MXPA97000089A - Systems of acceleration sensitivity microphone in site reduc - Google Patents

Abstract

The present invention relates to an electroacoustic assembly comprising a microphone having a diaphragm and supported on a front plate susceptible to vibratory effects. The sensitivity of vibration is reduced by opposing the effects of pressure on the diaphragm caused, on the one hand, by the vibration of the assembly in the mass of ambient air and by vibrations of the air mass leading from the mass of ambient air to the diaphragm, and on the other hand, by vibrating the effective mass of the diaphragm, generally increased with the additional mass, and including the effect of the internal air mass adjacent to the diaphragm. Applications include hearing aids in which the microphone and its support are mechanically coupled to receive components that can impart significant movement to the same devices.

Description

BN gITIQ RBPPCIPA Brief Summary of the Invention This invention relates generally to microphone systems. More particularly, this relates to improved microphone assemblies having applications in hearing aids in the ear (ITE). Such hearing aids include channel aids, which are used by inserting them mostly in the external auditory meatus of the user, and the auxiliaries completely in the canal (CIC) usually characterized by an outer face mounted inwardly of the outer terminus of the auditory meatus.

In auditory apparatus systems, the effective acceleration sensitivity of the microphone component is of primary concern due to the so-called mechanical oscillation potential in these low mass systems packed tightly having a substantial electronic gain in the circuit comprising the microphone and the receiver (the electroacoustic output transducer). Typically, the receiver is a magnetic mobile armature transducer having an appreciable effective mass in its armature. In operation, the vibrating armature has both the vibratory linear momentum and the angular momentum. These moments can be canceled approximately for the corresponding moments of another armor in a receiving system of a Siamese twin configuration, as described in the patent granted to Victoreen, of the United States of America No. 4,109,116. If these moments are not canceled, the entire receiver tends to vibrate, and vibrate the microphone through mechanical coupling through the body or shell of the hearing aid. This can result in an undesirable oscillation of the system.

Typically, mounting a receiver in a hearing aid cushions it against mechanical shock damage and somewhat attenuates vibration communication from the receiver to the body or shell of the hearing aid. In general, however, in smaller contemporary aufitive apparatuses such as CIC or channel auxiliaries, assembly is not completely effective in providing this attenuation. Consequently, it is important, in order to avoid oscillation of the system, that the effective acceleration sensitivity of the microphone be as small as possible.

Reduced acceleration sensitivity is one of the main reasons for the almost complete dominance of electret condenser microphones in current hearing aids. Typically the diaphragm of such microphones is a membrane stretched from a biaxially oriented polyester film (such as polyethylene terephthalate) of approximately 1.5 microns thick or less, and having a bulk density of about 1.39 grams / cm3. at a surface density of about 112 micrograms / cm2 In terms of strict diaphragm mass acceleration sensitivity, this in turn corresponds to a low frequency equivalent SPL (a sound pressure level relative to .00002 Pascals) of only 60 dB at a G of acceleration applied to the microphone.

However, it is observed in a Mead C. document.

Killion entitled "Vibration Sensitivity Measurements on Subminiature Condenser Microphones", Journal of the Audio Engineering Society, Volume 23, pages 123-127 (March 1975), that there are contributions to the acceleration sensitivity due to the acceleration of the mass of air in the front of the microphone that can be significant and can, in mounted microphone systems, exceed the contribution of diaphragm mass.

In the prior art, the acceleration sensitivity acoustically linked by Killion had been accepted as inevitable, and attention had been directed only to minimizing the surface density of the diaphragm by using thinner films. In such prior art microphone systems, the mass of the low frequency diaphragm and the acoustic contributions to the acceleration sensitivity have been additive.

According to the present invention, low frequency diaphragm mass and network acoustic contributions are caused as being remaining rather than additive, with the result that over a substantial frequency range the network acceleration sensitivity of the microphone is smaller than that of diaphragm mass effects alone or acoustic effects alone.

Therefore, the present invention comprises a set including a microphone and a front plate or similar support to which the microphone is secured. The microphone has a transducer cover which partially encloses an annular space and a diaphragm attached to the transducer housing and cover and virtually the cover of said space. The microphone also has sustained means inside the transducer cover and responds to a volume shift of the diaphragm to generate an electrical signal. The faceplate has a surface with an acoustic input and open to sound waves in a sound propagating medium. The microphone is secured to the front plate in a position whereby the internal space is located on the side of the diaphragm towards the acoustic input. The assembly of the invention also includes a conduit for said communication means between the acoustic input and the diaphragm side opposite said internal space.

Descri tion, of l9S Drawings Figure 1 illustrates the axially performed symmetric radiation of a sound from a part of a sphere, providing the basis for a theoretical and quantitative analysis of radiation impedance and an approximation of the conditions for an auditory apparatus in use.

