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Old 11-19-2009, 06:55 PM
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Speaker Testing

OK, my previous thread determined my factory radio is most likely an 8-10 ohm unit.

A friend suggested I test the speakers with an ohm meter. One speaker shows 0.01 ohms. The other shows 0.00 ohms.

Is this a valid test? If it is, my speakers are apparently way off for my radio.

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Old 11-19-2009, 07:45 PM
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Using an ohmmeter will not give you an accurate indication of your loudspeaker's impedance. The ohmmeter will measure the DC resistance of the voice coil, however, the AC impedance of the voice coil is something else altogether. The impedance is dependent on the AC frequency of the audio signal, and although an impedance meter can measure it, it's a specialized instrument that you would have trouble finding, unless you have a pro-audio shop nearby. The loudspeaker impedance actually varies with the frequency of the audio signal applied, so an "8 ohm" loudspeaker has an "average" impedance of 8 ohms, but if you looked at a graph of it's actual impedance, it can vary quite a bit, based on the frequency applied to it. I know it sounds confusing, so the best course of action is to find a loudspeaker that specifies it's impedance, and match it to your radio. Hope this helps, and doesn't confuse
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Old 11-19-2009, 08:14 PM
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Learn Something New

Hey Olguy, I'd like to add, I came into some unmarked speakers and couldn't remember just how a dam speaker impedance was figured out. I'll thank you for the refresher course. olnolan
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Old 11-19-2009, 10:27 PM
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Sounds like a dead short to me - unless your meter was on the 1000 or 10 K ohms scale?
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Old 11-19-2009, 11:17 PM
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Thanks, Oldguy. It seemed too easy.

Rusty, do you mean a short in the speaker or the wiring?
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Old 11-20-2009, 07:45 AM
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Your resistance readings from the meter are really low, it appears to be a straight short. Are you testing at the speaker directly or through the wiring?

Find the lowest range on the meter, if you can select them. Ideally you want a range suited for measuring around 3 to 15 ohms, so the X1 scale or a range that tops out around 200 ohms.

Is it an old-school analog meter or a digital one?
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Old 11-20-2009, 09:55 AM
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Get an AA battery. Hook it up to the speaker. You should see the cone move a little bit, and hear a distinct click. Reverse the polarity on the battery, the cone should move the other way, and again you should hear a click.
Gently push the cone in with your finger. You should not hear any rubbing sounds.
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Old 11-20-2009, 10:50 AM
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I just tested a few speakers I have using a regular ohm meter. With the speaker disconnected, the resistance between the + and - terminals was:
3.2 ohms on a 4 ohm speaker, and
6.8 ohms on a 10 ohm speaker.

I agree with 'Oldguy' that measuring the actual impedance of a speaker is not really this simple and requires specialized equipment, but I believe that measuring the basic resistance will give you a ballpark idea.

If you are using an original '86 Delco stereo, I would bet money that the original speakers were 8-10 ohm.

Here is a shop that specializes in car radio repair and manufactures factory correct speakers. http://www.turnswitch.com/speakers.htm

Hope this helps...
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Old 11-20-2009, 11:53 AM
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Thanks guys.

On the bench, and as suggested, I tried a lower ohm range and got 8 ohms in one speaker and 3 ohms in the newer (Chinese) speaker. That 3 ohm speaker was the one that seemed to "fail" first with the last radio. Then the whole radio went "dead".

Joe, I've tried Electro-Tech before for original kickpanel speakers for the '67 and they were great. I see they have 3 1/2" speakers that should fit.

Again, thanks to all who helped.
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