Two channel speaker cables

[DaveK]

When I built my T39s, I jumpered the Speakon jacks to pass through the +2/-2 inputs so I could feed both subs and tops from a 2 channel cable. Now I have a situation where I want to take advantage of that.

When I make up the 2 channel cable that runs from the amp to the subs, does each channel need a separate return conductor or can they share a common return? In other words, do I need 4 conducter cable or can I save some copper and use 3 conductor cable? I'm not running high amperage that will overload the common return conductor.

[Bill Fitzmaurice]

I'm not running high amperage that will overload the common return conductor.

The issue you'd still run into would be amp related. Using two amps and linking the grounds could cause ground looping, and even with one amp the two channels might not share a common ground on the outputs. I'd not take the chance and just use 4 conductors.

[koturban]

The ground may not actually be at ground, as in a bridged or push-pull output stage.

[Bruce Weldy]

I believe the old adage is penny wise and pound foolish

[Charles Jenkinson]

I didn't appreciate that the negative wire was a ground. I thought it had equal and opposite sign to the positive cable, which itself is alternating between plus and minus to make the driver move both ways either side of equilibrium. So, how does it work? I cannot get my head round how a neutral or ground closes a circuit if it doesn't do anything.

[erlinden]

Does damn electrons need a way to get out...hence the ground.

It's pretty much the same as running a light bulb...

[Charles Jenkinson]

[quote="erlinden"]Does damn electrons need a way to get out...hence the ground.
quote]

May be, but what I think is the case is that there is a lot less of them in the neutral (-ve) / ground cable, than in the +ve hot cable. Is that true? It just seems very odd that whilst they don't do much (in the neutral cable) if they weren't there, nothing would happen.

I always thought it was odd that a positive current in one direction was actually electrons (-ve) flowing in the opposite direction.

[byacey]

That's opening a big can of worms for learning. Conventional current flow is from positive to negative, but electron flow goes from negative to positive. Electron current flow is important in understanding semiconductor theory, but generally thinking in terms of conventional current flow is sufficient to gain an understanding of how a basic circuit works.

In all cases, any currents feeding a circuit is equal to the currents leaving the circuit; this means on a speaker cable, the current would be equal between the + or hot lead and the - or ground, common, return or whatever you wish to call it. Because speaker lines are typically an unbalanced circuit (except in the case of running bridge mode) you could theoretically share the same common ground between different channels, except wire has resistance and as a result, creates voltage drop across the speaker cable.

Because of this voltage drop, if two different signals try and share the same common return path, you could potentially get one signal modulating the other due to phase differences. Albeit, it would typically be a very small amount commensurate with the voltage drop of the wire, it's distortion nonetheless.

However in the case of running bridge mode, because of the low output impedance of a power amplifier, it will try and sink any currents placed on the output terminals when the amp is in a quiescent state, or if the imposed signal is different than what the amp is producing. This is responsible for the so called dampening effect. In the case of trying to share a common in a bridge mode config, the power amps will be bucking and sinking current produced by the other amp and will likely lead to amp failure.

Proper practice dictates using a individual return for every speaker line send.

[DaveK]

It's actually pounds that I'm trying to save. Copper is heavy!

The issue you'd still run into would be amp related. Using two amps and linking the grounds could cause ground looping, and even with one amp the two channels might not share a common ground on the outputs.

Thanks, Bill. I figured the only realistic way to do this is run both channels off the same amp. My QSCs feed channel 2 into the +2/-2 pins of the channel 1 speakon jack so it would be easy to cable up. I checked continuity between the black screw-on posts and there is no resistance. However, there is a diode drop difference (0.7V) between the speaker returns and frame ground so that may not be a direct connection.

I recognize that a specialized cable like we're discussing here has limited usefulness. However, I don't see much advantage for a small-time guy like me in owning 4 conductor cables. I might as well own a pair of 2 conductor cables instead of a 4 conductor cable that I don't need very often.

[Bruce Weldy]

I might as well own a pair of 2 conductor cables instead of a 4 conductor cable that I don't need very often.

And that my friend, is the answer to your own question.

[Charles Jenkinson]

I bought heafty 4 conductor cable (4mmsq each conductor I think). It wasn't exactly what I wanted but it was not an unreasonable price. I may wire as if one pair (2- & 2+) is 'unused', which gives the option of break out boxes (or 4 channel amps?), but I cannot think of the times when the amp and speakers are not reasonably near each other that it all just becomes superfluous hardware. You would put the amps either near the mains or the subs, not miles away from either...?

[Michael Murphy]

To make my system easy to set up I used 4 core 4 mm squared also. Im not running stereo, and the tops are on top of the bass cabs so 2 leads are designated for tops and the other 2 leads for bass. Que the proximity of the cores in one housing, although each is insulated from one another, can it degrade the current flow/ sound quality any. Never gave it much thought until reading the above.

Thanks

[DJPhatman]

and the tops are on top of the bass cabs so 2 leads are designated for tops and the other 2 leads for bass.

This would be a reason for "not enough bass" response. See http://billfitzmaurice.info/forum/viewt ... f=10&t=398 as it applies to all subwoofer cabinets.

[Michael Murphy]

DJP, even like this?
https://www.dropbox.com/s/l6ic1h42yu4yu ... .32.47.jpg

[racertomtom]

Using 4 conductor cable is probably the way to go, providing you have the need. I’m running a quad to both stacks of tops and one to the subs. Keep in mind my tops are bi-amped.
Pros:
1. Less entanglements, 3 cables are easier to wrap etc. than 6.
2. 100 ft. of quad 12 ga cable was cheaper than 200 ft of dual 14 gauge. Half the connectors and jacks on the tops.
3. Less chance of accidental hook ups.
Cons:
1. More weight in the cable box and more weight hanging from the jacks, especially the tops.

I’ve had no issues in countless gigs. Would I have used 4 conductor cable if I wasn’t bi-amped? Probably not.