Abstract:
An implantable microphone for use with an implantable hearing instrument that has a reduced vibration sensitivity in comparison with its acoustic sensitivity. The microphone utilizes a plurality of small diaphragms as opposed to a single large diaphragm in order to reduce vibration sensitivity caused by mass loading of the diaphragms by overlying skin and tissue. The acoustic outputs of the plurality of small diaphragms are summed (e.g., acoustically or electronically), which allows the microphone to maintain adequate acoustic sensitivity for hearing augmentation purposes while having a reduced vibration sensitivity. In one aspect, the plurality of diaphragms is formed from a single membrane and a multi-apertured support structure in contact with the membrane. Each aperture in combination with the membrane defines a single diaphragm.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C.  119  to U.S. Provisional Application No. 60/518,256 entitled: “MICROPHONE OPTIMIZED FOR IMPLANT USE,” having a filing date of Nov. 7, 2003; the contents of which are incorporated herein as if set forth in full. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to implanted microphone assemblies, e.g., as employed in hearing aid instruments, and more particularly, to implanted microphone assemblies having reduced sensitivity to undesired sources of vibration.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the class of hearing aids generally referred to as implantable hearing instruments, some or all of various hearing augmentation componentry is positioned subcutaneously on, within or proximate to a patient&#39;s skull, typically at locations proximate the mastoid process. In this regard, implantable hearing instruments may be generally divided into two sub-classes, namely semi-implantable and fully implantable.  
         [0004]     In a semi-implantable hearing instrument, one or more components such as a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit an audio signal to implanted components such as a transducer. In a fully-implantable hearing instrument, typically all of the components, e.g., the microphone, signal processor, and transducer, are located subcutaneously. In either arrangement, an implantable transducer is utilized to stimulate a component of the patient&#39;s auditory system (e.g., tympanic membrane, ossicles and/or cochlea).  
         [0005]     By way of example, one type of implantable transducer includes an electromechanical transducer having a magnetic coil that drives a vibratory actuator. The actuator is positioned to interface with and stimulate the ossicular chain of the patient via physical engagement. (See e.g., U.S. Pat. No. 5,702,342). In this regard, one or more bones of the ossicular chain are made to mechanically vibrate causing stimulation of the cochlea through its natural input, the so-called oval window.  
         [0006]     For a wearer of an implantable hearing instrument, the sound of a speaker&#39;s voice reaches his inner ear by at least three different pathways. One of them goes from the vocal chords through the vocal tract, the outer air, the external ear canal, and the middle ear and to the cochlea; this will be called the air conduction pathway. A second pathway includes the vocal chords, the bony structure of the head and the inner ear; this will be called the bone conduction pathway. In persons without hearing loss, the relative level of acoustic signals reaching the inner ear via these two pathways determines the particular sound quality of an individual&#39;s own voice. For persons wearing an implantable hearing instrument, a third pathway is added: sound emanating from the vocal chords passes through the bony structure of the head and reaches the implanted microphone of the implantable middle ear hearing system or fully implantable cochlear implant. The vibration reaches the microphone diaphragm and is amplified just like an external airborne sound would be amplified. Also, in systems employing a middle ear stimulation transducer, the system may produce feedback by picking up and amplifying vibration caused by the stimulation transducer. As such, the bone vibration undesirably limits the maximum achievable gain of the implantable hearing instrument.  
         [0007]     As may be appreciated, implantable hearing instruments that utilize an implanted microphone require that the microphone be positioned at a location that facilitates the receipt of acoustic signals. For such purposes, such implantable microphones are most typically positioned in a surgical procedure between a patient&#39;s skull and skin, at a location rearward and upward of a patient&#39;s ear (e.g., in the mastoid region). Because the diaphragm of an implantable microphone is covered by skin and this skin represents an additional mass loading of the diaphragm, vibration sensitivity of implanted microphones tends to be significantly higher than that of microphones in air. In order to achieve a nearly natural quality of the implant wearer&#39;s voice and increase achievable gain, the vibration sensitivity of the implanted microphone has to be reduced compared to its acoustic sensitivity. The aim of the present invention is to design an implantable microphone that achieves these goals.  
