HEARING SYSTEM HAVING IMPROVED HIGH FREQUENCY RESPONSE

Abstract

The present invention provides hearing systems and methods that provide an improved high frequency response. The high frequency response improves the signal-to-noise ratio of the hearing system and allows for preservation and transmission of high frequency spatial localization cues.

Claims

1. A hearing system comprising: an input transducer configured to capture ambient sound, including high frequency localization cues, and convert the captured sound into electrical signals; and a transmitter assembly configured to receive the electrical signals from the input transducer, the transmitter assembly comprising: a signal processor configured to generate filtered signals from the received electrical signals wherein the signal processor comprises: an analog to digital converter; a digital signal processor and a digital to analog converter, wherein the signal processor has a frequency response bandwidth that is larger than 6.0 kHz; a transmitter and a transmission element, the transmitter assembly configured to deliver both power and filtered signals from the transmitter through a tip of the transmission element to produce mechanical vibrations with an output transducer configured to be positioned on a tympanic membrane of the user, the filtered signals being representative of the ambient sound received by the input transducer; wherein the transmitter assembly comprises: a shell having an outer surface configured to conform to an inner wall surface of an ear canal wherein the shell is positionable at least partially within the ear canal; a coil having an open interior; a ferrite core sized to fit within the open interior; and an open canal through the transducer assembly to allow the ambient sound to pass through the open canal and bypass the transmitter assembly to directly reach the tympanic membrane of the user, wherein the signal processor is configured to amplify the high frequency localization cues when the magnitude of the high frequency localization cues is below a saturation level; wherein the transmitter assembly is configured to decrease current to the signal processor when the magnitude of the localization cues is above the saturation level, and, wherein the ambient sound passing through the open canal provides greater equivalent sound pressure to the eardrum than equivalent sound pressure of the output transducer when the magnitude of the high frequency localization cues is above the saturation level.

2. The hearing system of claim 1, wherein the frequency response bandwidth of the signal processor allows for delivery of high-frequency localization cues in a 7 kHz to 13 kHz range to a middle ear of the user.

3. The hearing system of claim 1, wherein the tip of the transmission element is positioned at a substantially the same distance and orientation relative to the output transducer when the transmitter assembly is positioned, removed, and repositioned within the ear canal.

4. The hearing system of claim 3, wherein the input transducer is positioned adjacent to an entrance of the ear canal of the user.

5. The hearing system of claim 1, wherein the signal processor is configured to be located behind a pinna of the user.

6. The hearing system of claim 1, wherein the signal processor, the transmitter, and the transmission element are configured to be disposed within the ear canal of the user.

7. The hearing system of claim 1, wherein the transmitter and transmission element are configured to be disposed within the ear canal of the user.

8. The hearing system of claim 1, wherein the output transducer comprises a permanent magnet.

9. The hearing system of claim 1, wherein the input transducer is configured to be positioned in an area of a pinna of the user, near an entrance of the ear canal of the user, at an entrance of the ear canal of the user, within the ear canal of the user, or in a temple piece of eyeglasses.

10. The hearing system of claim 1, wherein the input transducer is configured to receive an input sound signal from a sound producing or receiving device comprising a telephone, a cellular telephone, a radio, a digital audio unit, a portable entertainment unit, or other telecommunication and/or entertainment devices.

11. A method comprising: receiving electrical signals with a transmitter assembly positioned to provide an open ear canal, wherein the electrical signals are indicative of the sound captured by an input transducer, the sound including high frequency localization cues; filtering the signals at the transmitter assembly with a signal processor where in the signal processor has a frequency response bandwidth greater than 6.0 kHz, the signal processor comprising: an analog to digital converter; a digital signal processor; and a digital to analog converter; delivering both power and the filtered signals through a tip of a transmission element of the transmitter assembly to produce mechanical vibrations with an output transducer positioned on the tympanic membrane of the user, wherein the transmitter assembly comprises: a shell having an outer surface configured to conform to an inner wall surface of an ear canal wherein the shell is positionable at least partially within the ear canal; a coil having an open interior; a ferrite core sized to fit within the open interior; and an open canal through the transducer assembly to allow the ambient sound to pass through the open canal and bypass the transmitter assembly to directly reach the tympanic membrane of the user, amplifying the filtered signals that comprise the high frequency localization cues when the magnitude of the localization cues is below a saturation level; and switching off the filtered signals when the magnitude of the localization cues is above the saturation level.

