It's not a speaker? Many of them have enough of a bandwidth to produce barely understandable audio, I guess it depends on your qualifications for being a speaker.
you have to get into the physics behind it, not the specifiation or etc, its just as reverse as microphones. also only use for milli watt out puts, since they cant deliver more power as microphones does. also sensitive for audio high frequencies as condensor microphones.
At first please tell me if a capacitive speaker is equal to an electrostatic one? Or just are similar?
Second if they are just the same then I hate to wear on too