US3894196A - Binaural hearing aid system - Google Patents

Abstract

An improved binaural hearing aid system comprises two complete electronic hearing aids, one for each ear of the user, with the hearing aid for the dominant ear having an emphasized high frequency response relative to that of the other hearing aid. Preferably, ear molds are provided for occluding ambient sounds from direct access to the ears. Means are provided for establishing a phase delay in the response of one hearing aid relative to that of the other, with the preferred phase delay between the audio signal components being substantially 180*. The sensitivity of the hearing aid for the dominant ear is preferably at least 3 but no more than 6 db greater for frequency components in the range from 3,000 to 4,000 hertz than that of the hearing aid for the non-dominant ear. The system provides materially enhanced hearing response, and specifically substantially improved speech discrimination, in high ambient noise environments for individuals with substantially balanced or symmetrical hearing losses, a group representing about 85% of those with correctable hearing impairment.

Description

United States Patent [11] 3,894,196

Briskey July 8, 1975 BINAURAL HEARING AID SYSTEM two complete electronic hearing aids, one for each ear [75] Inventor: Robert J Briskey Des Plaines In of the user, with the hearing aid for the dominant ear having an emphasized high frequency response rela- [73] Assigneei Zenith Rad o Corp ra ion, cag tive to that of the other hearing aid. Preferably, ear

molds are provided for occluding ambient sounds from direct access to the ears. Means are provided for [22] Flled ay establlshing a phase delay In the response of one hear- [21] Appl. No.: 473,970 ing aid relative to that of the other, with the preferred phase delay between the audio signal components [52] U S Cl 179/107 179/1 G being substantially 180. The sensitivity of the hearing aid for the dominant ear is preferably at least 3 but no [51] Int. Cl H04r 25/00 more than 6 db greater for frequency components in 'ldf h ..l7 G,l7FD

[58] 9/1 0 the range from 3,000 to 4,000 hertz than that of the [56] References Cited hearing aid for the non-dominant ear. The system provides materially enhanced hearing response, and spe- UNITED STATES PATENTS cifically substantially improved speech discrimination,

Wengel G in ambient noise environments for individuals with substantially balanced or symmetrical hearing a on Primary ExaminerRalph D. Blakeslee Attorney, Agent, or FirmCornelius J. OConnor [57] ABSTRACT An improved binaural hearing aid system comprises losses, a group representing about 85% of those with correctable hearing impairment.

6 Claims, 2 Drawing Figures 1 13 I 1 l l I l I I I l I I I I I I l I P i 11 I f i i l l I l :14) 10 I I l l I I LEFT I RIGIHT I 15 I CHANNEL I CHANNEL r- AMPLIFIER AMPLIFIER I I I l I I I I I I i i l I i l I I l i I l A A I f-Q i i I l 7 I I r L i l I R IGHT CHANNEL AMPLIFIER FREQUENCY 5V JUL CHANNEL AMPLIFIER DECIBELS! BINAURAL HEARING AID SYSTEM BACKGROUND OF THE INVENTION This invention relates to electronic hearing aid systems and more particularly to binaural hearing aid systems for providing enhanced hearing response and substantially improved speech discrimination for most individuals suffering from correctable hearing impairment.

Heretofore electronic hearing aids have been developed in numerous styles and configurations and with diverse operating characteristics to compensate for various types of hearing impairment. The first electronic hearing aids were body-worn instruments connected by wire to an air conduction signal reproducer coupled to an earmold inserted in the ear canal. With the advent of the transistor and other miniature electronic components adapted for low voltage operation to permit the use of miniature batteries, various types of head worn electronic hearing aids have evolved, including eyeglass hearing aids, on-the-ear instruments suspended behind the external ear, and in-the-ear devices directly supported by the earmold. Different types of response characteristics have been devised for different types of hearing impairment, and other special features such as automatic gain control, vented earmolds, bone conduction reproducers, and the like have been provided for use in compensating special types of hearing deficiencies. With the advent of the head-worn instruments, binaural hearing assistance has been provided by the use of two independent instruments, one for each ear. At best however, even with all of the modern technological advances in circuits, components and manufacturing techniques, the quality and amount of hearing improvement has been undesirably limited, this in large part being due to frequency response limitations imposed by the use of miniaturized components.

