Volume Control setting corresponds to how many db down (-db) from 0db at full volume?

guys, 
i was thinking about this topic this morning & tell me why this won't work: 
elunkenheimer should use a voltmeter & measure the average voltage on the speaker binding posts (of amp or speaker - better at the speaker as it will take into account any I*R drop in the speaker cable). 
Then to calculate power simply do V^2/R where R is manuf specified average resistance of speaker (4 Ohms/6 Ohms/8Ohms, etc). 
elunkenheimer can do this calculation at several (or each if he wants to do the work) preamp volume knob settings.
Speaker impedance varies vs. freq but this will be a rough estimate of power being delivered to the speaker.

Bombaywalla, yes, that will work provided the meter has adequate speed and bandwidth.  And in fact about 35 years ago I had a Radio Shack audio power meter which worked in exactly that manner.

But the larger question I would raise about all of this is what's the point?  A brief dynamic peak in the music that is just 10 db louder than the level that is measured will require 10 times as much power.  A peak that is 20 db louder will require 100 times as much power.  In most circumstances most of the power capability of an amp is probably needed just for brief dynamic peaks.

It seems to me that it would be more meaningful to do an approximate calculation of the maximum SPL that can be generated at the listening position by the particular speaker/amp combo.  In past threads you and I have both posted info about how to do that.  For example see my second post in this thread.

Best regards,
-- Al
 

thanks Almarg.

But the larger question I would raise about all of this is what's the point?

let's hope the OP chimes in here & let's us know what is on his mind re. this.....