US 3570625 A
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United States Patent Derek R. Allen Montrose, Calif.
Sept. 8, 1969 Mar. 16, 1971 Allen Medical Instruments Division of Bio- Dynamics, Inc.
 Inventor [21 Appl. No.  Filed  Patented  Assignee  STETHOSCOPE WITH HIGH INTENSITY AUDIO OUTPUT 10 Claims, 7 Drawing Figs.
 U.S. Cl 181/24  lnt.Cl A61b 7/02  Field ofSearch 181/24, 23;
179/1 (Step). 182
 References Cited UNITED STATES PATENTS 1,560,303 11/1925 Pape 179/182 1,817,489 8/1931 Jones 181/24 2,827,514 3/1958 Murray... 179/1 3,217,831 11/1965 Scan lon 181/24 3,303,902 2/1967 Knot t 181/23 3,437,172 4/1969 Allen 181/24 Primary Examiner-Stephen J. Tomsky Attorney- Lynn l-I. Latta ABSTRACT: A stethoscope providing sound transmission air columns of unequal lengths such that sounds are delivered to respective ear tips with their resonance curves so related that sound of improved audibility is constantly being heard by one ear or the other. 1
' BACKGROUND OFTl-IEINVENTION For many years the major problem faced by designers of stethoscopes has been the need for improving its audio output in transmitting the fainter chest sounds for which the physician listens. Dual heads comprising selectively operable relatively large and small diaphragm and bell receivers for the low and high frequency ranges respectively, have been adopted and are now in common usage. The commonly used stethoscope with a single trunk tube extending from the'head to a T-junction connection to the binaurals (ear tubes) is inefficient for transmitting the fainter chest sounds for which a 15 physician may be listening. A stereophonic sound-transmitting head set for aircraft passenger television or sound movie viewers, disclosed in Scanlon US. Pat. No. 3,217,831, utilizes independent sound conduits of different length in order to provide an arrangement wherein both air conduits are embodied in a double tube rising on only one side of the wearers head, one ear tip being connected directly to the upper end of the double tube and the other car tip being connected through a bridging tube of loop form. The apparatus is not concerned with the problem of transmitting faint sounds purely by air column resonance, since it embodies electronic transducers providing any selected degree of electrically powered amplification. In this head set, the conduit arrangement results in an unbalanced acoustical condition which is undesirable and is corrected by venting to atmosphere 'an acoustical chamber connecting the one ear tip directly to one of the tubes of the double tube. I find that such a vented arrangement is useless in a stethoscope, since it results in a loss of 90 percent of intensity of the sound transmitted.
OBJECTS OF THE INVENTION The general object of the invention is to provide a binaural capable of an increased audio output in the range of I c.p.s. (cycles per second) through 3,000 c.p.s. inv auscultating sounds emanating from the human body and/or equipment such as rotating and reciprocating machinery and, in fact, for any purpose to which a "medical-type stethoscope or engineering stethoscope could be applied where the sound levels involved may be at threshold level or a very low amplitude.
In one aspect, the invention provides a crossover of peaks and valleys of the intensity curves of left and right ear deliveries, such that, over the principal portion of the frequency range, where the intensity of one curve dips toward an inaudible level for the one ear, the other curve dips to a much lesser extent and thus maintains amuch more satisfactory level of audibility for the other ear. In another aspect, the invention utilizes a phase shift in the resonant peaks of resonating independent air columns of different lengths, such as to stagger the peaksat the ear-tip delivery ends of the air columns so that thepeaks at one ear tip are phased substantially midway between the peaks at the other ear tip where the two ear tips collectively deliver (to the two ears of the listener) a succession of resonance peaks of intensity wholly above the median of the intensity variations of either air column alone.
These and other objects will becomeapparent in the ensuing specifications and appended drawings.
In the drawings:
FIG. I is a front view of a stethoscope embodying the invention;
FIG. 2 is detail sectional view of the junction between the trunk tube and one of the binaural tubes; I
FIG. 3 is .a cross-sectional view of the same, taken on line 3-3 of FIG. 2;
, FIG. 4 is a resonance diagram illustrating the output of the stethoscopes shown in FIGS. 1 and 5;
FIG. Sis a view, partially in section, of a modified form of the invention.
FIG. 6 is a fragmentary view, partially in section, of another modified form of the invention; and Y I FIG. 7 is a resonance diagram illustrating the output of the stethoscope of FIG. 6.
