THE HISTORY OF STETHOSCOPE

Stethoscope was found by René Laennec from France in 1816. He invented while he worked at Necker-Enfants Malades Hospital in Paris. The first ever stethoscope used a wooden tube and was monaural, similar with common ear trumpet. In that day, his invention was not called a stethoscope yet, but commonly called a "microphone". 

the modern stethoscope

 Golding Bird was made the first flexible stethoscope in 1840. Bird was the first to publish a description of such a stethoscope but he noted in his paper the prior existence of an earlier design which he described as the snake ear trumpet. Bird's stethoscope had a single earpiece.

 In 1851, Irish physician Arthur Leared invented a binaural stethoscope, and in 1852 George Cammann perfected the design of the instrument for commercial production, which has become the standard ever since.

Rappaport and Sprague made a new stethoscope design in the 1940s, and became the standard, consisting of two sides, one of which is used for the respiratory system, the other for the cardiovascular system.  The Rappaport-Sprague model stethoscope was heavy and short (18–24 in (46–61 cm)) with an antiquated appearance recognizable by their two large independent latex rubber tubes connecting an exposed-leaf-spring-joined-pair of opposing "f"-shaped chrome-plated brass binaural ear tubes with a dual-head chest piece.

David Littmann, a Harvard Medical School professor, in early 1960 created a new stethoscope that was lighter than previous models. In the late 1970s, 3M-Littmann introduced the tunable diaphragm: a very hard (G-10) glass-epoxy resin diaphragm member with an overmolded silicone flexible acoustic surround which permitted increased excursion of the diaphragm member in a "z"-axis with respect to the plane of the sound collecting area. The left shift to a lower resonant frequency increases the volume of some low frequency sounds due to the longer waves propagated by the increased excursion of the hard diaphragm member suspended in the concentric accountic surround.