'The Stethophone,' An Electrical Stethoscope

" T h e Stethophone," An Electrical Stethoscope B y H . A . F R E D E R I C K and H . F . D O D G E 1. ACOUSTIC STETHOSCOPES USCULTATION is commonly practiced by means of the ordinary stethoscope, a device with which the physician is able to study sounds produced within the heart, lungs, or other portions of the body and to determine whether such abnormal conditions exist as are evidenced by abnormal sounds. Of particular importance are the characteristics of the normal heart sounds, heart murmurs, breathing sounds and rales.1 It is well known that the intensity of certain of these sounds is not in itself of fundamental significance, that, for example, certain very faint murmurs may represent serious organic lesions; hence it is of pathological importance that these sounds be heard and understood. Most acoustic and mechanical vibratory systems introduce distortion by discriminating in favor of certain frequency bands. Extreme distortion may alter a sound beyond recognition. If a moderate amount of distortion is unavoidable, it may be possible to control it judiciously so as to give most accurate reproduction in the frequency region of major importance. From this standpoint it is of interest to consider the frequency characteristics of the two common types of stethoscopes shown in Figs. 1 and 2. The stethoscopes used in these tests were equipped with thick-walled soft rubber tubing such that the distance from the chest piece to the ear pieces was approximately 55 cm. The characteristic of the open bell stethoscope was obtained by picking up sound from the surface of a piece of fresh beef and measuring the relative intensity of sound on a condenser transmitter 2 with and 1 The presence of any one of several types of lesions in or near the valves of the heart "gives rise to eddies in the blood current and thereby to the abnormal sounds to which we give the name murmurs." " N o one of the various blowing, whistling, rolling, rumbling or piping noises to which the term refers, sounds anything like a ' m u r m u r ' in the ordinary sense of the word." (R.