A System Based On PSD And Laser Triangulation Method To Measure Vibration Mode Of Loudspeaker Shells

China is the largest Loudspeaker manufacturing country in the world, and Zhejiang is the largest loudspeaker yield province in china .However, China is far form a great power country producing quality loudspeakers. So it has an important practical signification to measure the loudspeaker vibration mode and to analyze its nonlinear distortion mechanism. Main studies are listed as follows:1. A new method using one-dimensional PSD (Position Sensitive Detector) and the laser triangulation method to measure the vibration mode of loudspeaker shell is proposed. Based on laser triangulation method designed by the formers, to satisfy the detection conditions of weak-reflection surface of loudspeaker shell as much as possible, several measures at the optics system are adopted to make the PSD receive signal luminous flux as many as possible and to eliminate the background light noise.2. A PSD signal processing circuit system is designed to overcome the difficulty measuring the small and wideband vibration of loudspeaker shell which has a weak reflection surface. The signal processing circuits consist of wholly. analog elements with a cutoff frequency about 10kHz. This system not only can be used to detect vibration of loudspeaker shell, but also to detect small and wideband vibration of an object with weak reflection surface, such as the loudspeaker shell.3. Several measurements of loudspeaker shell vibration are performed with the designed system and other instruments, such as the vibration at a point of loudspeaker shell at a fixed frequency and at frequency sweep, and the vibration mode along the circumference. These measurements validate the designed system in measuring small and wideband vibration of an object with weak reflection surface. The measurement results and analyses shows that the sub-harmonics in,loudspeaker shell are caused by the interaction of vibration modes.