Automatic measurement of electro-mechanical parameters of low-frequency loudspeakers

Abstract

This work is to present a system for automatic measurement of low-frequency loudspeaker electro-mechanical parameters. The proposed system is of virtual characteristics, consisting of a personal computer, dynamic data acquisition, displacement laser sensor, and voltage and current probes.  A computer programming was coded to control sine-sweep generation that was fed to a loudspeaker and to process electrical signals from a displacement laser sensor and electric probes. The analysis was done in frequency domain to yield loudspeaker parameters, such as mechanical quality factor (), total quality factor (), electrical quality factor (), force factor (Bl), voice coil’s electrical resistance (), and mechanical mass (), resistance (), compliance () and stiffness ().  The constructed system was tested for measuring the parameters of 8-inch and 12-inch loudspeakers, and results were compared to that utilizing a traditional mass-adding technique. It was found that the automated system was capable to complete the measurement in the frequency ranges of 20 Hz – 220 Hz within 3.34 minutes, much faster than that using the traditional approach that normally consumed time of 30 - 45 minutes. Most of the measured parameters from both the automated system and the traditional approach were similar, but some were quite different due to successive calculation and cumulative error. However, a further work could be done to reduce such the error.