Phonometer

A phonometer is an instrument invented by Thomas Edison for testing the force of the human voice in speaking. It consists chiefly of a mouthpiece and diaphragm. Behind the diaphragm is placed a delicate mechanism which operates a 15-inch flywheel by means of which a hole can be bored in an ordinary pine board.

References
  •  This article incorporates text from a publication now in the public domain: Beach, Chandler B., ed. (1914). "Phonometer" . The New Students Reference Work . Chicago: F. E. Compton and Co.
  • The dictionary definition of phonometer at Wiktionary
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