Granted Patent
Utility
US 4,258,235 · App. 05/957,060
Pressure gradient electret microphone
Inventor:
Alan R. Watson
Patented Case
View Patent ↗
Granted: Mar 24, 1981
Filed: Nov 3, 1978
Inventor
Alan R. Watson
Assignee (at issue)
Electro-Voice, Inc.
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.