12. The method of claim 11, wherein the signal processor has a bandwidth between about 6 kHz and about 20 kHz.

13. The method of claim 11, wherein the transmitter assembly comprises an electromagnetic transmitter and the transmission element, wherein the transmission element is in communication with the signal processor and wherein delivering filtered signals to the tympanic membrane of the user comprises: directing signals from the signal processor to the electromagnetic transmitter; and delivering filtered electromagnetic signals from the electromagnetic transmitter to the tympanic membrane through the transmission element.

14. The method of claim 13, wherein the output transducer is coupled to the tympanic membrane of the user, wherein delivering filtered electromagnetic signals from the electromagnetic transmitter to the middle ear through the transmission element is carried out by delivering the filtered electromagnetic signals to the output transducer which is mechanically vibrated according to the filtered electromagnetic signals.

15. The method of claim 13, wherein the electromagnetic transmitter and the transmission element are positioned in the ear canal and the signal processor is positioned outside of the ear canal.

16. The method of claim 13, wherein the tip of the transmission element is positioned at a substantially the same distance and orientation relative to the output transducer when the transmitter assembly is positioned, removed, and repositioned within the ear canal.

17. The method of claim 11, wherein the input transducer is configured to be positioned in an area of a pinna of the user, near an entrance of the ear canal of the user, at an entrance of the ear canal of the user, within the ear canal of the user, or in a temple piece of eyeglasses.

18. The method of claim 11, wherein the input transducer is configured to receive an input sound signal from a sound producing or receiving device comprising a telephone, a cellular telephone, a radio, a digital audio unit, a portable entertainment unit, or other telecommunication and/or entertainment devices.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a cross-sectional view of a human ear, including an outer ear, middle ear, and part of an inner ear.

[0030] FIG. 2 illustrates an embodiment of the present invention with a transducer coupled to a tympanic membrane.

[0031] FIGS. 3A and 3B illustrate alternative embodiments of the transducer coupled to a malleus.

[0032] FIG. 4A schematically illustrates a hearing system of the present invention that provides an open ear canal so as to allow ambient sound/acoustic signals to directly reach the tympanic membrane.

[0033] FIG. 4B illustrates an alternative embodiment of the hearing system of the present invention with the coil laid along an inner wall of the shell.

[0034] FIG. 5 schematically illustrates a hearing system embodied by the present invention.

[0035] FIG. 6A illustrates a hearing system embodiment having a microphone (input transducer) positioned on an inner surface of a canal shell and a transmitter assembly positioned in an ear canal that is in communication with the transducer that is coupled to the tympanic membrane.

[0036] FIG. 6B illustrates an alternative medial view of the present invention with a microphone in the canal shell wall near the entrance.

[0037] FIG. 7 is a graph that illustrates an acoustic signal that reaches the ear drum and the effective amplified signal at the eardrum and the combined effect of the two.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Referring now to FIG. 1, there is shown a cross sectional view of an outer ear 10, middle ear 12 and a portion of an inner ear 14. The outer ear 10 comprises primarily of the pima 15 and the auditory ear canal 17. The middle ear 12 is bounded by the tympanic membrane (ear drum) 16 on one side, and contains a series of three tiny interconnected bones: the malleus (hammer) 18; the incus (anvil) 20; and the stapes (stirrup) 22. Collectively, these three bones are known as the ossicles or the ossicular chain. The malleus 18 is attached to the tympanic membrane 16 while the stapes 22, the last bone in the ossicular chain, is coupled to the cochlea 24 of the inner ear.

[0039] In normal hearing, sound waves that travel via the outer ear or auditory ear canal 17 strike the tympanic membrane 16 and cause it to vibrate. The malleus 18, being connected to the tympanic membrane 16, is thus also set into motion, along with the incus 20 and the stapes 22. These three bones in the ossicular chain act as a set of impedance matching levers of the tiny mechanical vibrations received by the tympanic membrane. The tympanic membrane 16 and the bones may act as a transmission line system to maximize the bandwidth of the hearing apparatus (Puria and Allen, 1998). The stapes vibrates in turn causing fluid pressure in the vestibule of a spiral structure known as the cochlea 24 (Puria et al. 1997). The fluid pressure results in a traveling wave along the longitudinal axis of the basilar membrane (not shown). The organ of Corti sits atop the basilar membrane which contains the sensory epithelium consisting of one row of inner hair cells and three rows of outer hair cells. The inner-hair cells (not shown) in the cochlea are stimulated by the movement of the basilar membrane. There, hydraulic pressure displaces the inner ear fluid and mechanical energy in the hair cells is transformed into electrical impulses, which are transmitted to neural pathways and the hearing center of the brain (temporal lobe), resulting in the perception of sound. The outer hair cells are believed to amplify and compress the input to the inner hair cells. When there is sensory-neural hearing loss, the outer hair cells are typically damaged, thus reducing the input to the inner hair cells which results in a reduction in the perception of sound. Amplification by a hearing system may fully or partially restore the otherwise normal amplification and compression provided by the outer hair cells.