       SUMMARY OF THE INVENTION  
       [0008]     A simple dimensional analysis shows that the ratio of vibration sensitivity to sound sensitivity can be reduced by reducing the dimension of the sound receiving element, i.e., the implantable microphone diaphragm. It is generally known that the sensitivity of a microphone diaphragm increases with the area of the diaphragm, e.g., for a circular diaphragm the diameter squared. The vibration sensitivity of the microphone is dominated by the vibrating mass of skin on top of the diaphragm. The effective volume of skin that contributes to the vibration sensitivity may be thought of as dome-shaped as long as the thickness of the layer of skin is above a threshold value. This shape of effective mass can be thought of as similar to the dome shaped mass of effective air over the opening of a Helmholtz cavity. Because the shape of the effective mass remains constant, the vibration sensitivity increases with the volume of the mass and therefore, for a circular diaphragm, increases with the diameter cubed.  
         [0009]     It is therefore desirable to design an implantable microphone diaphragm which has the smallest possible area (e.g., diameter for a circular diaphragm) to achieve the lowest ratio of vibration to sound sensitivity and maximize achievable gain. On the other hand, absolute acoustic sensitivity is reduced as the area of the diaphragm becomes smaller, and therefore the input-referred noise floor of the microphone increases. The solution to this dilemma as described in the present invention is to replace one large microphone diaphragm with a plurality of smaller microphone diaphragms, the responsive sum of which will have adequate acoustic sensitivity and adequately low input referred noise while retaining the low ratio of vibration to acoustic sensitivity.  
         [0010]     In one aspect of the invention, an implantable microphone is provided that includes a plurality of diaphragms that are operative to transcutaneously receive acoustic signals and output a corresponding plurality of acoustic signals. The microphone further includes at least one electroacoustic transducer operative to receive the plurality of acoustic signals from the plurality of diaphragms and generate an audio output signal in response thereto. That is, an audio output signal may be generated that is indicative of a combination of the plurality of acoustic signals. This audio output signal may subsequently be utilized to drive or actuate an actuator of an implantable hearing instrument and thereby stimulate a component of the implant wearer&#39;s auditory system (e.g., tympanic membrane, ossicles and/or cochlea).  
         [0011]     Typically, the microphone will include an implantable housing (e.g., made of a biocompatible material) on which the plurality of diaphragms are mounted. These diaphragms may be mounted relative to a chamber within the housing for acoustic transmission purposes. More particularly, the diaphragms may be mounted relative to the chamber such that the chamber is sealed to prevent biological contamination of internal components of the microphone. In this regard, a structure including the plurality of diaphragms or operative to support a plurality of separately formed diaphragms may be sealably positioned across, for example, an aperture leading to the chamber within the housing. In any case, the housing may house the electroacoustic transducer(s) and/or additional hearing instrument componentry.  
         [0012]     In one arrangement, where a plurality of diaphragms is mounted relative to a chamber within a housing, the chamber may be designed such that a portion of the chamber is disposed behind each of the plurality of diagrams. In this regard, the acoustic signals generated by each diaphragm may be emitted into the chamber and may be acoustically summed. Accordingly, a single electroacoustic transducer may be operative to provide an audio output signal indicative of the summation of the acoustic signals. That is, a single electroacoustic transducer may be operative to generate an audio output from the acoustically summed signals in the chamber.  
         [0013]     The plurality of diaphragms may be separately formed diaphragms that are each mounted relative to a common housing and/or chamber. However, in another arrangement, each of the diaphragms may be at least partially formed from a common membrane structure. For example, the area of the common membrane structure may be sub-divided into a plurality of individual diaphragms, each of which will necessarily have a reduced size relative to the common membrane structure in accordance with the present invention. In order to sub-divide the membrane structure into individual diaphragms, a support structure may be located in contact with at least a portion of the membrane structure. For instance, a grid-like, rigid or semi-rigid, support structure defining a plurality of apertures may be placed in contact with a portion of the membrane structure. In this regard, each of the apertures defined by the support structure, in combination with the membrane, will define each of the diaphragms.  
         [0014]     When utilizing a multi-apertured support structure to sub-divide a single membrane into separate diaphragms, it may be necessary to maintain contact between the periphery of each aperture and the membrane throughout an acoustic vibration cycle in order to accurately reproduce received acoustical signals. That is, to accurately reproduce sound the support structure may have to maintain contact between the periphery of each aperture and the membrane structure during both inward and outward diaphragm deflections (i.e., relative to a static position) present during an acoustic vibration cycle. In this regard, the membrane structure may be attached to the periphery of the apertures of the support structure such that each resulting diaphragm maintains contact with the support structure throughout inward and outward diaphragm deflection.  
