How to Test Ohms Rating of Speakers???

[Jtwusmc]

I am installing 2 new speakers in a '75 Peavey Classic B. the speakers were said to be Jensens by my father in law, but have no Ohm rating. How can I test this with a voltmeter?

[olddawg]

I am installing 2 new speakers in a '75 Peavey Classic B. the speakers were said to be Jensens by my father in law, but have no Ohm rating. How can I test this with a voltmeter?

It varies a little bit from speaker to speaker, brand to brand, model to model, but the DC resistance of a voice coil will be slightly less than its impedance at 1khz. In general an 8 ohm speaker will measure around 7 ohms on a multimeter. A 4 ohm speaker about 3 ohms and 16 ohm speaker around 14 ohms. Bare in mind that you have to have good probes, a decent meter set to the low ohms scale, and a clean tight connection to the speaker terminals out of circuit.

[Jtwusmc]

OK, I put my voltmeter on impedance and just held the prongs to pos & neg. showed 3.2 for the Jensen speakers and 7.3 for the stock ??? speakers. Can I assume the Jensens are 4ohms and the stocks are 8ohms?

I also want to understand the wriring better. The 1/4" jack going from the amp to the speakers has 2 wires, 1 goes into each speaker. The speakers both just share anoother blue wire (it just goes from speaker 1 to speaker 2). Does this mean the cab is wired for the rated ohms or are they split because of the split 1/4" jack going to each (I.e the 4 ohm speakers are valued at 2ohms =4 total?)?

Most importantly, am I safe to run these 4ohm Jensens if everything above is accurate???

[Enzo]

You described two speakers wired in "series." That means the power fron the plug went to one speaker, through it to the other speaker and back to the plug.

Yes, I'd assume the speakers were 4 and 8 ohms from those readings.

[g1]

From your description the two 8ohm stock speakers wired in series make a 16ohm load for the amp. With the 4ohm Jensen's wired the same way you will have an 8ohm load for the amp.
I don't think the impedance mismatch will damage the amp but you will get a little less power from the amp with a mismatched load.