US 3019306 A
Description (OCR text may contain errors)
Jan. 30, 1962 E. M. WEISS TRANSDUCER SUSPENSION 2 Sheets-Sheet 1 Filed July 11, 1960 Arrolezxgys.
Jan. 30, 1962 E. M. wr-zlss TRANSDUCER SUSPENSION 2 Sheets-Sheet 2.
Filed July 11, 1960 INVENTIORJ Ill ATTORNEYS.
3,019,306 TRANEEDUCER SEUEENSHON Erwin M. Weiss, hicago, lllh, assignor to Beltane Hearing Aid Qompany, a corporation of lllinois Filed .luly E1, 1969, 42,152 ltl fist-Ems. (till. 179--i46) This invention relates generally to transducer suspension means, and more particularly to a new and improved means for mounting a transducer in a case, as for example, the case of a hearing aid of the type adapted to be worn on the head or body of a hard-of-hearing person.
Prior art means for mounting transducers in compact electrical apparatus, such as hearing aids, have certain characteristics in common. For example, those skilled in the hearing aid art know that some type of visco-elastic substance generally is used to suspend a microphone and a receiver within a hearing aid case. In some instances, the substance may take the form of a porous blown natural or synthetic rubber, and in other cases, this substance may take the form of a sheath of solid rubber.
A transducer mounting of the first type comprising suspension members of blown rubber cemented between the hearing aid case and the transducer is shown in Paent No. 2,894,076 granted to Sam Posen on March 17, 1959. In the second type of transducer mounting referred to above, the transducer is encased within a thin rubber enclosure and the entire assembly is positioned in the hearing aid case.
In order to provide proper isolation of a transducer Within a rigid case, it is necessary that the visco'elastic substance interposed between the transducer and the case be very compliant. As a result, blown rubber mountings frequently are used but it is diihcult to maintain uniformity therein due to the wide variations in the compliance characteristic which exists from batch to batch, and even from portion to portion within the same batch, in a blown rubber mounting.
Further, it usually is necessary to cement the blown rubber mounting to both the case and the transducer. Those skilled in the art appreciate that difiiculties often arise from such an arrangement due to the tendency of the cement to rise by capillary action into the porous rubber material. As a consequence, the porous rubber material is stiilened considerably after the cement is dried and the compliant property which is desired is substantially lost. An additional 'dilliculty arises where small sections of porous rubber are used in the form of buttons or washers. It is necessary to hold such parts to close dimensional tolerances due to the small size of the cavities in which the transducers are mounted, and it often is very difficult or even impossible to hold a piece of material with such poor dimensional stability as blown rubber to the desired close tolerances.
In those instances where a sheath of solid rubber is used to support a transducer within a case, other difficulties are encountered. For example, the compliance provided by such a solid rubber sheath is not very great, and consequently the transducer is not adequately isolated from case vibrations. Those skilled in the art appreciate that the poor isolation properties of a hard thin rubber sheath frequently necessitates considerable reduction in the average gain of the hearing aid.
It is further known that transducer mountings which utilize resilient rubber bumpers or washers form isolators which are compliant in horizontal as well as vertical modes. Thus, when a soft rubber bumper is used to support a microphone, the microphone tends to float sideways and as a consequence, the microphone may hit the case when the wearer moves his head sharply.
Accordingly, it is a general object of this invention to overcome the above-stated difi'iculties which characterize the transducer mounting means of the prior art.
More particularly, it is an object of this invention to provide a new and improved transducer mounting means which is characterized by its uniform and lasting compliance properties, by its efficiency of isolation in a desired mode, and by its relatively simple and low cost construction.
In accordance with one specific illustrative embodiment of this invention, the novel transducer mounting means takes the form of a flat metallic spring which is shaped to provide considerable effective length in a small area. Advantageously, the fiat metallic spring may comprise a plurality of beams connected in series with the opposed ends of the spring being fastened to the case and with the center beams being adapted to receive and support the transducer.
As explained in greater detail hereinbelow, the fundamental trequency of oscillation of the metallic spring isolator in combination with the transducer advantageously is made well below the lowest frequency to be amplified by the hearing aid. In addition, it is known that a transducer, such as a microphone, is much less sensitive to vibration in a horizontal plane than in a plane perpendicular to the diaphragm. The metallic spring isolator comprising the invention is made to be very stiff in a horizontal plane, but very compliant in the vertical plane so that a microphone may be supported in a small cavity with less concern about the problem of rapid head motion.
