HEARING DEVICE WITH ACTIVE FEEDBACK CONTROL

Abstract

An illustrative hearing device includes a housing configured to be partially inserted into an ear canal; an acoustic transducer having an oscillator element configured to generate sound waves, the housing accommodating the acoustic transducer inside an inner volume of the housing; and a sound outlet provided at the housing and configured to enable propagation of sound waves from the inner volume into the ear canal. The acoustic transducer and the housing are configured such that an output impedance of the hearing device measured at the sound outlet has a value of at most 3.5.Math.10.sup.7 kg/(m.sup.4.Math.sec) within a frequency bandwidth of at least 50 Hz comprised in a frequency range between 1000 Hz and 2000 Hz.

Claims

1. A hearing device comprising: a housing configured to be partially inserted into an ear canal; an acoustic transducer having an oscillator element configured to generate sound waves, the housing accommodating the acoustic transducer inside an inner volume of the housing; and a sound outlet provided at the housing and configured to enable propagation of sound waves from the inner volume into the ear canal; wherein the acoustic transducer and the housing are configured such that an output impedance of the hearing device measured at the sound outlet has a value of at most 3.5.Math.10.sup.7 kg/(m.sup.4.Math.sec) within a frequency bandwidth of at least 50 Hz comprised in a frequency range between 1000 Hz and 2000 Hz.

2. The hearing device of claim 1, wherein the housing further comprises a first housing portion enclosing a first volume portion of the inner volume in front of the oscillator element and a second housing portion enclosing a second volume portion of the inner volume behind the oscillator element, the first volume portion and the second volume portion acoustically coupled by the oscillator element.

3. The hearing device of claim 2, wherein the oscillator element is positioned inside the inner volume such that the first volume portion is at least two times smaller than the second volume portion.

4. The hearing device of claim 3, wherein the first volume portion has a value of at most 25.Math.10.sup.−8 m.sup.3.

5. The hearing device of claim 4, the hearing device further comprising: an inner acoustic port acoustically coupling the first volume portion and the second volume portion, the inner acoustic port physically separated from the oscillator element.

6. The hearing device of claim 2, characterized by an outer acoustic port acoustically coupling the inner volume with an ambient environment outside the inner volume.

7. The hearing device of claim 6, wherein the outer acoustic port is a first outer acoustic port acoustically coupling the first volume portion with the ambient environment, wherein the hearing device further comprises a second outer acoustic port acoustically coupling the second volume portion with the ambient environment.

8. The hearing device of claim 1, wherein the hearing device further comprises a resonant member configured to resonate with sound waves at a resonance frequency, wherein the resonant member is acoustically coupled with said inner volume.

9. The hearing device of claim 8, wherein: the housing further comprises a first housing portion enclosing a first volume portion of the inner volume in front of the oscillator element and a second housing portion enclosing a second volume portion of the inner volume behind the oscillator element; and the resonant member is acoustically coupled with the first volume portion.

10. The hearing device of claim 9, wherein the resonance frequency is comprised in a frequency range between 800 Hz and 4000 Hz.

11. The hearing device of claim 10, wherein the resonant member is a first resonant member, wherein the hearing device further comprises a second resonant member configured to resonate with sound waves at a different resonance frequency than the first resonant member is acoustically coupled with the inner volume.

12. The hearing device of claim 11, wherein the first resonant member is provided in front of the oscillator element.

13. The hearing device of claim 12, wherein the first resonant member is provided behind the oscillator element.

14. The hearing device of claim 13, wherein an active area of the acoustic transducer has a value of at least 5.Math.10.sup.−5 m.sup.2, the active area defined as a virtual plane delimited by a front end of the oscillator element.

15. The hearing device of claim 1, wherein the oscillator element has mass of at most 30.Math.10.sup.−3 g.

16. The hearing device of claim 1, wherein the output impedance is measurable at the sound outlet by producing an acoustic flow through the sound outlet into the inner volume and detecting an acoustic pressure at the sound outlet.

17. The hearing device of claim 1, further comprising a suspension member configured to support the oscillator element inside the housing, wherein the suspension member has a mechanical compliance of at least 12.Math.10.sup.−3 sec.sup.2/kg.

18. The hearing device of claim 1, further comprising a microphone configured to be acoustically coupled to the ear canal.

