Uneven Cable Length

A

AlinMV

New member
I've heard that speaker cables should be the same length from the Amplifier. I have PS8 active monitors, and because of my home studio's configuration, I have my mixer to one side, and as a result, one of my monitors has to be connected by a longer cable from my mixer's outs than the other. Is there a problem with that picture? If so what's the problem and is the remedy just connecting two longer cables to the Monitors?

Thanks for your input.

Al
 
The PS8's are active though, so the cables your running are line level cables to the input of the integrated poweramp. The speaker wires are inside the PS8. I wouldn't worry about the mismatched length, as long as their decent quality. If your running unbalanced patch cables, you may not want to exceed 10 or 15'. Ideally, use balanced XLR cable from your mixer (if it has XLR out's) out's to the input of the PS8's.
 
Emeric,

I'm not sure if it's an actual problem or not, but.... if we're talking about a phasing (or similar) effect of mismatched cable lengths, then it wouldn't matter if the cables were carrying line level or speaker level output would it? That is, just because the speakers are internally amplified, the signal to one speaker is still traveling farther, correct?

Slackmaster 2000
 
I don't believe that this is actually a problem of phase (delay). Doing a fair amount of handwaving over the math, light travels a foot per nanosecond, so we'll use that as the propagation speed up the wire (yes, I know that that's not strictly correct in a transmission line, but bear with me). How much differential wire length would be needed to induce a 10deg phase shift at 20 kHz (that would be a swag at a just-noticeable-difference)? Let's see: the period of a 20kHz signal is 5e-5 sec (50uS). A 10deg phase shift would be 1/36 of that period, or 1.3e-6 (1.3 uS). At a foot per nanosecond, that sounds like 1300 feet of wire to me.

So if you have one speaker wire that's 1300 feet longer then the other, you may experience some phasing problems in the high end. Assuming that you can get into the room with that huge freakin' spool of wire in the way, of course. (;-)

A much bigger problem comes from the inductive and especially capacitive loadings created by the wire, especially if you are driving line levels out to the power amps located in the active speakers. If one cable is much longer, and you are driving single-ended signals, you can expect parasitic RC losses to be noticeable in the high end *long* before you would see any phase delay nightwierdies. Even well-driven balanced differential signals will experience different attenuation over skewed cable lengths, and at some point (well less than 1300 feet!) you would be able to hear it. What point? Search me- that is completely installation dependent...

Anyway, if anybody really needs a rule of thumb, keeping the wires on the same order of magnitude lengthwise makes mathematical sense for loading the line drivers equally. And keeping them within a factor of 2 of each other would be in some sense "better", although I'm not at all convinced that you could actually hear it with decent quality interconnect cables. Perfectly matched identical lengths are always nice conceptually- but not worth losing sleep over, IMNSHO.

The wire, she ain't the problem...
 
Hey Slack, I only mentioned line level to clarify that we are not talking about speaker wires. But yes your right distance is distance.

Somehow I had a feeling this would go into some indepth analysis by someone! Thank god it was Skippy, and not some audiophile freak... :) Thanks for the info Skippy, always enjoy your posts.
 
Thanks, Emeric, for the kind words. I guess that I'm just kind of the nerd-at-large when it comes to this stuff.

Wire and I have a very long, and not at all pleasant, history. Thank *gawd* that nobody here wants to argue about transmission line behavior! Shoot, nobody's even argued about what "swag" means....

For the pedantic: it is "superficial wild-assed guess". Your mileage may vary.

When I originally posted this article, I then wrote "However, if you're an audiophile, that acronym means 'Marsh and Jung Blow Dead Goats'."

Upon some more sober reflection, I realize that I may have misstated the case somewhat, and allowed my own personal and widely-advertised biases to color my statements. For shame... Consequently, professional ethics compel me to retract my original comment, and restate that in a form more in keeping with accepted usage, to wit: "Sometimes Marsh and Jung blow Wild-assed dead Goats".

I hope that that hasn't caused and difficulties for anyone. Mea maxima culpa.

(;-)

[Edited by skippy on 12-01-2000 at 21:49]
 
skippy said:
I don't believe that this is actually a problem of phase (delay). Doing a fair amount of handwaving over the math, light travels a foot per nanosecond, so we'll use that as the propagation speed up the wire (yes, I know that that's not strictly correct in a transmission line, but bear with me). How much differential wire length would be needed to induce a 10deg phase shift at 20 kHz (that would be a swag at a just-noticeable-difference)? Let's see: the period of a 20kHz signal is 5e-5 sec (50uS). A 10deg phase shift would be 1/36 of that period, or 1.3e-6 (1.3 uS). At a foot per nanosecond, that sounds like 1300 feet of wire to me.

So if you have one speaker wire that's 1300 feet longer then the other, you may experience some phasing problems in the high end. Assuming that you can get into the room with that huge freakin' spool of wire in the way, of course. (;-)

A much bigger problem comes from the inductive and especially capacitive loadings created by the wire, especially if you are driving line levels out to the power amps located in the active speakers. If one cable is much longer, and you are driving single-ended signals, you can expect parasitic RC losses to be noticeable in the high end *long* before you would see any phase delay nightwierdies. Even well-driven balanced differential signals will experience different attenuation over skewed cable lengths, and at some point (well less than 1300 feet!) you would be able to hear it. What point? Search me- that is completely installation dependent...

Anyway, if anybody really needs a rule of thumb, keeping the wires on the same order of magnitude lengthwise makes mathematical sense for loading the line drivers equally. And keeping them within a factor of 2 of each other would be in some sense "better", although I'm not at all convinced that you could actually hear it with decent quality interconnect cables. Perfectly matched identical lengths are always nice conceptually- but not worth losing sleep over, IMNSHO.

The wire, she ain't the problem...
Click to expand...

I came across this post in a search I did for something else. I started reading some posts for the heck of it. This reply is great. Informative AND entertaining. :)

I get some great information from this BBS I otherwise don't think I'd be able to find.
 
Good post by skippy.

Having one 10 footer and one 100 footer will give you the same delay as if you used two equal length cables and had one speaker 1/10,000 of an inch closer to you.
 
boingoman said:
Good post by skippy.

Having one 10 footer and one 100 footer will give you the same delay as if you used two equal length cables and had one speaker 1/10,000 of an inch closer to you.
Click to expand...
Hehe. Good one.
 
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