# Speaker Interference / Induction from mains cables



## Bob Sanders (Nov 10, 2013)

may.dominic said:


> I'm even picking up some DC voltage when I test the speaker cable with a multimeter.


Pops and DC voltage on the output is usually a failed decoupling capacitor(s) somewhere in the amp.


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## may.dominic (Nov 21, 2015)

I'm picking up a slight voltage when all speakers are disconnected.


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## GrayHair (Apr 9, 2015)

may.dominic said:


> I'm picking up a slight voltage when all speakers are disconnected.


If you are using a digital meter, you're most likely reading "ghost voltage"; digital meters are high impedance and don't present enough of a load to sink induced voltage, even with little to no current behind it. Try using an analog meter.

Any meter will make a speaker give a "pop" if set to Ohms. That used to be a quick test for a dragging voice coil.


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## may.dominic (Nov 21, 2015)

Oh right, thanks for your input. I haven't got an analogue meter to check that way. Any ideas why the speakers would pop when everything is disconnected from the amp and I short the speaker cables from the amp end?


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## GrayHair (Apr 9, 2015)

All cables exhibit a littlecapacitance and the voice coil of a speaker is an inductor (a speaker is also an inefficient microphone). Any power lines running close to and parallel with your cables can induce a voltage in the cable. Also, a speaker in a active magnetic field (CRT or another speaker) will generate a little voltage.

Not anything I, personally, would be concerned about.

Edit: Crossover networks at or in speakers will also have an effect.


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