phoneidoscope

from The Century Dictionary.

• noun An instrument for observing the color-figures of liquid films under the action of sonorous vibrations.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physics) An instrument for studying the motions of sounding bodies by optical means. It consists of a tube across the end of which is stretched a film of soap solution thin enough to give colored bands, the form and position of which are affected by sonorous vibrations.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An instrument for studying the motions of sounding bodies by optical means. It consists of a tube across whose end is stretched a film of soap solution thin enough to give coloured bands, whose form and position are affected by sonorous vibrations.