Hearing Aid Adaptable for Telephone Listening

1. Field of the Invention

The present invention is directed to a hearing aid, and in particular to a hearing aid adaptable for telephone listening to produce a tone comfortable for the user.

2. Description of the Prior Art

Hearing aids are known which include a separate coil, in addition to the microphone normally used, to capture the magnetic field from a telephone receiver, and to convert it into corresponding signals for the hearing-impaired person. The accommodation of such an additional coil, however, is frequently impossible for space reasons in smaller hearing aids, such as in-the-ear hearing aids. Although it is theoretically possible to conduct telephone listening using the microphone present in the hearing aid for normal use, acoustic reproduction quality is poor when this microphone is used to receive signals from the telephone receiver because of the closeness of the hearing aid microphone to the transmitting speaker in the telephone hand piece. Hearing-impaired persons complain that an unnatural, piercing, shrill tone results under such circumstances.

It is an object of the present invention to provide a hearing aid adaptable for telephone listening so that the tone quality heard by the user is natural and comfortable.

The above object is achieved in a hearing aid constructed in accordance with the principles of the present invention which includes a frequency-defining element connected to the hearing aid amplifier. The frequency-defining element lowers amplitudes of the higher frequencies in the signal incoming to the hearing aid from the telephone hand piece speaker. The uncomfortable tone which hearing-impaired persons observe when using the telephone with a conventional hearing aid results from unnaturally strong treble reproduction. This unnaturally strong treble reproduction is compensated by the frequency-defining element. The frequency-defining element is a suitably dimensioned element connected in series with a switch which is closed for telephone use. The frequency-defining element may be a component in a frequency-dependent voltage divider, a component in a frequency-dependent negative feedback loop, or a component in a resonant circuit.

In one embodiment of the invention, the frequency-defining element is a capacitor having a selected suitable capacitance.

In an embodiment wherein the frequency-defining element is a part of a resonant circuit, the inductance of the hearing air receiver forms the resonant circuit in combination with the frequency-defining element, which is a capacitor switched into the circuit during telephoning. This resonant circuit attenuates the high frequencies so that a comfortable tone results.

A hearing aid wherein a capacitor connected in parallel with the receiver forms a resonance circuit in combination with the inductance of the receiver for attenuating high frequencies is known from European Application No. 0 124 798, corresponding to U.S. Pat. No. 4,689,818. In combination with an actuator, however, this capacitor functions to match the frequency curve during normal hearing via the microphone. The adjustment normally takes place in the factory, or is undertaken by a hearing aid technician. This known hearing aid thus does not permit selective adaptation to the special conditions present during telephone use, which adaptation can be undertaken by the hearing-impaired person during such telephone use.

The aforementioned circuitry of European Application No. 0 124 798 may, however, for the basis for a further embodiment of the present invention with a series circuit consisting of the switch and the frequency-defining element (i.e., a suitably dimensioned capacitor) connected in parallel with the receiver which already includes a parallel circuit consisting of a further capacitor and an actuator, as set forth in the European application. The series circuit of the capacitor and the switch could, however, alternatively be connected in parallel with a further capacitor which would replace the known series circuit of the capacitor and the actuator.

FIG. 1 is a schematic circuit diagram of a first embodiment of a hearing aid constructed in accordance with the principles of the present invention.

FIG. 2 is a schematic circuit diagram of a second embodiment of a hearing aid constructed in accordance with the principles of the present invention.

FIG. 3 is a schematic circuit diagram of a third embodiment of a hearing aid constructed in accordance with the principles of the present invention .

The hearing aid shown in FIG. 1 includes a microphone 1, an amplifier module 2 and a receiver 3. The amplifier module 2 includes a plurality of amplifier stages V1, V2 . . . Vn. In accordance with the principles of the present invention, one of the amplifier stages, such as the first amplifier stage V1, is followed by a series circuit consisting of a capacitor C and a switch S and an ohmic resistor R. These components form a frequency-dependent voltage divider.

