Theoretical basis for Bi-Wiring

PhysicsCoder

Just a quick question. I know that bi-wiring provides an improvement in sound quality (at least, it did for me). But how?

The only guess that I can make is that there are two phenomena at work:

1) the increased cross-sectional area of the conducting path leading to the speaker reduces the overall resistance seen by the amplifier. (probably not a very strong effect...I can't imagine my wires being more than an ohm or two at most.)

2) the added electrical distance between the high- and low-frequency circuits reduces interference caused by reflections off the crossover. The reflected waves would be attenuated somewhat (although, probably not too much with good wire) and would probably not be in-phase with the original signal. This would make sense as the greatest improvement in sound was in the upper-mids, close enough to the crossover point where reflected signals could leak into the other channel.

If #2 is correct, then it stands to reason that sound quality would improve with wire length (neglecting the impedance and dispersion of the wire, of course). Without bi-wiring, the two circuits are separated by only a few centimeters. Bi-wiring would increase this to a few meters. So, if we take this to infinity, then there would be no electrical interference between the high- and low-frequency circuits.

So, any thoughts? Am I close to the mark, or way off base?

dorokusai

You just opened up a can of worms

pjdami

Welcome to Club Polk Physicoder,

this has been a hotly debated topic in the past, hence the "open a can of worm" comment. Do a search for "bi-wire".

If you want theory and physics formulas check out this thread someone here posted a while back and forward through the pages:

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/biwire/Page1.html

PJ

gidrah

More surface area on speaker wire, more surface area on connectors, it divides the duties of the crossover in half and it (usually) removes that lousy jumper.

organ

With jumpers in place:
No speaker driver is perfect. When the woofer is asked to play something, it doesn't usually stop exactly when it should. In this case, it's not in total control of the sound it's producing. The woofer may still vibrate several times back and forth after it's supposed to. This introduces EMF (Electro Magnetic Feedback). The unwanted movements creates a charge from the coil and magnet(EMF). This electrical charge leaks out into the jumper and maks its way to the tweeter. The tweeter is then asked to play the unwanted signals and we get distortion. This is why most people hear a difference in the mids and highs.

Bi-wired:
Any unwanted charge produced by the woofer will have no choice but to be sent back to the amplifer. The charge is then dampened by the amplifier. IMO, the better the dampaning factor of the amp, the more benifits you'll get out of bi-wiring your speakers.

Maurice

danger boy

I'm thinking bi wiring works on three levels.. 1. being that you are now in effect doubling the amount of current being sent to your speakers.. hence the doubling up of wires/cables.

2. for me it gave me better seperation between the tweeter and mids/subs. but for me it added to much brightness in the tweeter. so while I still have my RT800i's biwired.. i did reinstall the metal jumper.

3. it just looks cool

None of my friends can biwire their speakers.

PhysicsCoder

Interesting, I had not considered the fact that a big ol' speaker will ring a little bit. That makes a heck of a lot of sense. However, there would still be a direct electrical connection between the woofer and tweeter, just back at the amp connectors instead of at the jumper. I still think it has more to do with signal attenuation and phase. But I could be wrong.

(Just a nit-pick: EMF stands for Electro-Motive Force. Basically, any electric or magnetic effect that induces a force on a charge. This usually refers to magnetic phenomena, where a changing magnetic flux causes charge to move in a circle around the field lines; or, in the case of a speaker, through the speaker coil and back out into the wire, just as you said.)

There shouldn't be any more current sent to the speaker, though. The amp will still see eight ohms (or four, whatever) with bi-wiring. In terms of simple resistance, there is no difference between the split in the curcuit occuring at the amp or at the jumper. The added wire area will decrease the total resistance of the wire only, not the speaker.

I agree that it looks totally cool. :cool: And it establishes me as the alpha-male of my herd.

pjdami: thanks for the link. I glanced at it last night, but was too tired to really pay attention. I'll check it out this weekend.

Didn't mean to open a can of worms

organ

Thanks for the correction there coder. Maybe the length has something to do with it as well. The resistance should be much greater when the unwanted signal has to go backwards to the amp and up the tweeter. It becomes harder for the unwanted current to make it's way back to the amp while the amp is pushing a lot more musical signals against it to get to the woofer. Man this bi-wiring thing is effed up. When will somebody do a scientific test to see if there's a difference.

Maurice

PhysicsCoder

LOL...give me a nice grant and a set of LSi's, and I'll write you a whole friggin paper about it!

HBombToo

If the following is what I think I'm reading then I'm probably following you guys:

1. Reduce resistance of the run due to an increase in effective surface area.

2. Provide additional high freq/low freq isolation at the crossover.

??? The issue of back emf I'm not quite following though ???

