Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having electrostatic element
Patent
1995-06-02
1997-07-08
Kuntz, Curtis
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having electrostatic element
381 68, 381200, H04R 2500
Patent
active
056470134
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electroacoustic transducers of the type which incorporate a reed armature.
An electroacoustic transducer of this general type is described in our British Patent 2095510, and typically includes a pair of spaced permanent magnets, a coil having a tunnel therethrough and a reed armature having a central portion which extends through the coil and a tip portion which lies at least partially between the magnets. The arrangement is such that when the moving part of the reed shifts in one direction or another away from a centralised position between the two poles, the magnetic flux is caused to flow in one direction or the other along the reed and hence through the coil. The reed is attached to a diaphragm and in this way the vibrations of the diaphragm caused by received sound are converted into corresponding currents in the coil or vice versa. It is very easy to damage the reed by over deflection, if the transducer experiences a shock e.g. from being dropped. In addition the tip portion may strike the magnet with considerable force. It will be understood that a similar configuration can be used for a receiver or loudspeaker.
In one transducer the coil tunnel has a restricted central portion which limits the degree of deflection available to the reed and hence reduces the possible damage. However because coils in such transducer are almost always formerless, this solution would apparently only be available when the coil is set in epoxy having been wound on a flexible removable plastic former. This method of construction is only appropriate for certain types of transducer and has a number of limitations.
From one aspect the present invention consists in an electroacoustic transducer including a pair of spaced permanent magnets, a coil having a tunnel therethrough and a reed armature having a central portion which extends through the coil and a tip portion which lies at least partially between the magnets, the reed being mounted for deflection towards or away from the respective magnets, wherein the central portion and/or the tip of the reed is provided with a formation and/or a restriction is provided between the coil and the magnets, or at the magnet end of the tunnel, for limiting the available deflection of the reed.
In a particularly preferred embodiment there may be formations on each side of the reed and the formation or formations may be deformations in the reed. The formations are preferably on the central portion to reduce distortion of the magnetic field. Where the reed is flat and elongate, the formations are preferably formed by pressing out sections of the reed at or adjacent the longitudinal axis of the reed. By pressing, or otherwise deforming, the formation or formations from the reed, the limitation on the movement of the reed can be achieved without adding any mass to the reed, or indeed the transducer as a whole. However by restricting the formation or formations to the area of the central axis of the reed, no additional restriction on the lateral position of the reed within the tunnel is introduced and extra restrictions on its rotational positions are limited. Further such formations can be pressed with considerable accuracy, which is important when the dimensions and tolerances involved are extremely small as is the case where the transducer is for use in a hearing aid.
In this construction the formation or formations may be semi-spherical, ridges or star shapes or a combination thereof.
In another arrangement the formation or formations may be constituted by a body or bodies mounted on the reed. For example the body may be in the form of a sleeve or may be in the form of some settable or deposited material or may simply be a body attached to the reed. These arrangements are somewhat less preferred, because they add weight to the reed and in the latter case the control of dimensions is more difficult. However, in certain cases, there may be advantages where the localised deformation of the reed undesirably affects its flexing properties.
In an alternative arrangement
REFERENCES:
patent: 3005880 (1961-10-01), Simshauser
patent: 3671684 (1972-06-01), Tibbetts et al.
patent: 3836733 (1974-09-01), Cragg
patent: 3885553 (1975-05-01), Vecchio
patent: 3935398 (1976-01-01), Carlson et al.
patent: 4272654 (1981-06-01), Carlson
patent: 5193116 (1993-03-01), Mostardo
patent: 5299176 (1994-03-01), Tibbetts
patent: B14473722 (1995-06-01), Wilton
Harrington Steven John
Salvage Richard James
Barnie Rexford N.
Knowles Electronics Co.
Kuntz Curtis
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