Electrical audio signal processing systems and devices – Hearing aids – electrical – Directional
Reexamination Certificate
1999-12-08
2001-08-07
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Hearing aids, electrical
Directional
C381S312000, C381S092000
Reexamination Certificate
active
06272229
ABSTRACT:
The invention relates to a hearing aid with a controllable directional characteristic, having at least two spaced apart microphones in at least two microphone channels, at least one signal processing unit, at least one output transducer and a directional controlling system, with means of adaptively matching the characteristics of at least two microphones.
BACKGROUND OF THE INVENTION
In hearing aid systems of this type using at least two spaced apart microphones, it is known that, in the technique for controlling the directionality and beam forming, using multiple microphones, usually two microphones, the realization depends on the microphones being matched as closely as possible with respect to their time an phase relationship as well as their sensitivity, because beam forming techniques make use of the time/phase difference between spaced apart microphones with respect to the direction of the sound received from a sound source.
The difference in the arrival time of signals at the microphone determines at which angles, the zeros in the directional characteristic will be generated.
Any disturbance in this difference in arrival time will disturb the position of the zeros in space, and the directional behaviour will, in this case, never become optimal.
Differences in the sensitivity between hearing aid microphones of the same type could be as large as 6 dB, which would result in a directional behaviour, that—for practical use—is not even there.
The difference in phase could be as large as 10° at low frequencies, which is due to production tolerances in connection with the lower cut-off frequency in the microphones.
In hearing aids with preferably two microphones they will be normally placed apart by a distance of 1 cm. This corresponds to an acoustical delay between the microphones of about 30 &mgr;s. Disturbances in the arrival times could of course be very severe, because they could in fact be larger than the actual acoustical delay between the two microphones.
A way to overcome this problem has until now been to use microphones, which were matched in their sensitivity and phase by the supplier.
However, there are some drawbacks in this method:
1. Microphones can not be matched better in their sensitivity by the supplier than to about 0.5 dB. However, o,5 dB is enough to degrade the directional behaviour heavily at 200-300 Hz.
2. Microphones can not be matched better in phase than about 2°, because of the needed precision in the equipment used to measure the microphones. 2° corresponds at 200 Hz to about 28 &mgr;s, which in many cases is enough to move the directional characteristic, so that directions which were actually intended to be damped, remain almost undamped, and therefore will be transmitted with the same strength as the signal coming from the desired direction.
3. The two electrical inputs in the hearing aid need to be matched as well, for the beam forming to work well. This implies a special selection of the components to be used, because the tolerances of e.g. capacitors are not sufficiently narrow.
4. In case of one microphone or other components becoming defective, it will be necessary to exchange all microphones (or other components) as matched sets which will make the necessary service operation much more expensive.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to create a hearing aid containing specific circuitry for performing a running adaptive matching between the inputs of microphones and electronics for both the low frequency phase/time response and also the sensitivity, so that there will be no need for precise selection of matching microphones and electronics. It will rather be sufficient to use randomly chosen microphones and components of their respective types as long as they are within their production tolerances.
This will also reduce service costs considerably, because microphones and components could be changed one piece at a time. Also, the effects of aging and changes due to environmental stress may then be compensated for by the present invention. Particularly, the new adaptive matching uses no additional signals but uses the acoustical signals being present at the microphones at any time.
These and other objects of the invention will be achieved by a hearing aid of the type referred to above by using an adaptive phase matching circuit inserted into said at least two microphone channels, the adaptive phase matching circuit having its outputs connected to an acoustical delay compensation means followed by a parameter control circuit, the output of which is applied to a controllable filter means inserted into at least one of said at least two microphone channels inside said adaptive phase matching circuit. It is of special advantage if filter means are provided in front of said acoustical delay compensation means.
The invention will now be described in detail in conjunction with the acompanying drawings.
REFERENCES:
patent: 5483599 (1996-01-01), Zagorski
patent: 5515445 (1996-05-01), Baumhauer, Jr. et al.
patent: 5524056 (1996-06-01), Brander
patent: 5627799 (1997-05-01), Hoshuyama
patent: 5757933 (1998-05-01), Preves et al.
patent: 5917921 (1999-06-01), Sasaki et al.
patent: 5978490 (1999-11-01), Choi et al.
patent: 6002776 (1999-12-01), Bhadkamkar et al.
patent: 6101258 (2000-08-01), Killion et al.
Kuntz Curtis
Ni Suhan
Sughrue Mion Zinn Macpeak & Seas, PLLC
Topholm & Westermann ApS
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