Only if you can pick up sub-1dB difference at 20kHz and can do a rapid (essentially instantaneous) switch.
But as several people have pointed out, it likely isn't. The far more valid measurement (electrical at the speaker terminals) is actually a lot easier.
What happens with 3 Ohms or maybe even less less? (blocked ports) Could it have an effect?
I do have a multimeter somewhere, so level match speakers at 1k, or measure watts with 1k tone, then do the same for 30, 40, 50, etc.? Yeah, that sounds like less trouble.
I'll definitely try that
(sorry haven't had time to read in depth and respond to all!)
Oh yeah btw, someone asked, from my cell dB meter app, measurements were probably something like 75dB at for first 2, then 80-85dB. But, initially the app mentioned calibration file for the mic I think, which I didn't have (built-in mic), so I didn't want to put too much faith into it... But I guess it must still be fairly accurate in the end... shrug