In accordance with a further feature of the invention, the metallic spring isolator is provided with particular damping means to prevent excitation into resonance at higher frequencies. Such damping means advantageously may comprise a visco-elastic substance sandwiched between the spring isolator and a thin sheet of metallic foil, or alternatively, it may take the form of a dynamic vibration absorber in which additional spring and mass means are secured to the spring isolator.
It is a still further feature of this invention to utilize the damped spring isolator as a two terminal electrical conductor to reduce lead breakage in the transducer. Thus, one electrical lead of the transducer is connected to the metallic spring of the isolator and the other electrical lead is connected to the metallic toll of the isolator. Since the connections are made at the geometric center of the suspension system when there is no relative movement between the transducer and the isolator, the leads are not caused to vibrate and breakage of the leads is substantially reduced.
The novel features which are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
FIGURE 1 is a side elevational view of a behind-theear type of hearing aid, partly broken away and partly in section, embodying the present invention;
FIGURE 2 is a cross-sectional view of a microphone supported by a metallic isolator taken substantially as shown along line 2-2 of FIGURE 1;
FIGURE 3 is a cross-sectional view of a receiver supported by a metallic isolator taken substantially as shown along 33 of FIGURE 1;
FIGURE 4 is a plan view of one specific illustrative embodiment of metallic isolator in accordance with the invention;
FIGURE 5 is an elevational view of a transducer sup ported by a damping metallic spring isolator;
FEGURE 6 is a schematic diagram of the electrical equivalent circuit of a damping dynamic vibration absorber in accordance with the invention;
FIGURES 7 and 8 are elevational and plan views respectively of one specific illustrative embodiment of a damping dynamic vibration absorber type of transducer isolator in accordance with the invention; and
FIGURES 9 and 10 are plan and elevational views respectively of a damped transducer isolator embodiment in which the metallic elements of the isolator also serve as a two terminal electrical conductor to reduce transducer lead breakage.
Referring now to the drawing, and more particularly to FIGURE 1 thereof, there is shown one specific illustrative embodiment of hearing aid in which a portion of the cover has been removed from the case to better illustrate the internal construction of the hearing aid. The present invention is shown in this application as used with a hearing aid for illustrative purposes only, and it will be obvious to those skilled in the art that the invention finds equally advantageous use in other types of compact, electrical devices which utilize a transducer, such as a microphone, a receiver, and the like.
FIGURE 1 shows a hearing aid of the type sometimes referred to as a behind-the-ear model, which is adapted to be supported upon the ear with the main case of the hearing aid resting on the back portion of the ear. As shown, the hearing aid v1t comprises a case 12 which advantageously is of channel shape to receive the hearing aid component therein. An air tube 14 extends from the upper end of case 12 and serves to convey sound from a receiver 16 within the case to a further air tube which extends into the ear of the hard-of-hearing person.
Those skilled in the art will appreciate that the air tube 14- advantageously may be formed of a stiff plastic material so that it may be shaped to fit the ear and rest comfortably thereon. The air tube 14 advantageously is embedded within the end piece 18, and is in sound communication with the receiver 16 through the aperture 24 in the nubbin provided in end piece 18, and through the sealing ring 22 positioned between the nubbin and the receiver 16. Advantageously, the end piece 18 may be secured to the hearing aid case 12 by means of any suitable fastener, such as the threaded screw fastener 24 which is positioned within a suitable threaded opening 26 in the hearing aid case.
In addition to the receiver 16, the hearing aid within the case 12 comprises an amplifier and control portion 28 which is positioned immediately adjacent the receiver portion 16. While the amplifier and control portion 28 is shown in FIGURE 1 as having a cover 30 thereover, it will be appreciated that the amplifier and control portion 28 may comprise any suitable transistorized amplifier and volume control assembly, the volume control being adjustable externally by means of volume control knob 32.
A microphone 84 is positioned adjacent the amplifier and control portion 28, and a combined On-Off switch and battery holder 36 is positioned adjacent the microphone. Advantageously, the combined On-Ofi switch and battery holder 36 is pivotally attached to the hearing aid case by means of the pivot member 38 so that the switch and battery holder 36 may be actuated to turn the hearing aid On or Off, or further actuated to be withdrawn from the case for replacement or checking of the battery. The switch and battery holder 36 is provided with the suitable central aperture 40 adapted to receive a battery therein and a pair of contacts 42 and 44 are provided for engaging the battery terminals in a selective manner to control the energized condition of the hearing aid.