DESCRIPTION 0 Referring now to the drawing in detail, I have shown in FIGS. 1, 2 and 3, as an example of one form in which the invention may be embodied, a stethoscope embodying, in general, a head 10, a trunk tube 11 providing a common portion of air columns of unequal length, a pair of binaural tubes 12 and 13 connected by a yoke tube 14 to constitute therewith a binaural yoke, a yoke spring 15 enclosed therein (as seen in FIG. 5) and a coupling sleeve 16 fitted over binaural tube 12 and having an integral elbow 17 connecting it to the upper end of head tube 11, to provide an L junction, the head 10 being connected to the lower end of tube '11. The cross-sectional area of the air passage in tube 11 is substantially larger than (e.g. double) that of the air passage defined within binaural tubes 12, 13. Elbow and sleeve 16 may be integral with tube 11. Binaural tube 12 has in its outer side a slot 18 (FIGS. 2 and 3) communicating with an elongated throat 19 of elbow 17.
- Throat 19 provides communication between the common air column in head tube 11 and which leads directly to an ear tip 22, and a continuation air column in binaural tube 12, the yoke tube 14, and the other binaural tube 13, leading to a second ear tip 24. The junction is located closely adjacent the ear tip 22, and thus provides a ratio of about 1:2 between the lengths of the air columns from head 10 to ear tips 22 and 24 respectively such that when the intensity at car tip 24 attenuates in a dip at d1 (broken line curve, FIG. 4) the intensity at ear tip 22 dips, at d2 (solid line curve) to a much lesser extent; and, at a higher frequency where the intensity at car tip 22 dips, at d3, toward an inaudible level, the corresponding attenuation at ear tip 24, in a dip d4, is much less, remaining at a satisfactory intensity level. This crossover of the intensity curves maintains a continuous transmission of sound to one ear of the other at a more satisfactory intensity level throughout the principal portion of the frequency range (up to 2,000 cycles) than it has been possible to attain in the conventional stethoscope of the T-junction type (with both air columns of equal length).
FIG. 5 illustrates another possible form of the invention in which-the trunk tube 113 is connected directly through a passage 29 in a coupling 30 to an integral ear tip 228 and is connected through a branch passage 31 in coupling 30 to binaural tube 128, binaural parts 14,15 and 13, and ear tip 248. F IG. 5 also shows another feature of the invention, comprising a detachable coupling between a nipple 35 on the lower end of trunk tube 118 and a counterbore in a boss 36 on the back of a head (e.g. a diaphragm) 108, with a press fit such that diaphragm 10B can be detached and replaced by a bell-type head having a similar counterbored boss for coupling to nipple 35.
l have found that in a stethoscope which is required to receive and transmit microsonic sounds (at threshold levels'of audibility) the use of air columns of widely differing lengths, preferably in a ratio of about 1:2, in the L-junction arrangement in which the air tube (trunk tube 11) leading to a first ear piece is in series with an air tube (binaural yoke' 12-14) leading from the first earpiece to the second earpiece, pro vides a greatly improved sustention of intensity level and resultant audibility of the transmitted sound over the important portion of the frequency range, as compared to the conventional T-junction stethoscope, provided that the air columns are not vented. The l:2 ratio of air column lengths is attained where the length of trunk tube 11 is. substantially the same as that of binaural yoke 12-14. Thus the air column for transmission of sound from the head 10 to earpiece 24 is equal to the combined lengths of the trunk tube 11 and yoke 12-14, while the air column for transmission of sound to earpiece 22 is restricted substantially to the length of trunk tube 11.
Even better results are attained where, instead of having a common trunk tube 131 for both air columns, the two columns are separate for their full lengths from the head to the respective earpieces, as shown in FIG. 6, the same substantial difference in lengths (e.g. at a ratio of about 1:2) being rnaintained. Except for the separation of the air columns, the stethoscope of FIG. 6 may be the same as that of FIG. 5. in FIG. 6, a double trunk tube 11A having its respective air passages of the same cross-sectional area as binaural tubes 12, 13 is utilized instead of the single tube 111 with its double area. The resonance characteristics of the stethoscope of HO. 6 are such that the resonance peaks at car tip 24 will be substantially a half cycle behind the resonance peaks at the ear tip 22 with reference to the various frequencies of which a chest sound is composed. Thus a sound which attenuates to minimum intensity at one frequency in one air column will, through resonance, build up to maximum intensity at that same frequency in the other air column, and vice versa. Hence, all frequencies will be heard in the one ear or the other, at intensity levels above the median, and the attenuation of some frequencies below the limit of audibility, may be avoided.
FIG. 7 illustrates the operation of the stethoscope of FIG. 6 graphically. Sound intensities in decibels are represented on the Y-axis, and sound vibration frequencies are represented on the X-axis on a logarithmic scale. Curves L and R represent intensity peaks due to resonance in the unequal-length left and right air columns occurring cyclically at varying frequencies. On the chart, the lowest frequency intensity peak Pl for the left ear is about 50 c.p.m. whereas the low frequency intensity peak P2 for the right ear is about 1 10 cycles. The next peak P3 for the left ear is at about 350 cycles. At about 1,200 cycles the intensity peak P4- is at the left ear. The median level of intensity for both curves is indicated by the broken line M. The high intensity peaks continue uninterruptedly above the median level. if the median level is above the lower limit of audibility all frequencies will be audible in one ear or the other, despite the fact that in the sound reaching only one ear, half of the frequencies may be inaudible. Since the recognition and identification of a chest sound (or of a fault sound in a mechanism) is largely dependent upon hearing all frequency components of the sound, the invention provides a greatly improved diagnostic facility.