19. The hearing device of claim 18, further comprising an active feedback control circuit electronically connected to the microphone and configured to provide an active feedback control signal to modify the sound waves generated by the acoustic transducer, wherein the active feedback control circuit is configured to provide an active noise control (ANC) or active noise reduction (ANR) of the sound waves generated by the acoustic transducer.

20. A hearing device comprising: a housing configured to be partially inserted into an ear canal; an acoustic transducer having an oscillator element configured to generate sound waves, the housing accommodating the acoustic transducer inside an inner volume of the housing; a sound outlet provided at the housing and configured to enable propagation of sound waves from the inner volume into the ear canal; a resonant member configured to resonate with sound waves at a resonance frequency in a frequency range between 800 Hz and 4000 Hz, wherein the resonant member is acoustically coupled with said inner volume; a microphone configured to be acoustically coupled to the ear canal; and an active feedback control circuit electronically connected to the microphone and configured to provide an active feedback control signal to modify the sound waves generated by the acoustic transducer, wherein the active feedback control circuit is configured to provide an active noise control (ANC) or active noise reduction (ANR) of the sound waves generated by the acoustic transducer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the drawings:

[0040] FIG. 1 schematically illustrates a hearing device comprising a housing accommodating an acoustic transducer, in accordance with some embodiments of the present disclosure;

[0041] FIG. 2 schematically illustrates the hearing device shown in FIG. 1 partially inserted into an ear canal;

[0042] FIG. 3 schematically illustrates a hearing device comprising a housing accommodating an acoustic transducer, wherein an inner volume of the housing is acoustically coupled with a plurality of resonant members, in accordance with some embodiments of the present disclosure; and

[0043] FIG. 4 schematically illustrates a hearing device comprising a housing accommodating an acoustic transducer, wherein an inner volume of the housing is acoustically coupled with a plurality of resonant members, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

[0044] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the subject matter herein. However, it will be apparent to one of ordinary skill in the art that the subject matter may be practiced without these specific details. In other instances, well known methods, procedures, techniques, components, and systems have not been described in detail so as not to unnecessarily obscure features of the embodiments. In the following description, it should be understood that features of one embodiment may be used in combination with features from another embodiment where the features of the different embodiment are not incompatible. The ensuing description provides some embodiment(s), and is not intended to limit the scope, applicability or configuration. Various changes may be made in the function and arrangement of elements without departing from the scope of the disclosure.

[0045] FIG. 1 schematically illustrates a hearing device 1, in accordance with some embodiments of the present disclosure. Hearing device 1 comprises an acoustic transducer 21 and a transducer housing 27 accommodating acoustic transducer 21. Acoustic transducer 21 comprises an oscillator element 22 and an oscillation drive 23. Transducer housing 27 comprises a transducer front port 28 and a transducer rear port 29 opposing each other. Oscillator element 22 is arranged in a transducer chamber 37 enclosed by transducer housing 27. Oscillator element 22 is located between transducer front port 28 and transducer rear port 29 such that the sound waves emanated from oscillator element 22 can propagate through transducer front port 28 and transducer rear port 29. Acoustic transducer 21 is a driver. Oscillator element 22 is a membrane.

[0046] Oscillation drive 23 comprises a magnet 24 and a voice coil 25. A suspension member 26 mechanically couples oscillator element 22 to housing 2. Suspension member 26 connects oscillator element 22 with an inner surface of housing 2. Suspension member 26 forms a mechanical compliance having a value characteristic for a flexibility of the mechanical coupling. Voice coil 25 is mechanically connected to oscillator element 22, in particular by a rigid connection. Voice coil 25 is constrained to move axially through a cylindrical gap in magnet 24. A variable magnetic field can be created by providing a changing electric current through voice coil 25. The variable magnetic field can cause voice coil 25 to move back and forth inside the magnetic gap by a magnetic interaction between magnet 24 and voice coil 25. A corresponding movement of oscillator element 22 coupled to voice coil 25 can produce sound waves emanated from an oscillating area 32 of oscillator element 22.

[0047] Oscillator element 22 comprises a conical portion. Oscillating area 32 constitutes an inner surface of the conical portion. An outer edge 33 surrounds oscillating area 32. Outer edge 33 constitutes a part of an outer circumference of oscillator element 22 at a front end 34 of the conical portion. An active area 35 of acoustic transducer 21 is defined by a virtual plane laterally delimited by front end 34 of oscillator element 22. Active area 35 constitutes a part of an infinite virtual plane 36 intersecting outer edge 33 at front end 34 of oscillator element. Active area 35 forms a virtual base line of the conical portion. Front end 34 is located on the virtual base line. A boundary of active area 35 intersects outer edge 33 at front end 34 of oscillator element 22. Active area 35 faces in a direction in which oscillator element 22 is configured to oscillate, in particular a direction in which sound waves propagate during oscillation of oscillator element 22.

