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

I have a question in an area I'm not too knowledgable about concerning the M80's.... since there are two sets of terminals on the back of the speaker (connected with a gold plated bridge) I was wondering what the effect of running two wire runs to the speakers would be and removing the bridge. Say for instance, I ran one wire run from the Emotiva to the bottom posts, and then another run from the Denon to the top posts, what would this do? I believe it's called 'bi-amping', but what is the positive or negative effects of doing this? Would this turn them into 8 ohm speakers? Do the bottom posts only feed the bottom two drivers and the top posts feed the top four? Or is it three and three? Or is there any separation at all if you remove the bridge and run them from separate amps?

Excuse my ignorance in this area, I'm just curious as to the possibilities of having the four post arrangement like the M80's have.

It would be bi-wiring. And it would cost you more. That's about all it would do.

Using two separate amps to power one speaker is bi-wiring? Then what is bi-amping?

whoop, you're right, that's bi-amping. But it really wouldn't do much, if any good. There's another discussion going now in the Tech forum. Or the Advice forum. Dunno, I'm drinking scotch.

You only really get a benefit from two amps if you have an electronic crossover before the amps that just sends low notes to one amp and high notes to the other amp. Without an electronic crossover you're still amplifying all the signals in both amps so you're not really gaining anything.

Then again I always thought the best thing about bi-amping was being able to crank the volume until the amp driving the woofers was clipping like crazy and still have clean sound coming out of the mids and tweets

IIRC the lower set of terminals on the M80 goes to the woofers through the woofer part of the crossover, and the upper set goes to the mids and tweets through the mid/tweed parts of the crossover.

Wow, I like my music loud... but this sounds absolutely mental!!! Bahahaha hahahaha hah hahah ah ha hahahah!!!



Ah, I see. This is what I suspected. So again I ask, by splitting the woofers from the mids/tweets wouldn't this change the ohm load? Wouldn't one amp push an 8 ohm load to the woofers and the other amp push an 8 ohm load to the other four speakers? Or does it work that way?

I would not waste your time, this topic comes up all the time.

No, I don't think it changes the impedance. I know that someone has the technical answer, and I've seen it before, but I don't remember what it is right now.

Useful, ain't I?

Um, still drinking scotch, Ken?

Given how my morning is going (not to mention the threads in this forum), it seems like a good idea, don't it?

Yup!

Maybe I should pour a wee bit in my coffee too?

My coffee was cold.

I just microwaved mine. Just to reheat it, though.

*slurp*

Want more coffee.

Call Starbucks, see if they deliver?

I said coffee, not charcoal-inna-cup.

Nah, I should just make more.

See? I knew that would get you motivated!

No... fresh... coffee.... urgh.
Must shop...

>>No, I don't think it changes the impedance. I know that someone has the technical answer, and I've seen it before, but I don't remember what it is right now.

The best way to think about it is that the woofers and mid/tweets are active in different frequency ranges and that the crossover makes them seem to have a very high impedence outside those ranges. At low frequencies you might have a 4 ohm woofer and a 200 ohm midrange, while in midrange frequencies the numbers would be reversed. At the crossover point both speakers would appear to have a higher than nominal impedence (say 8 ohms instead of 4) and in parallel that still gives you 4 ohm effective impedence.

I saw a post on another site suggesting that an active crossover is needed before the amps otherwise you are amplifying the complete signal through both amps before sending them through the speakers crossover circuitry loosing any potential gain. Basically you amplify the whole signal and then filter part of it out by passing it through the crossover?

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.