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To the Editor:—
For many years, I have used William J. Kerr's "Symballophone" which has been of great help in discerning the origin of murmurs. For example, if there is a systolic blow over the mitral and aortic areas and one must decide if it is the same murmur or two distinct murmurs, by placing one chest piece over each region, the ear perceives the differences in timing and quality.This stereophonic binaural stethoscope or the Symballophone might be used routinely whenever a murmur is audible, though the instrument is clumsy. Kerr showed illustrations of three stethoscopes, but favored the introduction of a "longer connecting-tube from each end piece to the opposite ear." Thus, the Symballophone is a little clumsier than Dr. Horowitz's stethoscope, in that altogether there are four rubber tubes instead of two.
Master AM. The Kerr Symballophone. JAMA. 1965;193(5):403. doi:10.1001/jama.1965.03090050079036