1. US5492129 - Noise-reducing stethoscope

A noise-reducing stethoscope comprising a body sound sensor for placement on a body to detect internal body sounds and output in response an electrical signal, an ambient noise sensor, proximate the body sound sensor, to detect ambient noise and output in response an electrical signal, and a difference comparator for accepting the electrical signals from both sensors and providing in response a difference signal, in which the difference signal contribution from ambient noise is less than the contribution from ambient noise to the body sound sensor electrical signal to cancel noise artifacts in the body sound sensor electrical signal.