         [0015]     In another arrangement, the support structure may be formed in a structural manner that maintains contact between the peripheries of each aperture and membrane throughout inward and outward deflection of the resulting diaphragms. For instance, a support structure having curved surface with a membrane tensioned over the outside of the curved surface may allow for maintaining contact between the peripheries of each aperture and the membrane through an acoustic vibration cycle. Such a curved support structure may be symmetric about on or more axes. For example, the curved surface may form a half-cylinder or a dome/spherical shape. However, it will be appreciated that such a curved surface may also be irregular. What is important is that the curvature of the surface allows for a diaphragm tensioned over the surface to be tensioned across apertures in the surface in a manner that prevents separation between the surface and the diaphragm during acoustic vibration. Alternatively, a second support structures having identical aperture patterns may be utilized on an opposing side of a membrane structure. In this arrangement two support structures may be disposed on opposing sides of a tensioned membrane.  
         [0016]     In another application, a multitude of small diaphragms may be created by pushing an irregular structure against a large membrane. The structure may consist of an open cell foam or a multitude of rigid small balls or differently shaped bodies, sintered or glued together, to define what may be referred to as a frit.  
         [0017]     In a further application, an integrated diaphragm/support structure may be utilized. In one arrangement, a block of a single material (e.g., titanium, stainless steel etc.) may be processed to have one or more integrally formed diaphragms. Such processing may include milling, electrochemically milling and/or etching to generate one or more areas of reduced thickness (e.g., diaphragms) within material. In another arrangement, a first material later may be bonded to a different second material layer. Portions of one of the layers may be etched away to define apertures through that layer (i.e., through the support structure). Alternatively, the first and second materials may be selected such that the integrated structure may be heated such that defined diaphragm elements are stretched or tensioned across corresponding apertures of a support structure.  
         [0018]     Irrespective of the support structure and/or membrane combination utilized, it will be appreciated that the diaphragms may comprise any suitable biocompatible material. By way of primary example, the diaphragms may comprise a material selected from a group consisting of titanium and titanium-alloys. Likewise, it will be appreciated that in addition to material, the area, thickness, tension, total number, and/or tension of the diaphragms may be selected for acoustic purposes. Finally, it will be noted that different diaphragms may have different properties to facilitate response to different acoustic frequency ranges. For instance, a combination of large and small diaphragms may be utilized that are adapted to respond to low and high frequencies, respectively.  
         [0019]     In another application, the microphone may further include an electrical summation means for combining audio outputs from at least two electro-acoustical transducers. In this regard, the summation of the acoustic signals from individual diaphragms may be effected electrically (i.e., by combinatively processing the output of the electroacoustic transducers) or as a combination of acoustical summation (i.e., where each single electroacoustic transducer may provide an output responsive to a small group of diaphragms) and electrical summation (i.e., by combinatively processing the output of the electroacoustic transducers). Accordingly, the audio output signal generated by each of these electroacoustic transducers may be combined to generate a composite output signal, the responsive sum of which will have adequate acoustic sensitivity for hearing purposes. In a similar manner, output signals from a plurality of separate microphones may be combined into a single composite audio output signal.  
         [0020]     In one application, a multitude of electroacoustic transducers may be utilized wherein each electroacoustic transducer is placed close to each or a group of the plurality of diaphragms. Such individual electroacoustic transducers may be realized either using conventional manufacturing methods or by using microelectromechanical systems (MEMS) technology. In one embodiment, a plurality of electroacoustic transducers corresponding to the plurality of diaphragms may be utilized. In this regard, each electroacoustic transducer may be juxtaposed adjacent to a corresponding diaphragm, which may increase the overall sensitivity of the microphone.  
         [0021]     According to another aspect of the present invention, a method for use in an implantable hearing instrument is provided that allows for achieving a low ratio of vibration to sound sensitivity while enhancing achievable gain. The method includes receiving at least first and second acoustic signals from at least first and second implanted microphone diaphragms and summing outputs associated with the acoustic signals to generate a composite output signal. This composite output signal may then be utilized to generate a stimulation signal for stimulating an auditory component of a patient. As will be appreciated, the present aspect allows for combining the acoustic signals from a plurality of microphone diaphragms such that vibration sensitivity may be reduced while maintaining adequate acoustic sensitivity for hearing purposes.  
