Speaker Efficiency

I do not have a lot of test equipment and I was wondering if it is possible to test the effieciency of a speaker with just a test tone signal, a multimeter and an spl meter?

I am probably wrong, but would you play the test tone signal (pink noise), one speaker at a time, place the spl meter 1 meter in front of the speaker and adjust the volume until 2.83 volts reads across the speaker terminals?

That will work reasonably well so long as the test tone is within the linear region for the driver you are testing. Also you would need to compensate for any humps or dips in the SPL meter response dependant on the frequency you are testing at. That will give you the 2.83V efficiency the 1Watt efficiency is a little harder to determine with the equipment you have.