Figure 2 is a schematic of a reactive component of radiation impedance corresponding to Figure 1.

Figure 3 is a schematic of the resistive component of a radiation impedance corresponding to Figure 1.

Figure 4 is a section elevation of a first embodiment of the invention having a microphone mounted level in a faceplate.

Figure 4a is an enlarged detail of the figure 4.

Figure 5 is an isometric view of the microphone of Figure 4.

Figure 6 is a partially exploded isometric view of the microphone of Figure 4.

Figure 7 is a plan view showing the circuit elements of the embodiment of Figure 4.

Figure 8 is an isometric view of the faceplate of Figure 4.

Figure 9 is an isometric view of the microphone of Figure 4 without the lid 88.

Figure 10 is a partially sectioned elevation of a second embodiment of the invention.

Figure 11 is a partially sectioned elevation of a third embodiment of the invention.

Figure 12 is an isometric view of an alternate form of a microphone according to the invention.

Figure 13 is a section elevation of the microphone in the embodiment of Figure 12.

Figure 14 is a schematic view of a first form of the CIC auxiliary according to the invention.

Figure 15 is a schematic view of a second form of the CIC auxiliary according to the invention.

Detailed description Figure 1 illustrates the axially symmetrical radiation of sound from a part of a sphere, which is assumed for explanation purposes to approximate one of the important acoustic contributions to the acceleration sensitivity of a microphone system in an ITE hearing device. In the results shown below, figure 1 together with the acoustic wave equation of losing less, has a solution that is an infinite expression only involving products of Legendre polynomials and spherical Bessel functions, and therefore is easily calculable. See Morse, Vibration and Sonic, 323-326 (second edition 1948).

In Figure 1, a rigid sphere 12 of a diameter 2a = 15 centimeters represents the head of a user of an auditory apparatus. The absorption or radiation by the head, and the spreading by the shell and the pinna of the ear, and the spreading by the neck, etc., are neglected. A circular piston 14, vibratory by translation along the axis of symmetry, and of the diameter of 2b = 1.2 centimeters represents the outer face of a channel apparatus extending outwardly, somewhat inside the shell cavity but which goes under the drink. In particular, the sound radiation by the piston 14 represents the outward radiation of the sound by a vibratory channel apparatus. Such vibration may result, from the vibration of the receiver's armature causing the body or shell of the apparatus to vibrate. Note that in this model, any vibration of the piston perpendicular to the axis of symmetry results in minimal radiation, and this also applies to a channel auxiliary except in regard to such vibration that excites vibration of the head or ear Exterior. It is also recognized that the axial vibrations of the ITE device can also be expected to couple something to the head.

Taking into account the previous comments, an analysis of the approximate system of Figure 1 has a qualitative as well as a quantitative meaning. In the following evaluation, the entrance port or going to the microphone is assumed to analyze the radiation pressure at a concentrated point "p" located in the center of the outer surface of the piston. In addition, the microphone is assumed to be mounted rigidly on the piston 14 so that its cover or covers undergo virtually the same vibrational acceleration as the piston. Correspondingly, in current hearing aids, the microphones of this invention are intended to be mounted rigidly on a front plate that provides the outer surface of the ITE apparatus.

Figures 2 and 3 correspond to Figure 1, and are linear-linear schemes of the reactive and resistive components, respectively, of the specific acoustic radiation impedance. This impedance is defined as the ratio of the pressure in the center of the piston to its mechanical speed, in each case divided by p0c, where p0 is the density of air and c is the speed of sound, both at 37 ° C. The frequency range f drawn is 100 to 10,000 Hertz. The straight line cut in Figure 2 shows the initial inclination of the specific acoustic radiation reactance Xs, and helps to show the almost proportional frequency reactance that corresponds to an almost constant inertia effect. In fact, the inclination corresponds to a pressure to acceleration ratio of .0740 poa = 6.31 (10"*) g / cm2, for example from 631 micrograms / cm2 to about three times that of the typical diaphragm surface density noted above There are other air masses associated with a practical microphone which are generally additive to the effect of radiation, with the result that the diaphragm mass effect is almost inconsequential in the electret condenser microphones of prior art.

The resistance to specific acoustic radiation Rs shown in Figure 3, even though it is relatively small at most frequencies of interest, causes a phase change in the radiation pressure and therefore has an importance on the remaining inertial effects that are achieved according to the present invention. The functions Xs and Rs are exact for the configuration of Figure 1, but are only indicative of the radiation impedance of a current channel acoustic apparatus when in use. In addition, the functions Xs and Rs depend on the diameter chosen for the piston of figure 1.

