that Yamahas could ever produce. But that is out of the question for a little while anyway. Someone must have examples of what they have seen once going to a bi-amp set-up. Since my speakers are 12 years old (just bought them used) I don't know if I can trust what Infinity says if I do get ahold of them. I have all the documents and there is nothing that is helpful. I have tried to measure the resistance with a multi-meter, but I never got any results that made any sense. How can I measure what I want to find out?
You don't really need to put the cross-over before the amps if your speakers have an internal cross-over designed for bi-amping. You pointed out that you don't want the amp to see the load (reduce the load), but the load is generated by the speaker, not by the incoming information. So, if the speaker only draws high pass information from one channel, that is the only load the amp sees. The additional low pass information you have sent the amp is just extra information and should really have no effect on the load of the amp (or it's performance). I don't know very much about your specific speakers, so I can't make specific comments, but perhaps someone else with those speakers can be of some help.
The posts above are all correct. Your speakers have a low impedance at a certain frequency and you don't know which frequency, so if you go with the amps per channel approach you are stuck at that freq. on each channel. However, if you isolate the problem to a frequency, and split up the amps over channels you can have a bigger amp take over ath the critical place.
You mid-fi stuff is really excellent!! At one time I thought the Kappa 9's were the best value in HIFI meaning the most drivers and woofer square inches for the buck. Congrats!