Electronics > Projects, Designs, and Technical Stuff
Speaker Wire and Calculating Guage
Bassman59:
--- Quote from: DW1961 on July 22, 2020, 08:05:16 pm ---The run is 24' one way.
It's just a home system with RM51 Klipsch speakers and a Chinese D amp rated at 100 watts RMS at 4 Ohms. The Klipsch speakers are SENSITIVITY 93 dB @ 2.83V/1M. So that really helps.
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Sensitivity just tells you the output you can expect to get for a given power input. Higher sensitivity speakers are more efficient. But it's not interesting for sizing wires.
--- Quote ---I never exceed 50% power level on the D Amp, as I mainly listen to Jazz at lower levels (I set the Amp at 50% then adjust the volume from my computer software So if I turn up the software volume to 100% the Amp is doing 50% power. I should probably turn it up to 80% and use a lower software volume, but I don't know if that matters or not.) The Amp uses the Texas Instruments 3116D amp chip. Since the speaker are 8 Ohms I'm only getting 25 Watts per channel, unless I misunderstand power and Ohms. Still sounds good for my needs.
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A "reasonable" way to set levels is to run the software level at maximum and then set the amplifier to "somewhat louder than you'd ever listen to it." Then you can use the software controls to set the computer/whatever output level to whatever is comfortable. This way, if the computer went wonky for some reason, the level won't blow your ears or your speakers.
--- Quote ---If this is correct below, then even with CCA wire, I should be golden:
"Russel is saying, "It was based on the resistance of the speaker wire not exceeding 5% of the rated impedance of the system. The wire length is for TWO-CONDUCTOR wire. This includes one wire out to the speaker and one wire back again."
So .05 * 8 = 0.4ohms
But if 16AWG is only .004ohms per foot, you could run 100 feet total wire and still meet his requirements? And that would mean his statement is 48 feet two wires one way?"
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You're still waaaaaaaay overthinking it.
The losses in the wire for the short distance you describe is not going to matter. I mean, you're not using 30 AWG wire-wrap wire for this, right?
donlisms:
As I understand it, the issue with speaker cables, particular for subwoofers, is damping factor, rather than just power loss. Damping factor is the ratio of the source resistance to the load resistance. We want the highest value possible, e.g. around 40 would be a reasonable minimum if the goal is tight, proper transients in the bass.
(I may not be able to explain this very well, but this is the kind of thinking I live with...)
As the driver voice coil moves according to the applied voltage, because it's a moving coil in a magentic field, it becomes a generator, essentially producing voltage back toward the amplifer. If this back EMF is shorted out by nearly zero ohms looking back toward the amp, it does not contribute to further motion of the driver; the voice coil is "stuck" at the position it was driven to by the input signal. You can observe the effect by shorting out a generator or DC motor and trying to turn it, and then again with the connection open. It will be obviously stiffer while shorted.
If the back EMF is not shorted out because the output resistance it sees is too high, it becomes part of the input signal again, and the driver is permitted to oscillate at the appropriate resonant frequency. This becomes ncone motion that was not originally requested. The result is that the kick drum, for example, instead of sounding like "Puh!" will now sound like "Fffluhh!". The volume is not the issue; power is not the issue. It is that the transient response is affected. The punchiness and snappiness of the low end sound is degraded.
If we assume the damping factor should be 40 or better, just to pick a number, then we'd want the output impedence of the amplifier and wires combined to be less than 8 / 40, or 0.2 ohms, total of amplifier and wire (and crossover... and... ugh).
The issue of damping factor was (is?) quite prominent with tube amplifers, where the output impedence is generally not as high as can be easily obtained with solid state, due to the Big Old Transformer and so on.
Me (bass player / sound guy), I hate fluffy bass. There are of course many other factors that can contribute to fluffy bass... we hates 'em all. :)
TimFox:
You should include the DC resistance of the voice coil in your circuit to determine the damping factor: it is in series with the cable resistance and amplifier output resistance. The DC resistance of the voice coil is, of course, less than the speaker impedance, which should be dominated by the electromechanical result of coupling the voice coil through the cone to the compressible air.
DW1961:
--- Quote from: TimFox on July 22, 2020, 08:50:03 pm ---He's talking about a two-wire cable, where the total wire length is twice the cable length.
Back in sixth grade arithmetic, we had a trick question where we had to know that the required length of rail is twice the length of the track in a railroad.
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So it's how I thought it is then, 96 total feet of wire for his 48' run, which is just under a .4 ohm loss?
DW1961:
--- Quote from: TimFox on July 23, 2020, 02:53:00 am ---You should include the DC resistance of the voice coil in your circuit to determine the damping factor: it is in series with the cable resistance and amplifier output resistance. The DC resistance of the voice coil is, of course, less than the speaker impedance, which should be dominated by the electromechanical result of coupling the voice coil through the cone to the compressible air.
--- End quote ---
Tim,
Yeah, I knew about the voice coil also, but I didn't account for that. It is, after all, wire too. But, no, I didn't.
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