[0040] A presently preferred coupling point of the output transducer assembly is on the outer surface of the tympanic membrane 16 and is illustrated in FIG. 2. In the illustrated embodiment, the output transducer assembly 26 comprises a transducer 28 that is placed in contact with an exterior surface of the tympanic membrane 10. The transducer 28 generally comprises a high-energy permanent magnet. A preferred method of positioning the transducer is to employ a contact transducer assembly that includes transducer 28 and a support assembly 30. Support assembly 30 is attached to, or floating on, a portion of the tympanic membrane 16. The support assembly is a biocompatible structure with a surface area sufficient to support the transducer 28, and is vibrationally coupled to the tympanic membrane 16.

[0041] Preferably, the surface of support assembly 30 that is attached to the tympanic membrane substantially conforms to the shape of the corresponding surface of the tympanic membrane, particularly the umbo area 32. In one embodiment, the support assembly 30 is a conically shaped film in which the transducer is embedded therein. In such embodiments, the film is releasably contacted with a surface of the tympanic membrane. Alternatively, a surface wetting agent, such as mineral oil, is preferably used to enhance the ability of support assembly 30 to form a weak but sufficient attachment to the tympanic membrane 16 through surface adhesion. One suitable contact transducer assembly is described in U.S. Pat. No. 5,259,032, which was previously incorporated herein by reference.

[0042] FIGS. 3A and 3B illustrate alternative embodiments wherein a transducer is placed on the malleus of an individual. In FIG. 3A, a transducer magnet 40 is attached to the medial side of the inferior manubrium. Preferably, magnet 40 is encased in titanium or other biocompatible material. By way of illustration, one method of attaching magnet 40 to the malleus is disclosed in U.S. Pat. No. 6,084,975, previously incorporated herein by reference, wherein magnet 40 is attached to the medial surface of the manubrium 44 of the malleus 18 by making an incision in the posterior periosteum of the lower manubrium, and elevating the periosteum from the manubrium, thus creating a pocket between the lateral surface of the manubrium and the tympanic membrane 10. One prong of a stainless steel clip device may be placed into the pocket, with the transducer magnet 34 attached thereto. The interior of the clip is of appropriate dimension such that the clip now holds onto the manubrium placing the magnet on its medial surface.

[0043] Alternatively, FIG. 3B illustrates an embodiment wherein clip 36 is secured around the neck of the malleus 18, in between the manubrium and the head 38 of the malleus. In this embodiment, the clip 36 extends to provide a platform of orienting the transducer magnet 34 toward the tympanic membrane 16 and ear canal 17 such that the transducer magnet 34 is in a substantially optimal position to receive signals from the transmitter assembly.

[0044] FIG. 4A illustrates one preferred embodiment of a hearing system 40 encompassed by the present invention. The hearing system 40 comprises the transmitter assembly 42 (illustrated with shell 44 cross-sectioned for clarity) that is installed in a right ear canal and oriented with respect to the magnetic transducer 28 on the tympanic membrane 16. In the preferred embodiment of the current invention, the transducer 28 is positioned against tympanic membrane 16 at umbo area 32. The transducer may also be placed on other acoustic members of the middle ear, including locations on the malleus 18 (shown in FIGS. 3A and 3B), incus 20, and stapes 22. When placed in the umbo area 32 of the tympanic membrane 16, the transducer 28 will be naturally tilted with respect to the ear canal 17. The degree of tilt will vary from individual to individual, but is typically at about a 60-degree angle with respect to the ear canal.

[0045] The transmitter assembly 42 has a shell 44 configured to mate with the characteristics of the individual's ear canal wall. Shell 44 is preferably matched to fit snug in the individual's ear canal so that the transmitter assembly 42 may repeatedly be inserted or removed from the ear canal and still be properly aligned when re-inserted in the individual's ear. In the illustrated embodiment, shell 44 is also configured to support a coil 46 and a core 48 such that the tip of core 48 is positioned at a proper distance and orientation in relation to the transducer 28 when the transmitter assembly 42 is properly installed in the ear canal 17. The core 48 generally comprises ferrite, but may be any material with high magnetic permeability.