[0048] Hearing device 1 comprises a housing 2. Transducer housing 27 is integrated with housing 2. Housing 2 encloses a front chamber 3 acoustically coupled with transducer chamber 37 via transducer front port 28. Housing 2 encloses a rear chamber 4 acoustically coupled with transducer chamber 37 via transducer rear port 29. An inner volume 5 enclosed by housing 2 thus comprises front chamber 3, transducer chamber 37, and rear chamber 4. The sound waves produced by oscillator element 22 propagate inside inner volume 5. Inner volume 5 thus provides an acoustic pathway for the sound waves. A first volume portion 6 of inner volume 5 is located in front of oscillator element 22. First volume portion 6 thus comprises front chamber 3 and a portion of transducer chamber 37 in front of oscillator element 22. A second volume portion 7 of inner volume 5 is located behind oscillator element 22. Second volume portion 7 thus comprises rear chamber 4 and a portion of transducer chamber 37 behind oscillator element 22.

[0049] A virtual partition 11 separating first volume portion 6 and second volume portion 7 is defined by oscillator element 22 within an inner radial region of inner volume 5 in which oscillator element 22 extends, and by virtual plane 36 within an outer radial region of inner volume 5 ranging outside oscillator element 22. First volume portion 6 is located in front of virtual partition 11. Second volume portion 7 is located behind virtual partition 11. First volume portion 6 and second volume portion 7 are acoustically coupled by oscillator element 22. The acoustic pathway inside inner volume 5 thus extends between first volume portion 6 and second volume portion 7 through oscillator element 22. Sound waves can traverse virtual partition 11 through oscillator element 22. Oscillator element 22 is configured to transfer pressure variations caused by the sound waves between first volume portion 6 and second volume portion 7.

[0050] Housing 2 comprises a first housing portion 18 enclosing first volume portion 6. Housing 2 comprises a second housing portion 19 enclosing second volume portion 7. Housing 2 comprises a front wall 13, a rear wall 14 opposing front wall 13, and a side wall 15 connecting front wall 13 and rear wall 14. Front wall 13 is adapted to face an ear canal when housing 2 is inserted into the ear canal. First housing portion 18 comprises front wall 13 and a portion of side wall 15. Second housing portion 19 comprises rear wall 14 and a portion of side wall 15. Virtual plane 36 intersects side wall 15 between first housing portion 18 and second housing portion 19.

[0051] First housing portion 18 comprises a sound outlet 17. Sound outlet 17 leads from inner volume 5 to an exterior of housing 2 such that sound outlet 17 is configured to release sound waves from inner volume 5 to the exterior. Sound outlet 17 extends the acoustical pathway for the sound waves from inner volume 5 to the exterior of housing 2. Inner volume 5 is acoustically coupled to the exterior via sound outlet 17. Sound outlet 17 is arranged in front of oscillator element 22. Oscillator element 22 faces sound outlet 17. A middle axis extends longitudinally through a cross-sectional center of housing 2 through oscillator element 22 and sound outlet 17 along the acoustical pathway. Sound outlet 17 is fixed to front wall 13. Sound outlet 17 is a tubular member, in particular a spout, having an open rear end adjoining an aperture in front wall 13 and an open front end opposing the rear end. The open front end is free such that the sound waves can be released from housing 2 to the exterior through the open front end of sound outlet 17.

[0052] Sound outlet 17 can be at least partially inserted into an ear canal. After insertion, a portion of sound outlet 17 comprising the open front end is positioned in an inner region of an ear canal and a portion of housing 2 enclosing inner volume 5 is located outside the ear canal in an ambient environment. Sound outlet 17 is therefore configured to release sound waves into the ear canal. First housing portion 18 is further configured to contact an ear canal wall of the ear canal. In this way, first housing portion 18 can form an acoustical seal with the ear canal wall. The acoustical seal can acoustically isolate the open front end of sound outlet 17 in the ear canal from the ambient environment outside the ear canal, at least to some extent. In this way, ambient sound from the ambient environment outside the ear canal can be at least partially blocked from entering an inner region of the ear canal.