         [0022]     In a first arrangement, the signals form the diaphragms may be acoustically summed. In this regard, two or more acoustic output signals form the diaphragms may be output into a common chamber to generate an acoustically summed signal. This acoustically summed signal may then be received by an electroacoustic transducer that is operative to generate the composite output signal. In another arrangement, outputs for the diaphragms (e.g., acoustic output signals) are received at two or more electroacoustic transducers. These transducers in turn generate a corresponding number of electrical outputs that are indicative of the received acoustic signals. These electrical outputs may then be summed to generate the composite output signal.  
         [0023]     According to another aspect of the present invention, an implantable hearing instrument is provided that includes a microphone having a plurality of diaphragms operative to transcutaneously receive acoustic signals and output a corresponding plurality of acoustic signals. The microphone further includes at least one electro-acoustic transducer to receive the plurality of acoustic signals and generate an audio output signal in response thereto. The hearing instrument further includes an actuator operative to receive the audio output signal and stimulate a component of an implant wearer&#39;s auditory system in accordance with the audio output signal in order to generate a sensation of sound.  
         [0024]     The actuator may be any one of a plurality of different types of actuators. For instance, in a middle ear hearing instrument, an actuator may be operative to mechanically stimulate (e.g., vibrate) one or more of the ossicles, which in turn causes stimulation of the cochlea through it&#39;s natural input, the oval window. Such mechanical stimulation may be through direct coupling with the ossicular chain or via a magnetic connection. Alternatively, the actuator may generate an audio signal for use in stimulating the tympanic membrane which in turn stimulates the ossicular chain and thereby the cochlea. Alternatively, the actuator may be operative to directly stimulate the cochlea and thereby produce the sensation of sound. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  illustrates a fully implantable hearing instrument.  
         [0026]      FIGS. 2A and 2B  show plan and cross-sectional views, respectively, of a first acoustic summation embodiment of the present invention.  
         [0027]      FIG. 2C  is a perspective view of a grid-like structure used in the embodiment of  FIGS. 2A and 2B .  
         [0028]      FIG. 2D  is an exploded cross-sectional view of the embodiment of  FIG. 2A .  
         [0029]      FIG. 3  shows a cross-sectional view of a second acoustic summation embodiment of the present invention.  
         [0030]      FIGS. 4A and 4B  show a cross-sectional view of a support structure including a plurality of integrally formed diaphragms.  
         [0031]      FIG. 5  shows a schematic of an electrical summation embodiment of the present invention.  
         [0032]      FIG. 6  shows a schematic of a combined acoustic and electrical summation embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     Reference will now be made to the accompanying drawings, which at least assist in illustrating the various pertinent features of the present invention. In this regard, the following description of a hearing aid device is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain the best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention.  
         [0000]     Hearing Instrument System:  
         [0034]      FIG. 1  illustrates one application of the present invention. As illustrated, the application comprises a fully implantable hearing instrument system. As will be appreciated, certain aspects of the present invention may be employed in conjunction with semi-implantable hearing instruments as well as fully implantable hearing instruments, and therefore the illustrated application is for purposes of illustration and not limitation.  
         [0035]     In the illustrated system, a biocompatible implant housing  100  is located subcutaneously on a patient&#39;s skull. The implant housing  100  includes a signal receiver  118  (e.g., comprising a coil element) and an integrated microphone assembly having a diaphragm  10  that is positioned to receive acoustic signals through overlying tissue. The implant housing  100  may be utilized to house a number of components of the fully implantable hearing instrument. For instance, the implant housing  100  may house an energy storage device, a microphone transducer, and a signal processor. Various additional processing logic and/or circuitry components may also be included in the implant housing  100  as a matter of design choice. Typically, the signal processor within the implant housing  100  is electrically interconnected via wire  106  to a transducer  108 .  
         [0036]     The transducer  108  is supportably connected to a positioning system  110 , which in turn, is connected to a bone anchor  116  mounted within the patient&#39;s mastoid process (e.g., via a hole drilled through the skull). The transducer  108  includes a connection apparatus  112  for connecting the transducer  108  to the ossicles  120  of the patient. In a connected state, the connection apparatus  112  provides a communication path for acoustic stimulation of the ossicles  120 , e.g., through transmission of vibrations to the incus  122 .  
         [0037]     During normal operation, acoustic signals are received subcutaneously at the diaphragm  10 . Upon receipt of the acoustic signals, a signal processor within the implant housing  100  processes the signals to provide a processed audio drive signal via wire  106  to the transducer  108 . As will be appreciated, the signal processor may utilize digital processing techniques to provide frequency shaping, amplification, compression, and other signal conditioning, including conditioning based on patient-specific fitting parameters. The audio drive signal causes the transducer  108  to transmit vibrations at acoustic frequencies to the connection apparatus  112  to effect the desired sound sensation via mechanical stimulation of the incus  122  of the patient.  
