Engineering:Phonometer
From HandWiki
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 Student's Reference Work. Chicago: F. E. Compton and Co.
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