In the embodiment of FIG. 2, the same components are indicated with the same reference symbols. Differing from the exemplary embodiment of FIG. 1, the series circuit in the embodiment of FIG. 2, again consisting of the capacitor C, the switch S and the ohmic resistor R, are connected to form a frequency-dependent negative feedback loop connected between the input and the output of the second amplifier stage V2.

The frequency-dependent voltage divider of FIG. 1 or the frequency-dependent negative feedback loop in the embodiment of FIG. 2 can be allocated to any one of the amplifier stages V1, V2 . . . Vn within the amplifier module 2.

In the embodiments of FIGS. 1 and 2, the switch S in the series circuit is closed by the hearing aid wearer only during use of the telephone. Due to the capacitance of the capacitor C, the amplitudes of high frequencies incoming to the microphone 1 from the speaker of the telephone handset are lowered to such an extent that a comfortable tone results for the hearing-impaired person during use of the telephone. At the conclusion of the telephone call, the switch S is again opened by the hearing-impaired wearer. The influence of the series circuit is thus interrupted, and normal operation of the hearing aid again takes place.

In the embodiment of FIG. 3, a microphone 1, an amplifier module 2 (in the form of an IC package) and an receiver 3 are again provided as part of the hearing aid. The hearing aid in the embodiment of FIG. 3 also includes a tone control 4, consisting of a capacitor 5 and a potentiometer 6. Blocking capacitors 7, 8 and 9 are so provided. A volume potentiometer 10 is connected in series with resistor 11, to set a voltage drop, and that series branch is connected in parallel with a resistor 12 for the purpose of setting the current. A battery 15 having an on/off switch 16 is also provided. To this extent, the circuit shown in FIG. 3 essentially corresponds to the circuit disclosed in the aforementioned European Application No. 0 124 798 for tone improvement in the use of resonant peak control. As already indicated above, this circuit may result in an unnaturally piercing, shrill tone when used to transmit signals from the speaker of a telephone handset.

To make this known circuit usable for telephoning as well, in accordance with the principles of the present invention the circuit shown in FIG. 3 additionally includes a capacitor C and a switch S connected in a series branch. This series branch is connected in parallel with the receiver 3. This series branch is also connected in parallel with the known series circuit consisting of the capacitor 13 and the actuator 14. The capacitor C is roughly twice as large as the capacitor 13. In a preferred exemplary embodiment, for example, the capacitor 13 has a capacitance of 0.047.mu.F and the capacitor C has a capacitance of 0.1.mu.F. Smaller or higher values for the capacitor C are, however, possible. The capacitor C may, for example, be roughly the same size as the capacitor 13, or may be larger than the 0.1.mu.F selected in the preferred exemplary embodiment. As the capacitance of the capacitor C increases beyond twice the value of the capacitor 13, however, the volume decreases. The roughly double value of the capacitance C with reference to the capacitor 13 is the optimum value. In other circuit embodiments wherein no parallel circuit consisting of the capacitor 13 and the actuator 14 are present, or wherein only the capacitor 13 is present, a value for the capacitance of the capacitor C should be selected which is approximately 0.15.mu. F. This value corresponds to the sum of the selected capacitance in the previously-described embodiment wherein both capacitors 13 and C are present.

In the embodiment of FIG. 3, the series circuit consisting of the capacitor C and the switch S is connected directly between the positive and negative outputs of the receiver 3. This series circuit may, however, alternatively be connected between the negative output of the receiver and the negative pole of the battery. The same result occurs because the series circuit consisting of the capacitor C and the switch S is still connected in parallel with the receiver 3, but via the battery 15. The battery 15 represents a short circuit in terms of alternating voltage.

The switch S may be a switch separate from the on/off switch 16, or the two switches can be combined. The switch S may be remote-controlled, as described in a hearing aid disclosed in European Application No. 0 175 909. The switch S may alternatively be activated by the magnetic field which is generated by the magnet in many telephone hand sets. In this case the switch S can be, for example, a reed contact.

Although modifications and changes may be suggested by those skilled in the art it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.