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Publication numberUS3472335 A
Publication typeGrant
Publication dateOct 14, 1969
Filing dateJan 2, 1968
Priority dateJan 2, 1968
Publication numberUS 3472335 A, US 3472335A, US-A-3472335, US3472335 A, US3472335A
InventorsAllen Derek R
Original AssigneeAllen Medical Instr Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Dual stethoscope microphone with switch-tube valve
US 3472335 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent Int. Cl. A611) 7/02 U.s.o|. 181-24 9 Claims ABSTRACT OF THE DISCLOSURE Disclosed herein is a stethoscope having a single tube for transmitting sound waves to binaurals through branch tubes'having aggregate bore area so related to the bore area of the single tube as to produce good sound-propagatingcharacteristics throughout the most useful range of frequencies in the acoustical spectrum, with improvement especially in the high frequency portion of the spectrum. The disclosed stethoscope has a microphone of the dual chest-piece type, and embodies a switch-valve for selectively connecting the sound the tube either to the low frequency, bell, or to the. high-frequency diaphragm'of the microphone. The outlets from the bell and diaphragm chambers respectively are equal in area to that of the tube bore, and in order to minimize the height of the microphone, these outlets are in the form of laterally-elongated slots. The valve embodies a switch-tube that is rocked on a transverse pivot to register its mouth selectively with either of the chest-piece outlets.

Background of invention This application is a continuation-in-part of my pending application Ser. No. 636,777, filed May 8, 1967, which discloses a stethoscope deriving improved acoustical performance through the use of two sound tubes extending from the microphone to the binaural fork.

' The most common and preferred type of stethoscope is the single-tube type wherein a single sound tube extends from the microphone all the way to the binaural fork, where it communicates with the branch tubes of the fork. This type has the advantages of being more compact, lighter, subject to less extraneous noise, and neater in appearance, but has been deficient acoustically in having a sharp drop-off in the ratio of output to input (attenuation) in the range above 400 cycles per second of the frequency spectrum. The double-tube type, while giving better acoustical performance, has the disadvantages of being heavier, clumsier, susceptible to the tubes knocking against one another and generating noises which are mingled with and obscure the heart-sounds for which the physician is listening, and sometimes become tangled together.

Paul Y. Ertel et al., in their article on Stethoscope- Acoustics in Circulation, vol. XXXIV, November 1966, have stressed the fact that a stethoscope is an acoustical instrument, that the measure of its efficiency is an acoustical one, and that there is a growing need for better acoustical performance in a broader spectrum of frequencies than has hitherto been available. They note that the single-tube design appears to be the current trend, but observe that it invariably results in excessive losses at the higher frequencies. As to the importance of the high frequency sounds, they state: the high frequency components contribute to the recognition of the distinctive characteristics of such lesions as mitral insufficiency in contrast to the murmur of a ventricular septal defect. Some murmurs which are of very low intensity (ator near the hearing threshold) are composed of high frequency components almost exclusively (for example, the murmur of aortic insufiiciency). Any stethoscope which attenuates high frequencies may render such a murmur inaudible. It is also worth pointing out that senior clinicians may have lost their hearing acuity at the higher frequencies due to presbycusis and truly need amplification in this range. Along this same line, they continue as follows: What is often overlooked is the critical nature of the performance of any stethoscope. Clinically significant sounds which are near the hearing threshold may be totally lost to the examiner if the stethoscope attenuates them by as little as 3 db. A soft highpitched murmur of aortic insufficiency may be completely inaudible to the physician whose stethoscope attenuates high frequencies, no matter how long he has owned it. The common need is for a stethoscope whose response pattern will not attenuate sounds at any clinically significant frequency, or one which will amplify at selected frequencies.

In an attempt to improve the acoustical performance of a single-tube stethoscope, an instrument having a sound tube tapering from a bore area of about Ms" diameter at its connection to the microphone to a bore diameter at the binaural fork larger than the bore diameter of the branch tubes, has displayed somewhat better transmission of high frequencies. The maker of that stethoscope has attributed its better performance to the tapered characteristic of the tube. Considerable room for improvement over this tapered-tube variation of the single-tube stethoscope has still remained, and the double-tube type has continued to be far superior, acoustically, to the single-tube type.

Summary of invention The present invention has a principal object to provide a single-tube stethoscope having greatly improved acoustical performance in the higher frequency range. I have discovered that this can be attained by providing an air column passage having a cross-sectional area substantially equal to the sum of the cross-sectional areas of the branch passages of the binaural fork, and by maintaining this area substantially undiminished from the chamber or chambers of the microphone, through the outlet throat or throats thereof, thence through the single sound tube and up to the fork.

