WO2014177214A1

WO2014177214A1 - Hearing instrument comprising an ear canal microphone with active control loop

Info

Publication number: WO2014177214A1
Application number: PCT/EP2013/059143
Authority: WO
Inventors: Roland Hug; Thomas Zurbruegg; Alfred Stirnemann; Christoph Leist; Jonas Meyer
Original assignee: Phonak Ag
Priority date: 2013-05-02
Filing date: 2013-05-02
Publication date: 2014-11-06

Abstract

The invention relates to a hearing instrument comprising: an earpiece (32) to be worn at least in part in a user's ear canal and comprising a shell (34), a loudspeaker (16) arranged within the shell for directing sound via a sound outlet channel (20) into a residual volume (18) of the ear canal, and an ear canal microphone (22) for capturing an ear canal audio signal from sound within the residual volume of the ear canal via a cavity (24) of the shell comprising at least one opening (40, 50) towards the residual volume of the ear canal; means (12) for generating an input audio signal; a compensator unit (26, 28, 30) for adding a compensation audio signal derived from the ear canal audio signal to the input audio signal in order to generate an output audio signal supplied to the loudspeaker in a manner so as to reduce or avoid an ear canal occlusion effect, with the loudspeaker, the ear canal microphone and the compensator unit forming an active control loop, wherein the cavity, including the at least one opening, is designed so as to act as an acoustic low pass filter having a cut-off frequency in the range from 0.2 kHz to 6 kHz.

Description

Hearing instrument comprising an ear canal microphone with active control loop

The invention relates to a hearing instrument comprising an earpiece including a loudspeaker for directing sound into a residual volume of the ear canal and an ear canal microphone for capturing a an ear canal audio signal from sound within the residual volume of the ear canal, and a compensator unit for adding a compensation audio signal derived from the ear canal audio signal to an input audio signal in order to generate an output audio signal supplied to the loudspeaker in a manner so as to reduce or to avoid an ear canal occlusion effect, with the loudspeaker, the ear canal microphone and the compensator unit forming an active control loop. An example of a hearing instrument using an active control loop for reducing ear canal occlusion is described in US 2008/0075310 Al, wherein the earpiece is provided with a double-channel tube projecting into the residual volume between the earpiece and the eardrum, which tube provides both for acoustic coupling of the loudspeaker and acoustic coupling of the ear canal microphone to the residual volume. US 2006/0239485 Al relates to an ITE (In-the-ear) hearing instrument comprising an ear canal microphone acoustically coupled to the residual volume of the ear canal, wherein a cerumen protection system is provided extending from the loudspeaker to the surface of the plastic mould of the earpiece, with the canal microphone being arranged in the cerumen protection system. US 2006/0120545 Al relates to another example of a hearing instrument using an active control loop including an ear canal microphone for reducing ear canal occlusion effects caused by the earpiece, wherein, however, no details concerning the structural design of the earpiece are described.

WO 98/47318 Al relates to a ITE hearing instrument wherein a Helmholtz resonator rather than an active control loop is used for reducing ear canal occlusion effects.

It is an object of the invention to provide for a hearing instrument utilizing an active control loop for reducing ear canal occlusion effects, wherein the active control loop should implemented in a simple, reliable and flexible manner.

According to the invention, this object is achieved by a hearing instrument as defined in claim 1. The invention is beneficial in that, by coupling the ear canal microphone via a cavity comprising at least one opening to the residual volume of the ear canal, wherein the cavity is designed so as to act as an acoustic low pass filter having a cut-off frequency in the range from 0.2 kHz to 6 kHz, the compensator unit can be simplified due to the fact that at least part of the filter function in the active control loop is shifted from the electronic part to the acoustic/mechanical part, the reliability of the operation of the ear canal microphone can be enhanced (for example compared to the design of US 2008/0075310 Al wherein a narrow tube is used for coupling the ear canal microphone to the residual volume), and the flexibility with regard to custom specific filter design and microphone positioning within the ear piece can be increased.

Preferably, the cavity is sized and shaped so as to act as a first order acoustic low pass filter, wherein the opening of the cavity or at least one of the openings of the cavity is provided with an acoustic resistor.

Further preferred embodiments are defined in the dependent claims.