***Back EMF originates at the speaker which is seperated from the amp by the crossover so how does bi wire reduce this effect?***

HBomb

Airplay355

can't touch this post...idk anything bout this...thanks for opening the can though so i can learn bout this stuff, i would have cept i wouldnt even know what to ask

DarqueKnight

The best thing you can do is try it with your setup and see if you hear a difference.

I experimented with bi-amping and bi-wiring for a while. Sometimes it provided improvements and sometimes it did not. Sometimes bi-wiring sounded worse than standard wiring.

It all depended on the speakers and amps I was using.

PhysicsCoder

Thanks for that link, pjdami. Interesting discussion about the interaction of the crossover with the wire pairs, and the resulting impedance effect. I imagine the effect would be stronger with a second-order crossover.

As for the back-EMF, HBomb, I doubt that the crossover network in any sane speaker is in any way directional. Putting isolation into the circuit would make it very complicated; in fact, it would probably have to be an active circuit with an optical isolator to be effective. A simple low-pass filter is just a single inductor, which has no preference for current or wavefront direction. Same goes for the capacitor of a simple high-pass filter (...unless it's an electrolytic capacitor...which I doubt would be used because of its polarity).

I'll bet that all of these effects contribute slightly. Anyway, I just like the way it sounds.

Would any of the Polk Engineers like to chime in?

HBombToo

Originally posted by PhysicsCoder

As for the back-EMF, HBomb, I doubt that the crossover network in any sane speaker is in any way directional. Putting isolation into the circuit would make it very complicated; in fact, it would probably have to be an active circuit with an optical isolator to be effective.

I did not, "in any way", imply directionality. My point was that the speaker itself is responsible for any back EMF so HOW does bi-wiring effect this phenomena? My only reason in mentioning the crossover was its place in the circuit.

BTW lets not forget about ELI the ICE man...

HBomb

PhysicsCoder

Oh, sorry, HBomb. I misunderstood you.

Don't know how it happens. I'm just making a bunch of guesses. And since most of my guesses turn out to be wrong anyway, I wouldn't waste too much time listening to me

(...ELI the ICE man?... )

HBombToo

Originally posted by PhysicsCoder
Oh, sorry, HBomb. I misunderstood you.

Don't know how it happens. I'm just making a bunch of guesses. And since most of my guesses turn out to be wrong anyway, I wouldn't waste too much time listening to me

(...ELI the ICE man?... )

I'm just trying to figure this whole thing out myself so no sweat.
I just can't figure how back emf is reduced by bi-wiring?

E leads I in an Inductor
I leads E in a capacitor

ELI the ICE man... just something I learned and never forgot about phase from the Army Tech school.

HBomb

PhysicsCoder

ELI the ICE man. That's clever (would've helped me back in my basic circuits class, too!). I was beginning to think that Eli was some sort of unfrozen caveman cowboy...who...um...would speak to people...about speakers...and sasparilla...umm....(never mind)

Army Tech School, eh? Well then, you probably know more about this stuff than I do. Lemme know if I'm being really stupid about anything!

You know, the more I think about it, though, the less I think this effect matters. The woofer should only resonate at its natural frequency (or frequencies). These would be the "ringing" frequencies in the back EMF, and should be well below the cutoff for the HPF in the crossover. I know that when I tap the 6.5" drivers in my speakers, the resulting "thump" is pretty low-pitched, certainly below anything that would come through the tweeter.

...hmmm...

HBombToo

Originally posted by PhysicsCoder
and should be well below the cutoff for the HPF in the crossover

Now your talking. The typical polk crossover is 2nd order and the response of the woofer will see and open from the high pass side and vice versa for the tweeter looking into the low pass.

HBomb

organ

The natural resonance freq of the woofer may be too low for the tweeter. It is probably the strongest resonance. But there will be many more above that freq, they just won't be as strong. Depending on the freq and volume the woofer is being asked to play, there will be different resonant freq produced, some strong and some weak. It's also possible that some of it could be in the range of the HP x-over and above.

Here's my take on the bi-wire and jumpers: We know that current follows the path of least resstance. Since the amp is always running, it becomes much harder for the electrons to travel back through the speaker cable. There is a much stronger flow coming towards the EMF from the amp. The resistance will probably be too great for the EMF to reach back to the amp that it's most likely dissapated as heat. It's like trying to have a skinny **** swimmer trying to swim upstream when the water flow is very powerul. When you have the jumpers in place, the distance is much shorter and the resistance will be minimal because the audio signal is flowing to the tweeter. So the EMF sees this as the path of least resistance on the branch.

