Higher-order harmonic signature analysis for loudspeaker defect detection

Abstract

Loudspeaker assembly faults, such as a rubbing voice coil, bent frame, loose spider, etc., have traditionally been detected using experienced human listeners at the end of a production line. Previous attempts to develop production measurement systems for on-line testing typically analyze only low-order harmonics for the primary purpose of measuring total harmonic distortion (THD), and thus are not specifically designed to detect defective rub, buzz, and ticking sounds. This paper describes a new method wherein the total energy of high-order harmonics groups, for example, 10th through the 20th or 31st through the 40th, are measured and analyzed. By grouping high-order harmonics and resolving their respective total energies, distinct signatures can be obtained that correlate to the root cause of audible rub and buzz distortions [Temme (2000)]. The paper discusses loudspeakers tested with specific defects, as well as results of a computer-based electroacoustic measurement and analysis system used for detection.