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In Reply to: Why Bi-wire? posted by markrohr on August 11, 2003 at 04:33:21:
Albert Von Schweikert had a rationale that "field interference" from a cable's "self inductance" caused sonic degradation, and such interference between low and high frequency signals would be reduced with bi-wiring, because such electric fields would then be "separated."
Follow Ups:
My Physics is definitely rusty, but I thought that the principle of superposition suggested mutiple signals (e.g at different frequencies) can travel in a medium (like a cable) without interacting. This means that there would not be magnetic field modulation.That's what I'm still struggling with -- a credible explanation for the interaction between HF and LF signals in the cable.
Doesn't mean I think it doesn't happen -- just that I can't explain it to my own satisfaction (yet).
That other factor is motor/generator action within a cable, and the related problem of the cable being vibrated by the sound output from the speakers.The current through the two bi-wire sections is different, and so the cable carrying the HF current will not get motor/generator modulated by the LF currents.
Current flow in the two bi-wire cables in a simple 2nd order crossover is shown at:
http://www.geocities.com/jonrisch/page7.htmThe other factor that I think bi-wiring addresses, is that of woofer to tweeter isolation, and I go through this aspect at this page:
http://www.geocities.com/jonrisch/biwiring2.htm
and the following one.
than interaction between the fields.The acoustic coupling of the drivers you described is the first explanation I have seen of driver A affecting driver B in the frequency range that driver B produces.
In other words, the acoustic output of the tweeter causes the woofer to act as a motor for signals within the tweeter's freq range. This would clearly cause a delayed, distorted version of the original signal to be reproduced by the tweeter.
The magnitude of the effect would be dependent on the xover topology. As an extreme case, there are some speakers that have no low-pass xover on the woofer. In that case, the full magnitude of the induced signal would be driving the tweeter xover, in parallel with the cable and amp impedance.
Fascinating.....
Sounds like time for an ABX test to prove we can't hear any of this.. ;-)
I think this is true for *series* crossovers (which cannot be bi-wired, BTW), because there is often a common "node" directly tied to both woofer and tweeter. In fact, I've seen tweeters go out quite often with such crossovers, because I think the woofer's "back EMF" energy can be transferred directly to the tweeter. (This could be why some series crossovers use a "blocking capacitor" in series with the tweeter.)
well my physics is non-existant, but the concept of skin effect where higher frequencies travel along the outer shell of the conductor could be another way to say what you suggested???the change in resistance is quite trivial by the math with the audible frequencies we are concerned with... but amps of current through the trivial could add up to something. (see crossover coments elsewhere in the thread)
you also say "can travel" is that the same as "does travel"??? just tryingto get the 99 cent physics lesson i slept through in highschool wondering "when will i ever use this junk"
now histery and english... them was naps well spent.
Unfortunately, it is not superposition that must be considered.For a wire, when skin effect occurs, the current will be excluded from the wire interior, in gradations of course.. So, a skinning current will have no internal inductance, hence no energy storage. Whereas, the lf info does not, and does have internal energy storage.
If an audio lf signal is pulled across zero by a hf signal, the internal stored energy will be pulled out by the slew rate of the hf information..it is not clear yet if that released energy is consumed in the re-distribution of the current density profile, or if it reacts externally, possibly time shifting the leading and trailing edges of the hf information, thereby blurring the interpreted soundstage. That would require time shifts in the 5 to 20 microsecond realm.
See, that wasn't so hard, now was it??
Superposition does not take into account "non ideal" devices and effects, including the "field" effects the AVS alluded to. (Other effects include ESR, leakage, mutual inductance, etc.) It is a good tool to approximate the characteristics of circuits, based on "ideal" devices. Especially circuits with *multiple* voltage and/or current sources.
Assuming perfect wire, yes. However, the signal to the speakers is high current, and the slight amount of inductance and resistance the cable presents becomes signifigant, and has to be considered part of the crossover network. By bi-wiring, each side of the crossover is connected to the feedback loop of the amplifier seprately, so the amp can damp out inductive kick back from the woofer before it gets to the tweeter.I am not aware if anyone has tried to compare speaker cables with low and high inductance to see if the effects of bi-wiring are dependent on this. I would think a braided design such as Kimber Cables would not show as signifigant a difference as straight designs do.
The liniear inductance of cable is also why fancy power cables do what they do.
...by sensing for the feedback loop at the speaker binding posts?
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