A preferred embodiment of the invention which provides a means to counterattack the radiation impedance predicted by the above approximate analysis, is shown in Figures 4, 4a and 5 to 8. Figure 4 is a diametral cross section of a microphone 16 mounted in a circular opening 18 of a front plate 20. Figure 4a is an amplified part of figure 4. Figure 5 is an isometric view of the entire microphone. Figure 6 is a view of the partially blown microphone along its axis. Figure 7 is a plan view of the electronic circuit incorporated in the microphone. Figure 8 is an isometric view of the electret-coated backing plate of the microphone.

In this embodiment of the microphone 16 it has a metal casing 22 having at least three integral spines 24 which spaced and mounted the microphone, while allowing the passage of sound approximately axially along the remaining cylindrical portions of its exterior .

The ridges 24 also allow the passage of flexion tips 26a, 26b and 26c from the internal electronic circuit of FIG. 7 to the outside of the microphone and to the electrical connections to another circuit of a hearing device or another electronic device.

A subset of electret cartridge 28 has a pull-out cup 30 covered with acoustic openings 32, and a retreat 34, pulled and coated to form a central opening, having a flange 36 with notch locally to prevent electrical cutting of the electrical conductors.

The cartridge 28 is shown in greater detail in Figure 4a. The cup 30 is wedged to sharpen its inner radius, and also to provide a flat edge 38. Typically, the cup 30 is covered in gold. At the edge 38 a diaphragm of polyester film 40 which is so thin that it is merely shown as a line in FIGS. 4 and 4a is attached with tension adhesive. The film from which the diaphragm 40 was made is gold coated in thin form, such as by vacuum evaporation, on the side which will face the cup 30. The gold coating makes the diaphragm 40 electrically conductive, and it enables it to function as the mobile electrode in a capacitive transducer comprising the diaphragm 40 and a backplate covered with electret 42. An aggregate mass 44 is attached to the diaphragm for the reasons discussed below. A spacer washer 46, typically photo-etched metal foil, separates the diaphragm at its peripheral edge from the electret-coated backing plate on the appendices 48 on the latter, shown in FIG. 8. The substrate 50 of the backing plate 42 is metallic, typically covered in gold to provide reliable electrical contact. An electret coating 52 on the backing plate is typically a discrete film of a fluorocarbon polymer, usually a copolymer of tetrafluoroethylene and hexafluoropropylene, which is coated with melt on a main face and the edges of the backing plate substrate. Even though most of the back plate is spaced radially inwardly from the separate washer 46 to allow acoustic passage between the diaphragm 40 and the main interior spaces of the microphone, and also to reduce the capacitance of electrical run-off between the plate backing and the surrounding structure of the cartridge 28, a central bore 54 is provided in the backing plate for an additional acoustic conduit and reduces the acoustic damping between the diaphragm 40 and the outer face of the electret cover 52. A very small opening 56 (FIG. 4a) is controllably produced, as by laser, in the diaphragm 40, to provide atmospheric pressure ventilation of the interior spaces of the microphone. It is desirable for practical reasons to locate the opening 56 in line with the opening 54, and in order to do so, the mass 44 is preferably in the form of a ring or washer. In Figures 4 and 4a, the thickness of the washer 46 and the mass 44 and the degree of bagging of the diaphragm 40 towards the electret covering 52 caused by the electrostatic attraction are exaggerated by way of clarity.

Before making the subassembly of the cartridge 28, the electret coating 52 can be negatively charged by a combination of the thermal and corona methods known in the art. The components of the cartridge 28 are completed by insulating washers 58 and 60 which spaced between the retainer 34 and the metal surfaces of the appendages 48 and applied moderate force to the appendages to ensure a stable subset of the electret cartridge 28. This force is maintained by the welds between the retainer 34 and the cup 30, as well as by small laser welds through the retainer wall inside the cup wall. In addition, the adhesive is applied to the seam between the cup 30 and the retainer 34 to seal acoustically therebetween. Washer 58 can be covered with a low dielectric constant film such as dispersion setting polytetrafluoroethylene. The washer 60 may be of the same material as the electret coating 52, and may for convenience merge the washer 58 to the retainer 34. Preferably, however, the washers 58 and 60 are manufactured in a pre-coated or pre-laminated film passage.

As described above, and upon completion of the assembly as described below, the setting 22 and the cartridge parts 28 partially define and enclose an interconnected internal space 62 on one side of the diaphragm 40, and as such these are collectively referred to herein as the "transducer cover" 63. The diaphragm 40 virtually completes the enclosure of the space 62 except for a very small opening 56. The spaces between the outer surfaces of the cover 22 and the inner surface of the opening 18 in the faceplate form an air duct shown by a cut line 65 going from an acoustic input 67 formed on the surface of the faceplate to a chamber 69 on the side of the diaphragm opposite the internal space 62.