[0046] In a preferred embodiment, coil 46 is wrapped around the circumference of the core 48 along part or all of the length of the core. Generally, the coil has a sufficient number of rotations to optimally drive an electromagnetic field toward the transducer 28. The number of rotations may vary depending on the diameter of the coil, the diameter of the core, the length of the core, and the overall acceptable diameter of the coil and core assembly based on the size of the individual's ear canal. Generally, the force applied by the magnetic field on the magnet will increase, and therefore increase the efficiency of the system, with an increase in the diameter of the core. These parameters will be constrained, however, by the anatomical limitations of the individual's ear. The coil 46 may be wrapped around only a portion of the length of the core, as shown in FIG. 4A, allowing the tip of the core to extend further into the ear canal 17, which generally converges as it reaches the tympanic membrane 16.

[0047] One method for matching the shell 44 to the internal dimensions of the ear canal is to make an impression of the ear canal cavity, including the tympanic membrane. A positive investment is then made from the negative impression. The outer surface of the shell is then formed from the positive investment which replicated the external surface of the impression. The coil 46 and core 48 assembly can then be positioned and mounted in the shell 44 according to the desired orientation with respect to the projected placement of the transducer 28, which may be determined from the positive investment of the ear canal and tympanic membrane. In an alternative embodiment, the transmitter assembly 42 may also incorporate a mounting platform (not shown) with micro-adjustment capability for orienting the coil and core assembly such that the core can be oriented and positioned with respect to the shell and/or the coil. In another alternative embodiment, a CT, MM or optical scan may be performed on the individual to generate a 3D model of the ear canal and the tympanic membrane. The digital 3D model representation may then be used to form the outside surface of the shell 44 and mount the core and coil.

[0048] As shown in the embodiment of FIG. 4A, transmitter assembly 42 may also comprise a digital signal processing (DSP) unit and other components 50 and a battery 52 that are placed inside shell 44. The proximal end 53 of the shell 44 is open 54 and has the input transducer (microphone) 56 positioned on the shell so as to directly receive the ambient sound that enters the auditory ear canal 17. The open chamber 58 provides access to the shell 44 and transmitter assembly 42 components contained therein. A pull line 60 may also be incorporated into the shell 44 so that the transmitter assembly can be readily removed from the ear canal.

[0049] Advantageously, in many embodiments, an acoustic opening 62 of the shell allows ambient sound to enter the open chamber 58 of the shell. This allows ambient sound to travel through the open volume 58 along the internal compartment of the transmitter assembly 42 and through one or more openings 64 at the distal end of the shell 44. Thus, ambient sound waves may reach and directly vibrate the tympanic membrane 16 and separately impart vibration on the tympanic membrane. This open-channel design provides a number of substantial benefits. First, the open channel 17 minimizes the occlusive effect prevalent in many acoustic hearing systems from blocking the ear canal. Second, the open channel allows the high frequency spatial localization cues to be directly transmitted to the tympanic membrane 17. Third, the natural ambient sound entering the ear canal 16 allows the electromagnetically driven effective sound level output to be limited or cut off at a much lower level than with a hearing system that blocks the ear canal 17. Finally, having a fully open shell preserves the natural pinna diffraction cues of the subject and thus little to no acclimatization, as described by Hoffman et al. (1998), is required.

[0050] As shown schematically in FIG. 5, in operation, ambient sound entering the auricle and car canal 17 is captured by the microphone 56 that is positioned within the open ear canal 17. The microphone 56 converts sound waves into analog electrical signals for processing by a DSP unit 68 of the transmitter assembly 42. The DSP unit 68 may optionally be coupled to an input amplifier (not shown) to amplify the electrical signal. The DSP unit 68 typically includes an analog-to-digital converter 66 that converts the analog electrical signal to a digital signal. The digital signal is then processed by any number of digital signal processors and filters 68. The processing may comprise of any combination of frequency filters, multi-band compression, noise suppression and noise reduction algorithms. The digitally processed signal is then converted back to analog signal with a digital-to-analog converter 70. The analog signal is shaped and amplified and sent to the coil 46, which generates a modulated electromagnetic field containing audio information representative of the original audio signal and, along with the core 48, directs the electromagnetic field toward the transducer magnet 28. The transducer magnet 28 vibrates in response to the electromagnetic field, thereby vibrating the middle-ear acoustic member to which it is coupled (e.g. the tympanic membrane 16 in FIG. 4A or the malleus 18 in FIGS. 3A and 3B).