Another object is to provide an improved bell-diaphragm double microphone of low height combined with good transmission characteristics, with a valve for switching from hell to microphone and vice versa. Low height in combination with high transmission efficiency is attained by utilizing a valve element having a throat of elongated cross section and of high area, of minimal height parallel to the common axis of hell and diaphragm and relatively wide transversely of said axis.

The invention has as a further object, to provide an improved, low-height microphone with a novel and more desirable valve for switching bell to diaphragm and vice versa. To this end, the valve embodies a tilting switchtube having a mouth in sliding engagement with an arcuate valve seat in a valve block having alternate throats opening into respective ends of the arcuate seat and adapted to communicate selectively with the mouth of the switch tube. The projecting end of the switch tube is coupled to the flexible sound tube. The projecting portion of the switch tube functions as a lever which may be grasped and tilted, with a snap action, from bell position to diaphragm position and vice versa.

Other objects Will become apparent in the ensuing specification and appended drawing, in which FIG. 1 is a plan view of a stethoscope embodying the several features of the invention;

FIG. 2 is a fragmentary sectional view of the binaural fork, the tube and the microphone, the latter shown largely in plan view;

FIG. 3 is a side elevational view of the microphone;

FIG. 4 is a longitudinal sectional view of the switch tube and valve structure of the microphone, on an enlarged scale, taken on line 44 of FIG. '2;

FIG. 5 is a side elevational view of the switch-tube and associated parts, the bell, housing and diaphragm parts being shown in section;

FIG. 6 is a longitudinal sectional view of the same, taken on line 66 of FIG. 5, in planes parallel to the diaphragm; and

FIG. 7 is a cross-sectional view of the same, taken on line 77 of FIG. 5.

Description Referring now to the drawing in detail, I have shown therein, as an example of one form in which the invention may be embodied, a stethoscope comprising, in general, a microphone A, a sound tube B, a binaural coupling fork C, a pair of binaurals D mounted in respective branch tubes of fork C, and a switch valve E embodied in microphone A.

Microphone A comprises a diaphragm 10 at one end, for picking up chest sounds of high frequency, a bell 11 at its opposite end, for picking up sounds of low frequency, and an intermediate housing 12, integral with bell 11 and secured to diaphragm 10 by suitable means such as screws 13. Diaphragm 10 and bell 11 have respective ports 14 and 15 for transmitting sound vibration into valve E. A switch tube 16 selectively transmits the vibrations from diaphragm 10, or from hell 11, to sound tube B. Sound tube B is of soft rubber or neoprene or equivalent plastic material. One end of tube B is coupled to switch tube 16, being stretched over the outer end thereof. The other end of tube B makes an integral junction with the two branch tubes 17 of coupling fork C. In its acoustical characteristic, the invention is characterized by a passage of substantially twice the bore diameter of branch tubes 17, so that the aggregate area of the branch passages is substantially equal to the area of the passage defined first by the outlet throats in valve E (hereinafter described) then by the switch tube 16 and finally by the tube B. I have found, by tests which stimulate the operational conditions existing when a physician listens to chest sounds transmitted by the stethoscope through binaurals plugged into his ears that sounds throughout the range within the useful stethoscope spectrum from its minimum frequency up to 2000 cycles per second in the high frequency range thereof, are transmitted without objectionable attenuation, i.e. with a loss of less than about 5-10 db (decibels) of sound intensity between input and output. In contrast to this, the results of a comparative test on a conventional single-tube stethoscope show a sharp drop in output approaching the inaudible level beginning at about 1000 cycles and at 2000 cycles the output is so attenuated as to be completely inaudible to normal ears (e.g. with a loss of as much as 15 db, or five times the maximum acceptable loss-3 db) where the sounds become so attenuated as to give difiiculty in interpreting them.

The improvement in acoustical performance afforded by the invention matches the performance of a two-tube stethoscope in the high frequency range, with all of the conveniences of a single-tube stethoscope, and is far superior to the performance of the tapered-tube stethoscope.

A bow spring 19 is encapsulated in the wall of fork C on its concave side, the two ends of the spring being formed with integral bearing bushings 20 encapsulated in the ends of branch tubes 17 and receiving the ends of stems 21 of binaurals D with a frictional clutching action to permit rotational adjustment thereof and to hold them in selected positions of adjustment.

