Hearing aid device

[57] ABSTRACT

The present invention relates to a hearing aid device having a sound receiving transducer with an acoustic inlet in the form of a relatively narrow aperture and means for locating said sound receiving transducer in a position relatively to the head of the user with the acoustic inlet being located substantially at a zone of the ear where increased sound pressure is built up in response to sound signals received. The signals from the signal receiving transducer are through suitable adjustable amplification means routed to the other ear and processed in a sound reproducing transducer from which the sound signals are supplied to the other ear.

Claims, 7 Drawing Figures

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PATENTED JAN 2 21974

3,787,643

SHEET 1 OF 2

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ATTORNEY

PATENTEDJAN22I974

3,787,643

SHEET 2 OF 2

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INVENTOR

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ATTORNEY

3,787,643

HEARING AID DEVICE

This is a continuation of application Ser. No. 882,150, filed on Dec. 4, 1969 now abandoned.

The present invention relates to a hearing aid device having a sound receiving transducer and a sound reproducing transducer of which the sound receiving transducer is supported adjacent one ear of the user of the device, and the sound reproducing transducer is adapted to be supported adjacent the other ear of the user. The two transducers are connected through suitable adjustable amplification means.

In devices of the kind here briefly referred to, the acoustic signals which are received in the first mentioned transducer are routed to the other side of the head and supplied to the opposite ear.

BACKGROUND OF THE INVENTION

Hearing aid devices of the kind referred to hereinbefore have specifically been developed for individuals with uni-lateral hearing impairment. Though it has been found that an individual with substantially normal hearing for speech in one ear and with usable residual hearing for speech in the other ear can benefit from a hearing aid in one ear with reduced hearing, in the following referred to as the bad ear, this is not always the case.

Various studies have shown that the main reason for the disadvantages encountered by individuals with unilateral hearing impairment is due to the “shadoweffect” of the head with respect to sound received from a source closest to the bad ear. This sound will undergo attenuation before reaching the other ear, in the following referred to as the good ear, not only with respect to amplitude, but also with respect to the frequency spectrum of the sound.

The result is that an individual with impaired hearing on one ear will receive sound signals such as speech directed to the bad ear in the good ear in more or less attenuated and distorted condition and with the good ear capable of receiving other sounds such as background noises which are not attenuated and distorted, the sound signal received from the side of the bad ear, will be dominated by the background noise which enters the good ear.

As a result of these studies a system has been developed, now internationally known as CROS, which stands for Contralateral Routing of Offside Signals. The basic idea of this system is to provide the individual with a hearing aid having a sound pick up at the bad ear and feeding the sound into the good offside ear adequately amplified so as to be mixed in correct proportion with the sound received naturally in the good ear. Experimental evidence has shown that this system appears to be the best known feasible solution to help individuals with uni-lateral hearing where the impaired ear has substantially reduced hearing for speech.

In reducing the CROS system to practice, various suggestions have been made, all of which include the mounting of a sound pick-up or microphone adjacent the bad ear and a transmission line across the head, for example through the front frame of a pair of spectacles, to a sound reproducer with an outlet into what is mostly suggested to be a skeleton type or open earmould which is able to pass the sound signals received directly to the good ear and in addition feeds the amplified sound from the reproducer into the ear and with an amplifier conveniently located.

In addition scientifical investigations have shown that in response to sound signals received in the human ear an increased sound pressure is built up in the exterior ear at various zones which depend on the anatomic individualities. This increased sound pressure is normally largest in the ear canal, but a substantially increased sound pressure is also built up at the entrance to the ear canal behind tragus in the concha cavity.

It is the purpose of the invention to provide a hearing aid device which utilizes the principles of the CROS system and takes advantages of the scientifical investigations here mentioned.

SUMMARY OF THE INVENTION

The improvement according to the invention is substantially to be seen therein that the sound receiving transducer is provided with an acoustic probe in the form of a tubular member with a relatively narrow aperture which is connected with positioning means for the sound receiving transducer in such a manner that when the hearing aid device is placed in position of use the aperture of the probe will be located in the concha cavity from where it can easily be pushed into the ear canal, if so desired.

By this location of the entrance to the probe the increased sound pressure at these zones is utilized with the result that an amplification which may be between 6 and 20 decibel is obtained. In addition, however, a plurality of other advantages are obtained which are not obvious.

The location of the entrance to the probe where an increased sound pressure is built up results in corresponding less necessity for electrical amplification and thereby less battery costs in the use of the apparatus and less distortion.

The sound pressure at the entrance to the probe is increased mostly in that frequency range which is important for the understanding of speech, i.e., in the frequency range between 1500 and 3500 cycles in which individuals with reduced hearing suffer most.

