I’ve used a 1 ohm load resistor in series with the speaker. I measured the voltage drop across the resistor with an HP rms volt meter while measuring spl at one meter on axis with a B&K spl meter. Source is a sine wave generator. I^2*R=power.
What is the name of the tool?
Forgive my absence of knowledge, but what is the name of the tool that one uses to measure the wattage coming out of ones speakers. I called it a watt meter to my family and got something that measures the watts and current coming from the outlet to the powered device I was using instead, for Christmas.