OBJECTS OF THE INVENTION It is a primary object of the invention to provide a new and improved binaural electronic hearing aid system.

A more specific object of the invention is to provide an improved binaural electronic hearing aid system which affords enhanced hearing response, and in particular substantially improved speech discrimination response, as compared with prior art techniques for providing binaural hearing assistance.

SUMMARY OF THE INVENTION In accordance with the invention, a new and improved system for binaurally enhancing auditory response in an individual having hearing impairments of comparable character in both ears comprises first and second electronic hearing aids each including a microphone, an amplifier, a reproducer and means for coupling the output of the reproducer to an ear of the user. The two electronic hearing aids have similar frequency response characteristics, but the instrument associated with the dominant ear of user is provided with an emphasized high frequency response relative to that of the instrument associated with the non-dominant ear. In addition, means are provided for establishing a phase delay in the response of one hearing aid with respect to that of the other.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which: 7

FIG. 1 is a schematic diagram of a binaural electronic hearing aid system embodying the present invention; and

FIG. 2 is a graphical representation of the frequency response characteristics of the two hearing aids embodied in the system of FIG. 1.

DESCRIPTION OF' THE PREFERRED EMBODIMENT Before proceeding with a description ofthe preferred embodiment of the invention, a consideration of some of the hearing phenomena associated with. normal binaural hearing may be helpful. sounds a rejdistingui shed by their characteristics of frequency, intensity and time. With normal hearing,,soundswhich are directly in front and in back ofan individual, and which are equal in frequency, intensity. and time, maybe literally indistinguishable one from the other. .However the hearing mechanism detects the slightest changes in any of these characteristicsand reacts to differences as new bits of information to be analyzed in binaural listening. Even a slight movement of the head will change some very small part of the acoustic signal and the location of the sound source will be better defined. In normal binaural hearing, or listening, the head is positioned to enhance one or several characteristics to provide additional clues about the sound and its source to assist in understanding the signal and interpreting it.

Intensity or loudness provides the most common clue used by the normal ear for locating sound sources. When a loud sound is heard on one side, a judgement is made that the source of the sound is on that side and a distance is estimated. This spatial judgement of place and distance could be and often is influenced by the frequency and the time of the acoustic signal; however, the loudness provides the initial clue.

The time characteristic, which is also referred to as phase, is related to the cyclical characteristic of sound. The frequency of a pure tone is defined in terms of the number of cycles occurring each sound. Each cycle of an acoustic signal consists of a compression segment of the wave and a rarefaction segment of the wave. If two pure tone signals are presented in-phase, the compressions of the wave arrive at the cars at the same time. If the two signals are presented out-of-phase, a compression wave arrives at one car at the same time that a rarefaction wave arrives at the other. Depending on the frequency and the environment, a sound will be received by the two ears either in-phase or out-of-phase, or both in the case of a complex sound.

Complex sounds are constantly changing in any listening environment, and this requires continual analysis of differences in the acoustic signal which represent clues used in realizing a binaural hearing experience. I-Iead movement helps accentuate differences in the clues. A slight movement of the head alters the relative intensity, time of arrival, and phase of the signals representing the difference clues at each respective ear. All of these effects provide the auditory system with different bits of information. These differences are analyzed physiologically to assist in identifying the meaningful part of the signal and its direction of origin.