A second sub-assembly is made prior to insertion into the cover 22, and comprises a partially detailed conductor and circuit sub-assembly in Figure 7. A laminated circuit 64, including the conductors 26a, 26b and 26c is photoetched in the plane from a laminate suitable such as a polyimide film / copper foil. Preferably the exposed surface of the copper is covered with gold, with an intermediate coating virtually suppressing the diffusion of copper into the gold coating. As part of the process for manufacturing the laminated circuit 64 while it is flat, a U-shaped groove, partially shown at point 66, is cut into the polyimide film. This allows a connector 68 to be formed up and over in an operation that also forms the conductors 26a, 26b and 26c. The formed laminated circuit 64 is adhesively bonded to an electrically mechanically rigid insulating substrate 70 (Figure 6). The substrate 60 may likewise comprise a circuit board, and may be formed of a high alumina ceramic, for example.

With reference to the plan view of Figure 7 the conductor 26c is a ground conductor and extends to a pad 72. The conductor 26b is a power supply conductor and extends to a pad 74. The driver 26a is a outlet conductor and extends to a pad 76. The connector 68 extends to a pad 78. The metal sheet lying beneath a semiconductor amplifier array 80 extends to a pad 82. The array 80 is mechanically mounted and electrically connected on its lower surface by means of a silver pigmented matrix epoxy.

The pads 72, 74, 76 and 78 are connected by connecting wires 84 to the corresponding pads 86 as supplied on the die 80. Each of the tie wires 84 exits outward from the pair of wire junctions at their ends, especially for clearing the bond wires 84 from the remaining surface of the die 80. In particular, the wire circuit attached from the pad 72 to its corresponding die pad 86 also clears the driver lead 26a to the pad 76 , to avoid cutting the output conductor to ground.

Matrix 80 preferably comprises a preamplifier and may be of the type described in the co-pending application by Madaffari and Collins, Series No. 08 / 447,349, filed on May 23, 1995. In the Madaffari and Collins structures, a discrete capacitor connected in bypass typically progressively attenuates the high frequency noise, and the capacitor can be physically larger than the matrix 80. Although not shown in Figure 7, such a capacitor can be located on the side of the substrate 70 opposite the matrix 80, and can be electrically connected to the amplifier array 80 by a wire connection to the pad 82.

After appropriate cleaning operations, the matrix 80 and all its bonding wires 84, including the wire joints, are encapsulated in a bubble tip class semiconductor (not shown) the latter being pigmented black to make it virtually opaque to the light. The high temperature furnace setting of the complete bubble tip encapsulant, the circuit subassembly and conductor.

By means of the conductors 26a, 26b and 26c, the amplifier circuit of the matrix 80 is connected to additional circuits (not shown) comprising the receiver of the auditory apparatus. Typically, the receiver includes a magnetic mobile armature transducer for converting electric to acoustic energy and is partially contained by a relief cover of which the faceplate 20 is a part.

With particular reference to Figures 4 and 6, the circuit and conductor subassembly can now be bonded with adhesive within the cover 22. The corners of the substrate 70 rest on the terminal planes such as 87 of the loins 24. The conductors 26a and 26b are electrically isolated from the loins 24 by the extra width of their insulating film, but the ground conductor 26c has a full width of its blade to help enable the reliable electrical contact required from the ground conductor to the cover 22. This can be achieved with the silver epoxy inside the corresponding spine 24 near the pad 72, provided that the cover 22 has a noble metal surface such as a gold coating.

Thereafter, the electret cartridge 28 can be attached with adhesive within the location on the cover 22, the adhesive sealing peripherally except where the ridges 24 are located, and with the flange 36 locating the cartridge against the edge of the cover. The notches in the flange 36 are aligned with the conductors 26a, 26b and 26c. Preferably the flange 36 is welded to the edge of the cover 22 in at least one location to establish a defined electrical contact. The connector 68 jumps against the back plate 42 to provide electrical contact, and if desired this can be increased with silver epoxy. Sufficient adhesive is applied between the inside of the spines 24 and the adjacent wall of the retainer 34, near the outer edges of the spines 24, and on both sides of the conductors 26a, 26b, and 26c, to ensure an acoustic seal in each case. one of these regions.

The microphone assembly described above is completed by the addition of a slotted cover 88, which with its grooves 90, threaded by the conductors 26a, 26b and 26c, is set lengthwise against the opposite edges of the ridges 24.

