Hearing aid

Abstract: A hearing aid is disclosed in which outside sound collected by a microphone (3) is amplified and radiated from an earphone unit (2) so as to be conducted to the user's external auditory meatus (A). An acoustic tube (1) is of an inside diameter (W) approximately equal to that (Wo) of the user's external auditory meatus (A) and has one end (1 a ) provided as a section for attachment to the user's auricle (D) and the other end (1 b ) arranged as a reflectionless terminal. The earphone unit (2) is mounted on the peripheral surface of the acoustic tube (1) with the sound radiating surface facing the inside of the tube (1).

Description: The invention relates to a hearing aid. A hearing aid is so designed that external sounds, such as voice sounds, are converted by a microphone into electrical signals which are amplified by an amplifier and supplied to an earphone after correction of frequency characteristics thereof in accordance with the characteristics of the user's auditory sense, and the thus corrected voice output is supplied from the earphone to the user's external auditory meatus. Conventionally, hearing aids have been of a two unit kind comprising a main body provided with a microphone unit and an earphone section separate from the main body. However, such hearing aids are not popular because they are difficult to handle and are very conspicuous in use. Recently, with miniaturisation of components, brought about with progress in production technology, a unitary hearing aid, in which a microphone unit, an earphone unit, an amplifier and a storage battery are all accommodated in a single main body, has become available. In general, a hearing aid is attached to the user's auricle, with the earphone stopping up the external auditory meatus. The user of the hearing aid may hear the sound output emanating from the attached earphone unit by such sound output reaching the tympanic membrane by way of the external auditory meatus and vibrating the tympanic membrane. Since the conventional hearing aid is attached to the user's auricle, with the earphone stopping up the external auditory meatus, the sound signal reaching the user's tympanic membrane is reflected thereat to return to the earphone unit by way of the external auditory meatus and is reflected again by the diaphragm or the housing of the earphone unit to proceed again towards the tympanic membrane. In this manner, both sound directly emanating from the earphone unit and sound emanating from the earphone unit and reflected by the tympanic membrane and the earphone unit reach the tympanic membrane. With such a conventional hearing aid, in which both sound directly emanating from the earphone unit and reflected sound reach the user's tympanic membrane, the user may be fatigued as he feels oppressed or as if the sound source were located within his or her own head. In addition, because of the presence of the reflected sound, it is difficult to carry out a suitable correcting operation for the voice output by an electrical circuit. A unitary type hearing aid is also liable to howling and unstable operation, because the microphone unit and the earphone unit are mounted close to each other. Outside noise also tends to be intrusive and render it difficult for the user to hear the desired sound. Patent Specification US-A-4 354 065 discloses a miniature hearing aid having an acoustic tube one end of which can be engaged in the user's auditory canal, a microphone, an earphone and an amplifier to amplify signals from the microphone and supply them to the earphone for reconversion into acoustic signals and supply, through the acoustic tube, to the user's auditory canal. According to the invention there is provided a hearing aid comprising: an acoustic tube having an inside diameter approximately equal to the inside diameter of the user's external auditory meatus, and having one end thereof provided as a section for attachment to the user's auricle; a microphone unit to convert outside sound into electrical signals; an earphone unit; and an amplifier to amplify electrical signals outputted from the microphone unit and to supply the amplified signals to the earphone unit; characterised in that the other end of the acoustic tube is provided as a terminal where sound reflection is precluded; the earphone unit is mounted on the peripheral surface of the acoustic tube with its sound radiating surface facing the inside of the acoustic tube; the acoustic tube presents a constant acoustic impedance; and the sound radiating surface of the earphone unit is flush with the inner surface of the acoustic tube. With such a hearing aid, voice output may be corrected in accordance with characteristics of the user's auditory sense. Not only can the hearing aid avoid the