         [0038]     To power the fully implantable hearing instrument system of  FIG. 1 , an external charger (not shown) may be utilized to transcutaneously re-charge an energy storage device within the implant housing  100 . In this regard, the external charger may be configured for disposition behind the ear of the implant wearer in alignment with the implant housing  100 . The external charger and the implant housing  100  may each include one or more magnets to facilitate retentive juxtaposed positioning. Such an external charger may include a power source and a transmitter that is operative to transcutaneously transmit, for example, RF signals to the signal receiver  118 . In this regard, the signal receiver  118  may also include, for example, rectifying circuitry to convert a received signal into an electrical signal for use in charging the energy storage device. In addition to being operative to recharge the on-board energy storage device, such an external charger may also provide program instructions to the processor of the fully implantable hearing instrument system.  
         [0000]     Microphone:  
         [0039]     As noted above, it is desirable to design an implantable microphone diaphragm having the smallest possible area (e.g., diameter for a circular diaphragm) to achieve the lowest ratio of vibration to sound sensitivity and thereby maximize achievable gain. However, absolute acoustic sensitivity is reduced as the area of the diaphragm becomes smaller, and therefore the input referred noise floor of the microphone increases. To strike a balance between these competing goals, the present invention utilizes a multitude of smaller microphone diaphragms, the responsive sum of which will have adequate acoustic sensitivity and adequately low input referred noise while retaining the low ratio of vibration to acoustic sensitivity.  
         [0040]     In a first embodiment, a plurality of individual diaphragm elements are disposed relative to a common chamber that allows for acoustically summing the output of the individual diaphragm elements. In one arrangement of the acoustic summing embodiment shown in  FIGS. 2A-2D , a large primary diaphragm  10  of the microphone assembly is subdivided into multiple smaller diaphragm elements  12  by placing a grid-like, rigid or semi-rigid, support structure  20  having a plurality of apertures  26  in contact relation with the diaphragm  10 .  
         [0041]     As shown in  FIG. 2D , the diaphragm  10 , which is formed from a single membrane, may be tensioned over the curved outside surface of the support structure  20 .  
         [0042]     Once tensioned over the support structure  20 , a retaining ring  22  may clamp the diaphragm  10  and support structure to the housing  30 . The diaphragm  10  may be tensioned across each aperture  26  such that the resulting diaphragm elements  12  are operative to vibrate in response to received acoustic signals (e.g., sound). By disposing the diaphragm  10  on the outside curvature of the support structure  20 , contact may be maintained between the peripheries of the apertures  26  and the diaphragm  10  throughout an acoustic vibration cycle of the resulting diaphragm element  12 . Further, an adhesive may be applied to the peripheries of the apertures  26  to adhere the diaphragm  10  to the support structure  20 . Though shown as utilizing a generally dome-shaped support structure  20 , it will be appreciated that any curved support structure including a plurality of apertures may be utilized to create a multi-diaphragm microphone having a single membrane tensioned over its outside curved surface.  
         [0043]     For enhanced ruggedness and/or acoustic matching, a thin layer of a selected, bio-compatible material (e.g., a silicone-containing material) may be provided (e.g., cast) over the diaphragm  10 , or over an external support structure  20  if utilized.  
         [0044]     The diaphragm  10  and support structure  20  may be supportably interconnected to the implant housing  100  as shown in  FIG. 1 , or, supportably interconnected to a separate implantable microphone housing that may be, for example, electrically interconnected to the implant housing  100 . Though discussed herein as being interconnected to a separate microphone housing  30  as shown in  FIGS. 2A-2D , it will be appreciated that various aspects of the invention are equally applicable to an embodiment interconnected to an implant housing  100 .  
         [0045]     A microphone transducer  40  may be disposed within the microphone housing  30  that is operable to provide an output signal, for example via wire  42 , that responsive to movement of the multiple diaphragm elements  12 . As may be appreciated, the output signal from the microphone transducer  40  may be amplified/processed/conditioned and supplied to a middle ear transducer or cochlear implant for stimulation thereof. An example of a middle ear stimulation transducer arrangement is described in U.S. Pat. No. 6,491,622, hereby incorporated by reference.  
