If you send a sine wave signal to an amplifier with voltage gain and voltage output (so no funny Bakoon current-output business), the signal that the headphone should receive will be a sine wave at the same voltage amplitude but with different frequencies.

I assume you meant the opposite?

Well you kinda confirmed that friction does not depend on mass.

God, I thought we were over this air resistance thing after the second post. I think you guys are taking advantage of an entry-level "engineer's" use of language.

Marv makes a good point about the constant of air resistance/air pressure versus the resistance from a driver's drag. The only problem in carrying the point further would be calculating the Cd for any given driver. As someone who has done quite a bit of that in the automotive world at a rather rudimentary level, I can say doing it with all sorts of varying driver technologies will not be easy or cheap. Ultimately, it's likely the smallest concern in the grand scheme of things so I wouldn't sweat it too much until the rest of the data suggests looking there.

Anyway, wake me up when the discussion moves to sound pressure versus sound intensity.

Classical air resistance calculations also assume uniform/constant air flow etc. At the scale of the stuff we're talking about (both the physical size as well as the movement), it's less about the air resistance and more about the fluid boundary layers... and even then, it's not going to have the kind of macroscopic effect of dragging down the driver. You also really really do not want to do these sorts of calculations. Seriously, this coming from a guy who's undergrad degree ostentatiously has the word "aerospace" in it.

fluid dynamics..... the stuff of nightmares. I quit that track well before then. More fun to brute force the calcs and have a computer do the simulations.