The development of headphones in the early 20th century caused a controversial stir of philosophical debate that reshaped the overall perception of acoustics and sound production worldwide. During the peak of the enlightened era, from the emergence of neurology and medical engineering, came the invention of the stethoscope - the binaural stethoscope created an “in-head” acoustic experience allowing medical practitioners to listen to the body in an honest, unbiased way. This Cartesian-inspired medical instrument followed Descartes’ philosophical theory that the body was the seat of the soul and that an interior sound experience enlivened the senses. The stethoscope was a pivotal artifact in the development of headphones and the birth of modern listening.