[0053] An inner acoustic port 44 is positioned between first volume portion 6 and second volume portion 7. Inner acoustic port 44 provides an acoustical coupling between first volume portion 6 and second volume portion 7, in addition to the acoustical coupling provided by oscillator element 22. The acoustic pathway between first volume portion 6 and second volume portion 7 thus extends through inner acoustic port 44. Inner acoustic port 44 provides a reactive element between first volume portion 6 and second volume portion 7. Inner acoustic port 44 extends through virtual partition 11. Inner acoustic port 44 is a tubular member connecting first volume portion 6 and second volume portion 7. Inner acoustic port 44 has an acoustic mass that can be modified by selecting a length and/or a cross sectional size of the tubular member. In this way, the output impedance of hearing device 1 can be influenced by selecting an appropriate acoustic mass of inner acoustic port 44.

[0054] A first outer acoustic port 45 is positioned between first volume portion 6 and the ambient environment outside housing 2. Outer acoustic port 45 is provided at first housing portion 18. Outer acoustic port 45 comprises a tubular member extending from side wall 15 into first volume portion 6. A second outer acoustic port 46 is positioned between second volume portion 7 and the ambient environment outside housing 2. Outer acoustic port 46 is provided at second housing portion 19. Outer acoustic port 46 comprises a tubular member extending from rear wall 14 into second volume portion 7. Outer acoustic ports 45, 46 each provide a reactive element extending the acoustic pathway from inner volume 5 to the ambient environment. An acoustic mass of outer acoustic ports 45, 46 can be set by selecting a length and/or a cross sectional size of the respective tubular member allowing to influence the output impedance of hearing device 1.

[0055] An acoustic resistance 51 comprises a first terminal 58 and a second terminal 59. Acoustic resistance 51 is configured to attenuate a sound pressure of sound waves propagating between first terminal 58 and second terminal 59. The attenuation of the sound waves can be provided by a sound resistive body between first terminal 58 and second terminal 59. The sound resistive body can comprise, for instance, a grid structure such as a wire mesh and/or a damping material such as a cloth. Acoustic resistance 51 provides a resistive element. Acoustic resistance 51 is positioned such that it provides an acoustical coupling between two volume portions, the first volume portion adjoining first terminal 58 and the second volume portion adjoining second terminal 59. Acoustic resistance 51 thus provides an acoustical coupling between the two volume portions. Acoustic resistance 55 can allow a damping of resonances over a defined frequency range, for instance a damping of high frequency and/or low frequency resonances. In this way, a frequency output of hearing device 51 can be reduced at a desired frequency range and/or increased at a desired frequency range relative to another frequency range. The frequency output can be defined by amplitudes of a frequency spectrum of sound waves released through sound outlet 17. The output impedance of hearing device 1 can thus be influenced, in particular for a selected frequency range.

[0056] The first terminal of acoustic resistance 51 is oriented towards first chamber 25. The second terminal of acoustic resistance 51 is oriented towards the ambient environment outside inner volume 5. Acoustic resistance 51 thus provides an acoustical coupling between two volume portions, namely first volume portion 6 and the ambient environment, corresponding to the volume portions acoustically coupled by outer acoustic port 45. Acoustic resistance 51 is placed in parallel to first outer acoustic port 45. Acoustic resistance 51 is provided separate from outer acoustic port 45. Acoustic resistance 51 is provided at first housing portion 18 at a distance to outer acoustic port 45. An acoustic resistance 52 is placed in parallel to second outer acoustic port 46. The first terminal of acoustic resistance 52 is oriented towards second volume portion 7. The second terminal of acoustic resistance 52 is oriented towards the ambient environment. Acoustic resistance 52 thus provides an acoustical coupling between the volume portions acoustically coupled by outer acoustic port 46. Acoustic resistance 52 is provided separate from outer acoustic port 46. Acoustic resistance 52 is provided at second housing portion 19 at a distance to outer acoustic port 46. An acoustic resistance 53 is placed in parallel to inner acoustic port 44. The first terminal of acoustic resistance 53 is oriented towards first volume portion 6. The second terminal of acoustic resistance 53 is oriented towards second volume portion 7. Acoustic resistance 53 thus provides an acoustical coupling between the volume portions acoustically coupled by inner acoustic port 44 and oscillator element 22. Acoustic resistance 53 is provided separate from oscillator element 22. Acoustic resistance 53 is provided separate from inner acoustic port 44. Acoustic resistance 52 is provided inside inner volume 5 at a distance to oscillator element 22 and inner acoustic port 44.

