The Collaborative International Dictionary
Phonoscope
Phonoscope \Pho"no*scope\, n. [Phono- + -scope.] (Physics)
An instrument for observing or exhibiting the motions or properties of sounding bodies; especially, an apparatus invented by K["o]nig for testing the quality of musical strings.
An instrument for producing luminous figures by the vibrations of sounding bodies.
Wiktionary
phonoscope
n. a device that shows an image representing the acoustical properties of a musical instrument etc.