Cork, the digital version of the Radio Shack SPL meter is well-suited for this use. It has a provision(the analog doesn't)for measuring the maximum level reached either briefly or over an extended period. You'd read the max level at the volume setting you usually use and then convert that to power used at that level. To do this you'd start with the sensitivity spec for the M22, which was 89dB for 1 watt at 1 meter distance for my M22s(and I assume yours). Recently Axiom changed this by 4dB to 93dB, and it would be helpful if Ian or Alan would clarify this, since this would indicate better than a doubling of sensitivity.
However, using the previous 89dB figure, it would be decreased by about 3dB per doubling of listening distance beyond 1 meter, according to research reported by Dr. Toole in his book. For example, at a distance of 9-10', about 4dB should be dropped, down to 85dB for 1 watt. So, if a max reading of 95dB was measured this would use 10 watts, if it was 98dB, this would bring it to 20 watts, etc. This follows the formula for power increases which can be summarised as a doubling of power needed for each 3dB increase and 10 times the power for a 10dB increase. This can be done approximately in your head, or a formula can be plugged into a pocket scientific calculator(you always carry one; right?)for more precision, or probably easiest, there are online power calculators, such as
this one .