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

Fig, 1 is a block diagram of the audio signal processing in an example of a hearing instrument according to the invention;

Fig. 2 is a schematic longitudinal sectional view of an earpiece of a hearing instrument when inserted into the ear canal, with also the audio signal processing being shown schematically;

Fig. 3 is a schematic representation of an acoustic filter of the ear canal microphone of Fig. 2 when implemented as a first order acoustic low pass filter;

Fig. 4 is an illustration of the electrical analogy of the acoustic filter of Fig. 3;

Fig. 5 is a longitudinal sectional view of the proximal end of an example of an earpiece of a hearing instrument according to the invention when inserted into an ear canal;

Figs. 6A to 6C are a front views of variants of the earpiece of the example of Fig. 5;

Fig. 7 is a view like Fig. 5 wherein an alternative example of the acoustic filter cavity is shown; and Fig.8 is a diagram of showing the required volume of a cavity of a first order acoustic low pass having a cut-off frequency of 1 kHz as a function of the acoustic resistance.

In Fig. 1 a block diagram of the audio signal processing in an example of a hearing instrument according to the invention is shown schematically; in Fig. 2 a schemtic example of the mechanical strcuture of such hearing instrument is shown.

According to the example of Figs. 1 and 2, the hearing instrument 10 comprises a microphone arrangement 12 which is acoustically oriented towards ambiance for capturing audio signals from ambient sound, an audio signal processing unit 14 for processing the audio signals captured by the microphone arrangement 12 and a loudspeaker 16 for directing, via a sound outlet canal 20, sound into a residual volume 18 of the ear canal formed between the proximal end (in sense of the end closer to the center of the body) of a shell 34 of an earpiece 32 and the eardrum 42. The hearing instrument 10 comprises an ear canal microphone 22 for capturing an ear canal audio signal from sound within the residual volume 18 via a cavity 24 and a compensator unit 26 comprising an electrical compensator filter 28 for filtering ear canal audio signal captured by the ear canal microphone 22 in order to obtain a compensation audio signal and an adder 30 for adding the compensation audio signal to the input audio signal provided by the microphone arrangement 12 and the audio signal processing unit 14.

Both the sound outlet channel 20 and the cavity 24, which serve to acoustically couple the loudspeaker 16 and the microphone 22, respectively, to the residual volume 18, act as an acoustic compensator filter. The loudspeaker 16, the ear canal microphone 22 and the compensator unit 26 form an active control loop (via the acoustic filters 20, 24 and the residual volume 18) in a manner so as to reduce or avoid an ear canal occlusion effect caused by the presence of the earpiece 32 in the ear canal. The shell 34 houses at least the loudspeaker 16 and the ear canal microphone 22, with the acoustic filters 20 and 24 likewise forming part of the earpiece 32.

The outlet opening of the sound outlet channel 20 typically will be covered by a cerumen protector 38.

It is to be understood that the loudspeaker 16 and the ear canal microphone 22 are connected to the respective signal processing circuitry via digital-to-analog converters (indicated at 36 in Fig. 2). The cavity 24 comprises at least one opening 40 towards residual volume 18 and is shaped and sized so to act as an acoustic low pass filter having a cut-off frequency in the range from 0.2 kHz to 6 kHz. Thereby the electrical compensator filter 28 of the compensator unit 26 may be simplified, since at least part of the filtering function required in the active control loop is taking over by the cavity 24.

Preferably, the cavity 24 is shaped and sized so as to act as a first order acoustic low pass filter. To this end, the opening 40 of the cavity 24 may be provided with an acoustic resistor 44 which may be formed , for example, by a cerumen protector; alternatively a cerumen protector 46 may be provided in addition to the acoustic resistor 44, as indicated in Fig. 3 and 4, in which case the cerumen protector 46 will act as an acoustic resistor in addition to the acoustic resistor 44. According to one example, the cerumen protector 46 of the cavity 24 may form part of a combined cerumen protector 48 including a part 38 acting as a cerumen protector for the loudspeaker outlet canal 20, as indicated in Fig. 2. Alternatively, each of the outlet canal 20 and the opening 40 of the cavity 24 may be provided with a separate cerumen protector 38, 46 respectively.

By selecting a cut-off frequency in the range from 0.2 kHz to 6 kHz the probability of a potential overload of the ear canal microphone 22 can be reduced at frequencies which the hearing instrument provides for the highest amplification of sound (which typically is a range of2 to 6 kHz). For a given cut-off frequency of a first order low pass filter the required acoustic resistance of resistor 44 is a function of the volume of the cavity 24 (or vice versa; an example of such function is given in Fig. 8 which shows the required volume for a 1 kHz low pass filter as a function of the acoustic damper resistance).

