WO2011050862A1

WO2011050862A1 - Hearing system comprising an earpiece

Info

Publication number: WO2011050862A1
Application number: PCT/EP2009/064472
Authority: WO
Inventors: Gerard Palix; Patric Dissard
Original assignee: Phonak Ag
Priority date: 2009-11-02
Filing date: 2009-11-02
Publication date: 2011-05-05

Abstract

The invention relates to a hearing system, comprising at least one earpiece (10, 12) to be worn at least partly in a user's ear canal, comprising a shell (22) and an insert unit (24, 124), the shell comprising an inwardly oriented sound tube portion (44) and an outwardly oriented interface portion (40) comprising a receptacle (42) for detachably receiving the insert unit, wherein the insert unit is a filter unit (124) comprising at least one sound attenuation filter (170) or an active electronic unit (24) comprising at least a loudspeaker (30), wherein the interface portion is provided with a laterally projecting holding element (70) extending around the receptacle and wherein an elastic membrane element (72) is stretched over the holding element in a manner so as to cover the receptacle and the insert unit in a liquid-tight manner.

Description

Hearing system comprising an earpiece

The invention relates to a hearing system including an earpiece comprising a shell and an insert unit detachably connected to the shell.

Such a system may be used for wireless communication with other persons, if the insert uni t is an active electronic unit which is connected via a cable to an external electronic unit. Typically, the communication is bi-directional, with the active unit then comprising at least one microphone for capturing the user's voice. The external electronic unit typically comprises a mobile phone or a radio device. The external audio signals received by the external communication device are supplied to the loudspeaker of the active unit, and the audio signals captured by the microphone(s) of the active unit are transmitted to a corresponding wireless communication device used by another person. In addition to the communication function, the hearing system may provide for a hearing protection function, which requires an appropriate design of the earpiece which has to act as a hearing protection earplug. In this case, for enabling a noise level dependent dynamic hearing protection function, the active unit may be provided with a microphone for capturing ambient sound, and the external unit may be provided with an appropriate audio signal processing unit which supplies the processed ambient audio signals to the loudspeaker of the active unit. There are also cases in which the system comprises only the dynamic hearing protection function but not a bi-directional communication function. In the most simple case, for realizing a passive hearing protection function, the insert unit comprises at least one acoustic attenuation filter, but no electronic components. By selecting different filters, the attenuation may be individually adjusted to some extent.

-The shell of the earpiece, in particular if a hearing protection function is desired, may be manufactured as a customized shell having a shape which is adapted to the individual shape of the user's ear, usually by manufacturing the shell according to an impression taken from the user's ear. Customized shells provide for optimal retention within the user's ear and for optimized acoustic sealing. While customized earpieces may provide for improved retention and sealing properties compared to generic earpieces (i.e. earpieces having a standard shape), manufacturing of customized earpieces is more complicated, in particular because it involves participation of the user for taking an impression of the user's ear.

Examples of customized earpieces for hearing protection systems comprising bidirectional communication functions are found in EP 1 674 059 Al, WO 2007/082579 A2 and US 6,661,901 Bl . An example for an active hearing protection system without bidirectional communication function is described in EP 1 071 307 Al . Further examples of earpiece communication systems are found in WO 2009/047369 A2.

It is known, for example, from DE 297 18 483 Ul, EP 1 448 014 Bl, WO 2007/014950 A2 or WO 2007/147416 Al, to provide hearing aids to be worn at least partly in the ear canal with an elastic C-shaped bow-like element for improving retention of the shell in the ear canal, wherein the retention force is provided by the elastic deformation of the retention element which engages with the concha when worn by the user. US 2006/0067556 Al relates to an earpiece comprising a bow-like retention element and a sound channel, which may be connected in a releasable manner with an acoustic device which may be a hearing aid or a wireless communication device. The wireless communication device may form a wireless headset for a mobile phone.

EP 1 364 553 Bl relates to an earpiece comprising an elastic concha bow and a sound channel as well as a microphone and a loudspeaker which are connected via a cord with an external audios signal processing unit for realizing a headset for wireless communication. EP 1 377 1 13 Al relates to a headset comprising an earpiece which carries a boom microphone and comprises an elastic concha bow.

