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Knowles Corporation

A maker of tiny electronic components, Knowles supplies high-performance capacitors and RF filters for defense and industrial gear, plus the balanced armature speakers and microphones tucked inside hearing aids. Founded in 1946 by acoustical engineer Hugh S. Knowles, the company pioneered the miniature microphone that let hearing aids shrink to nearly invisible devices. It became an independent, publicly traded company in 2014 when Dover Corporation spun it off.