feeling to the user of being oppressed or as if the sound source were located within the user's own head but the microphone unit and the earphone unit can be mounted close to each other but still obtain a sufficient howling margin to provide for stable operation. The outside voice sound is converted by the microphone unit into electrical signals which are amplified by the amplifier and supplied to the earphone unit. The earphone unit transmits the voice output corresponding to these electrical signals, and hence to the outside voice signal, to the external auditory meatus by way of the acoustic tube. Since the acoustic tube is of an inside diameter approximately equal to the external auditory meatus it can function as an acoustic duct having the same acoustic impedance as that of the external acoustic meatus. By providing the acoustic tube with one end formed as an attachment section to attach the hearing aid at the user's auricle and the other end as the terminal free from sound reflection, there is no risk that sound once reflected by the tympanic membrane will again be reflected towards the tympanic membrane. Voice output from the earphone unit is transmitted to the external auditory meatus by way of the acoustic tube, so that the voice output from the earphone unit reaches the tympanic membrane by way of an acoustic duct having a constant acoustic impedance. Since there is no risk that the sound once reflected by the tympanic membrane will be reflected at the terminal of the acoustic tube to be again transmitted to the external auditory meatus, the user will feel that the sound source is at a fixed position without feeling oppressed or as if the sound source were within his or her own head. Thus a hearing aid according to the invention can be stable in acoustic characteristics and free from sound reflection, because the acoustic tube can be attached at the user's auricle in a constant state at all times by means of the attachment section at one end of the tube and functions as an acoustic duct having the same acoustic impedance as that of the external acoustic meatus. The voice output may be corrected in accordance with characteristics of the user's auditory sense by adjusting the amplifier characteristics. In addition, since the earphone unit is mounted within the inside of the acoustic tube, the hearing aid is of the unitary type capable of performing a stable operation with an enlarged howling margin, in which outside noise may hardly be intrusive and solely desired sound may be heard easily. The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which:- Figure 1 is a block diagram showing the basic structure of a hearing aid according to the invention, with an annexed electrical circuit; and Figure 2 is a perspective view showing a hearing aid according to the invention. Referring to the drawings, a hearing aid has a main body 10 including an acoustic tube 1, an earphone unit 2 attached to the peripheral surface of the acoustic tube 1 with a sound radiating surface 2 a thereof facing the inside of the tube 1, a microphone unit 3 to convert external sound into electrical signals, and an amplifier 4 to amplify electrical signals outputted from the microphone unit 3 and to supply the amplified signals to the earphone unit 2. The main body 10 of the hearing aid is also provided with a variable resistance 5 variably to set the characteristics of the amplifier 4 to adjust the sound quality, an operating knob 5a for the variable resistance 5, a battery 6 as a driving electrical source, a power source switch 7 and an operating knob 7 a for the switch 7. Referring to Figure 2, the acoustic tube 1 may be flexed along the contour of an auricle D so as to function as an ear hanger led out from the main body 10 which is located behind the auricle D. As shown in Figure 1, the acoustic tube 1 has a uniform inside diameter W approximately equal to the inside diameter W₀ of the external auditory meatus A. The acoustic tube 1 is in the form of an elongate tube having the uniform inside diameter W, one open end 1 a of which is provided with an attachment section 8 for attachment to the auricle D and the other open end 1 b of which is formed as a terminal where sound reflection is precluded. The attachment section 8 for attachment to the auricle D is formed as a flexible piece of synthetic resin material having an end section of small thickness which is inserted into and attached to an entrance C of the external auditory meatus A. The inside diameter W₁ of the attachment section 8 is selected to be equal to the inside diameter W of the auditory tube 1, that is, approximately equal to the inside diameter W₀ of the external auditory meatus A. The earphone unit 2 is mounted on the acoustic tube 1 with its sound radiating surface 2 a