Valve E comprises a valve block 25 which is rectangular with the exception of one end thereof, which has a concave segmental-cylindrical valve seat 26 generated on the axis of pivot trunnions 27 on which switch tube 16 is mounted for tilting movement, the tube having on its inner end a convex arcuate face 28 slidably mating with valve seat 26. Valve block 25 is embraced between the fiat, parallel arms 29 of a spring yoke having a bridging web 30 connecting the arms 29. Switch tube 16 has a rectangular section 31 formed with flat, parallel sides 32 which are spaced apart the same distance as the flat sided faces of block 25 which are embraced by spring yoke arms 29. Arms 29 also embrace the sides 32 of tube 16 so as to align block 25 and tube 16 in assembly, and are latched to block 25 by the engagement of trunnions 27 in apertures in the ends of arms 29. This latching connection is secured by a close fit of trunnions 27 and the end portions of arms 29 between fiat, parallel inner side walls 33 (FIG. 6) of a bracket portion 34 of intermediate housing 12. Bracket portion 34 projects radially beyond the cylindrical periphery of housing 12 to provide for the pivotal mounting of switch tube 16 at a satisfactory radius from valve seat 26, and cooperates with diaphragm 10 to define, between walls 33, a pair of wedge-shaped cavities 35 and 36 flaring away from the axis of trunnions 27 so as to provide room for tilting of switch tube 16 to the alternate operative positions shown in FIGS. 4 and 5 respectively. Valve block 25 is positioned in shallow rectangular recesses 37 and 38 in the opposed faces of diaphragm 10 and bell 11 respectively, and is located against longitudinal displacement, by transversely extending thin locating lugs 39 engaged in shallow conforming grooves 40 in diaphragm 10 and bell 11 respectively.

Valve block 25 has a pair of valve throats 41 and 42 of elbow configuration, beginning in opposite faces of block 25 and terminating in adjacent relation in valve seat 26. In the opposite faces of block 25, the throats 41, 42 register with the ports 14, 15 of diaphragm 10 and bell 11 respectively. In the position shown in FIG. 4 switch tube 16 communicates through throat 41 and port 14 with diaphragm 10, and in the alternate position shown in FIG. 5, it communicates through throat 42 and port 15 with bell 11. Switch tube 16 is latched in these alternate positions by yielding engagement of inwardly projecting dimples 43 in spring arms 29, in mating recesses 44 in opposite sides of the inner end portion of switch tube member 31. There are two of the dimples 43 in each arm 29, one at one side of the arm (the one seen in FIG. 5) for holding switch tube 16 in the position shown in FIG. 4, and the other at the opposite side of the arm (directly above the recess 44 seen in FIG. 5) for latching the switch tube 16 in the position shown in FIG. 5.

The bridge portion 30 of the spring yoke has a reentrant, bowed central portion 45 which presses against the adjacent end of valve block 25 so as to develop springloading of switch tube 16, such as to seat its end valve face 28 snugly against valve seat 26, spring-loaded pull being transmitted through arms 29 and trunnions 27. The ends of spring arms 29, being trapped between the sides of switch tube member 31 and the internal side walls 33 of bracket extension 34, are positively coupled to trunnions 27 in the assembled microphone, and thus the switch tube and flexible sound tube B are securely attached to the microphone.

Throats 41, 42 are each of slot form, wider in a transverse direction (parallel to the switch pivot axis) than its depth parallel to the common axis of diaphragm 10 and bell 11. A suitably proportioned throat may have a width of .289 inch, and a depth of .127 inch, its ends being full semicircles. The resulting cross-sectional area is about .0333 square inch. The cumulative saving in depth of the two throat openings in valve seat 26 is substantial, making possible a substantial reduction in the height between the rim planes of hell and microphone. The cross sectional area of these throat openings and of the passage in switch tube member 31 is substantially equal to the cross sectional area of the cylindrical air passage in the outer end of switch tube 16 and in the sound tube B, which in turn is substantially equal to the aggregate cross-sectional areas of the branch tubes 17 and of the ear tubes 21. The sound tube B is fabricated as a cylindrical tube throughout its length, and is deformed to flattened form in its end portion stretched over the end of switch tube 16. Its internal diameter in its circular cross-section may be about .206 inch and its area about .033 inch. Thus the air columns extending from the microphone to the users ears, first as a single column and then as two branching columns, have an aggregate area which remains substantially the same from the microphone to the ears.

I claim.

1. In a stethoscope, a microphone comprising, in combination:

a low frequency sound receiving bell;

a high frequency sound receiving diaphragm;

an intermediatae body joining said bell and diaphragm and providing a valve housing; I

said bell and diaphragm being in fixed relation to one another and arranged substantially on a common axis and facing in opposite directions;

means in said valve housing defining a valve chamber having a valve seat and a pair of fixedly positioned valve throats of generally elbow form having respective inlets communicating with said bell and diaphragm respectively, and adjacent throat outlet openings facing in a common direction transversely of said common axis and terminating in said valve seat; and

a switch tube pivotally mounted in said housing for tilting movement on an axis transverse to its own longitudinal axis, said switch tube having an open inner end arranged for communication selectively with either of said adjacent throat openings upon tilting of said tube to respective limit positions, and having its outer end adapted for connection to a sound tube.

