Page "Stethoscope" Paragraph 7

Several other minor refinements were made to stethoscopes, until in the early 1960s Dr. David Littmann, a Harvard Medical School professor, created a new stethoscope that was lighter than previous models and had improved acoustics.

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.

Conversely, restricting excursion of the diaphragm by pressing the stethoscope diaphragm surface firmly against the anatomical area overlying the physiological sounds of interest, the acoustic surround could also be used to dampen excursion of the diaphragm in response to " z "- axis pressure against a concentric fret.

This raises the frequency bias by shortening the wavelength to auscultate a higher range of physiological sounds.

3-M Littmann is also credited with a collapsible mold frame for sludge molding a single column bifurcating stethoscope tube with an internal septum dividing the single column stethoscope tube into discrete left and right binaural channels ( AKA " cardiology tubing "; including a covered, or internal leaf spring-binaural ear tube connector ).