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(Circulation. 1966;34:899.)
© 1966 American Heart Association, Inc.

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Stethoscope Acoustics

II. Transmission and Filtration Patterns

PAUL Y. ERTEL M.D.¹; MERLE LAWRENCE PH.D.¹; RICHARD K. BROWN PH.D.¹; AARON M. STERN M.D.¹

¹ From the Department of Pediatrics and Communicable Diseases, The University of Michigan Medical Center, Ann Arbor, Michigan. Laboratory facilities were provided by the Kresge Hearing Research Institute.

This paper describes a fully calibrated and standardized acoustical test method for evaluating the transmission patterns and the filtration patterns of intact stethoscopes. An essential component of the test system is the artificial ear which duplicates the acoustical contribution of the average human ear to the stethoscope's acoustics. The transmission patterns of bell-type stethoscopes fall into four distinct groups which correspond to their basic design features. Shallow bells and single tubing design both result in attenuation at higher frequencies. A deep, trumpet-shaped bell with double tubing design may provide amplification at higher frequencies. Diaphragms attenuate the transmission acoustics of stethoscopes. When the low frequencies are selectively attenuated, high frequencies are heard more distinctly. Some diaphragms were found to attenuate at all frequencies.

The acoustical performance of any stethoscope is critical. Any attenuation of clinically significant sounds of low intensity may render them totally inaudible. The majority of stethoscopes tested (bell and diaphragm chestpieces) attenuate high frequency sounds. The adoption of stethoscopic performance criteria is urged. Few modern stethoscopes show any significant acoustical improvement since the time of Laennec.

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