While the details of the hearing aid shown in FIGURE 1 are described for purposes of illustrating one specific preferred embodiment of the invention, manifestly, the invention is not limited to the hearing aid of FIGURE 1 and may be used with equally advantageous results in other hearing aids as well as other compact electrical structures employing transducers.
In accordance with a salient feature of this invention, the transducers of the hearing aid are suspended within the case in a unique and highly advantageous manner. The novel suspension means differs from the visco-elastic isolators and suspension means of the prior art and overcomes the difiiculties associated therewith, as described in detail hereinabove.
One specific illustrative embodiment of transducer suspension means in accordance with the invention is shown in FIGURES 1, 2, 3, and 4, of the drawing. Advantageously, this illustrative embodiment takes the form of a fiat, metallic spring which preferably comprises a plurality of sinuous beams and which further comprises an isolator secured to the geometric center of the fiat, metallic spring for supporting the transducer in non-contacting relation with the spring and with the Walls of the transducer case.
The nature of the properties required for a transducer suspension member of the type contemplated by the present invention are as follows. First of all, the fundamental frequency of oscillation of the suspension member in combination with the transducer must be well below the lowest frequency being amplified by the electrical device. For example, in the case of a hearing aid in which the lowest frequency being amplified is approximately 400 cycles, the transducer suspension member in combination with the transducer should have a natural period of oscillation of no greater than cycles per second. Secondly, those skilled in the art will appreciate that a transducer, such as the microphone, is much less sensitive to vibration at a plane parallel to the microphone diaphragm than in a plane perpendicular to the diaphragm. As a result, the transducer suspension member advantageously is made very stiff in a horizontal plane but very compliant in the vertical plane. This requirement is admirably met by the present invention since the fiat, sinuous, metallic spring has much greater stiffness in the plane in which vibration isolation is not required.
One practical result of this unique arrangement is the use of smaller cavities for the transducers. Thus, a microphone in the hearing aid, when suspended by the invention, may be placed in a small cavity with much less concern about the problem of rapid head motion than is the case with present day transducer suspension members.
A still further advantage of the fiat, metallic transducer suspension member of the present invention is the fact that its properties can be held to very close tolerances. Thus, metallic materials, such as stainless steel, do not deteriorate with time as is the case of sponge rubber or other visco-elastic materials, and therefore the suspension member can be maintained to a desired degree of performance.
In the specific illustrative embodiments of transducer suspensions shown in FIGURES 1 to 4, the transducer suspension member 56 is a fiat, metallic spring which is sinuous in shape and which is provided at its ends with the terminal pieces 52 and 54, respectively. The sinuous shape of the transducer suspension member 50 is highly advantageous to give the suspension member a greater effective length in a relatively small area. Those skilled in the art will appreciate that this action of the suspension member 50 may be viewed as the action of several F springs in tandem. Effectively many beam means are provided in series to permit efficient isolation of the transducer from case vibration.
As shown in FIGURES l, 2, and 3 of the drawing, the terminals 52 and 54 of the transducer suspension member 52 are positioned on the shoulders 56 and 58, respectively, of the transducer cavity provided in the hearing aid case. The transducer suspension member 50 can be held in position by any suitable means and the cover of the case is positioned thereover to maintain the suspension member securely in its desired position.
FIGURE 2 shows the microphone 34 of the hearing aid as suspended from the transducer suspension member 59 by means of the isolator or separator element 58. Similarly, FIGURE 3 shows a receiver 16 of the hearing aid as suspended from the transducer suspension member 559 by means of the isolator element 58. in accordance wit a feature of this invention, the isolator element 58 is mounted at geometric center of the transducer suspension element 58 so that the transducer is in non-contacting relationship with the suspension member 50 and further in non-contacting relationship with the walls of the transducer cavity in the case 12 Due to the low internal damping of the fiat metallic transducer suspension members 50, there is a possibility that such a member may be excited into substantial resonance at higher frequencies. In accordance with a further embodiment of this invention, such oscillation or vibration at higher frequency modes may be suppressed by providing sufficient damping for the metallic spring suspension member. Thus, as illustrated in FIGURE 5 of the drawing, a transducer such as the microphone 34 may be suspended by the isolator from a transducer suspension member 62 of damped construction. As shown in FIGURE 5, the transducer suspension member 62 advantageously comprises a layer of visco-elastic material as which is sandwiched between a flat, metallic spring member 55 and a very thin layer of stiff constraining material, such as a sheet of aluminum foil d6. Those skilled in the art will readily appreciate that the damping action provided by the damped suspension member arrangement of FIGURE 5 will serve to inhibit or suppress any tendency of the transducer suspension member to vibrate at igher frequencies.
