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[Seth Hochberg]

Crown has this nifty line loss calculator (with equations). Those should help you do some figuring for your particular amps/speakers.

  http://www.crownaudio.com/apps_htm/designtools/line-loss.htm

Generally speaking, your potential signal loss will be far greater using long speaker runs as opposed to long line level runs (though you already knew that). It is also worth noting that if you are running your speaker returns and snake parallel to each other on the way to FOH, you are placing yourself at a much higher risk of interference due to crosstalk between the low-power signal and high-power signal. Not returning speaker lines from FOH is an easy remedy to that problem.


edit: edited for clarification

[Maury McCown]

Seth Hochberg wrote on Tue, 09 March 2010 17:35

Crown has this nifty line loss calculator (with equations). Those should help you do some figuring for your particular amps/speakers.   http://www.crownaudio.com/apps_htm/designtools/line-loss.htm Generally speaking, your potential signal loss will be far greater using long speaker runs as opposed to long line level runs (though you already knew that). It is also worth noting that if you are running your speaker returns and snake parallel to each other on the way to FOH, you are placing yourself at a much higher risk of interference. Not returning speaker lines from FOH is an easy remedy to that problem.

Hm, I'm only looking at -.33dB loss. I just used my peak settings for my amps: 1120w at 67v using 12 awg.

[Gerry Seymour]

My last big event had 200' of XLR (actually DMX) to amps backstage, then  100' of Speakon to the mains. No real problems, but with some of the equipment in my rig, it would take a pretty big loss to notice it.

[Rob Spence]

Seth Hochberg wrote on Tue, 09 March 2010 18:35

Generally speaking, your potential signal loss will be far greater using long speaker runs as opposed to long line level runs (though you already knew that). It is also worth noting that if you are running your speaker returns and snake parallel to each other on the way to FOH, you are placing yourself at a much higher risk of interference due to crosstalk between the low-power signal and high-power signal. Not returning speaker lines from FOH is an easy remedy to that problem. edit: edited for clarification

When you say "speaker returns" are you talking about speaker level cables or line level?

Assuming (ya, I know) that you are not running speaker levels in the snake, there is NO issue on interference between speaker cables and the snake cables. That problem only really exists with unbalanced lines which isn't an issue here.

The only issue here is how long the speaker cables are vs cable size vs current in the cables.

As the op says, half a dB of loss over 100ft isn't something to spend money on to fix.

[Art Welter]

Maury McCown wrote on Tue, 09 March 2010 19:50

Seth Hochberg wrote on Tue, 09 March 2010 17:35 Crown has this nifty line loss calculator (with equations). Those should help you do some figuring for your particular amps/speakers.    http://www.crownaudio.com/apps_htm/designtools/line-loss.htm Generally speaking, your potential signal loss will be far greater using long speaker runs as opposed to long line level runs (though you already knew that). It is also worth noting that if you are running your speaker returns and snake parallel to each other on the way to FOH, you are placing yourself at a much higher risk of interference. Not returning speaker lines from FOH is an easy remedy to that problem. Hm, I'm only looking at -.33dB loss. I just used my peak settings for my amps: 1120w at 67v using 12 awg.

The signal loss is inconsequential.
The loss of damping factor is what makes the difference, your high damping factor amp is turned to flab with long speaker cables.

You want the DF at the speaker to be above 20.

I did the math in a previous post, here it is again (note that you use even longer cable):
79 feet of  of 12 gauge copper wire (158 feet round trip) is .25 ohms.

An amp with an output impedance of .004 Ohms:
DF=8 /.004=2000            
Now, add a .25 Ohm speaker cable and  the damping factor at the speaker is:
New source impedance = 0.004 + 0.25 = 0.254 Ohms (at the speaker)
8 / .254 = 31.4 DF
4/.254=15.75 DF  (at 4 ohms)  Not so good.

With a  damping factor of 500:
DF=8/.016=500
Again, add a .25 Ohm speaker cable:
New source impedance = 0.016 + 0.25 = 0.266 Ohms (at the speaker)
8 / .266 = 30.07
4/.266=15.04

The amp with 4 times the damping factor results in barely any difference at the speaker.


79 feet of  of 10 gauge copper wire (158 feet round trip) is .158 ohms.

DF=8 /.004=2000            
Now, add a .158 Ohm speaker cable and  the damping factor at the speaker is:
New source impedance = 0.004 + .158 = .162 Ohms (at the speaker)
8 / .162 =49.4 DF
4/.162= 24.69 DF  (at 4 ohms)  Now we meet the “not flabby” specification!

With a  damping factor of 500:
DF=8/.016=500
Again, add a .158 Ohm speaker cable:
New source impedance = 0.016 + .158 = .174 Ohms (at the speaker)
8 / .174  = 46 DF
4/.174 = 23 DF  (at 4 ohms)

Use fat cables and high impedance loads on long runs.
If you have the choice,(which you do) always put your racks behind the stacks and use the shortest, fattest cables you can.

Art Welter