[0057] An acoustic resistance 54 is placed in series with first outer acoustic port 45. The first terminal of acoustic resistance 54 is oriented towards first volume portion 6. The second terminal of acoustic resistance 54 is oriented towards the ambient environment. Acoustic resistance 54 thus provides an acoustical coupling between the volume portions acoustically coupled by outer acoustic port 45. Acoustic resistance 54 is provided at outer acoustic port 45. An acoustic resistance 55 is placed in series with second outer acoustic port 46. The first terminal of acoustic resistance 55 is oriented towards second volume portion 7. The second terminal of acoustic resistance 55 is oriented towards the ambient environment. Acoustic resistance 55 thus provides an acoustical coupling between the volume portions acoustically coupled by outer acoustic port 46. Acoustic resistance 55 is provided at outer acoustic port 46. An acoustic resistance 56 is placed in series with inner acoustic port 44. The first terminal of acoustic resistance 56 is oriented towards first volume portion 6. The second terminal of acoustic resistance 56 is oriented towards second volume portion 7. Acoustic resistance 56 thus provides an acoustical coupling between the volume portions acoustically coupled by inner acoustic port 44. Acoustic resistance 56 is provided at inner acoustic port 44. An acoustic resistance 57 is placed in series with transducer rear port 229. The first terminal of acoustic resistance 56 is oriented towards transducer chamber 37. The second terminal of acoustic resistance 56 is oriented towards rear chamber 4. Acoustic resistance 57 thus provides an acoustical coupling between the volume portions acoustically coupled by transducer rear port 229. Acoustic resistance 56 is provided at transducer rear port 229. Acoustic resistances 51-57 can be selected to influence the output impedance of hearing device 1 in a desired way, in particular in a frequency dependent manner.

[0058] A microphone 62 is provided in first volume portion 6. Thus, microphone 6 is acoustically coupled to an ear canal, when housing 2 is at least partially inserted into the ear canal. In particular, microphone 6 can be located inside the ear canal and/or outside the ear canal when it is acoustically coupled to the ear canal via first volume portion 6. Microphone 62 is an ear canal microphone. Microphone 62 is provided in proximity to sound outlet 17. Microphone 62 is mounted on an inner surface of first housing portion 18. Hearing device 1 further comprises an active feedback control (AFC) circuit 65. AFC circuit 65 can be provided at housing 2, in particular inside inner volume 5 and/or outside inner volume 5. AFC circuit 65 can also be provided remote from housing 2. AFC circuit 65 is configured to provide an active feedback control signal to modify the sound waves generated by acoustic transducer 21. AFC circuit 65 is connected to microphone 62. Microphone 62 is configured to provide a feedback microphone signal to AFC circuit 65. Microphone 62 may thus also be referred to as a feedback microphone. An active feedback loop comprises microphone 62 and AFC circuit 65. The active feedback loop can modify the sound waves generated by acoustic transducer 21 depending on the feedback signal of microphone 62. The active feedback loop can be configured to provide an active noise control (ANC) or active noise reduction (ANR) of the sound waves output from the hearing device.

[0059] The general operating principle of such an active feedback loop is well known in the art. For instance, a circuit as described in U.S. Pat. Nos. 4,985,925, 8,682,001 B2, 9,792,893 B1, US 2018/0286373 A1 or US 2018/0197527 A1 can be applied. It has been found, however, that an application of the active feedback loop can result in an instable behavior of the sound output of the hearing device. The instabilities can be partially circumvented by a suitable signal processing performed by AFC circuit 65. But an effective suppression of the instable behavior based on the signal processing can depend on an actual size and geometry of the ear canal. While the instabilities may be decreased or avoided for some ear canals, they can still be present or even more pronounced in other ear canals.

[0060] FIG. 2 schematically illustrates hearing device 1 partially inserted in an ear canal 71. Further symbolized by a respective arrow are an input impedance 75, or load impedance, and an output impedance 77 of hearing device 1. Output impedance 77 refers to an impedance value measured at sound outlet 17 in a calm environment, in particular when no sound waves are generated by acoustic transducer 21. Output impedance 77 can be a value measured at sound outlet 17 by feeding sound waves into inner volume 5 through sound outlet 17, in particular from the free end of sound outlet 17, and detecting the sound waves returning from inner volume 5 at sound outlet 17, in particular at the free end of sound outlet 17. Techniques for measuring input impedance 75 and output impedance 77 are described, for instance, in Leo L. Beranek, “Acoustical Measurements”, published by the American Institute of Physics, 1988, and in Alfred Stirnemann, “Impedanzmessungen and Netzwerkmodell zur Ermittlung der Uebertragungseigenschaften des Mittelohrs”, published by ETH Zurich, 1980.

