Measurement of vibration modes of thin shell of loudspeaker using laser triangulation method

• Using two-dimensional PSD instead of one-dimensional PSD sensor to meet the conditions of differential amplification circuit. • Accurately separate and suppress common mode signals, without compromising the integrity of the original differential mode signals. • Accurate measurement of nonlinear harmonic distortion in speakers has been achieved at low cost. • The system is a non-contact measurement system that accurately monitors the vibration status of the target without interference. PSD sensors can easily receive common mode signals, including ambient light, temperature drift, electromagnetic interference, background noise of the laser output, etc. Most of the existing one-dimensional vibration measurement systems on the market use one-dimensional PSD sensors and do not introduce differential amplification circuits, so they are not able to eliminate the common mode interference signals, and their use environments are also limited This paper innovatively proposes to introduce the 2D PSD into the 1D vibration measurement system, constructs the conditions of differential amplification, designs and introduces the two-way differential amplification circuit, so that the system has the ability to eliminate common mode signals. The results of the system anti-interference experiments show that, with the continuous enhancement of the ambient light intensity, the accuracy of the traditional PSD measurement system has been reduced from 5.0 μm to about 59.8 μm, while the measurement accuracy of the PSD measurement system proposed in this paper with a two-way differential amplification circuit is almost unchanged, and the accuracy of the system is reduced from 5.0 μm to 12.1 μm only when the illumination level reaches its maximum value. At this time, the system’s measurement accuracy is more than five times that of conventional PSD measurement systems, which demonstrates that this system is very effective for the removal of common-mode interference signals. In addition, this paper also proposes a variety of protective measures such as PCB version Guard-ring design, common mode signal zero compensation circuit, laser background noise elimination, etc., which ensures the accuracy and reliability of the data acquisition of the amplifier circuit preamplifier system. In terms of system application experimental testing, the speaker thin shell vibration, fixed-point sweep measurement, circumferential modal measurement, subharmonic distortion and other aspects of the measurement, to verify the feasibility of the system weak reflection and broadband microvibration measurement. The measurement results show that the generation of the subharmonic of the loudspeaker thin shell originates from the interaction of the loudspeaker thin shell modes. The main innovativeness of this paper lies in the fact that changing to a two-dimensional PSD sensor and designing a dual-channel differential amplification circuit improves the ability of the system to suppress common mode signals, ensures the stability of the system’s measurement accuracy, and broadens the application environment of the system; the other aspect of this paper’s innovativeness is also shown in the field of sensors, especially in this paper’s design of the dual-channel differential amplification idea, which points out a new direction for other sensors to suppress the interference of common mode signals. This paper is also innovative in the field of sensors.