how do I determine ohms of an unmarked speaker?

[green shag]

I have (2) 12" Sunn guitar transducer speakers with the aluminum cones and they no markings. How do I determine if they are 4 ohm or 8 ohm speakers. I've installed the speakers in a 2-12 configuration wired in series. Do I double the resistance in ohms when wired in series?  

[green shag]

On 2002-05-09 12:08, green shag wrote:
I have (2) 12" Sunn guitar transducer speakers with the aluminum cones and they have no markings. How do I determine if they are 4 ohm or 8 ohm speakers. I've installed the speakers in a 2-12 configuration wired in series. Do I double the resistance in ohms when wired in series?  

[JoeArthur]

The DC resistance of the voice coil is usually less but close to the impedance rating of the speaker.  For example, a 4 ohm speaker usually has a DC resistance of 3.2 ohms.  So... measure the resistance of the voice coil and round UP to the closest common impedance.

Speakers connected in series should have their individual impedances summed to determine the total impedance.  Two 4 ohm speakers will give 8 ohms total - it's double only because it is two speakers with identical impedance ratings.