The outer diameter of the lid 88 is nominally the same as the diameter of the cover 22 generally including its ridges 24. Preferably the lid 88 is tightly attached to the cover 22 by small laser welds which overlap the seams between the lid and the spines 24 .

The lid 88 also has a protuberance formed 92 which is attached with adhesive to the cup 30. The assembly is completed with adhesive which strongly bonds and seals in the slots 90 all around the electric conductors 26a, 26b and 26c where it is threaded.

Figure 4 shows the microphone 16 attached and sealed in the front plate of the auditory apparatus 20 within its circular opening 18. Preferably the outer face of the cover 22 is virtually even with the outer surface of the front plate. Starting with a ring 94, conduits such as 65 transmit an acoustic vibratory flow to and from the front chamber 69 between the diaphragm 40 and the cup 30. The flow conduits are quite long, but their relatively long area maintains the acoustic input impedance to the camera 69. Therefore, when the microphone 16 is not vibrating as a whole, it operates in an essentially conventional manner.

When the microphone 16 is operating in an auditory apparatus, it is vibrating with the front plate 20, primarily in response to the vibration of the auditory apparatus induced by the receiver, as discussed above. In general, a substantial component of the vibration will be along the axis of the microphone and it is this component that causes the highest radiation pressure associated with the vibrating outer surfaces of the front plate 20 and the microphone cover 22 in combination. Therefore, the microphone perceives two superimposed pressure signals: (1) the pressure associated with the waves emanating from external sources, as affected by passive head scattering, etc., and (2) the radiation pressure associated with the vibration of the auditory apparatus (and head), as it is increased by the masses of air forming the conduit 65. It is the pressure (2) that is of primary concern, since this creates the potential of a feedback oscillation.

The operation of the invention can be explained to an approximation by considering the operation at a low frequency in which the air masses of the conduit 65, the mass of air in the interior space 26 of the microphone, the mass 44, and the automasa of the diaphragm 40, all move substantially even when not exactly with microphone 16 when vibrating this one. For an approximation, the radial resistance such as Rs (figure 3) is neglected. As these assumptions, when the microphone 16 is accelerated in a direction 96 (Fig. 4) the radiation reactance such as Xs (Fig. 2), virtually augmented by the air masses in the conduit 65 produces a positive signal pressure in the chamber 69 and an upward force in the direction 96 on the diaphragm 40. However, the acceleration in the direction 96 of the diaphragm automasa 40, the mass 44, and the effective air mass in the space 62 produces a downward reaction force in and on the diaphragm 40 in the direction opposite to the direction 96. Since the reactance of substantially proportional radiation of frequency such as Xs corresponds to a virtually constant mass type effect, the significant cancellation of the forces up and down of the diaphragm 40 results, thereby achieving the primary object of the present invention.

The following considerations are also relevant to the previous low frequency approach. The acoustic impedance of the vent opening 56 in the diaphragm 40 is essentially resistive and is frequency independent, and is required to be virtually high to be acoustically insignificant at the frequencies of interest from the point of view of cancellation of the acceleration signals. . Due to the conservation of approximate volume in space 62, about half of the mass of air in this space is effective to produce a reaction pressure on the diaphragm. Consequently, the air mass effect in the conduit 65 considerably exceeds that of the space 62. The aggregate mass 44 is required to bring the cancellation effect approximately into balance, and therefore to sufficiently individualize the choices of the available microphones. The inclination of the radiation reactance such as Xs depends on the size of the face of the auditory apparatus, and also on its location on the ear, thus requiring a choice of different masses 44. The choice of a small washer or additional ring for the mass 44 is dictated by the practical need to have a constant film thickness and an elastic tension for the diaphragm 40. Ideally the aggregate mass can be evenly distributed over the diaphragm without altering its other characteristics.

A simplified equivalent circuit model of the accelerated microphone, in which the mass 44, the diaphragm self-mass 40 and the effective air mass of the space 62 are grouped together in a single mass, indicates that the complete cancellation of the acceleration signals is not it can still be achieved in principle over a finite frequency range. The radiation reactance such as Xs from part of a constant inclination, the resistance to radiation such as Rs becomes non-negligible, and the impedance and coupling of the air masses in the conduit 65 are changed by viscosity and other effects. In addition, the inductance representing approximately the radiation reactance plus the duct mass effects 65 is bypassed by a capacitance representing the chamber 69 plus some of the compressibility effects of the conduit 65, while the heaped mass associated with the diaphragm 40 it is not put in derivation. However, if the resonant frequency of the inductance-capacitance pair is placed well above the required pitch band of the microphone, and if the ratio of Rs / Xs of the radiation impedance is quite small over that of the passband , a substantial degree of cancellation of the acceleration signals on the full pass band of the microphone can be achieved, and generally this is sufficient for practical applications. Even though the specific acoustic radiation impedance is usually not eligible, the higher inductance-capacitance resonant frequency will usually be obtained by designing the cross-sectional areas in conduit 65 as large as practical.

