testing speakers

[frosty55]

Howdy chaps. I have a pair of celestion G12M speakers I want to put in a 2 by 12. Theyre 20 years old, I want to test them to see if theyre worn out or if the voicecoils have gone. Are there ways of doing this? Any advice appreciated. :unsure:

[smalljoshua]

Wire them into an Amp with A Test tone playing within the speakers range?

 

Josh

[paulears]

flash a 9v batt aross the terminals and see if the cone moves. If it doesn't, it's dead. If it does power them up - but be warned, they are pretty useful for guitars but will sound rather 'vintage' for pa cabs.

[johndenim]

One way to test the coils it to use a multimeter with an ohms test facility.

 

You could get one of these for less than a tenner at wilkinsons/screwfix that kind of place.

This will test the coil by giving you a reading of the voice coil, depending on the impedence, it will read 4 or 8 (or 16!)ohms.

 

If it reads nothing then its open circuit.

 

John Denim.

[Simon Lewis]

Howdy chaps. I have a pair of celestion G12M speakers I want to put in a 2 by 12. Theyre 20 years old, I want to test them to see if theyre worn out or if the voicecoils have gone.

 

To test the voice coil, measure with a multimeter set to the lowest Ohms scale. As you are measuring resistance, not impedance, the meter's resistance reading will probably be an ohm or two below the nominal impedance rating - not the nominal impedance as suggested above. If it reads open circuit, the coil has a break in it. It's not usually possible to check for visible damage to the voice coil.

 

The battery test will determine whether the coil is working, and will also help determine polarity - just in case the sticker or blob of red varnish denoting the +ve terminal isn't visible. Positive voltage on the positive terminal will push the cone forward.

 

The remaining tests are visual and tactile:

 

Check the suspension for signs of cracking, rips or breakdown of the cambric edging. Then place the speaker magnet down, and gently spread your fingers and palms around the upper edge of the cone. press down gently, making sure you apply an even, light pressure. The cone should move up and down, with no "feel" or resistance other than the restraining force of the suspension. If there is any grittiness or a 'rubbing' feeling, then the coil is in contact with the pole piece (which could signify frame damage), or the varnish/copper/former has boiled/melted/caught fire and it will need reconing (if the overall speaker is not too far damaged).

 

HTH,

 

Simon

[Biskit]

One way to test the coils it to use a multimeter with an ohms test facility...

...depending on the impedence, it will read 4 or 8 (or 16!)ohms.

 

This is not necessarily true: a standard multimeter on 'Ohm' setting measures Resistance using by passing a DC current through the load. An 8 ohm speaker will probably have a DC resistance of about 5 ohm IIRC, with an AC phenomenon known as Reactance (also measured in ohms) coming into play at audio frequencies, making the overall Impedance up to the nominal 8 ohm during normal audio use.

 

So if you don't get the reading you are expecting, this doesn't necessarily mean the speaker is damaged!

 

As a quick and dirty test, most speakers fail open-circuit, so if you get a reading of open circuit (no continuity) then it is almost certainly dead.

 

Ben.

 

Edit: Sorry just realised Simon has already said virtually the same thing.

[johndenim]

I thought Impedance was resistance?

OH!

 

Doing a google on 'Impedance' alerts me to the term'reactance'

in case anyones interested:

 

http://en.wikipedia.org/wiki/Electrical_impedance

Time to brush up on Ohms law me thinks!

 

John Denim.

Cheers guys.