Maurice

PhysicsCoder

Ahhh...but an electron near the amp will probably never get all the way to the speaker anyway. In most electric currents (through metal wire) the electrons only move on the order of centimeters per second. With a constant DC voltage it would probably take a few seconds at least for a given electron to travel from the amp to the speaker. Also, the signal going to the speaker is an AC signal; the electrons are wiggling back and forth, not really "flowing."

It's the wave traveling through the wire that matters, not the medium carrying the wave. Think of talking to a friend through a long tube. The air in the tube is pretty much stationary, but the information moving through that air (sound) gets through just fine. What's more, you and your friend can both talk simoultaneously, and the sound waves will move through the tube just fine in both directions. It's an analgous situation with electrons in a wire.

...all that being said, I'm still not sure why the heck bi-wiring works!

BeginnersLuck

Originally posted by PhysicsCoder
...all that being said, I'm still not sure why the heck bi-wiring works!

So are you saying bi-wiring works , your just not sure why? Because some will argue that it makes no sonic differences compared to using equivalent gauge wires...at least to the human ear...

So I'm not sure why people think it works...most speaker runs are way to short to gain an advantage from the different characteristics that a single/bi-wiring configuration can offer...

Oh and one other thing, electrons do not flow through wire like the waves traveling through a hollow tube...certain frequencies will make it throught the tube depending on the length of the tube and the wavelength of the frequencies beign sent, also if two people are talking through the tube at the same time, you will most definitely get some cancelation resulting in sound waves that will not be heard. When electrons travel along wire, they are taveling along the outter core of the copper strands, they are not bouncing up and down like a sine wave. They (the electrons) are looking for the quickest path from the destination to the source...Therefore, I would assume the electrons are flowing and not wiggling...please correct me if I am wrong...Thanks.

Later,
-BL

PhysicsCoder

Hi, BL.

No, I'm not saying that they're moving up and down like a sine wave. The electrons are actually moving in random directions, with only minor biases in one direction or another depending on the voltage accross the wire (technically, the electric field at any point). The back and forth bulk motion of electrons is what propogates the wavefront, just like the back and forth motion of air molecuels propogates the pressure wave that is sound. All I really wanted to say is that the electrons don't move nearly as far as one might think, and that a huge amount of energy can be transmitted by moving all the electrons in a wire a surprisingly small distance. Moreover, since the current being carried in speaker wire is basically a bunch of sine waves, then any given electron can be expected to oscillate about its point of origin.

Current is evenly distributed through a wire. If a wire had a static charge on it, then that charge would be distributed along the surface of the wire. But a wire conducting electricity is still neutral (prependicular to the current), and there's no bias for the charge carriers to move to the outside edge. The only field present is the electric field pointing along the axis of the wire.

I was just making the point about sound in air by way of analogy, to show that waves can pass through eachother going in opposite directions (think of your telephone: incoming and outgoing sounds are carried through the same wire pair). I didn't want to get into interference, waveguides, and mode selection...I'm already being annoying enough in this thread :rolleyes:

BUT, I think bi-wiring works. At least, my speakers sound clearer (not that they sounded bad to begin with). I just thought I'd beat a dead horse and ask "how?" Get a good thread going with lots of technical jargon, ego, and fistfights. It would be interesting to see if theres any difference between bi-wired 12 gauge and single-wired 8 gauge (or whatever the equivalent cross-section is). But 12-gauge is hard enough to get into those little holes...

BeginnersLuck

Originally posted by PhysicsCoder
BUT, I think bi-wiring works. At least, my speakers sound clearer (not that they sounded bad to begin with). I just thought I'd beat a dead horse and ask "how?" Get a good thread going with lots of technical jargon, ego, and fistfights. It would be interesting to see if theres any difference between bi-wired 12 gauge and single-wired 8 gauge (or whatever the equivalent cross-section is). But 12-gauge is hard enough to get into those little holes...

Hello PC-

I think that is the main point I'm trying to hammer home concerning bi-wiring. Most people who try it out are upgrading from a single 12/14 gauge run of wire to two pairs of 12 gauge wire. I just say that if the person went out and instead of bying two 12 gauge runs just bought a 10 gauge wire and ran it to the speaker they would notice the exact same diffenece.