The junction 16, 17 may be molded around the binaural tube 12 and simultaneously molded onto the end of head tube 11. For good sound-transmission efficiency, the cross-sectional area of head tube 11 may be equal to the combined cross-sectional areas of binaural 12-14, in accordance with the disclosure in my pending application Ser. No. 695,208 filed Jan. 2, 1968, now US. Pat. No. 3,472,335. By combining high sound transmission efficiency with the out-of-phase peaking of sound intensities in the two binaurals at successive sound frequencies, lam able to provide a stethoscope of vastly improved sound recognition capabilities;
The invention makes use of the discovery that so long as the intensity of transmitted sound is maintained at a sufficiently high level in one ear or the other at each stage of the frequency range, good auscultation can be provided, even though the intensity of delivery to the other ear is below the audibility level.
lclaim: 1. A stethoscope comprising: a head; a pair of ear tips; tube means including a trunk tube and a binaural yoke, said ear tips being located at the respective ends of said yoke;
said trunk tube having one end thereof connected to said head; 1
a junction connecting the other end of said trunk tube to a first ear tip at one end of said yoke to provide a relatively short resonant air column extending from said head to sad first ear tip within said trunk tube and communicating with said head and first ear tip;
said trunk tube also being connected to said one end of said yoke to provide a relatively long resonant air column extending through said trunk tube and through said yoke to the other ear tip and communicating with said head and other car tip;
the total air column cross-sectional area in said trunk tube being substantially larger than in said yoke; and
the proportions of said air columns being such as to develop resonance cycles of sound intensity delivered at the respective ear tips, so related that frequencies attenuated at one ear tip will have substantially higher intensity at the other ear tip over the auscultation range of sound frequencies.
2. A stethoscope as defined in claim 1, wherein said trunk tube defines an air column common to both of said resonant air columns extending from said head to said first ear tip.
3. A stethoscope as defined in claim 1, wherein said air columns are separate for substantially the entire distance from the head to the nearest ear tip, whereby the resonance peaks of sound intensity delivered at the respective car tips will be distributed in out-of-phase, alternating succession over the auscultation range of sound frequencies, so that frequencies attenuated at one ear tip will be resonance peaked at the other ear tip.
4. A stethoscope as defined in claim 1, wherein said tubes means defines a pair of separate air columns each extending from said head to its respective ear tip; said' separate air columns each being of uniform cross-sectional area throughout its respective length.
5. A stethoscope as defined in claim 11, wherein the effective air column length from said head to the farther ear tip is approximately twice the effective air column length from the head to the nearer ear tip.
6. A stethoscope as defined in claim 1, wherein said tube means comprises;
the trunk tube extending from said head to a junction near one of said car tips;
the binaural yoke comprising a pair of binaural tubes connected to one another in the form of a yoke and collectively defining an extended air column communicating with said trunk tube at said junction and extending therefrom to the other ear tip, said binaural tubes having free ends carrying the respective ear tips; and
said trunk tube and said binaural collectively defining resonant air columns for auscultative transmission to the respective ear tips of sounds of a selected frequency range so related one to the other that the resonance cycles of sound intensity delivered at the respective ear tips will be so related that frequencies attenuated at one ear tip will have substantially higher intensity at the other car tip.
7. A stethoscope as defined in claim 1, wherein said tube means includes the binaural yoke comprising binaural tubes having free ends carrying said ear tips and having their opposite ends joined by a binaural yoke tube having a yoke spring resiliently urging said free ends toward one another;
the trunk tube extending from said head to said binaural yoke; and
said junction comprising a fitting communicating with the end of said trunk tube remote from said head and having a throat communicating with a port in one of said binaural tubes near the ear tip thereof.
8. A stethoscope as defined in claim 1, wherein said junction is embodied in said nearer ear tip.
9. A stethoscope as defined in claim 1, wherein said tube means includes the trunk tube embodying a single air passage forming a common portion ofdual air columns extending from said head to the respective ear tips, having respective lengths related to one another in the ratio of approximately 1:2.
10. A stethoscope as defined in claim 1, wherein said tube means comprises the binaural yoke having respective ear tubes terminating in said ear tips, and the trunk tube in the form of a double tube having separate air passages communicating with binaural ear tubes to define separate resonant transmission columns extending from said head to the respec-