An Optical Wave Microphone System (O.W.M.S) is a new sound measuring device witch dose not need to install a device at measuring point directly like a condenser microphone and to mix particulate materials like Leaser Doppler Velocimetry. Therefore O.W.M.S can measure sound without disturbing sound fields. Study on the reduction of jet noise has already been carried out, and the Perforated Tube could decrease jet noise at high pressures. However at low pressure peculiar sound noises were detected. It is very difficult to identify the source of those noises with ordinary measuring devises. In the present paper, the development of the method to measure the source of these noises by using O.W.M.S has been reported