The foregoing discussion has been directed to a consideration of binaural hearing with the ears unoc- :luded. When the ears are occluded by the insertion of ear molds to provide amplification of sounds by wearable electronic hearing aids, the clues are altered by restriction of the acoustic input in bandwidth or frequency, intensity, or phase relationship. Moreover, the total hearing aid system (comprising microphone, amplifier, reproducer and ear canal coupling) not only compresses the dynamic intensity range and the bandwidth and alters the phase relationships by the inertia of the system elements, but it also adds artificial noise from the electronic circuits. In a quiet acoustic environment, sufficient clues, still exist to give localization and enhance intelligibility when using two independent monaural hearing aids. However, when the acoustic environment includes a background of substantial noise or undesired signals, the remaining clues are further reduced or obscured completely. The additional noise from the electronic circuitry reduces the usable dynamic range of the aid and the resulting signals reaching the occluded ears become dimensionally uniform. Because of the random characteristic of background noise, it has no discrete phase identification and this renders it non-directional, causing it to be perceived or sensed equally by both ears and yielding a sensation of sound located in the center of the head. Localized sources of desired signals are characterized by phase differences which, if detected, lateralize the signal away from the center of the head to one side or the other toward the point of origin.

It is known that additional information and improved binaural hearing can be provided for hearing-impaired persons by simply employing two monaural hearing aids that are 180 out of phase with each other. It has been observed that most individuals experience a greater capacity for processing binaural information in this anti-phasic condition and also that they accept the use of amplification more readily. In accordance with the present invention, however, it has been discovered that still further improvement in binaural hearing and in speech discrimination may be achieved, for persons with a relatively balanced or symmetrical hearing impairment, by additionally providing a deliberate mismatch in the frequency response characteristics of the two instruments.

It has been known for some time that the same hemispheric asymmetry of the human brain which leads to natural dominance of one hand over the other also establishes natural visual and aural superiority of one side over the other. Just as most people are right handed, most exhibit right-eye and right-ear dominance or superiority. An article reporting on recent experimental work in this field and on findings that right-ear superiority is widespread appears in the Journal of the Acoustical Society ofAmerica, Volume 55, No. 2, Feb., 1974,

* pages 319-327.

system comprising two deliberately mismatched electronic hearing aids, with the instrument for the dominant ear exhibiting a stronger frequency response for signal components in the range from 3,000 to 4,000 hertz, and by providing a phase delay in the output of one hearing aid with respect to that of the other. Preferably, the instrument for the dominant ear provides not less than 3 db and not more than 6 db greater response in the frequency range from 3,000 to 4,000 hertz, and the phase delay between the respective signal components is substantially In the preferred embodiment of the invention shown in FIG. 1, left and right electronic hearing aids 10 and 11, comprisingmicrophones 12, 13, amplifiers l4, l5 andsound reproducers 16, 17, respectively, are provided. Hearing aids l0 and 11 are preferably of the head-worn type, i.e., eyeglass hearing aids, on-the-ear aids, or in-the-ear instruments, and sound reproducers l6 and 17 are coupled byair conduction tubes 18, 19 respectively to full-occlusion type ear molds (not shown) inserted in the left and right ear canals of theuser 20, who is assumed to have a right-side dominant ear. Means are provided for establishing a phase delay in the response of hearingaid 11 relative to that of hearingaid 10; in the preferred embodiment of FIG. 1, this is accomplished by reversing the output connections betweenright channel amplifier 15 andreproducer 17 of hearingaid 11 relative to those between left channel amplifier l4 andreproducer 16 in hearingaid 10 thus providing a phase delay of substantially 180 between the respective left and right signal components.

In an alternative embodiment of the invention the substantially 180 phase delay between the respective left and right signal components is accomplished by adding a phase reversal circuit in the right channel amplifier.

The respective frequency response characteristics of hearing aids l0 and 11 are plotted in FIG. 2, in which the solid-line curve represents the frequency response characteristic of hearingaid 10 for the non-dominant ear, while the frequency response characteristic of the dominant-ear instrument 11 is essentially the same except for frequency components in the range between 3,000 and 4,000 hertz as shown by the dot-dash curve. In this frequency range, from 3,000 to 4,000 hertz, the response of the dominant-ear instrument 11 is materially emphasized relative to that of thenon-dominantear instrument 10; it has been found that by emphasizing the dominant-ear response by at least 3 db in this frequency range, a substantial improvement in speech lateralization and binaural separation, as well as a significant improvement in speech discrimination, is achieved. Little or no improvement is realized in quiet environments, but in high background noise situations or environments, where the hard of hearing experience the most serious difficulty because of their hearing impairment, a marked improvement is realized. It has also been found, however, that if the dominant-ear instrument 11 is provided with more than a 6 db stronger response in the frequency range from 3,000 to 4,000 hertz, little or no improvement is realized. Accordingly, in the preferred embodiment of the invention, the amount of emphasis in the response of the dominantear instrument relative to that of the non-dominant-ear instrument, in the frequency range from 3,000 to 4,000 hertz, is at least 3 db but not more than 6 db.

