Electrical audio signal processing systems and devices – Hearing aids – electrical – Specified casing or housing
Patent
1991-12-13
1993-09-07
Ng, Jin F.
Electrical audio signal processing systems and devices
Hearing aids, electrical
Specified casing or housing
381194, H04R 2500
Patent
active
052436624
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a miniaturized, electrodynamic sound generator, especially for hearing aids and with a diaphragm essentially formed as a spherical cap segment, a permanent magnet with pole pieces, a magnet yoke and a coil, arranged as stated in the preamble of claim 1. The sound generator according to the invention is intended for placement in the meatus of an adult human being.
An open electrodynamic sound generator with small dimensions, suitable for use in heat- or earphones e.g. for music reproduction, is known from U.S. Pat. No. 4,472,887. By the sound generator disclosed in this patent the damping of resonance in the range 3-5 kHz is especially emphasized for in this way to achieve a better quality of sound reproduction. Another electrodynamic sound generator, particularly in form of a small loudspeaker for use in headphones or a microphone, is know from De-OS 30 48 779 and discloses a magnet system which concentrically surrounds an air gap, wherein a oscillating coil is provided, attached to the diaphragm. A miniaturized electrodynamic sound generator for hearing aids is shown in U.S. Pat. No. 4,380,689. The miniaturization is hereby achieved in that the magnet does not surround the iron core, but is provided at its side around the same axis as the core. A miniaturized electrodynamic sound generator for use in hearing aids has also been developed by the firm Westra Electronic GmbH of Germany. This sound generator has a frequency range from 20 to 20,000 kHz and very small dimensions, viz. a diameter of 5.5 mm and a length of 5.5 mm, but is still too large to be easily located in the human meatus.
It is known that the meatus of humans has an acoustic resonance which generates a peak in the frequency response for the acoustic amplification of the sound pressure from the ear opening and to the tympanus. The frequency and amplitude of the resonance peak vary individually, but usually it is located within the range of 2 kHz to 4 kHz and has an amplitude of 10- 15 dB. Such an increase of the amplification in this range is very important for how the sound is perceived and the individuals's perception of sound quality. If the meatus is closed by a hearing aid plug, the individual who wears the hearing aid looses the resonance in this important frequency range.
Electrical filtering of the input signal to the sound generator in a hearing aid may be used in order to restore the desired frequency response. Using electrical filtering is however connected with a number of disadvantages, as the necessary electrical components need a lot of space, consume electrical power and adds up to an expensive addition. The need for space and the consumption of power are especially detrimental for hearing aids which shall have small dimensions and are powered by a small battery.
The object of the present invention is to provide an electrodynamic sound generator of very small dimensions in order that it can be located in the meatus near the tympanus and is designed such that its main resonance falls in the frequency range of interest, that is 2-4 kHz, and which further has an acoustic attentuation such that the desired meatus resonance may be recreated. Another object of the sound generator according to the invention is that is shall be employed in a hearing aid which does not close the meatus in order that a possible hearing residue at low frequencies is taken care of.
These objects are achieved with an electrodynamic sound generator according to the present invention and with features disclosed by the appended claims.
The electrodynamic sound generator according to the invention will be described in greater detail below in connection with an exemplifying embodiment and with reference to the accompanying drawing.
FIG. 1a shows an electrodynamic sound generator according the invention.
FIG. 2a shows a diagrammatical plan view of the cabinet or the yoke of the sound generator of FIG. 1, seen from below.
FIG. 2b shows a diametrical section through the cabinet or the yoke.
FIG. 3 shows the graph of the frequency res
REFERENCES:
patent: 2551447 (1951-05-01), Marquis
patent: 4320263 (1982-03-01), Thiele
patent: 4380689 (1983-04-01), Giannetti
patent: 4742887 (1988-05-01), Yamagishi
patent: 4752963 (1988-06-01), Yamazaki et al.
Krokstad Asbjorn
Sogn Bjorn
Svean Jarle
Ng Jin F.
NHA A/S
Tran Sinh
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