Abstract: An optical fiber is used as a transducer to convert a low frequency mechanical disturbance into low frequency amplitude modulated optical energy. According to the preferred embodiment of the invention transduction occurs by means of a multi-path interference phenomena capable of responding to acoustic information ranging from less than one hundredth of a cycle per second to several hundred thousand cycles per second. This feature of the invention makes the general concept applicable to use in musical instruments or as a security sensing device. When the concept is applied to a musical instrument it would preferably include the following elements in series: a solid state laser, a multi-mode or single index optic fiber, a square law detector, such as a photodiode, an audio amplifier and a speaker. When the concept is applied in the embodiment of a security sensing apparatus it would preferably include the same active elements (i.e.