Two Subs, Do RCA Cables Lengths Need to be Equal

BIC2 said:

Two JTR 118 HTs. Should the two sub RCA cables be the same length? One needs either a 50 or 75 ft cable; the other, about 15 ft will do it. Thanks.

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Well, the sound will lag 35 or 60 feet behind, if that's OK with you?
Just kidding! The delay would be umptillionths of a second, don't worry about it. Do get well shielded cables-50 and especially 75 feet are long runs.

Disparate lengths will make no difference. I highly recommend Blue Jeans Cables, they will make them to your custom lengths and are very high quality.

head_unit said:

The delay would be umptillionths of a second, don't worry about it. Do get well shielded cables-50 and especially 75 feet are long runs.

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But there would be a difference in internal resistance, wouldn't there?

I suppose that can be compensated with the volume knob on the sub though.

BIC2 said:

Two JTR 118 HTs. Should the two sub RCA cables be the same length? One needs either a 50 or 75 ft cable; the other, about 15 ft will do it. Thanks.

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They do not need to be the same length at all. I bought different lengths of rca cable for trying out the subs in different locations throughout the room, and just kept with cables used for testing in the front of the room that were much longer than needed rather than pulling and swapping cables.

The output of an AVR or preamp is typically ~100 ohms or so, the input of a sub or amp typically 10k ohms or more, and the wire is usually in the milli-ohm or fraction of an ohm region. The difference is negligible and completely inaudible. The vast majority of the time it is completely swamped by gain variance amp-to-amp.

Numbers without looking anything up:

Measure at preamp output (so no need to worry about its output impedance for this) and 10k amp input:

- Wire = 0 ohms: For 1 V at preamp out, 1 V at amp in = 0.0 dB loss
- Wire = 1 ohm (much higher than you are likely to have): For 1 V at preamp out, 0.9999 V at amp in = -0.0008685 dB loss

Be not worried.

No, same as speaker wire length. Unless very extreme

Darth

Pete7874 said:

But there would be a difference in internal resistance, wouldn't there?

I suppose that can be compensated with the volume knob on the sub though.

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The sub may have an input impedance of 10k ohms. Cheap copper coated steel RG6 coaxial cable is listed with a DC resistance of 28 ohms per 1000 feet (300m). For a 75 foot cable, that'd give a DC resistance of approx. 2.1 ohms. That'd give a drop less than 0.001 dB. I think that you'd have trouble adjusting a gain knob that finely.

The shunt capacitance is more significant, but still negligible. (Varies a lot, depending on the coax cable's insulation.)