A still further embodiment of the invention which is adapted to provide greater isolation at frequencies above the natural period of the spring is shown in FIGURES 6 and 7 of the drawing. As illustrated in these figures, this embodiment comprises the transducer suspension element 50 dscribed hereinabove, and an isolator or spacer 58 secured to the suspension member, which in turn supports a transducer, such as a microphone 34. In addition to these elements, which correspond to the constuctions described in respect to FIGURES 1 through 4, this embodiment further comprises an additional spacer or isolator 70 secured to the opposite side of the transducer suspension member fit for supporting an additional spring and mass arrangement to provide damped dynamic vibration absorption.
The equivalent circuit for the damped dynamic vibration absorber is shown in FIGURE 6 of the drawing wherein the microphone 34 is shown as suspended by a spring element K. Spring element K corresponds to the spring suspension provided by the transducer suspension member 50. Suspended from the microphone 34 is shown an additional spring k and an additional damping means 1', shown in parallel and supporting an additional mass m. The additional spring damping means and mass are provided in one practical form of such a suspension by a thin, rubber disc '72 mounted on the isolator '79. The additional mass m is provided by the actual ettective mass of the rubber disc '72 and the additional Spring 11' is provided by the compliance of the rubber disc 72 when it vibrates in the umbrella mode.
In another embodiment of the damped dynamic vibration absorber arrangement, the total mass would be the actual effective mass of the rubber disc 72 in addition to the mass of an annular lead ring 74 positioned around the rubber disc 72. Thus, the mass element 212 could be provided by a rubber disc alone or by the combination of a rubber disc and a metal ring thei'earound.
One typical value for such mass would be approximately /5 of the mass of the transducer. Thus, in a microphone having a mass of 2 grams, for example, the mass of the damped dynamic vibration absorber element would be approximately of a gram.
While many other embodiments of transducer suspension members will be suggested in accordance with the teachings of the present invention, the above specifically described embodiments are merely illustrative of several practical forms of the invention to comply with the requirernents of the patent statutes.
In addition to overcoming many of the problems of prior art visco-elastic transducer suspension members, the transducer suspension member of the invention also may be used in providing highly eificient acoustic isolation between a receiver and a microphone in a hearing aid case. Thus, those skilled in the art know that a certain amount of the acoustic output from the receiver normally is incident upon the microphone within the same hearing aid case. Some of this output comes from the leaks around joints, which usually are in the places where the receiver is connected to the nubbin.
The output then travels to the microphone through the case cavity. Some acoustic output may be radiated into the case cavity from the vibration on the walls of the receiver itself. if a receiver in a a hearing aid is viewed as a miniature loud speaker, it can be appreciated how sound pressure developed in the receiver can vibrate the walls of the receiver case. This acoustic output adds to the acoustic output leaks and also reaches the microphone.
In accordance with a feature of this invention, such acoustic feedback may be reduced for transducers suspended by flat, metallic spring suspension members Si? by placing the entire receiver in a scaled cavity with stiil walls, or by molding a simple acoustic attenuator into the hearing aid case. In the latter, such an attenuator may take the form of a quarter-wave acoustic trap for frequencies at which the receiver develops its peak output.
Another highly advantageous embodiment of the invention is illustrated in FIGURES 9 and 10 of the draw ing. Those skilled in the art will readily appreciate that the vibration of a transducer during its normal operation requently results in breakage of the relatively thin transducer electrical leads. This serious problem is overcome in accordance with a feature of the invention by the utilization of the metallic elements of the damped vibration isolator of FIGURE 5 as two terminal electrical conductors. Thus, as shown in FIGURES 9 and 10, the transducer 34 normally is provided with the electrical conductor leads and 84. One lead 84 is electrically connected to the metallic spring member 50 of the suspension member 62 and the other lead 80 is electrically connected to the sheet of metallic foil 66 positioned on n e layer of visco-elastic material 64 opposite the spring mem ber 50.
