Patented June 2, 19251,540,585




Application filed October 27, 1922. Serial No. 597,407.

To all whom it may concern:
   Be it known that I, RAYMOND B. ABBOTT, a citizen of the United States, and a resident of West Lafayette, in the county of Tippecanoe and State of Indiana, have invented a new and Improved Electrical Stethoscope, of which the following is a full, clear, and exact description.
   This invention relates to electrical stethoscopes.
   In contemplating the invention, consideration must be given to the fact that in using an instrument of this sort the beats which are generally measured are those of very low frequency, and it must necessarily be understood that the ordinary electrical device for transmitting sound, such as a telephone transmitter, is not especially adaptable to use as a stethoscope because the diaphragm of such transmitter is tuned to frequencies far different than those which are measured when using an ordinary stethoscope. If, therefore, an electrical sound transmitter device, such as an ordinary telephone transmitter, particularly an especially sensitive one, is properly treated it can be made to respond to vibrations or variations in sound produced within a narrow limit of frequency ranges; therefore, it can be and has been tried, in accordance with my invention, to make it respond only to those vibrations which are within the range of those corresponding to the frequency of vibrations of the heart action in the human body. If the transmitter can be tuned to this type of frequency, then it is true that other sounds occurring in the immediate vicinity of the instrument are not received clearly if at all.
   To this end, therefore, my invention has for an object the provision of a telephone transmitter with the vibrating parts so arranged and constructed as to be responsive with a high degree of sensitiveness to low frequency vibrations, such as those produced by the heart beat, and to be practically nonresponsive to any other frequencies of beats.
   Another object is to provide an electrical sound-receiving device, such as a telephone transmitter, modified by the application thereto of my inventive idea, the application of which to the transmitter, however, does not involve any such change in the transmitter as will require its being rebuilt or redesigned. In other words, my inventive idea can be readily applied to any ordinary
telephone transmitter of a degree of sensitiveness suitable for the requirements of the work.
   The invention is illustrated in the drawings, of which--
   Figure 1 is a section taken through the transmitter.
   Figure 2 is a sectioin taken on the line 2-2 of Figure 1.
   The form of the invention shown in the drawing is a preferred form, although it is understood that modifications in the construction and arrangement of the parts and in the character of the materials used may be adopted without departing from the spirit of the invention.
   As illustrated in the drawings, the preferred form of the invention includes a cup-shaped metallic casing 1 having a central aperture 2 into which the usual mouthpiece 3, preferably of hard rubber, is screwed. This mouthpiece, in the operation of the device in accordance with my invention, is provided with a plain thin diaphragm 4, preferably of some material such as hard rubber or celluloid. This diaphragm may be fastened to the end of the mouthpiece by any suitable means, such as adhesive. The metallic casing 1 has a back plate 5 screwed thereto. This black plate provides a support for a plurality of stub shafts such as 6 and 7 supporting resistance cells 8, preferably containing material such as 9, which may be and generally is loose or granular carbons. These cells with the contained carbon are similar to the ordinary telephone transmitter buttons. The resistance to the flow of current through the carbon is varied as the pressure upon the carbon granules is varied. The ends of the cells 8 are connected to a diaphragm 10, preferably made of thin metal, brass or aluminum. This diaphragm is held in the metal case 1 by means of felt washers 10a disposed on either side and held in place by a metal ring 10b. This ring and these washers are held in the casing by being disposed between its front wall and the back plate 5. The center of the back plate 5 is aperatured to receive a hard rubber screw plug 11 to which a connection 12 is made by wire 13 to the diaphragm 10 and then back through the buttons or cells 8 to the back plate 5, to a wire 14, which may be connected to a suitable device such as a battery 15 in circuit with which is a primary 16 of a transformer, the secondary 17 of which is

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