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Author Topic: Accidental use of speaker cable instead of instrument/guitar cable  (Read 1844 times)

Tony Mamoh

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Recently my crew reported crackling noise when they hooked up two separate guitars via their  separate cables, through a DI box via an XLR  cable to a PA system. They  swapped the instrument cable and DI box, yet had the same crackling noise. Ultimately, they had to get alternative guitars , with cables provided  by the guitarists before they could proceed with the gig.

Today, I decided to test every single instrument cable in our inventory  with a guitar amp and combo . I found that anytime some particular cables were used as instrument/guitar cable, there was a buzzing sound......even when not connected to the guitar (obviously connected only to the combo). It turned out that this happened only to the live wire solutions speaker cable , which is of relatively heavier gauge (I think gauge 12 or so...but need to verify). This live wire solution cable is supposed to be guaranteed for life....and is terminated with a 1/4" TS jack.....so apparently was mistaken for an instrument/guitar cable by my crew. The live wire so,unions cables are even labeled on their outer sheath as speaker cables, so someone simply didn't read...or perhaps the stage was dark as usual during night gigs .

As soon as I used a standard instrument/guitar cable of approx gauge 20 or 24, there was no hum, noise or buzz with any guitar.

So I concluded that the noise experienced by my crew  on that day, was as a result of incorrectly using a speaker cable as an instrument cable.

I'd like to know the features in a speaker cable which generated the noise. Is there no shielding around the speaker cable to handle RFI/ EMI?  So the speaker cable is just basically two wires?

I though in an emergency, a  speaker cable could be used to improvise an instrument /guitar cable provided it is terminated with a 1/4" TS jack???
 
« Last Edit: September 16, 2018, 05:57:58 PM by Tony Mamoh »
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Rick Powell

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #1 on: September 16, 2018, 06:12:53 PM »

Correct, the lack of shielding on a speaker cable makes their use as an instrument cable susceptible to noise. The other way around, using an instrument cable as a speaker cable, can sometimes work in a pinch, except that instrument cable usually has a much smaller center conductor (i.e. 24 gauge instead of 16 gauge) so it is not ideal either. For low-level signals may be OK, but makes the amp work harder at higher volumes, potential distortion and cable overheating.
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Paul Miller

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #2 on: September 16, 2018, 06:25:35 PM »

but makes the amp work harder at higher volumes

Actually, the higher resistance of the smaller gauge instrument cable would present an easier load for the amp to drive. I=E/R says that current goes down as resistance goes up.
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Jay Barracato

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #3 on: September 16, 2018, 06:39:07 PM »

Actually, the higher resistance of the smaller gauge instrument cable would present an easier load for the amp to drive. I=E/R says that current goes down as resistance goes up.
A guitar amp probably has an input resistance of about 300 Kohm.

The resistance of the 20 ft instrument cable or speaker cable is less than 1ohm.

The current through both is fundamentally the same.

Sent from my Moto Z (2) using Tapatalk

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David Sturzenbecher

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #4 on: September 16, 2018, 06:39:23 PM »

Actually, the higher resistance of the smaller gauge instrument cable would present an easier load for the amp to drive. I=E/R says that current goes down as resistance goes up.
The amp would have to produce a higher voltage to get the same acoustical output.  It will either have the capability to provide the greater voltage before you hit the rails.... or it wont.


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Mike Caldwell

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #5 on: September 16, 2018, 06:42:14 PM »

I get at two or three guitarist a year with a "guitar cable" they have been and are using is actually a speaker cable.
Some have never noticed the noise, others say it's been doing that for while.

Paul Miller

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #6 on: September 16, 2018, 06:47:49 PM »

The current through both is fundamentally the same.

The amp would have to produce a higher voltage to get the same acoustical output.  It will either have the capability to provide the greater voltage before you hit the rails.... or it wont.

And in neither situation will the amp "work harder". That's the misconception I was trying to correct.
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Erik Jerde

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #7 on: September 16, 2018, 07:08:30 PM »

You should open up each kind of cable and compare.  The difference should be very obvious.  You’ll also then be prepared to tell the difference when the jacket doesn’t say.
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Dave Pluke

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #8 on: September 16, 2018, 07:35:57 PM »

This live wire solution cable is supposed to be guaranteed for life....and is terminated with a 1/4" TS jack.....so apparently was mistaken for an instrument/guitar cable by my crew. The live wire so,unions cables are even labeled on their outer sheath as speaker cables, so someone simply didn't read...or perhaps the stage was dark as usual during night gigs .

Precisely why my Monitor and FOH speaker cabinets use NL4, NL8 or XLR connectors.  No need to keep 1/4" in that inventory.

You can lessen the risk of someone grabbing a backline speaker patch cable by keeping them short (6' or less) and using jumbo barrel plugs.  Spray painting an obnoxious color (eg. hot pink) can also help.

Dave
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Chris Grimshaw

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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #9 on: September 17, 2018, 03:24:17 AM »

For low-level signals may be OK, but makes the amp work harder at higher volumes, potential distortion and cable overheating.

Extra resistance on the speaker output will give the amp a slightly easier life, as mentioned here:

Actually, the higher resistance of the smaller gauge instrument cable would present an easier load for the amp to drive. I=E/R says that current goes down as resistance goes up.

Which is correct.

A guitar amp probably has an input resistance of about 300 Kohm.

The resistance of the 20 ft instrument cable or speaker cable is less than 1ohm.

The current through both is fundamentally the same.

Sent from my Moto Z (2) using Tapatalk

Is all true for using them as input cables, except we're on a slight side-track of using shielded guitar cables in place of speaker cables.

And in neither situation will the amp "work harder". That's the misconception I was trying to correct.

There'll be a difference. Amplifiers are usually voltage sources. Add an ohm of resistance to the output, and now you've got a slightly-squishy voltage source. The frequency response of the driven speaker will change (since it has an impedance that varies with frequency), and current flow will decrease for a given voltage output.


Chris
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Re: Accidental use of speaker cable instead of instrument/guitar cable
« Reply #9 on: September 17, 2018, 03:24:17 AM »


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