[Measurement of the frequency response of several stethoscopes in common use. Consequences for cardiac and pulmonary auscultation].

We measured the frequency response of eight stethoscope membranes and of thirteen types of stethoscopes. Measurements were made in an anechoic chamber calculating the ratio between the intensity of a sinusoidal sound coming from a loud speaker and the intensity of the transmitted sound through the membrane of the stethoscope. Small membranes have a bandwidth (without attenuation or amplification) between 10 and 600 Hz while large membranes have a bandwidth twice the size (10-1200 Hz). This good result does not appear in the case of stethoscopes showing increasing attenuation versus frequency, with a mean value from -2.5 to -10.5 dB and variations of 10 dB in the range 50-1200 Hz which is the useful bandwidth for cardiac and pulmonary auscultation. By contrast, fidelity of the measured stethoscopes was good. Discussion of the results suggests modification of stethoscope design to eliminate faults of sound transmission and to elaborate a microphone sensor allowing an electric transmission.