Could someone explain the reasoning behind biwiring? (1 Viewer)

[Chu Gai]

this of course assumes, with respect to the damping factor, that it is the major contributor in controlling the vibrations of the speaker, no. quite often, though, it represents but a small percentage, shall we say less than 10 of the system as a whole. I recall some studies some time back with Richard Davies I think who was able to vary the damping factor and it wasn't till around 10 or 20 that people were statistically able to determine a difference. Hence, it'd seem to me that going up by say a factor of 10, provides a rather decent margin beyond which it becomes academic and a matter for the copyrighters in sales promotions. That roughly 58% drop Bruce, in dB that would be what?

 

[brucek]

Chu Gai,
Well, 58% is about -3.75dB loss. Clearly, greater than half the signal at that frequency. But don't confuse high frequency roll-off with damping. Damping is generally considered a low frequency concern with how tight your bass is reproduced.
Yep, I've certainly read the figure of >10 for damping as the audible standard. I suspect it's true. Don't confuse legitimate tests with what audiophiles think they can hear. I'm not questioning or willing to discuss that......
brucek

 

[John Royster]

BruceK,

Given my speaker in question (martin logan request - 4x2 foot panel, drops to 1.2 ohm at 20K, even lower beyond that) is there a reason why I hear differences among speaker wire and bi-wiring? I'm not saying any one is better than the other but they do sound different to me. Maybe this speaker isn't the norm when talking about speaker wire or nicely behaving tweeters and crossovers? I'm intrigued and curious. I don't have an impedance chart for the speaker unfortunately.

 

[Chu Gai]

i quite agree brucek regarding the damping issue. just wanted to point out that quite typically it's not the dominant part of the speaker equation and often too much weight is given towards this specification. but then audiphiles agonize over everything. give them a damping factor up the wazoo and they're rushing to buy that amp. then someone tells them, but that amplifier uses large amount of negative feedback to achive the large DF and 'didn't you know, that negative feedback ist verbotten'. off they run to sell the amp and the circle begins. finally they buy a tube amp and then they're finally glowing. of course for the careful consumer who waits like a vulture this can be a goldmine.
To keep it relativly simple, lets consider three lossless 100 ft cable where for the moment we neglect the resistance and even the contribution that capacitance can play. If we further assume an 8 ohm speaker with an 8 ohm inductance at 20 kHz. Usiing only inductance for the calculation we have the formulas:
Z = 2 * pi * f * L which gives the impedance of this inductance at 20 kHz.
attenuation = 20 * log ( R1/R2 ) where R1 is the the speaker and R2is the sum of the impedence of the speaker at 20 kHz plus the contribution of the wire.
Here are our 3 candidates. Sorry the gauges weren't all the same but cut me some slack and say they're close enough.
0.25uH / ft = 25uH / 100 ft. (a typical 12 gauge zip)
Z = 2 * 3.14 * 20,000 * 0.000025
Z = 3.14
attenuation = 20 * log (8/11.14) = -2.88 dB
0.025uH / ft = 2.5uH / 100ft. (like Dunlavy's 11 gauge Z6)
Z = 2 * 3.14 * 20,000 * 0.0000025
Z = 0.314
attenuation = 20 * log (8/8.314) = -0.33 dB
0.004 uH / ft = 0.4uH / 100 ft. (like Alpha Goertz' 13 gauge MI-1)
Z = 2 * 3.14 * 20,000 * 0.0000004
Z = 0.050
attenuation = 20 * log (8/8.05) = -0.05 dB
Now if the distance were 10 feet and just looking at the 'worst' case, good old zip, priced right!
attenution = -0.33 dB
Unfortunately, virtually none of us have any significant hearing up in that range. Also it takes something like a 2+ dB change before we can even detect a difference up around there. So what does all this tell us? It tells us if we use a long enough wire and if we had great hearing at 20 kHz that we'll just be able to hear the difference between $60 of zip (don't forget we need a total of 200 ft.) and $1240 for the MI 1 (okay, maybe they'll cut you a break...)
of course, if you're a masochist, you could always get some of 32 wire computer ribbon cable, parallel all the odd wires, make em positive, do the same with the even numbers, make em negative and there's your low inductance wire. and now, it lays under that carpet to boot. seeing as each wire is 24 gauge i think, that'll give you roughly 12 gauge when you're finished punishing yourself. All this assumes of course that your amp will not have an issue with the capacitances of the cables.
Now it's just my opinion, but you'd get a ton of mileage using that money to improve your room with some treatments. Or what about subscribing to something useful like http://www.greatclubs.com/beerclub.html where for $28 you can get a 12 pack of 4 different beers.
For those who are further interested, some papers on this are the following:
Fred E Davies, "Effects of cable, loudspeaker and amplifier interactions", AES, June 1991
Egar Villchur, "Speaker Cables: Measurements vs. Psychoacoustic Data", Audio, July '94
Local library might be able to get them for you, if you're interested that is.

 

[brucek]

John,
I don't know a lot about electrostatics, so it's hard to comment. I do know they require power amplifiers that can handle extremely low impedance loads. One ohm loads are a tall order for an amplifier.
Speaker cables will be quite important for you, because your cable's impedance becomes an appreciable portion of the overall load the amplifier sees, particularly at higher audio frequencies where the cables inductive reactance and the speaker's impedance are simultaneously working against you. As the frequency increases, the cable's reactance increases while your speaker's impedance drops - bad combination. So, no doubt you will easily hear differences between cable types and configurations .
Chu Gai,
Well, now you're questioning whether someone can hear the difference in cables that the math doesn't support. I'm certainly not one to argue that point. We can both do the math all day and it doesn't really convince someone who hears what they hear.
I'm afraid I have to argue a little with your math though. Your decibel calculations indicate the decibel difference in the voltage ratio, not the power loss in the cable. When we deal with power loss, the decibel formula is 10log(ratio) and not 20log(ratio).
There are indeed many speaker cable configurations that can produce lower inductance figures and if someone feels they're getting some rolloff and wants to experiment, why not. Usually this lowered inductance is at the expense of higher capacitance, but so what .. As you point out, most solid state amplifiers can easily tolerate this without any fear of oscillation.....
But yeah, I'm all for some good beer deals.......funny how it makes my system sound so good...
brucek

 

[Mark Austin]

Chu,

Also it takes something like a 2+ dB change before we can even detect a difference up around there. So what does all this tell us? It tells us if we use a long enough wire and if we had great hearing at 20 kHz that we'll just be able to hear the difference between $60 of zip (don't forget we need a total of 200 ft.) and $1240 for the MI 1 (okay, maybe they'll cut you a break...)

I'm curious as to why there has to be a change in db's for there to be considered a detectable change? Couldn't a change or a difference be something other than a db increase or decrease?

 

[Chu Gai]

well Mark, I was just looking at it from the point of view of how the inductance shaped the frequency response. no doubt one could take a stab at the effect on something else, maybe phase angle? Hey I can appreciate, strictly on the basis of theoretical grounds of making the 'perfect' speaker cable. And I can appreciate a person, who whether they can hear the difference or not, of once having spent oodles of money on his amp, wants to maximize the power throughput to his speakers in any way possible. But just to touch upon phase angle for a moment, just what is the sound we want? Is it the sound at the recording as if you were sitting there? Is it the sound after the people who mic'd the performance introduced their own phase angles? What if one of the mic's was out of phase? Didn't our player also screw with the phase angle? And what about the contribution of the amp towards f*cking with the phase angle? Too much agonizing. It's time for the great equalizer, beer. Maybe we need to cook our cables in beer huh?
bruce, i'm pretty sure it's 20 for insertion loss.