opeidoscope

plural opeidoscopes

1. An instrument, consisting of a tube with one end open and the other end covered with a thin flexible membrane with a mirror attached to its centre, used for exhibiting upon a screen, by means of rays reflected from the mirror, the vibratory motions caused by sounds that enter the tube.

   I can't help thinking that, had he lived to see the electronic cricket sensor, the inventor of the opeidoscope probably would have approved.

   2009, May Berenbaum, The Earwig's Tail: A Modern Bestiary of Multi-legged Legends

   2 more examples

   Among many experiments in transmitting speech I tried that of a conical point of iron fastened to the middle of an opeidoscope membrane, the point being attached to a fine wire in such a manner as not to interfere with its freedom of movement […]

   1878, George Bartlett Prescott, The Speaking Telephone, Talking Phonograph, and Other Novelties

   This is a modification of the opeidoscope. A thin membrane of goldbeater's skin or rubber is stretched over a wooden or metallic cell and secured by a winding of thread. To the center of the membrane is cemented a small thin mirror.

   1902, George Milton Hopkins, Experimental science