Reproduction of sound from old wax phonograph cylinders using the laser-beam reflection method

A laser-beam reflection method was developed to reproduce the sound from old wax phonograph cylinders. Since this optical method is noncontacting and nondestructive, the sound even from repaired wax cylinders can be reproduced. In principle, the method is based on geometrical optics. However, the reflection phenomenon from the grooves of a wax cylinder does not exactly obey the law of geometrical optics because of the finite width of the illuminating beam. Severe problems concerning the properties of the reproduced sounds were found in developing the optical method; they were solved fairly well from quantitative investigations of the reproduced sound. As a result, the laser-beam reflection method is practical and powerful enough to reproduce the sound from all kinds of old wax cylinder.