Figure 9 shows a microphone 98 comprising a variation of the microphone of Figures 4 to 7, the variation differing only in that the cover 88 is omitted. As shown in Figure 10, the microphone 98 is adapted to be mounted from the outside of a faceplate 100 in a semicircular circular recess 102 molded in the faceplate 100, with the electrical conductors 104 threaded through the acoustically sealed grooves 106. Tightened by the manufacturer of the hearing aid around each driver. A molded protrusion 108 separates the microphone rate 98 from the remainder of the bottom of the recess, to provide acoustic access to the openings in the rate. This variation and its assembly avoids the tendency towards constricting the conduit 65 in the microphone (Figure 4) between the eyebrow of the lid 88 and the parts spaced inward from the eyebrow of the cover 22.

A further variation is shown in Figure 11, in which the microphone 98 described with reference to Figure 10 is welded into a circular outer cover 110 which provides suitable slots and locatable protuberances 112. In this embodiment, the microphone 98 has its conductors 113 tightly and tightly joined within each of the slots 114. This variation is for applications which require mounting on the inside of a faceplate 116. The edge of the outer cover 110 extends beyond the outer bottom of the cover. cover 22, and its rim assembles and seals within a scarce circular recess 118 in the faceplate. An opening 120 in the faceplate 116 provides acoustic input to the internal microphone 98, but also results in considerably longer acoustic conduits than the conduit 65 of the microphone 16 as shown in Figures 4 to 7.

An alternative embodiment of the microphones of the present invention is shown at point 122 in figures 12 and 13. This embodiment is intended to be assembled as in figure 11, but with the recess in the front plate by adjusting the cross-sectional shape of an outer cover 124. FIG. 13 is a section of the microphone 122 as cut by a plane containing the central core of the microphone and a diagonal passing through the points 126-126 shown in FIG. 12.

The outer cover 124 is provided with a slot 128, recessed on one side, as shown at point 130, to receive by translating a circuit and a terminal board 132. The board 132 typically of high alumina ceramic has a multiplicity of terminal pads at point 134 for welding connections, and surface conductors on the board running from the terminal pads to the interior of the microphone under the recess 130, which avoids the shorting of the conductors. The microphone 122 also has an inner cover 136 which, when assembled, is welded inside the outer cover 124. The inner cover 136 has four acoustic openings 138, and is wedged at the point 140 to receive and locate a cover 142. The inner cover 136 is grooved in the same pattern as the recessed groove 128, 130 on the side adjacent thereto. On the opposite end of its diameter the cover 136 is slotted as in point 144 with the pattern of the slot 128 but without the recess 130. Prior to the positioning of the cover 142, the board 132 and the semiconductor and other circuits (not shown) mounted on it, can slide axially into the slots, the grooves in both covers locating and holding the board.

The inner radius of the inner cover 136 is sharpened in a secondary operation to receive a diaphragm support and tension ring 146. To this is attached with tension adhesive a gold-coated diaphragm 148, which bears a washer or mass of additional ring 150, and also has an atmospheric pressure vent 152. The diaphragm subassembly is joined within the inner shell 136 with silver epoxy in the metal ring 146. A spacer washer 154 is empty between the diaphragm flange 148 and the appendages of a backing plate coated with electret film 156 in the manner shown in Figure 8. The backing plate 156 is fixed to the inner cover 136 by adhesive rims of insulating epoxy paste (not shown) on the metal surfaces. of the three back plate appendixes.

The electrical contact to an input conductor on a board edge 132 is made by a silver epoxy rim to the exposed metal surface of the back plate. Similarly, the ground contact between the appropriate conductor on the board 132 and the inner cover 136 is made by a silver epoxy rim. Typically the inner cover 136 and the metal part of the backup plate 136 are covered in gold for this purpose, and typically the conductors on the board 132 are bonded coatings of noble metal melt at a high temperature.

The lid 142 has the filler key 158 welded thereon. When the microphone assembly 122 is contemplated by adhesive bonding of the plate 142 in place against the coin passage 140, the key 158 virtually fills the remainder of the slot left by the board 132. Enough adhesive should be used to block all potential drains, except for the vent, between all corner spaces 160 and outside of microphone 122 or interior space 161. In particular, sufficient adhesive should be used to block the remainder of slot 144 and recess 130 in both of covers 124 and 136.

Figures 14 and 15 schematically illustrate the application of the microphones of the present invention to CIC hearing aids. The hearing aids CIC 162 and 164, respectively, are shown in position in the auditory meatus 166 of the user.

