phonoscope

[ foh-nuh-skohp ]
/ ˈfoʊ nəˌskoʊp /

noun

an instrument for making visible the motions or properties of a sounding body.
a device for testing the quality of strings for musical instruments.

Origin of phonoscope

First recorded in 1880–85; phono- + -scope

British Dictionary definitions for phonoscope

phonoscope
/ (ˈfəʊnəˌskəʊp) /

noun

a device that renders visible the vibrations of sound waves