         [0046]     Of note, sound pressure variations on the outside of diaphragm  10  will cause movement of the plurality of the small diaphragm elements  12 . The movements of diaphragm elements  12  will combinatively result in pressure variations in a trapped volume of air in one or a plurality of interconnected chambers  50  behind the diaphragm elements  12 . In turn, such pressure variations will be reflected by the output signal from the microphone transducer  40 . In this way a summation of the output of the individual diaphragm elements  12  is effected acoustically.  
         [0047]     The microphone transducer  40  may be defined by any of a wide variety of electroacoustic transducers, including for example, capacitor arrangements (e.g., electret microphones) and electrodynamic arrangements. Further, one or a plurality of tuning elements may be employed in conjunction with the microphone transducer  40  to optimize frequency response. For example, one or more additional diaphragms may be located in chamber(s)  50 .  
         [0048]     In another acoustic summing embodiment shown in  FIG. 3 a  plurality of individual diaphragm elements  70  are attached to a support structure  80 . That is, as opposed to utilizing a single membrane tensioned over the outside surface of a curved support structure, this arrangement utilizes a plurality of individually formed diaphragm elements  70 . In this arrangement, the individual diaphragm elements  70  are attached (e.g., adhered) to the support structure  80  and extend across corresponding apertures  82  within the support structure  80 . Such diaphragm elements  70  may be pre-tensioned, or, may be tensioned once interconnected to the support structure  80 . In the latter regard, the diaphragm elements  70  may be, for example, heat treated to produce a desired tension.  
         [0049]     The support structure  80  is sized to be supportably interconnected to the microphone housing  30 . Likewise, the plurality of individual diaphragm elements  70  may be disposed relative to a common chamber  50  for acoustic summation. Generally, the support structure  80  and the individual diaphragm elements  70  will hermetically seal the housing  30  prevent contamination by body fluids. In further arrangement that may be utilized with the embodiment shown in  FIG. 3  an integrated diaphragm/support structure is provided as shown in  FIGS. 4A and 4B . That is, as opposed to utilizing separately formed diaphragm elements  70  attached to a support structure  80 , a single structure including a plurality of integrally defined diaphragms is utilized. In such approach, a first material layer  84  may be bonded to a different second material layer  86  that will define a diaphragm in the resulting integrated support structure  88 . Then, portions of the first material layer  84  may be etched away to define areas of reduced thickness in the support structure  88 . Optionally, the first and second materials may be selected so that the integrated support structure  88  may be heated to an annealing temperature that yields a plurality of diaphragm elements that are stretched, or tensioned, across corresponding apertures of the integrated support structure  88 . Further, it will be appreciated that diaphragms defined by areas of reduced thickness may be machined into a single material (e.g., titanium) to form an integral one-piece structure.  
         [0050]     In a second embodiment of the present invention, the output signals of a plurality of small diaphragm elements are electronically summed. As shown in  FIG. 5  plurality of individual diaphragm elements  90  are juxtaposed relative to a corresponding plurality of microphone transducers  40 . The output of each microphone transducer  40  is electronically summed by a summation circuit  60 . That is, the summation circuit  60  combines the outputs from the transducers  40 . Accordingly, the output signals generated by each of these transducers  40  may be combined to generate a composite output signal, the responsive sum of which will have an adequate acoustic sensitivity for hearing purposes.  
         [0051]     The plurality of individual diaphragm elements  90  and corresponding transducers may be individual units (e.g., separate microphones) or may share one or more structures. For instance, the plurality of diaphragm elements may be formed into an integrated structure as discussed above, or share a common diaphragm.  
         [0052]      FIG. 6  shows a combined embodiment that utilizes both acoustic and electrical summation. As shown, the embodiment utilizes first and second support structures  20   a ,  20   b  each having a plurality of apertures that in combination with tensioned diaphragms  10   a ,  10   b  define a plurality of diaphragm elements. Each set of diaphragm elements are disposed relative to an acoustic summation chamber  50   a ,  50   b , respectively. As discussed above, the output signals of the diaphragms elements are acoustically summed in the chambers  50   a ,  50   b . The transducers  40   a  and  40   b  are then able to generate first and second outputs indicative of the acoustically summed output signals. The first and second outputs may then be electrically summed by summation circuit  60 .  
         [0053]     Those skilled in the art will appreciate variations of the above-described embodiments that fall within the scope of the invention. As a result, the invention is not limited to the specific examples and illustrations discussed above, but only by the following claims and their equivalents.