[0061] In the context of the present disclosure, it has been found that acoustical instabilities provoked by the active feedback loop can be remedied by providing output impedance 77 with a value of at most 2.Math.10.sup.7 kg/(m.sup.4.Math.sec) at a frequency range between 1000 Hz and 1500 Hz. The acoustical instabilities can be further improved by providing output impedance 77 with a value of at most at most 10.sup.8 kg/(m.sup.4.Math.sec) at a frequency range of 100 Hz and below. A reduction of the feedback instabilities can thus be achieved for a large variety of sizes and geometries of ear canal 71. A rather ear canal independent behavior of hearing device 1 can thus be provided. An aspect of the present disclosure therefore aims to equip hearing device 1 in such a way that the desired behavior of output impedance 77 can be achieved. It has been found that at least one of the following technical features can be exploited to obtain the desired impedance behavior. A combination of a plurality of the following features can lead to a further improvement of the intended output impedance adjustment: [0062] providing first volume portion 6 at least two times smaller than second volume portion 7, in particular at a value of first volume portion 6 of at most 25.Math.10.sup.−8 m.sup.3 and/or a value of second volume portion 7 of at least 50.Math.10.sup.−8 m.sup.3; [0063] providing at least one of outer acoustic ports 45, 46, preferably at least rear acoustic port 46 and more preferred both outer acoustic ports 45, 46, in particular by providing a comparatively small acoustical mass of the respective acoustic port 45, 46; [0064] providing inner acoustic port 44, in particular by providing a comparatively small acoustical mass of the acoustic port 44; [0065] providing at least one of acoustic resistances 51, 52, 53 in parallel to a respective acoustic port 44, 45, 46, preferably at least acoustic resistance 52 at second housing portion 19 and/or acoustic resistance 53 inside inner volume 5; [0066] providing at least one of acoustic resistances 54, 55, 56 in series to a respective acoustic port 44, 45, 46, preferably at least acoustic resistance 55 at rear port 46 and/or acoustic resistance 56 at inner port 44; [0067] maximizing oscillating area 32 of oscillator element 22, preferably by providing a value of active area 35 of at least 5.Math.10.sup.−5 m.sup.2; [0068] minimizing a mass of oscillator element 22, preferably by providing oscillator element 22 with a value of its mass of at most 30.Math.10.sup.−6 kg; [0069] minimizing a mechanical compliance of suspension member 26, preferably by providing a value of the mechanical compliance of at least 12.Math.10.sup.−3 sec.sup.2/kg; and [0070] minimizing an acoustical mass of sound outlet 17.

[0071] The provision of output impedance 77 in the above described way can account for a desired value of a microphone position acoustic impedance measured at an input of microphone 62. In particular, the microphone position acoustic impedance can be selected such that it has a value of at most 1.Math.10.sup.7 kg/(m.sup.4.Math.sec) at a frequency range between 1000 Hz and 1500 Hz and/or a value of at most 5.Math.10.sup.7 kg/(m.sup.4.Math.sec) at a frequency range of 100 Hz and below. Such an acoustic impedance value at the position of the input of microphone 62 can allow to reduce and/or avoid instabilities of the feedback loop by rendering the acoustic impedance at the feedback origin, at which the microphone input is located, substantially independent from variations of input impedances caused by different ear canal geometries. In particular, a ratio of the microphone position acoustic impedance and the input impedance can thus be substantially kept constant for different ear canals.

[0072] FIG. 3 schematically illustrates a hearing device 101, in accordance with some embodiments of the present disclosure. Corresponding features with respect to previously described embodiments of hearing device 1 are illustrated by the same reference numerals. Hearing device 101 comprises a plurality of resonant members 111, 121. Resonant members 111, 121 are acoustically coupled with first volume portion 6. By acoustically coupling resonant members 111, 121 with inner volume 5, acoustic properties of the acoustic pathway inside inner volume 5 can be modified in a frequency dependent manner. In particular, the output impedance of hearing device 101 can thus be adjusted. The acoustical coupling of resonant members 111, 121 to first volume portion 6 can allow a particular effective lowering of the output impedance of hearing device 101 at the respective frequency range. Resonant members 111, 121 are Helmholtz resonators.

