Depew 1926
John Depew, of New York. "Capacitatively Actuated Loudspeaker". Filed: February 12, 1926 U.S. Patent 1,631,583 Granted: June 7, 1927

Depew 1926

  You don't have a pdf plugin, but you can download the pdf file.  

Filed: February 12, 1926
U.S. Patent 1,631,583
Granted: June 7, 1927

John Depew, of New York.
"Capacitatively Actuated Loudspeaker".

Referenced by Walker and Williamson in U.S. Pat. 3,008,014