To accurately measure noise in a duct by allowing a pipe with length for preventing a standing wave from being generated at a frequency to be measured by the sound absorption operation of an inner-wall surface to branch off from the duct, and by providing a microphone at the middle part of the pipe.
A pipe 10 being formed by metal such as steel, synthetic resin, or the like is provided so that the pipe can branch off from a duct 1 of the exhaust gas of, for example, a gas turbine or the like. Length L of the pipe 10 is set to a value for preventing a standing wave from being generated at a frequency to be measured by the sound absorption operation of the inner-wall surface of the pipe 10. Then, to avoid damage caused by the heat of high- temperature gas in the duct 1, a microphone M is mounted to the middle part of the pipe 10 other than root and tip parts 11 and 12 of the pipe 10 and a part near them. Although a sound wave being propagated is successively attenuated, it is attenuated by only approximately 1 dB while it is propagated over distance K (approximately 0.3 m) from the root part 11 of the pipe 10 to the microphone M, thus detecting a value close to a noise level nearly in the duct 1.
ISHIHARA KUNIHIKO
SAKAI HARUHISA
Next Patent: THERMAL TYPE INFRARED SENSOR AND THERMAL TYPE INFRARED ARRAY ELEMENT