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Cable length?

#21
dj150888 said:
My point was more that its not in significant fractions of the speed of light, its usually measured in cm/s, or decimals of that. The speed the actual electrons travel at won't even approach the speed of sound. The electromagnetic wave propogation could very well be up at your 0.7c figure, but the actual speed the electrons travel at won't even be in the same ballpark.

Like I said, I'm open to correction if I'm wrong. I gave a rough figure for the sort of ballpark figures the actual electrons will travel at when I said, "a copper wire of radius 1 mm carrying a steady current of 10 amps, the drift velocity is only about 0.024 cm/sec". Thats a tiny fraction of the speed of sound, let alone the speed of light.
Click to expand...
The wave propagation speed is the speed the signal travels at, not the speed of the electrons. Since its an alternating current wave, the electrons move back and forth, so with a long enough cord, and not all that long with the velocity you cite, the signal would be stuck in the cord and never exit the other end if it was dependent on the electron movement speed to propagate the signal rather than the wave propagation speed.

Randy
 
#22
billfitzmaurice said:
What matters to us is how long it takes the applied electrical impulse at one end of a wire to arrive at the other end, and that's on average based on a speed of 0.7C.
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This is correct.
We can keep using the analogy of sound since it's easy to understand for most of us.

The electricity going through the wire is a wave transmitted across the electrons, just like sound is a wave transmitted across the atmosphere.

A soundwave travels, well, at the speed of sound, but the air transmitting the wave doesn't move. It just vibrates to transmit the wave.

Just like sound can move at different velocities depending on the fluid it goes through, the actual speed of electromagnetic waves varies depending on the nature of the conductor.

As for the OP, indeed, even with a difference of length on a scale of 1 to 100 from one cable to the other, a listener wouldn't be able to hear the phase decay occuring between signals.
 
#23
Sorry if I've confused things. I merely stated it because in Bill's post he stated specifically the speed of the electrons. I repeatedly stated in my posts that it was seperate to the propogation speed, even stating that I thought it was most likely the propogation speed that Bill was speaking about. Just semantics on my part really.
 
#24
Yes, what is germane to this thread is the propagation velocity of the electromagnetic wave, which is a large fraction of the speed of light in free space.

That fraction depends on the dielectric constant of the medium surrounding the conductor. Specifically, in our case, the wave propagation velocity is inversely proportional to the square root of the dielectric constant of the speaker wire's insulation.

Eg.
If the dielectric constant is 4, propagation velocity is half the speed of light.
If the dielectric constant is 2, propagation velocity is 0.7 times the speed of light.

Hence, a wave propagates faster in Teflon insulated wire than in PVC insulated wire. Does the difference matter to us? No!

Assume cheap wire, with propagation at 1/2 speed of light. Each meter (~3.3 ft) of wire represents 6.7 nanoseconds of delay (or 2 nanoseconds per foot). Compare that to the period of a 10 kHz sine wave, which is 100 microseconds. To get 180 degree phase difference at 10 kHz one speaker's wire would have to be 25 thousand feet longer than the other one. At lower frequencies, even more.
 
#25
PhiDeck said:
<snip> To get 180 degree phase difference at 10 kHz one speaker's wire would have to be 25 thousand feet longer than the other one. At lower frequencies, even more.
Click to expand...

At lengths of considerably less, would there be any phase shift at all - even incrementally?

It wouldn't have to be a full 180º shift to be 'hear-able' right?

I might imagine that at the lower freqs, this partial shift might be much more pronounced.
 
#26
So, I'm guessing from the foregoing discussion that if I use a 3' cable to get to one cab, and a 6' cable to get to the other (because those were the only 2 lengths available), that there won't be any audible problems with the sound in the situation I described? :hiding:

Thanks to (almost) all who chimed in....
 
#27
jeffbrown said:
So, I'm guessing from the foregoing discussion that if I use a 3' cable to get to one cab, and a 6' cable to get to the other (because those were the only 2 lengths available), that there won't be any audible problems with the sound in the situation I described? :hiding:

Thanks to (almost) all who chimed in....
Click to expand...

That's right -- even in "crappy" cable, and assuming you could discern a 1 degree phase shift at 10 kHz, one cable would need to be 139 feet longer than the other.

Trouble yourself no longer. :D
 
#28
SurferJoe46 said:
I might imagine that at the lower freqs, this partial shift might be much more pronounced.
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Not sure what you're saying...

The cables length difference that yields 1º shift at 10 kHz (139 ft) also yields:
- 0.1º shift at 1 kHz
- 0.01º shift at 100 Hz

At practical lengths, say a 3 ft difference between the two cables, all of the above phase shifts divide by ~46.

Conclusion:
- Keep speaker cables as short as is practical
- Don't sweat the difference
 
#30
From a working class perspective, in my project studio one of the guitar cabs is in an iso room that requires a 30ft speaker cable to get to, and then a 30 ft mic cable to get back to the protools. We've recorded along with a DI that gets used for reamping, and the phase difference is just incredibly small, so i cant imagine that's going to matter in the real world for you. We've also compared these cable runs of the same with very short ones of the same brand, and the loss in tone is also so small that it might be imaginary. 'Lectricity is FAST.
 
#31
TripleDouble said:
From a working class perspective, in my project studio one of the guitar cabs is in an iso room that requires a 30ft speaker cable to get to, and then a 30 ft mic cable to get back to the protools. We've recorded along with a DI that gets used for reamping, and the phase difference is just incredibly small, so i cant imagine that's going to matter in the real world for you. We've also compared these cable runs of the same with very short ones of the same brand, and the loss in tone is also so small that it might be imaginary. 'Lectricity is FAST.
Click to expand...
Keep in mind that the OP probably saw what he did on an oddiophile site, where not only do they claim being able to hear a hummingbird fart from 100 yards away, if blindfolded they can tell what color the bird is by the timbre. :hyper:
 
#32
IMHO, speaker cables should be as short as practical and use a reasonably fat wire gauge. I like 12 gauge or bigger, preferably jacketed. I make my own cables - the only tools required with Speakon connectors are a knife (or razor blade) to peel back the cable jacket, a wire cutter, a wire stripper, and a couple small screwdrivers. You can make them exactly the length you need. Speakons will take up to 11 gauge IIRC.

Ignore the audiophool blather about velocity, they're imagining effects that don't have anything to do with transmission of audio signals to speakers.
 
#33
billfitzmaurice said:
Piffel. Electrons pass through wire at 0.7x speed of light. I'll let you try and figure out the time differential between those passing though 3 feet versus even 300 feet of wire.
BTW, definition of Audiophile: Someone who'll believe anything.
Click to expand...

1pif·fle verb \&#712;pi-f&#601;l\
pif·fledpif·fling\-f(&#601;-)li&#331;\
Definition of PIFFLE
intransitive verb
: to talk or act in a trivial, inept, or ineffective way
Origin of PIFFLE
perhaps blend of piddle and trifle
First Known Use: circa 1878
 

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