EP 0 310 866 Al relates to a hearing aid, wherein the sound inlet opening and the sound outlet opening are covered by a micro-porous PTFE-membrane in order to prevent humidity from entering the interior of the hearing aid. DE 11 2006 000 463 T5 relates to a water-proof hearing aid, wherein the sound inlet opening and the sound outlet opening are covered by a water-proof PUR-film. Similar hearing aids are known from DE 102 14 189 Al and from US 2007/0086611 Al . It is an object of the invention to provide for a hearing system comprising an earpiece comprising a shell with a receptacle for detachably receiving an insert unit, wherein the insert unit is to be protected from environmental impact, such as cerumen, water, sweat and dust, without significantly deteriorating sound quality. According to the invention, these objects are achieved by a hearing system as defined in claim 1. The invention is beneficial in that, by providing the interface portion with a laterally projecting holding element extending around the receptacle and by stretching an elastic membrane element over the holding element, the receptacle and the insert unit can be easily covered in a liquid-tight manner once the insert unit has been inserted into the receptacle, while the sound quality is not compromised too much.

Preferred embodiments of the invention are mentioned in the dependent claims.

Hereinafter, examples of the invention will be illustrated by reference to the attached drawings, wherein:

Fig. 1 is a block diagram of the most relevant electronic components of an embodiment of a system according to the invention;

Fig. 2 is a perspective view of an example of an earpiece according to the invention;

Figs. 3A and 3B are a perspective view of the earpiece of Fig. 2 seen at a different angle, wherein the earpiece is shown prior to and after connecting at to an active unit, respectively, without a membrane element of the invention being shown; Fig. 4 is a side view of the earpiece of Fig. 2;

Fig. 5 is a top view of the earpiece of Fig. 2;

Fig. 6 is a view of the earpiece of Fig. 3B when worn by a user;

Fig. 7 is perspective view of a pair of earpieces for the right ear and the left ear, respectively;

Fig. 8 is a schematic view of an earpiece of the invention which acts as a passive hearing protection device; Figs. 9A and 9B are a perspective view of the miiTor-symmetrical variant of the earpiece of Fig. 2 seen at a different angle, when connected to an active unit like in Fig, 3B, wherein the earpiece is shown with a membrane element prior to and after fixation at the shell, respectively; Fig. 10 is a sectional view of the sound tube portion of the earpiece of Fig. 2; and

Fig. 11 is a perspective view of an example of a protective filter to fixed at the end of the sound tube portion.

The hearing system shown in Fig. 1 comprises a left ear earpiece 10, a right ear earpiece 12, an external electronic unit 15 and an active electronic unit 24 for each of the earpieces 10, 12. Each earpiece 10, 12 comprises a shell 22 which has a receptacle 42 into which the active unit 24 is inserted in a releasable manner. The shell 22 is provided with a sound channel 26 through which the active unit 24 is acoustically connected to the ear canal. The active unit 24 comprises a first microphone 28 for capturing audio signals from ambient sound and a loudspeaker 30 for providing audio signals into the user's ear canal via the sound channel 26. One of the active units 24 also may comprise a second microphone 31 for capturing the user's voice. Alternatively, one of the active units 24 may be provided with a boom microphone 16 carried by a an elastic bow 68. An elongate elastic retention element 23 is fixed at the shell 22. It is to be noted that the representation of the earpieces 10, 12 in Fig. 1 is not representative of the actual geometry of the earpieces 10, 12 (which is rather shown in Figs. 2 to 1 1) The external unit 15 comprises a wireless communication device 20, such as a mobile phone or a radio device, and a central unit 14 which may be worn at the user's body, e.g. by a loop 32 around the user's neck. The central unit 14 comprises an audio signal processing unit 34 for receiving in processing the audio signals captured by the microphones 28, 31 and for supplying the loudspeaker 30 with audio signals to be reproduced to the user's ear. To this end, the active unit 24 is connected to the central unit 14 via cable connections 36. The processed audio signals are supplied to the wireless communication device 20 via a cable connection 37 in order to be transmitted to a wireless communication device used by another person. In the other hand, audio signals received from such other wireless communication device by the device 20 are supplied via the cable connection 37 to the central unit 14 in order to be reproduced by the loudspeaker 30.

The boom microphone may be omitted if the central unit 14 is capable of performing blind source separation (BSS) on the audio signals provided by the microphones 28, 31 in order to separate the user's voice from background noise. To this end, each microphone 28 has to be acoustically oriented towards ambient in order to capture primarily ambient sound, and the microphone 31 has to be acoustically oriented towards the ear canal in order to capture primarily the user's voice.