Thus the invention provides a new and improved binaural auditory response enhancement system which, in noisy environments, and for hearing-impaired persons with relatively balanced or symmetrical hearing impairment, provides a marked improvement in lateralization or source localization, in speech discrimination, and in general comfort in wearing the instruments as compared with prior binaural hearing aid systems.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A system for binaurally enhancing auditory response in an individual having hearing impairments of comparable character in both ears, which system comprises:

a first electronic hearing aid having a predetermined frequency response characteristic and comprising a microphone, an amplifier, a reproducer, and means for coupling the output of said reproducer to the non-dominant ear of said individual;

a second electronic hearing aid having a similar frequency response characteristic but with emphasized high-frequency response relative to that of said first hearing aid and comprising a microphone, an amplifier, a reproducer, and means for coupling said reproducer to the dominant ear of said individ 6 ual;

and means for establishing a phase delay in the response of said second hearing aid relative to that of said first hearing aid.

2. A binaural auditory response enhancing system according to claim 1, in which said means for coupling the outputs of said reproducers to the non-dominant and dominant ears comprise respective ear molds adapted to be inserted in the ear canals of said individual for occluding direct aural response.

3. A binaural auditory response enhancement system according to claim 1, in which the response of said second hearing aid is emphasized by from 3 to 6 db relative to that of said first hearing aid in the frequency range from 3,000 to 4,000 hertz.

4. A binaural auditory response enhancement system according to claim 1, in which said phase delay in the response of said second hearing aid relative to that of said first hearing aid is substantially 5. A binaural auditory response enhancement system according to claim 4, in which said phase delay is established either by adding a phase reversal circuit in the amplifier or by reversing the output connections be tween the amplifier and the reproducer in said second hearing aid relative to those in said first hearing aid.

6. A binaural auditory response enhancement system according to claim 1, in which said first and second hearing aids are adapted to be head-worn with their microphones in the vicinity of the non-dominant and dominant ears, respectively.

l l l

Claims (6)

1. A system for binaurally enhancing auditory response in an individual having hearing impairments oF comparable character in both ears, which system comprises: a first electronic hearing aid having a predetermined frequency response characteristic and comprising a microphone, an amplifier, a reproducer, and means for coupling the output of said reproducer to the non-dominant ear of said individual; a second electronic hearing aid having a similar frequency response characteristic but with emphasized high-frequency response relative to that of said first hearing aid and comprising a microphone, an amplifier, a reproducer, and means for coupling said reproducer to the dominant ear of said individual; and means for establishing a phase delay in the response of said second hearing aid relative to that of said first hearing aid.

2. A binaural auditory response enhancing system according to claim 1, in which said means for coupling the outputs of said reproducers to the non-dominant and dominant ears comprise respective ear molds adapted to be inserted in the ear canals of said individual for occluding direct aural response.

3. A binaural auditory response enhancement system according to claim 1, in which the response of said second hearing aid is emphasized by from 3 to 6 db relative to that of said first hearing aid in the frequency range from 3,000 to 4,000 hertz.

4. A binaural auditory response enhancement system according to claim 1, in which said phase delay in the response of said second hearing aid relative to that of said first hearing aid is substantially 180*.

5. A binaural auditory response enhancement system according to claim 4, in which said phase delay is established either by adding a phase reversal circuit in the amplifier or by reversing the output connections between the amplifier and the reproducer in said second hearing aid relative to those in said first hearing aid.

6. A binaural auditory response enhancement system according to claim 1, in which said first and second hearing aids are adapted to be head-worn with their microphones in the vicinity of the non-dominant and dominant ears, respectively.

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