OT - Oh yeah, but what about the the membrane "drum-head" resonance and dipole energy cancellation. Like I know what I'm talking about. <g> I did a quick google search to see what they use and got http://www.soundlab-speakers.com/
Won't bore everybody here but it appears that even they have drawbacks and speaker design is curcial. I'm not going to bother to look up if the membrane material eventually degrades and needs replacing.
First, the resonance peak exhibited by all stretched membranes (the drum-head membrane is a good example) can be a serious drawback in the electrostatic speaker (or any type of membrane speaker) if it is not eliminated. It can cause a large acoustical energy peak at the resonant frequency that can be as high as 30 dB. This sonic peak not only "colors" thesound but it also limits the usable dynamic range of the speaker.