Preferably, the resistance of the acoustic resistor 44 is in the range from 100*10⁵ kg*sec/m⁴ to 10.000* 10³ kg* sec/m⁴. The higher the resistance value, the lower the impact of blocking, typically by ear wax, on the acoustic low pass filter will be. As can be seen from Fig. 8, the volume of the ear canal microphone (which typically is around 10 mm³) will be significantly smaller than the required volume of the cavity 24 for implementing a 1 kHz low pass filter, so that the microphone load (input impedance) usually will not be relevant. However, if a larger microphone is selected, the input impedance of the microphone has to be taken into account with regard to the acoustic low pass filter. According to Fig. 4 the acoustic resistor 44 (and eventually the cerumen protector 46) in the electrical analogy act as electrical resistors R, while the volume of the cavity 34 acts as a capacitor C, with the pressure in the residual volume 18 of the ear canal acting as a voltage.

Preferably, the dimension of the cavity 24 in the direction towards the residual volume 18 is smaller than the dimension of the cavity 24 in the direction perpendicular to that direction. For example, the cavity 24 may have a spherical, cuboid (i.e. the shape of a rectangular parallel epiped) or cylindrical shape.

For example, the cavity 24 may have a circular cylindrical shape, wherein the length of the cylinder is from 1/3 to 3 times of the diameter of the cylinder. For example, the length of the cylinder may be from 8 to 15 mm, and the diameter of the cylinder may be from 5 to 7 mm.

In case that the cavity has a cuboid shape, the lengths a, b, c of the three sides may be connected by the relationship a* α = ^β= ο*γ, wherein a, /?and yare from 1/3 to 3.

In Fig. 5 an example is shown wherein the cavity 24 at least partially encloses the sound outlet channel 20 in the transversal/radial direction of the sound outlet channel 20 (see also Fig. 6). The opening 40 of the cavity 24 at least partially surrounds the proximal end of the sound outlet channel which is provided with a cerumen protector 38.

According to the example of Fig. 6A the sound outlet channel 20 is tubular, with the cavity 24 surrounding the sound outlet channel 20 as a concentric cylinder. In the example of Fig. 6A the opening 40 of the cavity 24 is circular and completely surrounds the cerumen protector 38 of the sound outlet channel 20. One benefit of such spread-out design of the opening 40 of the cavity 24 is the effect that blocking of a certain, even relatively large, area of the proximal end of the shell 34 by ear wax would not result in complete blocking of the opening of the cavity 24. In the example of Fig. 6A the opening 40 has a flower-like shape, but also other shapes are possible; examples of such variants are shown in Figs. 6B and 6C. It is also to be understood that the opening 40 does not necessarily have to completely surround the cerumen protector 38 without interruptions.

Generally, in case that the cavity 24 comprises a plurality of openings or the opening has a shape extending through a relatively large area of proximal end of the shell 34, the acoustic properties of the cavity 24 are less dependant on blocking of part of the opening(s) (i.e. blocking of one of the openings or part of the single opening has less severe impact than blocking of a single small opening), so that the active feedback loop works in an more reliable manner, and problems with λ/4 resonances in the ear canal (which may result at certain frequencies in destructive interference of the signal at the the entrance of the microphone volume) may be reduced (in case that the microphone has a plurality of entrances such resonances are less pronounced). An alternative embodiment of the cavity 24 is shown in Fig. 7, wherein the cavity 24 is provided with two openings: a first opening 40 which is provided close to the proximal end of the sound outlet channel 20, which may be provided with a combined cerumen protector 48 acting also for the opening 40 or with two separate cerumen protectors, and a second opening 50 which connects the cavity 24 to a vent 52 of the ear piece 32. In the example of Fig. 7, each of the openings 40, 50 is provided with an acoustic resistor 44, 54 respectively.

In all embodiments the shape of the cavity 24 and the position of the ear canal microphone 22 may be determined as a function of the individual shape of the ear canal of the user. In addition, the outer shape of the shell 35 is preferably determined according to the individual shape of the ear canal. To this end, the shell 34 preferably is produced by an RSM (rapid shell moulding) process, wherein a three dimensional model of the user's ear canal is computed from an optically scanned impression of the ear canal.

According to one embodiment, the hearing instrument 10 may be designed as an ITE hearing aid, wherein the earpiece 32 also includes the microphone arrangement 12, the audio signal processing unit 14 and the compensator unit 26. According to an alternative embodiment, the hearing instrument may be designed as a BTE (behind-the-ear) hearing aid comprising a BTE unit including the microphone arrangement 12, the audio signal processing unit 14 and the compensator unit 26.