The apparatus according to the invention improves, therefore the frequency characteristic with respect to speech. Though no scientifical explanation of this phenomenon has been found, the reason is believed to be that the sound signals are processed in the human ear before they reach the ear drum. By locating the entrance to the probe in the ear where this processing has taken place before the signals enter the probe, the anatomy of the ear is utilized and the signals which reach the off-side ear are already processed with respect to the frequency range.

In addition, the sensibility to wind noise is completely eliminated. Wind noise is a phenomenon which bothers most individuals with reduced hearing using hearing aid because at outdoor use the wind noise mixes with the other signals and forms a highly disturbing background noise.

The sound pressure built up at the locations mentioned has been found to be largest in response to sound signals received from the front, i.e., within an azimuth of substantially 45° on each side of a vertical plane symmetrically through the head. This represents for an individual using a hearing aid device according to the invention an improved way of determining the direction from which the sound comes which for many individuals with impaired hearing has been difficult.

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As apparent from the foregoing summary of the invention individuals with uni-lateral hearing impairment will be able to benefit substantially from the improvements. It would be believed, however, that individuals with substantially the same amount of reduced hearing on both ears using a hearing aid device according to the invention would have their sense of direction substantially distorted. This has surprisingly not been found to be the case. The reason which cannot be scientifically explained, may, however, be due to the fact that the increased sound pressure at the entrance to the probe which is connected with the sound receiving transducer, especially when the probe extends into the ear canal, results in an increased effect on the ear drum of the ear in question, because the probe partly fills out the ear canal and thereby prevents the increased pressure to escape.

The invention will be described in the following with reference to the accompanying drawing in which

FIG. 1 is a side view of a human ear,

FIG. 2 is a cross section of a human ear,

FIG. 3 is a perspective view of a hearing aid apparatus according to the invention in one embodiment,

FIG. 4 is a schematic view of an apparatus according to the invention,

FIG. 5 is a cross section of the human ear in similarity with FIG. 2 illustrating an ear mould for insertion in the exterior ear,

FIG. 6 is the ear mould shown in FIG. 5 in side view, and

FIG. 7 is a curve illustrating the increased sound pressure by apparatus according to the invention compared with apparatus in which the entrance to the sound receiving transducer is located at the side of the head of the user.

In FIGS. 1 and 2 a human ear is illustrated. The exterior part of the ear outside the head which is normally referred to as the auricle, is designated by 0. In the cross section of FIG. 2 the ear canal is designated by M and the ear drum by D. The other parts of the ear are not illustrated, in as far as these parts are without importance for the present invention. In the auricle a projection C is found which normally is known as tragus and which extends in the front of the entrance to the ear canal. In the auricle a cavity referred to by CH is found which extends behind the tragus and is known as the concha cavity.

Scientific investigations have shown that sound waves which hit the head result in the building up of an increased sound pressure in the ear canal as well as in the concha cavity, especially for frequencies between 1500 and 3500 cycles, which is the frequency range which especially is of importance for the understanding of speech. The magnitude of this increased sound pressure is different for different individuals, but can at a point B in the ear canal as shown in FIG. 2, be up to 20 decibel and may at a point A as shown in FIG. 1 behind tragus in the concha cavity vary between 6 and 10 decibel and even more.

The invention makes use of this discovery by providing an acoustic entrance for the sound receiving transducer which is located at one ear in the form of a probe having a narrow entrance which is located at or near one or the other of the points A and B in FIGS. 1 and 2. The result is that the sound enters the acoustic entrance with an increased sound pressure which prevails at the points in question whereby an amplification with out any costs is obtained. Due to the fact that the entrance to the probe is located at a point in the ear where the sound signals have been processed according to the anatomy of the ear, the frequency characteristic of the signals which are supplied to the sound receiving transducer, is improved in comparison with signals received in a transducer located on the exterior of the head outside the ear.

This is further illustrated by means of FIG. 7 which shows the increased sound pressure as a function of the frequency. The curve A of FIG. 7 illustrates the sound increase for an apparatus according to the invention in . which the entrance of the probe is located in the ear canal. The curve B illustrates the sound increased in an apparatus in which the transducer is located on the outside of the head. The sound increase according to the invention corresponds to the hatched area between the two curves. As apparent the curve A has a peak within the frequency area between 1500 and 3500 cycles. The two curves correspond to sound coming in substantially at an angle of 45°.

In reducing the invention to practice, various possibilities can be found.

In the embodiment of FIG. 3 the hearing aid device comprises two casings 10 and 12 of the behind-the-eartype. The two casings are arcuate, and each provided with ducts 14 and 16, respectively, in the form of hooks, by means of which the casings are kept in position behind the ear. The sound receiving transducer is located in the casing 10 and communicates with the hook 14 which has an open end adapted to communicate with an open end of a portion 18 of the probe which has a transverse portion 20 at such a location that when the casing 10 is supported in correct position behind the ear the narrow aperture at the end of the probe portion 20 will be located in the concha cavity and can easily be pushed into the ear canal if desired.

