Axiom Home Page Forums General Discussion Technical Questions bi amping

if you were to bi amp your speakers,would that change the impedance?also, how would the route of the signal change?...thanks...ron

The load of a speaker is determined by the physical characteristics of the speaker itself. It's impedance is what it is. I assume that is to what you are refering.

I have absolutely no idea what you mean by the "route of the signal".

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if you were to bi amp your speakers,would that change the impedance?

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It entirely depends on the specific design of the speaker and its crossover design. But I believe that the "nominal" impedance (i.e., the minimal impedance across the audio frequencies) remains about the same in the majority of cases. So, for example, when you bi-amp the M80, you should consider that the nominal impedance for each amp is still 4 ohms (Alan, please correct me if I am wrong here).

If you were to bi-amp your speakers, as many audiophiles are wont to do, wouldn't you have to be extremely careful as to the length of your speaker wires? If one wire was a little longer than the other the speaker would be receiving one signal slightly in advance of the other signal.

No, Mark, speaker cable lengths don't matter at all. The electrical signal takes about 1 nanosecond to travel over one feet of copper cable. Just in comparison, the sound wave takes as much as about 1 millisecond per feet in air -- Six orders of magnitude slower. So, before you get anal about 10 feet of cable length difference, you have to be careful NOT to move your head by more than 0.0001 inch while listening to music.

Incidentally, I am HIGHLY skeptical of the sonic benefits of bi-amping. In usual bi-amping configuration, you are still driving each power amp with a full-range audio signal -- in other words, each power amp channel is not "relieved" of its duties in any way under this situation. Everything else being equal, you will get much higher max available power by using the same two channels of power amp in a "bridged" configuration (the power amp has to be designed bridgeable, though).

In other words, you are basically "wasting" the power amp channels by investing them for a bi-amped, rather than bridged, configuration. In this sense, bi-amping is an audiophile myth, IMO.

It would be a different story if you entirely bypass the passive crossover circuits within the speakers, and replace them with an active crossover inserted before the power amps -- the only configuration that I consider as a "real" multi-amping. But this is much more involved, since you have to design the active crossover parameters essentially from scratch. You have to know exactly what you are doing. And even in these configurations, the sonic benefits would be relatively small, if any.

Oh, sushi, you seem to be indicating that he meant the impedance that each amp would see. He was so unclear in his original post, that I thought he was talking about the speaker.

In that case, assuming that the higher frequency speakers share no connection with the lower frequency speakers and that they're normally wired in parallel, the impedance the amps would see would be some multiple of the original. However, exactly what that multiple is would be dependant upon the individual cones and the other components involved.

Loads in a parallel structure add like this:

1/Rt = 1/R1 + 1/R2 + ... + 1/Rn

BigWill,

Precise signal length is irrelevent at these frequencies. You're not capable of hearing the difference.

It is a concern in trace lengths on circuit boards operating at very high speeds, but we're talking more like a factor of a million or so over the audio range. In that case, the trace routes are either run back and forth to result in an identical total length or programmable delay ICs are utilized like our MC100EP195. To give you an idea, that device has a delay range from 2.2ns to 12.2ns in 10ps steps. That's way outside what any home theater should be concerned with.

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In that case, assuming that the higher frequency speakers share no connection with the lower frequency speakers and that they're normally wired in parallel, the impedance the amps would see would be some multiple of the original. However, exactly what that multiple is would be dependant upon the individual cones and the other components involved.

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What Semi described above is correct only if both the mid/tweeter and woofer terminals of the speaker present a purely resistive load that is completely flat over the audio frequencies. But that is far from reality in most cases. For example, the impedance across the woofer terminals on a bi-wirable speaker usually gets progressively higher above the low-pass crossover frequency, because of the serial inductor in the crossover circuit. The same is true for the mid/tweeter terminals, and the impedance progressively increases below the high-pass crossover frequency due to the serial capacitor.

So, in the single-amp configuration where these terminals are connected together in paralell. the woofer (and mid/tweeter) port becomes progressively "invisible" to the amp above (and below) the crossover frequency, respectively. And hence, in the bi-amp configuration, the minimal impedances across the individual mid/tweeter and woofer terminals (which occur at totally different frequencies) are usually not much higher than the minimal impedance when they are connected in parallel.

what i meant by route of the signal was, how does the path from the amp change when it gets into the speaker,meaning-do the low inputs get routed to the 6.5 woofers-and the high inputs go to the mids and tweeters-or does the low input go to the 6.5s and the mids-and the high go to the tweeters alone...i hope i wrote that so you can understand me....Sushi,your responses really make me realize that i should have stayed in school 20 years ago...lol...thanks again....ron

You're quite right sushi. I was not thinking in terms of the frequency domain.

Ron,

Ah, I understand what you mean now. I would assume the mids and highs are grouped together and the woofer is on the other channel.