Preferably, the point of connection for each of the leads is at the geometric center of the suspension system. Since there is no relative motion between the transducer 34- and the geometric center of the suspension system the leads an and are not caused to vibrate and the breakage problem is substantially reduced. The electrical output from the transducer 3 is obtained from the two conductors :52 and 3:? attached to the extrem ends of metallic elements 66 and 5% respectively. As the extreme ends of the spring Ell are supported by the case wall, there is no relative motion on these points. Consequently, relatively heavy electrical leads 82 and 86 may be alrlxed in a suitable manner at these points to carry the electrical output from the transducer to the electrical amplifying system of the hearing aid or other compact el ctrical device.
While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the inven tion and, therefore, it is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.
What I claim as my invention is:
1. The improvement of transducer mounting means for supporting a transducer within a hearing aid case comprising a plurality of sinuous, series connected beam secured to the walls of a transducer cavity within the case, a transducer, attachment means secured to said beams and supporting said transducer in non-contacting relation with said beams Within said transducer cavity, said transducer also being supported by said attachment means in noncontacting relation with the walls of said transducer cavity.
2. The improvement of transducer mounting means for supporting a transducer within a cavity in a hearing aid case comprising flat, metallic beam means, said beam means comprising a plurality of series connected beams having a pair of opposed terminal ends secured to the walls of said case, a transducer, attachment means secured to said beam means and to said transducer for supporting the latter in non-contacting relation with said beam means within said transducer cavity.
3. The improvement of transducer mounting means for supporting a transducer within a hearing aid case comprising fiat, resilient beam means secured to the Walls of a transducer cavity within the case, a transducer, separator means geometrically centered on said beam means and supporting said transducer in non-contacting relation with the walls of said transducer cavity, and damping means secured to said beam means for damping vibrations at higher frequencies to prevent said beam means from becoming excited into resonance at such higher frequencies.
4. The improvement of transducer mounting means in accordance with claim 3 wherein said damping means comprises a layer of a visco-elastic material adjacent said beam means and a sheet of stiff constraining material positioned on the visco-elastic layer.
5. The improvement of transducer mounting means in accordance with claim 4 wherein said sheet of stiff constraining material comprises a sheet of aluminum foil.
6. The improvement of transducer mounting means for supporting a transducer Within a hearing aid case comprising flat, metallic beam means secured to the walls of a transducer cavity within the case, a transducer, first isolator means located at the geometric center of one side of said beam means and supporting said transducer in non-contacting relation with the walls of said transducer cavity, second isolator means located at the geometric center of the other side of said beam means, and clamped dynamic vibration absorber means supported by said second isolator means.
7. The improvement of transducer mounting means in accordance with claim 6, wherein said damped dynamic vibration absorber means comprises a thin resilient disc, the mass of said disc serving as the mass of the vibration absorber means and the compliance of said disc serving as the spring of said vibration absorber means.
8. The improvement of transducer mounting means in accordance with claim '7 further comprising an additional mass for said vibration absorber means formed of an annular lead ring mounted around said resilient disc.
9. The improvement of transducer mounting means for supporting a transducer within a case containing electrical circuitry comprising fiat, resilient, metallic beam means secured to the walls of a transducer cavity within the case, a transducer, separator means secured to said beam means and supporting said transducer in non-contacting relation with the walls of said transducer cavity, damping means secured to said beam mean for damping vibrations at higher frequencies, said damping means comprising a layer of visco-elastic material positioned on said metallic beam means and a sheet of thin metallic foil positioned on said visco-elastic layer, and means connccting one electrical lead of said transducer to the metallic beam means and the other electrical lead of said transducer tothe sheet of metallic foil whereby the latter serves as two conductive terminals for connecting said transducer to the remainder of the electrical circuit.
10. The improvement of transducer mounting means in accordance With claim 9 wherein said transducer electrical leads are connected to the geometrical centers of said beam means and metallic foil sheet to minimize vibration of said leads and thereby reduce lead breakage problems.
References Cited in the file of this patent UNITED STATES PATENTS 2,260,727 Sears et al. Oct. 28, 1941 FOREIGN PATENTS 104,229 Sweden Apr. 14, 1942