[0051] In one preferred embodiment, the transmitter assembly 42 comprises a filter that has a frequency response bandwidth that is typically greater than 6 kHz, more preferably between about 6 kHz and about 20 kHz, and most preferably between about 6 kHz and 13 kHz. Such a transmitter assembly 42 differs from conventional transmitters found in conventional hearing aids in that the higher bandwidth results in greater preservation of spatial localization cues for microphones 56 that are placed at the entrance of the auditory ear canal or within the ear canal 17. The positioning of the microphone 56 and the higher bandwidth filter results in a speech reception threshold improvement of up to 5 dB above existing hearing systems where there are interfering speech sources. Such a significant improvement in SRT, due to central mechanisms, is not possible with existing hearing aids with limited bandwidth, limited gain and sound processing without pinna diffraction cues.

[0052] For most hearing-impaired subjects, sound reproduction at higher decibel ranges is not necessary because their natural hearing mechanisms are still capable of receiving sound in that range. To those familiar in the art, this is commonly referred to as the recruitment phenomena where the loudness perception of a hearing impaired subject “catches up” with the loudness perception of a normal hearing person at loud sounds (Moore, 1998). Thus, the open-channel device may be configured to switch off, or saturate, at levels where natural acoustic hearing takes over. This can greatly reduce the currents required to drive the transmitter assembly, allowing for smaller batteries and/or longer battery life. A large opening is not possible in acoustic hearing aids because of the increase in feedback and thus limiting the functional gain of the device. In the electromagnetically driven devices of the present invention, acoustic feedback is significantly reduced because the tympanic membrane is directly vibrated. This direct vibration ultimately results in generation of sound in the ear canal because the tympanic membrane acts as a loudspeaker cone. However, the level of generated acoustic energy is significantly less than in conventional hearing aids that generate direct acoustic energy in the ear canal. This results in much greater functional gain for the open ear canal electromagnetic transmitter and transducer than with conventional acoustic hearing aids.

[0053] Because the input transducer (e.g., microphone) is positioned in the ear canal, the microphone is able to receive and retransmit the high-frequency three dimensional spatial cues. If the microphone was not positioned within the auditory ear canal, (for example, if the microphone is placed behind-the ear (BTE)), then the signal reaching its microphone does not carry the spatially dependent pinna cues. Thus there is little chance for there to be spatial information.

[0054] FIG. 4B illustrates an alternative embodiment of a transmitter assembly 42 wherein the microphone 56 is positioned near the opening of the ear canal on shell 44 and the coil 46 is laid on the inner walls of the shell 44. The core 62 is positioned within the inner diameter of the coil 46 and may be attached to either the shell 44 or the coil 46. In this embodiment, ambient sound may still enter ear canal and pass through the open chamber 58 and out the ports 68 to directly vibrate the tympanic membrane 16.

[0055] Now referring to FIGS. 6A and 6B, an alternative embodiment is illustrated wherein one or more of the DSP unit 50 and battery 52 are located external to the auditory ear canal in a driver unit 70. Driver unit 70 may hook on to the top end of the pinna 15 via ear hook 72. This configuration provides additional clearance for the open chamber 58 of shell 44 (FIG. 4B), and also allows for inclusion of components that would not otherwise fit in the ear canal of the individual. In such embodiments, it is still preferable to have the microphone 56 located in or at the opening of the ear canal 17 to gain benefit of high bandwidth spatial localization cues from the auricle 17. As shown in FIGS. 6A and 6B, sound entering the ear canal 17 is captured by microphone 56. The signal is then sent to the DSP unit 50 located in the driver unit 70 for processing via an input wire in cable 74 connected to jack 76 in shell 44. Once the signal is processed by the DSP unit 50, the signal is delivered to the coil 46 by an output wire passing back through cable 74.

[0056] FIG. 7 is a graph that illustrates the effective output sound pressure level (SPL) versus the input sound pressure level. As shown in the graph, since the hearing systems 40 of the present invention provide an open auditory ear canal 17, ambient sound is able to be directly transmitted through the auditory ear canal and directly onto the tympanic membrane 17. As shown in the graph, the line labeled “acoustic” shows the acoustic signal that directly reaches the tympanic membrane through the open ear canal. The line labeled “amplified” illustrates the signal that is directed to the tympanic membrane through the hearing system of the present invention. Below the input knee level L.sub.k, the output increases linearly. Above input saturation level L.sub.s, the amplified output signal is limited and no longer increases with increasing input level. Between input levels L.sub.k and L.sub.s, the output maybe be compressed, as shown. The line labeled “Combined Acoustic+Amplified” illustrates the combined effect of both the acoustic signal and the amplified signal. Note that despite the fact that the output of the amplified system is saturated above L.sub.s, the combined effect is that effective sound input continues to increase due to the acoustic input from the open canal.

[0057] The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the following claims and their equivalents.