Stethoscope Acoustics

IT is an anachronism that the stethoscope, introduced in 1819, remains an indispensable medical tool today although no standards have ever been set for its acoustical performance.' Neither has a standard test been established for evaluating the acoustics of the intact instrument. Furthermore, there is no information on the intimate acoustical interaction of the stethoscope with the doctors' ears.2 Our initial approach to these problems was to adapt an aheady established technique of testing insert-type earphones3' 4 (hearing-aid types) to the testing of stethoscopes which are also acoustical devices of insert type. A deficiency in the method is its exclusion of human ears at the stethoscope earpiece. Since any stethoscope has little utility in the absence of a human listener, a fundamentally different test method was devised in our laboratory which does include the acoustics of human ears in testing the acoustics of stethoscopes. This paper presents an evaluation of both objective test methods. Good agreement has been attained between the objective frequency response curves of the second method and the results of subjective listening tests with the same stethoscopes. The acoustical interactions of human ears with stethoscopes are also delineated.