[0073] Resonant members 111, 121 each enclose a cavity 112, 122 and an opening 113, 123 leading to cavity 112, 122. Resonant members 111, 121 can each comprise a vessel enclosing cavity 112, 122. Opening 113, 123 can be formed in the vessel. Opening 113, 123 is smaller as compared to a cross sectional size of cavity 112, 122. The acoustical coupling of resonant members 111, 121 with first volume portion 6 is provided via opening 113, 123. In particular, opening 113, 123 can be provided inside first volume portion 6 and/or adjoin first volume portion 6. Opening 113, 123 can be formed through a tubular member leading from cavity 112, 122, in particular from the vessel enclosing cavity 112, 122, to first volume portion 6. Cavity 112, 122 is filled with a medium adapted to resonate with sound waves. The medium is also provided at opening 113, 123. Part of the medium at opening 113, 123 forms an inertance and the remaining medium inside cavity 112, 122 forms a compliance. The medium inside resonant member 111, 112 is thus configured to vibrate at a resonance frequency when sound waves impinge on opening 113, 123. The resonance frequency depends on the size and shape of cavity 112, 122 and opening 113, 123, and the medium inside.

[0074] Resonant members 111, 121 are provided in front of oscillator element 22, in particular in front of virtual partition 11 comprising oscillator element 22. Resonant members 111, 121 are enclosed by first housing portion 18. Resonant members 111, 121 are arranged between transducer chamber 37 and front chamber 3. At least part of resonant members 111, 121 are configured to resonate with sound waves at a resonance frequency comprised in a frequency range between 1000 Hz and 1500 Hz. Alternatively or additionally, at least part of resonant members 111, 121 are configured to resonate with sound waves at a resonance frequency comprised in a frequency range between 1000 Hz and 1500 Hz. In this way, the output impedance of hearing device 101 can be lowered at the respective frequency range. At least two of resonant members 111, 121 are configured to resonate with sound waves at a different resonance frequency. For instance, a different size and/or shape of cavity 112, 122 and/or opening 113, 123 and/or a different medium inside at least two of resonant members 111, 121 can be provided. Thus, the frequency dependent adjustment of the acoustic properties of the acoustic pathway inside inner volume 5 can be further refined and/or extended over a larger frequency range. The resonant members comprise a first resonant member 111 and a second resonant member 121.

[0075] FIG. 4 schematically illustrates a hearing device 201, in accordance with some embodiments of the present disclosure. Corresponding features with respect to previously described embodiments of hearing devices 1 and 101 are illustrated by the same reference numerals. Resonant members 111, 121 are provided behind oscillator element 22, in particular behind virtual partition 11 comprising oscillator element 22. Resonant members 111, 121 are enclosed by second housing portion 19. Resonant members 111, 121 are arranged between transducer chamber 37 and rear chamber 4. By providing resonant members 111, 121 behind virtual partition 11, space can be saved in front of virtual partition 11. This can allow to provide first housing portion 18 at a rather compact size, in particular such that first housing portion 18 can optimized regarding an ear canal geometry and/or desired acoustical properties of first volume portion 6.

[0076] An acoustic port 211 acoustically couples resonant members 111, 121 with first volume portion 6. Acoustic port 211 is an inner acoustic port extending between first volume portion 6 and second volume portion 7. Acoustic port 211 traverses virtual partition 11. Acoustic port 211 is connected to resonant members 111, 121 at their opening 113, 123. Acoustic port 211 is closed inside second volume portion 7, in particular such that a portion of acoustic port 211 located inside second volume portion 7 is isolated from a remaining portion of second volume portion 7 except for the connection to resonant members 111, 121. Acoustic port 211 comprises an opening leading to first volume portion 6. Acoustic port 211 comprises a tubular member. An acoustic mass of acoustic port 211 can thus be modified by selecting a length and/or a cross sectional size of the tubular member. Another inner acoustic port 244 acoustically couples first volume portion 6 with second volume portion 7. Inner acoustic port 244 substantially corresponds to inner acoustic port 44 described above in the context of hearing devices 1, 101. Inner acoustic port 244 extends in parallel to acoustic port 211.