2. A stethoscope microphone as defined in claim 1, wherein said bell and microphone have respective rims disposed in substantially parallel planes;

wherein said adjacent throat openings are spaced from one another in a direction parallel to said common axis;

wherein said throats are disposed in a common plane of said axis; and

wherein said switch tube has an axis of tilt disposed at right angles to said common plane;

3. A stethoscope microphone as defined in claim 2, wherein said throat openings are elongated in a direction parallel to said tilt axis.

4. In a stethoscope, a microphone comprising, in combination:

a low frequency sound receiving bell;

a high frequency sound receiving diaphragm;

an intermediate body joining said bell and diaphragm and providing a valve housing;

a valve block disposed in said housing, said block having at its front end a segmental cylindrical concave valve seat and having duel valve throats of elbow form commencing in opposite faces of said block in communication with said bell and diaphragm respectively, and terminating in adjacent throat openings in said valve seat; and

a switch tube pivotally mounted in said housing for tilting movement, said switch tube having an open inner end arranged for communication selectively with either of said adjacent throat openings upon tilting of said tube to respective limit positions.

5. A stethoscope microphone as defined in claim 4,


a spring yoke comprising opposed parallel arms embracing said valve block and having, at their ends, pivotal connections to said switch tube providing the pivot axis thereof; and

a transverse bridge joining said spring arms and yieldably pressing aaginst the back of said valve block to spring-load said open inner end of the switch tube against said valve seat.

6. A stethoscope microphone as defined in claim 5,


said spring yoke is of ribbon metal, and said spring arms have end portions disposed in spaced parallel planes in embracing relation to said switch tube, and provided with transversely aligned pivot apertures; and

wherein said switch tube is provided with pivot means engaged in said apertures to provide said pivotal connections.

7. A stethoscope microphone as defined in claim 6,


said end portions of said arms are confined between the sides of said switch tube and flat parallel inner walls forming part of said housing; and wherein said pivot means consist of integral trunnions on opposite sides of said switch tube, said trunnions having a height not substantially greater then the thickness of said ribbon metal.

8. A stethoscope as defined in claim 4, including:

a spring yoke of ribbon metal including opposed arms disposed in spaced parallel planes in embracing relation to said valve block and having, at their ends, pivotal connections to opposite sides of said switch tube; and

a transverse bridge joining said arms and pressing against the back end of said valve block to springload said open inner end of the switch tube against said valve seat;

at least one of said arms having a dimple projecting inwardly for yielding latching engagement in a recess in the adjacent side of said switch tube, to latch the tube in an operative position thereof.

9. A stethoscope as defined in claim 4, including:

a spring yoke of ribbon metal including opposed arms disposed in spaced parallel planes in embracing relation to said valve block and having, at their ends, pivotal connections to opposite sides of said switch tube; and

a transverse bridge joining said arms and pressing against the back end of said valve block to springload said open inner end of the switch tube against said valve seat;

said bridge including a reentrant bowed central portion providing yielding spring loading between said switch tube and said valve block.

References Cited UNITED STATES PATENTS 8,591 12/1851 Marsh 181-24 999,225 8/ 1911 Hopewell 18 l--24 1,671,936 5/1928 Rieger 181-24 3,193,047 7/ 1965 Allen 181-24 FOREIGN PATENTS 255,086 3/ 1963 Australia.

STEPHEN I. TOMSKY, Primary Examiner

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US8591 *Dec 16, 1851 Stethoscope
US999225 *Mar 9, 1911Aug 1, 1911Charles F HopewellVibroscope.
US1671936 *Jan 23, 1927May 29, 1928 Vania
US3193047 *May 25, 1964Jul 6, 1965 Stethoscope with dual convertible receiver
AU255086B * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3630308 *May 28, 1969Dec 28, 1971Ravin AbeStethoscope
US3951230 *Jan 31, 1975Apr 20, 1976Minnesota Mining And Manufacturing CompanyMulti-sound chamber stethoscope
US5663532 *Nov 27, 1995Sep 2, 1997Minnesota Mining And Manufacturing CompanyErgonometric stethoscope chestpiece
EP0035511A1 *Feb 24, 1981Sep 16, 1981Minnesota Mining & MfgStethoscope chestpiece.
EP0035511A4 *Feb 24, 1981Jan 8, 1982Minnesota Mining & MfgStethoscope chestpiece.
U.S. Classification181/137
International ClassificationA61B7/02, A61B7/00
Cooperative ClassificationA61B7/026
European ClassificationA61B7/02D
Legal Events
Oct 20, 1986ASAssignment
Effective date: 19861008
Mar 15, 1984ASAssignment
Effective date: 19831028