Loudspeaker defect analysis using ultrasonic harmonic characterization

Abstract

This study presents the results of an ongoing investigation of defect detection in transducers. 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, or through the use of low‐order harmonics for total harmonic distortion measurement. The findings of Thompson et al. [‘‘Higher‐order harmonic signature analysis for loudspeaker defect detection,’’ J. Acoust. Soc. Am. 114, 2400 (2003)] described a new method wherein the total energy of high‐order harmonics groups (10th through the 20th, or 31st through the 40th), were measured and analyzed. This approach demonstrated the ability to delineate distinct signatures that correlated to the root cause of audible rub and buzz distortions. This paper presents the results of a follow‐up study using equipment that collected harmonic data up to 100 kHz. Results are presented for ten 5‐in. midrange loudspeakers, in which trends for specific acoustic signatures were correlated to known defects. The use of a computer‐based electroacoustic measurement and analysis system using frequencies that are inaudible but beneficial for analysis of defects are discussed. [Work supported by Listen Inc., Boston, MA.]