Preferably the earpiece 10, 12 are designed to provide for a hearing protection function, wherein a sound attenuation of at least 10 dB averaged over the audible frequency range should be provided. In this case, the microphones 28, the central unit 14 and the loudspeakers 30 may be used to provide for an active hearing protection function, wherein, depending on the noise level, sound captured by the microphone 28 is supplied into the user's ear canal via the central unit 14, the loudspeaker 30 and the sound channel 26. For example, if the ambient noise level is low, ambient sound captured by the microphone 28 may be supplied by the loudspeaker 30 at a close to natural level in order to enable direct communication with a person speaking to the user of the hearing system despite wearing the hearing protection earpieces 10, 12.

While a combination of an active hearing protection function and a wireless communication function may be preferred, the system may be modified in such a manner that only the active hearing protection function is realized (in this case the wireless communication device 20 and the microphones 31 and the boom microphone 16 would be omitted) or that only the wireless communication function may be realized (in this case the earpieces 10, 12 need not to provide for a significant acoustic attenuation). When realizing a communication function without hearing protection, one of the two earpieces, 10 12 may be omitted.

The system of Fig. 1 may comprise a remote control 18 and or a push-to-talk (P I T) button (not shown). The system of Fig. 1 may realize a passive hearing protection function rather than an active hearing protection function. In this case no ambient sound would be reproduced via the speaker 30. Rather, the active unit 24 then may include at least one (passive) acoustic attenuation filter (not shown) which may be exchangeable in order to adjust the acoustic attenuation provided by the earpiece 10, 12.

In Fig. 8 a passive hearing protection system is shown which does not include any electronic components. In this case the active unit 24 of Fig. 1 is replaced by an insert unit 124 comprising at least one passive acoustic attenuation filter 170 which preferably is exchangeable in order to individually adjust the attenuation provided by the earpiece 10, 12. An example of an earpiece 10, 12 according to the invention is shown in Figs. 2 to 11.

The shell 22 has a standard shape, i.e. the shape is not specifically adapted to the individual shape of the user's ear, and comprises an outwardly oriented interface portion 40 comprising a receptacle 42 for detachably receiving the active unit 24, a sound tube portion 44 for carrying a soft tip 46 which is to be inserted into the user's ear canal, and an engagement portion 48 located between the sound tube portion 44 and the interface portion 40 for engaging with the tragus/antitragus region of the user's ear. Preferably the shell 22 is made of a thermoplast .

The retention element 23 is connected to the engagement portion 48 in a releasable manner. The retention element 23 preferably is provided in two different sizes, wherein the user may select the most appropriate one of the two sizes. The retention element 23 may be changed or removed for cleaning purposes at any time; typically it has a lifetime of several months. Preferably, the retention element 23 is made of a material having a hardness of 60 Shore A to 90 Shore A. According to the example shown in the Figures, the retention element 23 is substantially straight and has a constant cross section with a tapered end. It extends substantially perpendicular with regard to the axial direction of the sound tube portion 44 and substantially tangential with regard to the interface portion 40 and is located below the upper end 50 of the interface portion 40 (see in particular Fig. 4). In general, the material and the dimensions of the retention element 23 are selected such that the retention element 23 can be brought into engagement with the user's concha and helix area by manual deformation by the user, wherein the retention element 23 is bent according to the shape of the user's ear (see Fig. 6).

The soft tip 46 may be made of foam or of silicone (see Fig. 2). The soft tip 46 is exchangeable so that it can be changed at any time (typically, the foam tip has a lifetime of some days or weeks, whereas the silicone tip has a lifetime of several months); the silicone tip may be removed for cleaning purposes. The soft tip 46 preferably is provided in three different sizes, wherein the user may select the most appropriate size in order to achieve a high fit rate. The soft tip 46 allows the earpiece 10, 12 to be positioned in such a manner in the concha that it does not extend out of the pinna. The sound tube portion 44 preferably has a length of 4 to 7 mm and is substantially straight. As shown in Fig. 4, it may be provided with beads 66 for promote retention of the soft tip 46 on the sound tube portion 44. For achieving enhanced wearing comfort, the sound tube portion 44 may be bendable, i.e. flexible with regard to bending forces, i.e. forces acting in a direction perpendicular to the axial direction of the sound tube portion 44, but it is substantially rigid along its axial direction. The sound tube portion 44 also may twistable around ist longitudinal axis to some extent.

