This study presents a new measuring system that visualizes sound pressure spatial distributions. In the system, microphone 3-D position is found by the combination of an image processing and an ultrasonic ranging technique, and the measured sound field will be overlapped on a camera-captured image. Since the system detects the microphone position automatically, a user can scan a microphone by hand without microphone moving equipment. We propose a PC-based system that consists of a CCD camera, a 40 kHz ultrasonic transducer and a hand-held microphone with an LED optical marker. The transverse position of the LED marker is detected by processing the CCD camera image, and the distance to the microphone is measured by the ultrasonic pulse method. To check the feasibility of the proposed system, two verifications were performed. First, the position measurement accuracy was studied at 0.5 m distant from the camera. The position sensing error was 31 mm, and has been reduced to 5 mm by compensating the longitudinal position error. Second, practical demonstrations of sound source visualization were carried out successfully for a vacuum cleaner and a cooling fan.
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