Axiom Home Page Forums General Discussion Home Theater M80's and Bi-Amping???

I see. Well I was basically just asking because I was curious as to why Axiom builds them this way? I've never seen it before, which doesn't mean nobody else does this, just I haven't seen it. So I wondered just what the advantage of putting four posts on them was. There must be some reason... perhaps one of our resident Axiom experts could chim in and let us know why they are designed this way. And what perceived advantages bi-amping the M80's may have in their opinion?

Oh, many higher end speakers are set up for bi or even tri wiring. Many audiophiles feel there is a difference, so it's generally expected. The only high end manufacturer that doesn't that I can think of off the top of my head is M&K.

Yeah... normal (not biamped) operation is to amplify everything and then use a passive crossover in the speaker to separate out the frequency ranges. For effective biamping you put the crossover before the amps, so one amp only amplifies low frequencies and the other only amplifies high frequencies.

Micah, quite a few speaker manufacturers include two sets of speaker terminals, primarily as a concession to certain audiophile delusions regarding bi-wiring(aka "buy-wiring").

No, at a frequency where a speaker has an impedance of 4 ohms(the M80s are 8 ohm speakers over the majority of their frequency range)this isn't the result of two 8 ohm sections working in parallel to result in a net 4 ohms. As John B. pointed out, the effect of the crossover is to greatly increase the impedance of the section that's being rolled off. So, for example, at low frequencies the 4 ohm woofer might be operating in parallel with an upper frequency section which has an effective impedance around 100 ohms at those low frequencies. The net impedance in parallel would be around 3.9 ohms. At higher frequencies(if the impedance was 4 ohms, which isn't the case with the M80s)the effect of the crossover would be to raise the woofer impedance to maybe 100 ohms, which run in parallel with a 4 ohm high frequency section would again result in about a net 3.9 ohm impedance.

Ok, this is all Greek to me, but I think I get the jist of it & I appreciate everyone's input even though it sounds as if this horse has been beaten to death already, been revived, & beaten to death again on a number of occasions.

I'll now ask another dumb question... where I was trying to go with this is, if you were to hook up a 200 watt amp to the bottom posts, and another 200 watt amp to the top posts, does this power the individual speakers with any more power than if I were to just hook one 200 watt amp up to the bottom posts with the bridge in place? I've never really understood the way electricity works in this area. Like is the 200 watts divided up amoung the 6 separate speakers inside the M80 cabinet so that they are each only being pushed with 32 watts? Or do they each receive the full 200 watts in some way?

I was really curious about this when I purchased the EP800. At first I though, "cool, I'm getting 200 more watts of power than the EP600. But then it occured to me that the EP600 is driving its speaker with 600 watts, and the two drivers in my EP800 are only being pushed with 400 watts a piece. But I wasn't sure if this was really the case or not?

Anyway you don't have to break it down into micro mathmatics if you don't want to, just telling me if they each receive the full 800 watts is good enough for me. That's all I really want to know... well, that and how to properly inflate a bicycle tire tube.

If the same signal is fed into the two 200W amps then you're generally going to get the same effect as a single 200W amp. If you had a crossover before the amps so that LF went into one amp and HF into the other you would get the effect of a more powerful amp, although the benefit you get would be a function of how power is split between HF and LF.

In "real" biamp systems the LF amp is normally quite a bit more powerful than the HF amp, so that both amps reach their limits at about the same volume. If the really low notes are being filtered out and sent to the subwoofer (and not to the two amps) it's possible that the power distribution between the remaining LF and the HF might be more balanced, not sure.

In terms of "how power works" the main thing to remember is that a 200W amp is rated to put 200W into a specific impedence, which really translates into "putting enough voltage to get 200W into that impedence" without going into current limiting in the process. The current drawn by the speaker is a function of both the voltage and the impedence (in DC terms it's voltage squared over resistance), so a bigger amp needs to be able to output more voltage *and* more current.

If you have a 4 ohm speaker it will draw more current at a given voltage than an 8 ohm speaker, which will give you more power at the same volume control setting -- assuming the amp is able to actually provide that much current. This is why you see amp ratings like "200W at 8 ohms, 400W at 4 ohms, not recommended for <4 ohms". It's also why you see questions about whether a specific amp is a good match for a 4 ohm speaker.

In the case of the EP800 you really are getting the full 800W since both voice coils are handling the same frequency range.

Yeah, Micah; but I think it's a bit more interesting than Mike Drew vs Larry on how to inflate bike tires in the other thread. I'd suggest forgetting this "pushed" terminology; an amplifier doesn't force a speaker to take any more power than it wants for a given sound level at a given instant. For a comfortably loud level with speakers of typical sensitivity this is about 1 watt and doesn't vary regardless of the maximum output capacity of the amplifier.

No, the power capacity of the amplifier isn't divided according to the number of drivers in the speaker. So, for example, an amplifier that could output 200 watts if necessary could send that maximum output to any of the drivers that needed it.

Good to know, thank you for that information.