As can be best seen in Fig. 5, the sound tube portion 44 is laterally offset with regard to the interface portion 40 in two dimensions, i.e. both with regard to the longitudinal and the transverse direction of the interface portion 40. By "laterally offset" it is meant that, when seen as a projection along the axial direction of the sound tube portion, the sound tube portion 44 is displaced with regard to any symmetry axis of the interface portion 40; in particular, the sound tube portion 44 is located "ouside" the interface portion 40 in the view of Fig. 5. The arrangement of the sound tube portion 44 with regard to the interface portion 40 is excentric and asymmetric. The receptacle 42 has a substantially cup-like shape with a flat upper rim 50. It extends substantially perpendicular to the axial direction of the sound tube portion 44.

As can be best seen in Fig. 5, the cross section of the receptacle 42 in a plane perpendicular to the sound tube portion 44 has a substantially pear-like shape, wherein the "elongate" end 52 of the receptacle 42 is adjacent to the engagement portion 48. The outer contour of the interface portion essentially corresponds to the shape of the receptacle and likewise has a pear-like shape. Preferably, the width of the interface portion 40 is from 8 to 14 mm, while the length of the interface portion 40 is from 13 to 20 mm. The interface portion 40 is "flat" in the sense that the dimension along the axial direction of the sound tube portion 44 is smaller than the dimension along a direction perpendicular thereto. As can be seen in Fig. 4, the dimension along the axial direction of the sound tube portion 44, i.e. the "height", preferably is about 8 to 12 mm.

The active unit 24 comprises two spring clips 56 for detachable engagement with corresponding mating structures 58 provided within the receptacle 42. In the example shown in Figs. 3 A, 3B and 6 the active unit comprises a boom microphone 16 carried by a bow 68.

The sound channel 26 extends from the elongate end 52 of the receptacle 42 through the engagement portion 48 and the sound tube portion 44 to a sound outlet opening 54 at the end of the sound tube portion 44. The engagement portion 48 connects the interface portion 40 and the sound tube portion 44 and it has substantially a knee-like shape with a bead-like ridge portion 60 which projects in a direction perpendicular to the axial direction of the sound tube portion 44. The ridge portion extends like a helicoidal spiral starting from the upper end of the sound tube portion 44 and terminating in an end portion 62 which is oriented substantially tangential with regard to the interface portion 40. The end portion 62 of the ridge portion 60 is adapted to detachably connect with the retention element 23. The ridge portion 60 partly surrounds the sound channel and the elongate end 52 of the receptacle 42.

The "top", i.e. the rounded edge indicated at 64 in Fig. 4, of the ridge portion 60 preferably is located 4 to 7 mm below the upper end 50 of the interface portion 40 and at a distance of 3 to 6 mm from that end of the interface portion 40 which is closer to the sound tube portion 44.

As can be best seen in Fig. 7, the geometry of the earpiece 10 for the left ear and the earpiece 12 for the right ear is mirror symmetrical.

Retention of the earpiece within the concha is particularly promoted by the following features: The engagement portion comprises a bead-like ridge portion which projects in a direction perpendicular to the sound tube portion; the ridge portion extends like a helicoidal spiral starting from the sound tube portion and terminating in an end portion which is oriented substantially tangential with regard to the interface portion and substantially perpendicular with regard to the axial direction of the sound tube portion, wherein the end portion of the ridge portion is adapted to detachably connect with the retention element in such a manner that the retention element extends substantially perpendicular to the axial direction of the sound tube portion and substantially tangential with regard to the interface portion; - the sound tube portion is flexible with regard to bending forces; the sound tube portion is laterally offset with regard to the interface portion; the interface portion extends substantially perpendicular to the sound tube portion; the cross section of the interface portion in a plane perpendicular to the sound tube portion has a substantially pear-like shape; - the specific dimensions of the earpiece: the top of the ridge portion is located 4 to 7 mm below the upper end of the interface portion, the top of the ridge portion is located at a distance of 3 to 6 mm from that end of the interface portion which is closer to the sound tube portion, the width of the interface portion is from 8 to 14 mm, the length of the interface portion is from 13 to 20 mm, the sound tube portion has an axial length of 4 to 7 mm.

