New digital displacement measuring circuit for aperiodic vibration using self-mixing type LDV

It has been confirmed by the novel method that the vibrational displacement of a loudspeaker can be measured easily by a laser Doppler velocimeter (LDV) using a self-mixing semiconductor laser diode. The number of waves in the Doppler beat signal which is counted up or down from the output of the new counter circuit is stored in a computer. Then the digital displacement information of the aperiodic vibration of the loudspeaker surface also is obtained as the actual surface motion. In this measurement the speaker vibration driven by an audio signal also can be measured. This method will be applied to various vibrational measurements for its simplicity