In Figure 14 the outer face 168 of a front plate of the CIC 162 apparatus is almost level with the outer terminus of the meatus 166. A microphone 170 is mounted level in the front plate as in Figure 4 or Figure 10 and is located more or less centrally on the outer face 168. The electrical conductors 172 of the microphone 170 are shown schematically as in Figure 5 or Figure 9, and the inside of the front plate of the CIC 162 apparatus is not indicated. The receiving elements 174 of the apparatus 162, the cause of their vibration, are located at or near the end 176 towards the tympanic membrane 178. The specific acoustic radiation impedance, as defined above, of the outer face 168 the CIC 162 apparatus is typically smaller than that of a typical channel apparatus due to the smaller area of the face 168, even when there is an additional air mass in the shell space 180. During the vibration of the apparatus 162, the microphone 170 perceives the pressure of resulting radiation, in addition to its internal inertial effects, on the annular entry, essentially at the effective center of the outer face 168. When the aggregate mass 44 (figure 4a) of the microphone 170 is appropriately chosen, say from a discrete set of choices for practical reasons, the total acceleration induced signal of the microphone 170 is much smaller compared to the prior art microphones over a range of Very substantial frequency.

In Figure 15, the CIC apparatus 164 is mounted with its outer face 182 inwardly and its inner end 184 is inserted deeper into the tympanic membrane 178. Generally, the specific acoustic radiation impedance of the outer face 182 will be greater than that of the outer face 168 of Figure 14, as a result of an additional air mass in the auditory meatus 166 between the outer face 182 and the shell space 180.

When the user of an ITE hearing aid incorporating a microphone system of this invention attempts to use a telephone while the assistant is in the acoustic mode, the hearing aid is apt to swing, particularly if this microphone system is necessary for Avoid oscillation in normal use. This is because the complex radiation impedance such as Rs + iXs is considerably affected by the proximity of the telephone receiver. Consequently, a telecoil mode is necessary in the hearing aid of this type. Such hearing aids will tend to be cosmetically acceptable and often inaccessible when used, so that switching between the acoustic mode and the telecoil mode will be more convenient if done remotely or is achieved automatically.

In the above description references are made to specific applications of the invention to hearing aids. However, it is not inherently limited to such applications. For example, references are made to a "front plate". In microphone or other hearing aid applications, the face plate described herein may be replaced by a frame, an outer shell, a support or other structure case retaining a microphone and structured according to the teachings of this invention as described and claim here. Therefore, the term "front plate" is intended to include generically any replacement or alternating means as well as the front plates of hearing devices.

Similarly, even when the invention has been described in relation to an air environment, other applications may involve its use in other means of acoustic transmission comprising the environment such as other gases or liquids including water, for example.

Claims (29)

R B I V I M D I C A C OM OM S

1. A microphone taking in combination, a transducer box having a surface available in a sound propagation medium and partially enclosing an internal space, means that form an acoustic input external to the space and open to the medium, a flexible diaphragm fastened on its periphery to the transducer box and virtually completing the enclosure of said space, said space being located on the side of the diaphragm towards the acoustic input, means forming a conduit for said medium communicating between the acoustic input and the diaphragm side opposite said internal space, and media supported within the transducer box and responding to a volume shift of the diaphragm to generate an electrical signal.

2. A microphone as claimed in clause 1, characterized in that the microphone includes a backplate covered with electret, and retainer means for supporting the diaphragm and the backing plate in a mutually spaced relationship.

3. A microphone as claimed in clause 1, characterized in that the response means are located within said internal space.

4. A microphone as claimed in clause 1, characterized in that the transducer cover encloses a space on the side of the diaphragm opposite the internal space and communicating with said conduit.

5. An electroacoustic set having, in combination, a microphone having a transducer box partially enclosing an internal space, a flexible diaphragm attached at its periphery to the transducer box and virtually completing the confinement of said space, and means supported within the transducer box and responding to volume displacement of the diaphragm to generate an electrical signal, and a front plate having a placeable surface in a sound propagating medium with an acoustic input in said surface opening to the sound waves in said medium, the microphone being secured to the front plate with said space located on the side of the diaphragm towards the acoustic entrance, said assembly has a conduit for said communicating means between the acoustic entrance and the diaphragm side opposite said internal space.

6. A set as claimed in clause 5, characterized in that the microphone includes a backplate covered with electret, and retainer means for holding the diaphragm and the backing plate in a mutually spaced relationship.

7. An assembly as claimed in clause 5, characterized in that said response means are located within said internal space.

8. An assembly as claimed in clause 5, characterized in that the transducer box houses a space on the side of the diaphragm opposite said internal space and in communication with said assembly.