In a similar manner the other casing 12 has a hook 16 which is connected with the probe structure 22, 24 of which the extension 24 will be located in the concha cavity when the casing 12 is brough into working position behind the ear.

In the embodiment shown in FIG. 3, the amplification means and the sound reproducing transducer is supposed to be located in the casing 12 together with a battery. The connection between the sound receiving transducer and the amplifier is in the form of an electric cable 26 which extends between the two casings.

The device of FIG. 3 can without any cosmetic disadvantage be used by a lady who wears her hair sufficiently long to hide the casings and enables the electric wire to be hidden in the hair also.

It would be appreciated that the amplifier may instead of being mounted in the casing 12 be mounted in the casing 10 and that the dimensions of the casing which only contains a transducer may be substantially reduced compared with the casing in which an amplifier is enclosed.

In the embodiment of FIG. 4 the apparatus according to the invention is in the form of a pair of hearing aid spectacles having a front frame 28 and a pair of temple members 30 and 32, respectively. In the embodiment illustrated the sound receiving transducer is supposed to be located in the temple 32. As usual in hearing ai spectacles a stub is provided in communication with the transducer enclosed in the temple and as shown in FIG. 4 the sound receiving probe 18, 20 is adapted to

3,787,643 be mounted on the stud which communicates acoustically with the sound receiving transducer.

In a corresponding manner the sound reproducing transducer is in communication with a stud which extends from the temple 30 and on which one end of the tubular duct 22, 24 is mounted. In addition the temple 30 contains the battery and amplifier, but the manner in which these parts are designed and mounted in the temple will not be further described, because it is well known to those skilled in the art.

In order to fix the acoustic ducts in predetermined relationship relatively to the exterior ear, modifications are possible in which the ducts extend to an ear mould and have the aperture in the ear mould or at the end of a tubular duct which extends through the ear mould.

In the case of such embodiment it will be necessary to provide at the ear at which the sound receiving transducer is located a so-called open ear mould which has an aperture through which the sound can enter substantially unobstructed into the concha cavity and the ear canal and from there into the inlet to the probe which is connected with the sound receiving transducer.

In FIGS. 5 and 6 the open ear mould is designated by 34. The ear mould is produced in traditional manner by making an impression of the user’s ear. The open ear mould is also known in the field of hearing aid as a skeleton type ear mould and has a skeleton or frame 38 with a main portion 36 which is adapted to be received in the various grooves of the outer ear so as to locate the ear mould in position relatively to the ear. The main portion or body portion 36 is provided with an aperture 40 which, when the ear mould is placed in operative position, communicates with the concha cavity. In the neighbourhood of the aperture 40 a further aperture 42 is provided which communicates with the acoustic duct 44 which at the receiving ear is communicating with the sound receiving transducer and at the offside ear communicates with the sound reproducing transducer.

It will be obvious that with respect to people having uni-lateral hearing impairment using the CROS system also an open ear mould should be used in the ear adjacent which the sound reproducing transducer is located so as to enable this ear to receive a proper mixture of amplified signals from the sound receiving transducer and natural signals coming into the ear with substantially normal hearing.

As indicated in dotted lines in FIG. 5 it will be possible to extend the acoustic duct 44 with an extension 46 which, when the ear mould is placed in operative position, extends into the ear canal.

As mentioned hereinbefore, an electrical connection must be provided between the sound receiving transducer and the sound reproducing transducer. In the embodiment of FIG. 4 this electrical connection can be in the form of an electrical wire which extends through the front frame 28 of the hearing aid spectacles.

It will be understood that it will be possible within the scope of the invention when using an ear mould to avoid a separate casing for the sound receiving transducer which can be enclosed in the ear mould.

When using an apparatus according to the invention by an individual having uni-lateral hearing impairment it will be obvious that the sound receiving transducer must be located at the ear with reduced hearing and that at the other offside ear the acoustic inlet must be so provided that the amplified signals mix with the nat ural sound signals coming into that ear and that therefore, if an ear mould is used it must be of the open type.

It will be appreciated that the invention is not limited to the embodiments illustrated in the drawing and described hereinbefore. It is immaterial whether the amplifier is mounted in the casing where the sound receiving transducer is mounted or in the other casing. It may also be possible to locate parts of the amplifier in one of the casings and other parts of the amplifier in the other casing. It will, however, also be possible to design apparatus according to the invention with a completely separate casing which is adapted to be worn elsewhere — the so-called pocket-hearing aid — and from which electrical connections are provided to the sound receiving transducer and the sound reproducing transducer, respectively, each of which are supported adjacent the respective ear. In such events no sound receiver is enclosed in the casing which only contains the batteries and the amplifier. This has the advantage that by such embodiment noise due to scratching between the clothes and the casing is completely eliminated.