At first I was running 12 gauge wire to my speakers. Later, I decided to try bi-wiring and added another pair of 12 gauge wire to each run. Later, I was presented with an opportunity to try out some 10 gauge wire in place of the two 12 gauge runs. Could I notice a difference? No, niether me nor my fiance noticed any difference. (Notice: all speaker wire was from the same line from the same manufacturer, Tranparent Cable) I imagine different cables have different characteristics, so to keep it fair I used the same wire. So like I said earlier, while bi-wiring may look cool, at short runs (<100ft. or so) it offers no sonic benefits over its equivalent single gauge counterpart.

2 16 gauge runs are equivalent to one 14 gauge run...
2 14 ... ...12...
2 12 ... ...10...

So in the end I went with the single run of 10 gauge and have not looked back...

Oh, and welcome the forums, it's always nice to have more technically inclined people aboard...

-BL

HBombToo

PC, does mean free path ring a bell?;)

BL, I'm with you on this... its all about guage which is indeed surface area and not much more hocus pocus than that for the effects of Bi-Wire.

I have really enjoyed this thread BTW... Keep em comeing PC.

HBomb

PhysicsCoder

"Mean Free Path"...hehehe...you're bringing up bad memories from college, man . Yes, thermal noise matters, and the electrons are far from "stationary" when no current is flowing. I'm just a-talking about average bulk movements here .

You've got a good point there, BL. I upgraded from a single pair of 12 gauge to a double pair of the same stuff. I did notice a slight improvement, but I freely admit that I WANTED to hear an improvement. It's very possible that I'm only hearing what I want to hear.

Maybe I'll get some big-**** 0-gauge wire! Get some $400, inches-thick copper rope, and spot-weld it to the amp and speakers!

...Er...perhaps not...

PhysicsCoder

You know, the more I think about it, the more I'm starting to agree with you guys. Reflected waves would be conducted through the wire with minimal attenuation, resonance from the driver would be filtered out by the HPF, phase changes should make for more noise, not less, and so on. The only thing that stays consistant is the increased surface area of the wire(s).

I'm still going to beleive in bi-wiring for at least a little while, tho...just because...besides, it truly does look cool :cool:

(must think harder! There's got to be some bizarre, half-assed, second-order phenomenon at work!)

Oh, and thanks for the welcome, guys. I'm having fun here.

HBombToo

Originally posted by PhysicsCoder


(must think harder! There's got to be some bizarre, half-assed, second-order phenomenon at work!)

Consider the Damping Factor of you amplifier. We talked about this a long time ago but in short its your amps ability to overcome the standing waves over the run which has alot to do with your cable runs resistance.

Get your learn on then teach me:D

HBomb

HBombToo

Originally posted by PhysicsCoder


(must think harder! There's got to be some bizarre, half-assed, second-order phenomenon at work!)

Consider the Damping Factor of you amplifier. We talked about this a long time ago but in short its your amps ability to overcome the standing waves over the run which has alot to do with your cable runs resistance.

Get your learn on then teach me:D

HBomb

BeginnersLuck

Ok, here is my basic knowledge of damping factor...the damping factor is calculated based on the load impedance and the amplifiers impedance...Load/Amp impedance give you the damping factor of the amp. So lets say you have an 8 ohm load and the impedance output at the receive is measured to be .01 ohms. The damping factor would be 8/.05 = 160. The higher the damping factor, the more control the driver has to stop ( less "ringing" as most people put it) The damping factor also varries with different frequencies. This is where the size of the wire comes into play. The thicker wires allow a damping factor than thinner wires. Most really good amps have very high damping factors usually well above 1K. This works because the EMF of the driver naturally brings the driver to a stop, thus a receiver with a high damping factor has a low output impedance. This low impedance allows the back EMF to control the driver more accurately. (think of it as an air brake) The higher the receivers impedance, the more restriction that applied to the brake thus makeing the driver appear to have less control over its movements becasue the brakes natural control (EMF) is now limited. The lower the impedance, the less restriction that is applied allowing the back EMF to act more natural to counteract the drivers excess movements....

So in the end you want EMF to control the driver, but higher impedance outputs from the amp cripple its effects...
thus causeing the drivers to "ring" or produce unwanted frquencies....however, this mostly a concern with speakers that use large driver...large driver, naturally, are harder to control and benefit most from high damping factors...

Hope this is not too confusing!
-BL

HBombToo

YUP!!! This is probably why I'm on the side of decreased impedance due to the bi-wire application haveing the biggest impact. No other real hocus pocus IMO.

Good Job BL!

HBomb

OH BTW... this is also why the effects and perceptions of the bi-wire application change from 1 system to the next because of all the different hardware out there. For a solid state amp though the impact is still marginal at best.

PhysicsCoder

Wow, I'd never heard of that effect before, BL. Nice description, that makes a lot of sense.