The upper/outer end of the interface portion 40 is provided with a laterally projecting holding element 70 extending around, i.e. surrounding, the receptacle 42. In the example, the holding element is designed is a rounded rib or bead and forms a substantially flat trajectory, i.e. the holding element 70 is extends substantially within a single plane. In the example, the holding element 70 forms the flat upper rim of the interface portion 40 and has a rounded, namely substantially oval, trajectory/contour. The holding element 70 is provided for fixing a membrane element 72 at the shell 22, which serves to provide for preferably liquid-tight sealing/coverage of the receptacle 42 and the respective insert unit 24, 124 received in the receptacle 42.

In Figs. 9A and 9B an example is shown wherein an active electronic unit 24 has been inserted into the receptacle 42 in the manner shown in Figs. 3 A and 3B (however, the active unit 24 of Figs. 9A and 9B does not comprise a boom microphone 16 and hence has no elastic bow 68). The cable 36 of the active unit 24 is provided with membrane element 72, with the cable 36 passing through a cylindrical feed-through sleeve 74 of the membrane element 72 which serves to guide the membrane element 72 along the cable 36. Preferably, the cylindrical sleeve 74 provides for liquid-tight sealing with regard to the cable 36.

The membrane element 72 is pre-shaped into a dome-like shape, with the cylindrical portion extending substantially perpendicular to the dome portion 78. The membrane element 72 is made of an elastic water-resistant material, such as silicone, having a thickness of preferably 0.2 to 0.5 mm and having an elasticity of preferably 25 to 35 Shore A. Alternatively, only the outer side of the membrane element 72 may be water-resistant. The membrane element 72 has a ring-like reinforced base portion 76 which may have a bead-like shape and which may be made of the same material as the dome portion 78 but having a larger thickness.

In Fig. 9A the situation is shown after the active unit 24 has been fixed in the receptacle 42. The membrane element 72 is moved along the cable 36 towards the shell 22. Then the base portion 76 of the membrane element 72 is - usually manually - forced over the holding element 70 and remains, due to elastic forces, in a position slightly below/beyond the holding element 70 (see Fig. 9B) in a liquid tight manner, thereby fixing the membrane element 72 at the shell 22. Thus, the base portion 76 engages with the holding element in a liquid-tight manner. The dome portion 78 extends over the active unit 24 and the outer opening of the receptacle 42, whereby the active unit and the receptacle 42 are protected from ingress of water and/or dust. Typically, the active unit 24 extends beyond the outer end of the receptacle 42 (see Figs. 9A and 9B). The membrane unit 72 is shaped such that the dome portion 78 rests at the outwardly oriented surface of the active unit 24, which surface may comprises an opening 80 for the outwardly oriented ambient microphone 28. Thereby the membrane element 72 is placed close to the microphone, so that sound pick-up quality is not significantly deteriorated.

The sound tube portion 44 comprises a sound channel 26, the inner end of which is protected by a hydrophobic filter element 82 which is received in a corresponding receptacle 84. Typically, the filter element 82 has a circular shape and comprises a ring-like frame 86 for being fixed within the receptacle 84 and a screen-like element 88 surrounded by the frame 86. The screen-like element 82 may be made of a polymer, such as a fluorpolymer. For example, the screen-like element 82 may be made of Sefar Hydrophob V-07-15/9 having a thickness of 0.15 mm and an opening percentage of about 9% (i.e. the area fraction of the openings is about 9%).

The filter element 82 serves to protect the sound channel 26, and in particular also the speaker of the active unit 24 (not shown), from environmental impact like cerumen, sweat and dust.

The sound channel 26 comprises a portion having a relatively small diameter, preferably less than 1 mm, in order to reduce the ingress of liquids, such as water, towards the active unit 24, see Fig. 10. The volume between the loudspeaker and the screen-like element 82 should be as small as possible. The length of the sound channel 26 may be, for example 3.9 mm.

The above-described design of the earpiece 10, 12 with regard to protection of the active unit 24 by the membrane element 72 and the filter element 82 are applicable also of a sound attenuation filter 170 is inserted into the receptacle 42 rather than an active unit 24.