9. An assembly as claimed in clause 5, characterized in that the front plate has an opening and the transducer box is received in said opening, said conduit includes spaces formed between the box and the opening.

10. An assembly as claimed in clause 9, characterized in that the transducer cover includes wall portions forming edges fitted to said opening.

11. An assembly as claimed in clause 10, characterized in that said response means includes a plurality of electrical conductors each extending within an edge to the outside of the transducer box, the diaphragm extends internally of said conductors.

12. A microphone as claimed in clause 1, characterized in that the transducer cover includes a plurality of wall portions forming virtually parallel ridges, and electrical conductors each extending within each of the ridges from the interior space to the exterior of the transducer housing, the diaphragm extends internally from said conductors.

13. An assembly as claimed in clause 5, characterized in that an outer wall of the transducer box is virtually even with the front plate near the acoustic input.

14. An auditory device that comprises, in combination, a microphone having a transducer box partially enclosing an internal space, a flexible diaphragm attached at its periphery to the transducer box and virtually completing the enclosure of said space, and media supported within the transducer box and responding to volume displacement of the diaphragm to generate an electrical signal, a front plate having a surface placed in a sound propagating medium with an acoustic input in said surface opening to the sound waves in said medium, the microphone being secured to the front plate with said space located on the side of the diaphragm towards the acoustic input, means that form a conduit for the communication of the medium between the acoustic input and the diaphragm side opposite the internal space, a receiver that responds to said signal to produce an acoustic output, and means connected to the front plate and partially enclosing and mechanically coupling the microphone and the receiver.

15. An auditory apparatus as claimed in clause 14, characterized in that the microphone includes a backplate covered with electret, and retainer means for holding the diaphragm and the backing plate in a mutually spaced relationship.

16. An auditory apparatus as claimed in clause 14, characterized in that the responding means are located within the internal space.

17. An auditory apparatus as claimed in clause 14, characterized in that the transducer box houses a space on the side of the diaphragm opposite the internal space and communicating with said conduit.

18. A set as claimed in clause 5, including an outer box secured to the front plate, the transducer box being secured inside the outer case, the outer case having an opening to said conduit.

19. A microphone as claimed in clause 1, including an aggregate mass attached to the diaphragm to increase its reactance to vibration.

20. A microphone as claimed in clause 1, characterized in that said internal space has a pressure ventilation communicating with said means and having a sufficient acoustic impedance to virtually eliminate its effect on the active acceleration forces on the diaphragm and that are caused by the vibration of the microphone.

21. An auditory apparatus comprising, in combination, a structure a vibratable surface and insertable into the ear with said surface facing out from the ear and exposed to external acoustic signals, a microphone having a docile diaphragm held there and means responsive to the vibrations of the diaphragm to produce electric signals, the diaphragm having a face surface thereof generally inwardly of the ear, the microphone being mechanically coupled to said structure, and means forming a conduit for said acoustic signals external to said diaphragm surface .

22. An auditory apparatus as claimed in clause 21, characterized in that it includes means comprising an electroacoustic receiver and adapted to convert said electrical signals to amplified acoustic signals transmitted to the ear tympanic membrane.

23. An auditory apparatus as claimed in clause 22, characterized in that the receiver is mechanically coupled to said structure.

24. An auditory apparatus as claimed in clause 21, characterized in that said structure defines an opening open to said external acoustic signals and communicating with said conduit.

25. An auditory apparatus as claimed in clause 21, characterized in that said structure and said microphone define an opening open to said external acoustic signals and communicating with said conduit.

26. An auditory apparatus as claimed in clause 21, characterized in that said conduit is open to said external acoustic signals near said vibratable surface.

27. An auditory apparatus as claimed in clause 21, characterized in that said surface of the diaphragm virtually closes a space communicating with said conduit.

28. An auditory apparatus as claimed in clause 21, characterized in that the microphone includes an electret-coated backing plate, the diaphragm and the backing plate form an electret condenser transducer.

29. An auditory apparatus as claimed in clause 21, characterized in that the diaphragm comprises a film and a mass on the film to increase the reactance to vibration. R B 8 ü M B N An electroacoustic assembly comprising a microphone having a diaphragm and supported on a front plate susceptible to vibratory effects. The sensitivity of vibration is reduced by opposing the effects of pressure on the diaphragm caused, on the one hand, by the vibration of the assembly in the mass of ambient air and by vibrations of the air mass leading from the mass of ambient air to the diaphragm, and on the other hand, by vibrating the effective mass of the diaphragm, generally increased with the additional mass, and including the effect of the internal air mass adjacent to the diaphragm. Applications include hearing aids in which the microphone and its support are mechanically coupled to receive components that can impart significant movement thereto.