Quality control in the mass production of transducers and electro-acoustical systems requires an objective technique for reliable selection of defective units. A new technique is presented for detecting defects which produce almost inaudible symptoms during testing but may degrade sound quality in the final application (e.g. loose particles in the gap). Here the regular distortion which is characteristic for good units is modeled and actively compensated in the measured signal of a device under test to reveal symptoms of irregular defects (meta-hearing technology). The paper shows ways to perform high-speed measurements close to the physical limits and how to cope with ambient noise in a production environment. Traditional and more advanced techniques for separating passed and failed units are compared and their integration into process control is discussed. Finally, the paper addresses cost effective implementation in a robust hardware, flexibility to customer’s needs, simple handling and other practical requirements.
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