Well thats good, not a total loss then.
Purely out of curiosity, what would be the answer to my original question be if those theoretical values I gave were the AC impedance?
Is your question what the impedance would be for the stated wattage-or the stated wattage for the measured impedance.
It is either one or the other.
As Mac has eluded, one of the "numbers that should be remembered"-is 1 watt at 70V is 4900 ohms. Or with some rounding say 5000 watts.
So 10 watts would be 500 ohms and 50 ohms would be 100 watts.
You can quickly figure out impedances in between the basic numbers.
Many things in audio are not about exact numbers-but quickly getting close to what should be answer.
If you were expecting to see 200 ohms on a line-and you read 30 ohms, then you have a problem. It doesn't matter whether it is 30 or 40 or 20 ohms at this point.
And ALSO remember-that the impedance will vary a good bit-depending on the freq. So a simple 1000Hz tone impedance will very often give a WRONG answer. Yes it is correct at 1000Hz, but what if that is am impedance peak in the response? The actual load presented to the amp could be quite a bit lower.
Once again-the simple answer is WRONG.