substantially flush with the inner peripheral surface of the tube 1 and facing the inside of the tube 1. With the sound radiating surface 2 a substantially flush with the inner peripheral surface of the acoustic tube 1, the earphone unit 2 is mounted on the acoustic tube 1 without the risk of disturbing the acoustic impedance characteristics of the acoustic tube 1. With the acoustic tube 1 mounted in position and with the foremost part of the attachment section 8 introduced into the entrance C to the external auditory meatus A, the acoustic tube 1 provides a sound duct having a substantially constant inside diameter from a tympanic membrane B in the external auditory meatus A to the other open end 1 b as the reflectionless terminal of the acoustic tube 1 and thus exhibiting a constant acoustic impedance. Thus voice output from the earphone unit 2 is not reflected when propagated towards the external auditory meatus A by way of the acoustic tube 1, while the sound reflected back at the tympanic membrane B is also not reflected when propagated from the external acoustic meatus A towards the acoustic tube 1. In addition, since the other open end 1 b of the acoustic tube 1 is formed as the terminal where sound reflection is precluded, there is no possibility that voice output propagated from the earphone unit 2 towards the acoustic tube 1 or the reflected sound propagated from the external auditory meatus A will be reflected at the other open end 1 b . Hence, there is no possibility that sound reflected at the tympanic membrane B will be reflected back at the earphone unit 2 to be propagated back towards the external auditory meatus A. With the above described hearing aid, since the reflected sound at the tympanic membrane B is not again reflected at the earphone unit 2 so as to be propagated back towards the external auditory meatus A, the sense of location of the sound source may be clearer, such that the user is free from fatigue or oppression or the sense of a stationary sound source caused by sound reflection. On the other hand, extremely stable acoustic characteristics may be achieved since the acoustic tube 1 is attached to the user's auricle D in the same state at all times by means of the attachment section 8 functioning as the sound duct having the same acoustic impedance as that of the external acoustic meatus A. Besides, since no sound reflection occurs, as mentioned previously, the voice output may be suitably corrected in accordance with the acoustic characteristics of the user's auditory sense by operating the variable resistance 5 so as variably to set the characteristics of the amplifier 4 and thereby suitably adjusting the sound quality. The earphone unit 2 is arranged within the inside of the acoustic tube 1 to improve howling margin and ensure stable operation. On the other hand, the desired sound may be heard more easily, inasmuch as sound from outside can hardly intrude and a wider dynamic range may be achieved.

Claims: A hearing aid comprising: an acoustic tube (1) having an inside diameter (W) approximately equal to the inside diameter (W₀) of the user's external auditory meatus (A), and having one end (1 a ) thereof provided as a section for attachment to the user's auricle (D); a microphone unit (3) to convert outside sound into electrical signals; an earphone unit (2); and an amplifier (4) to amplify electrical signals outputted from the microphone unit (3) and to supply the amplified signals to the earphone unit (2); characterised in that the other end (1 b ) of the acoustic tube (1) is provided as a terminal where sound reflection is precluded; the earphone unit (2) is mounted on the peripheral surface of the acoustic tube (1) with its sound radiating surface (2 a ) facing the inside of the acoustic tube (1); the acoustic tube (1) presents a constant acoustic impedance; and the sound radiating surface (2 a ) of the earphone unit (2) is flush with the inner surface of the acoustic tube (1). A hearing aid according to claim 1 wherein the inside diameter (W) of the acoustic tube (1) is substantially uniform from the attachment section end (1 a ) to the reflectionless terminal end (1 b ). A hearing aid according to claim 1 or claim 2, wherein the amplifier (4) may be adjusted from outside to vary its amplification factor. A hearing aid according to anyone of claims 1 to 3, wherein the acoustic tube (1) is flexible.

Inventors: IIDA YASUHIRO C O PATENTS DIVI, INANAGA KIYOFUMI C O PATENTS D, MIURA MASAYOSHI C O PATENTS DI, SOGAWA KIROYUKI C O PATENTS DI, IIDA, YASUHIRO, C/O PATENTS DIVISON, INANAGA, KIYOFUMI, C/O PATENTS DIVISON, MIURA, MASAYOSHI, C/O PATENTS DIVISON, SOGAWA, KIROYUKI, C/O PATENTS DIVISON
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: H04R25
IPC codes: A45C13, H04R25, H04R1