Yes, an electrostatic that was enclosed was the Dayton-
Wright speaker, made in Canada by Mike Dayton-Wright back
in the Seventies. It contained a gas inside the envelope
containing the electrostatic drivers and had a good sound
in the midrange and midbass, but lacked extension on the
highs. It was problematic in the first designs, but later
iterations seemed to work well. They were not my cup of
tea as a preferred speaker. ...Carl