Claims

1. A hearing system, comprising at least one earpiece (10, 12) to be worn at least partly in a user's ear canal, comprising a shell (22) and an insert unit (24, 124), the shell comprising an inwardly oriented sound tube portion (44) and an outwardly oriented interface portion (40) comprising a receptacle (42) for detachably receiving the insert unit, wherein the insert unit is a filter unit (124) comprising at least one sound attenuation filter (170) or an active electronic unit (24) comprising at least a loudspeaker (30), wherein the interface portion is provided with a laterally projecting holding element (70) extending around the receptacle and wherein an elastic membrane element (72) is stretched over the holding element in a manner so as to cover the receptacle and the insert unit in a liquid-tight manner.

2. The hearing system of claim 1, wherein the holding element (70) is designed is a rounded rib.

3. The hearing system of claim 2, wherein the holding element (70) forms a flat trajectory around the receptacle (42).

4. The hearing system of claim 3, wherein the holding element (70) forms a flat upper rim of the interface portion (40).

5. The hearing system of one of the preceding claims, wherein the holding element (70) forms a rounded trajectory.

6. The hearing system of claim 5, wherein the holding element (70) forms a substantially oval trajectory.

7. The hearing system of one of the preceding claims, wherein the membrane element (729 is pre-shaped into a dome-like shape.

8. The hearing system of claim 7, wherein the membrane element (72) has a ring-like reinforced base portion (76).

9. The hearing system of claim 8, wherein the base portion (76) has a bead-like shape.

10. The hearing system of one of claims 8 and 9, wherein the base portion (76) engages with the holding element (70) so as to fix the membrane element (72) at the shell (22).

11. The hearing system of one of claims 7 to 10, wherein the insert unit (24, 124) extends beyond the outer end of the receptacle (42).

12. The hearing system of claim 11, wherein the insert unit (24) comprises an outwardly oriented ambient microphone (28).

13. The hearing system of one of the preceding claims, wherein the membrane element (72) is made of silicone.

14. The hearing system of one of the preceding claims, wherein the material of the membrane element (72) has a thickness of 0.2 to 0.5 mm.

15. The hearing system of one of the preceding claims, wherein the membrane element (72) has an elasticity of 25 to 35 Shore A.

16. The hearing system of one of the preceding claims, wherein the outer side of the membrane element (72) is water-resistant.

17. The hearing system of one of the preceding claims, wherein the sound tube portion (44) comprises a sound channel (26), the inner end of which is protected by a hydrophobic filter element (82).

18. The hearing system of claim 17, wherein the sound tube portion (44) comprises a receptacle (84) for receiving the filter element (82).

19. The hearing system of one of claims 17 and 18, wherein the filter element (82) has a circular shape.

20. The hearing system of claim 19, wherein the filter element (82) comprises a ring-like frame (86) for being fixed within the receptacle (84).

21. The hearing system of one of claims 17 to 20, wherein the filter element (82) comprises a screen-like element (88).

22. The hearing system of claim 21, wherein the screen-like element (88) is made of a polymer, such as a fluorpolymer.

23. The hearing system of one of claims 21 and 22, wherein the screen-like element (88) has an opening percentage of about 9%.

24. The hearing system of one of the preceding claims, wherein the sound channel (26) of the sound tube portion (44) comprises a portion having a diameter of less than 1 mm.

25. The hearing system of one of the preceding claims, further comprising an external electronic unit (15, 34, 20) which is to be worn at the user's body below the user's neck and which is connected to the active electronic unit (24) via a connection cable (36), wherein the membrane element (72) comprises a feed-through sleeve (74) for the connection cable.

26. The system of claim 25, wherein the active unit (24) comprises an ambient microphone (28) for capturing ambient sound and wherein the external unit (15) comprises an audio signal processing unit (34) for processing the audio signals captured by the ambient microphone (28) in order to supply the processed audio signals to the loudspeaker (30) of the active unit (24) for realizing a sound level dependent active hearing protection function.

27. The system of one of claims 25 and 26, wherein the external unit (15) comprises a wireless communication device (20), such a mobile phone or a radio device, for exchanging audio signals with another wireless communication device.

28. A use of a hearing system of one of the preceding claims, wherein the insert unit (24, 124) is inserted into the receptacle (42) of the interface portion (40) and wherein the membrane element (72) is fixed at the interface portion by elastically forcing a base portion (76) of the membrane element over the holding element (70).