Title:
Microphonic material and method of producing the same
United States Patent 1833640

Inventors:
Frederick, Fruth Hal
Publication Date:
11/24/1931
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Assignee:
WESTERN ELECTRIC CO
Primary Class:
204/192.100
Other Classes:
313/311, 204/298.240, 252/512, 174/126.400
International Classes:
H04R21/00