Claims

1. A hearing instrument comprising: an earpiece (32) to be worn at least in part in a user's ear canal and comprising a shell (34), a loudspeaker (16) arranged within the shell for directing sound via a sound outlet channel (20) into a residual volume (18) of the ear canal, and an ear canal microphone (22) for capturing an ear canal audio signal from sound within the residual volume of the ear canal via a cavity (24) of the shell comprising at least one opening (40, 50) towards the residual volume of the ear canal; means (12) for generating an input audio signal; a compensator unit (26, 28, 30) for adding a compensation audio signal derived from the ear canal audio signal to the input audio signal in order to generate an output audio signal supplied to the loudspeaker in a manner so as to reduce or avoid an ear canal occlusion effect, with the loudspeaker, the ear canal microphone and the compensator unit forming an active control loop, wherein the cavity, including the at least one opening, is designed so as to act as an acoustic low pass filter having a cut-off frequency in the range from 0.2 kHz to 6 kHz.

2. The hearing instrument of claim 1 , wherein the opening (40) of the cavity or at least one (50) of the openings of the cavity is provided with an acoustic resistor (44, 54), and wherein the cavity (24) is shaped and sized so as to act, together with the resistor, as first order acoustic low pass filter.

3. The hearing instrument of claim 2, wherein the resistance of the acoustic resistor (44, 54) is from 100*10⁵ kg * s / m⁴ to 10,000 *10⁵ kg * s / m⁴.

4. The hearing instrument of one of the preceding claims, wherein the dimension of the cavity (24) in the direction towards the residual volume (18) of the ear canal is smaller than the dimension of the cavity in the direction perpendicular to said direction towards the residual volume of the ear canal.

5. The hearing instrument of claim 4, wherein the cavity (24) has a spheric, cuboid or cylindric shape.

6. The hearing instrument of claim 5, wherein the cavity (24) has a circular cylindric shape, wherein the length of the cylinder is from 1/3 to 3 times of the diameter of the cylinder.

7. The hearing instrument of one of the preceding claims, wherein the cavity (24) comprises at least two openings (40, 50) towards the residual volume (18) of the ear canal.

8. The hearing instrument of claim 7, wherein at least one of the openings (40, 50) of the cavity towards the residual volume (18) of the ear canal is provided with a cerumen protector (46, 48).

9. The hearing instrument of claim 8, wherein the cerumen protector (48) is a combined cerumen protector for also covering the end of the sound outlet channel (20).

10. The hearing instrument of claim 8, wherein the end of the sound outlet channel (20) is provided with a separate cerumen protector (38).

11. The hearing instrument of one of the preceding claims, wherein the cavity (24) at least partially encloses the sound outlet channel (20) in the transversal direction of the sound outlet channel.

12. The hearing instrument of claim 11, wherein the opening (40) of the cavity (24) or at least one of the openings of the cavity at least partially surrounds the end of the sound outlet channel (20).

13. The hearing instrument of claim 12, wherein the opening(s) (40) of the cavity (24) surround(s) a cerumen protector (38) positioned in the end of the sound outlet channel (20).

14. The hearing instrument of one of claims 1 1 to 13, wherein the sound outlet channel (20) is tubular, and wherein the cavity (24) surrounds the sound outlet channel as a concentric cylinder.

15. The hearing instrument of one of the preceding claims, wherein at least one of the openings (50) of the cavity (24) connects the cavity to a vent (52) of the earpiece (32).

16. The hearing instrument of one of the preceding claims, wherein the means for generating an input audio signal comprises a microphone arrangement (12) including at least one microphone acoustically oriented towards ambience and an audio signal processing unit (14) for processing the audio signals captured by the microphone arrangement.

17. The hearing instrument of claim 16, wherein the earpiece (32) forms an ITE hearing instrument, and wherein the microphone arrangement (12), the audio signal processing unit (14) and the compensator unit (26) form part of the earpiece.

18. The hearing instrument of claim 16, wherein the hearing instrument comprises a BTE unit including the microphone arrangement (12), the audio signal processing unit (14) and the compensator unit (26).

19. A method of manufacturing a hearing instrument of one of the preceding claims, wherein the shape of the cavity (24) and the position of the ear canal microphone (22) are determined as a function of the individual shape of the ear canal of the user.

20. The method of claim 19, wherein the outer shape of the shell (34) is determined according to the individual shape of the ear canal of the user.

21. The method of one of claims 19 and 20, wherein the shell (34) is produced by an RSM process.