Help with speaker wire

[zabba]

I recently moved into my first house, and fortunately there is speaker cable built behind the plasterboard for rear speakers.

However, while one of the cables is marked with positive and negative the other isn't. There is no marking at all!! Is there a way I can test the cable so that I can ensure I get the positives/negatives at both ends correct?

[LordHaveMurci]

One of the strands often has writing on, the other doesn't. Worth checking, beyond that you need somebody more knowledgable than me I'm afraid.

[skilly1]

I normally charge £450 per day to create drawing like this. However as it is PH I will do it for free.

[zabba]

Excellent, many thanks that makes sense!

[cjs]

You may find there is a ridge along one edge of the twin cable.

[TonyRPH]

1) Connect cables to speaker as normal.
2) Remove speaker grille so woofer is visible.
3) Get a 1.5v 'AA' battery.
4) Momentarily* touch wires on the '+' and '-' of the battery. (you will hear a 'pop' noise' which is harmless.)
5) When the woofer cone moves forward, the wire attached to the '+' of the battery is your '+' on the speaker.

HTH.

• don't keep the battery connected for too long - although I've yet to damage a speaker with an 'AA' battery using this method.

[Crackie]

TonyRPH said:

1) Connect cables to speaker as normal.
2) Remove speaker grille so woofer is visible.
3) Get a 1.5v 'AA' battery.
4) Momentarily* touch wires on the '+' and '-' of the battery. (you will hear a 'pop' noise' which is harmless.)
5) When the woofer cone moves forward, the wire attached to the '+' of the battery is your '+' on the speaker.

HTH.

• don't keep the battery connected for too long - although I've yet to damage a speaker with an 'AA' battery using this method.

OK but it makes sense to choose an old / tired 'AA' or small button type watch battery with limited current for this.

[TonyRPH]

Crackie said:

OK but it makes sense to choose an old / tired 'AA' or small button type watch battery with limited current for this.

It doesn't really matter.

1.5v into an average 8 ohm speaker load will result in a current flow of 187mA and a power dissipation of 0.28W (280mW).

It's highly unlikely that you would blow a speaker with this.

ETA: Corrected spelling.

Edited by TonyRPH on Tuesday 14th August 17:34

[cjs]

I've used a 9 volt battery hundreds of times to test speaker circuits.