Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1999-02-12
2001-01-23
Kuntz, Curtis A. (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S398000, C381S423000, C181S164000, C181S173000
Reexamination Certificate
active
06178252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electroacoustic transducer comprising a voice coil and further comprising a diaphragm which is intended for cooperation with an air mass in an acoustic free space situated in front of the diaphragm and which can be set into vibration by means of the voice coil substantially parallel to a direction of vibration. The diaphragm has an annular outer zone, end a central zone which is convex with respect to the acoustic free space situated in front of the diaphragm, and a peripheral zone which diverges towards the acoustic free space in front of the diaphragm. The peripheral zone is connected to the central zone by an annular intermediate zone and terminates in the outer zone of the diaphragm, the annular intermediate zone being constructed for securing the voice coil of the transducer to the diaphragm.
The invention further relates to a diaphragm for an electroacoustic transducer, which diaphragm is intended for cooperation with an air mass in an acoustic free space situated in front of the diaphragm, and which can be set into vibration by means of a voice coil substantially parallel to a direction of vibration. The diaphragm has an annular outer zone a central zone which is convex with respect to the acoustic free space situated in front of the diaphragm, and a peripheral zone which diverges towards the acoustic free space in front of the diaphragm. The peripheral zone is connected to the central zone by an annular intermediate zone and terminates in the outer zone of the diaphragm, the annular intermediate zone of the diaphragm being constructed for securing the voice coil of the transducer to the diaphragm.
2. Description of the Related Art
An electroacoustic transducer of the type defined in the first paragraph and a diaphragm of the type defined in the second paragraph are known, for example, from the document U.S. Pat. No. 5,303,209. It is to be noted that a known transducer of the type defined in the first paragraph is commercially available from the Applicant in several versions, for example, under the type number WD 02901/Y50L. In the known transducer, the convex central zone is spherical and the diverging peripheral zone has a flared shape corresponding to a part of a torus. In the known transducer, the annular intermediate zone, which serves as a mounting zone for securing the voice coil of the transducer to the diaphragm, takes the form of an annular disc, a plane through this annular disc extending perpendicularly to the transducer axis. Due to this shape of the intermediate zone in the known transducer, this intermediate zone is situated comparatively far away from the magnet system of the known transducer, as a result of which the voice coil must be comparatively high in order to extend into the air gap of the magnet system. This, in turn, results in the voice coil being comparatively heavy, which is unfavorable for a maximal sensitivity—i.e., for a maximal conversion factor between the applied electric power and the delivered sound pressure—and which also makes the voice coil more expensive, because the voice coil should have a comparatively large number of turns in order to obtain the required height. Moreover, as a result of the comparatively high voice coil, the position of the voice coil with respect to the air gap of the magnet system exhibits a comparatively high degree of asymmetry, which leads to a comparatively large amount of non-linear distortion in the known transducer.
SUMMARY OF THE INVENTION
It is an object of the invention to preclude the above-mentioned problems in a simple manner and by simple means and to provide an improved electroacoustic transducer and an improved diaphragm for an electroacoustic transducer.
According to the invention, in order to achieve the afore-mentioned object with an electroacoustic transducer of the type defined in the first paragraph, the annular intermediate zone has angularly spaced-apart portions which are substantially trough-shaped in cross-section and which are each bounded by a trough bottom wall and two trough side walls, of which each radially inner trough side wall adjoins the central zone and each radially outer trough side wall adjoins the peripheral zone. In each of these trough portions the bottom wall is connected to the side walls at those ends of the side walls which are remote from the free space in front of the diaphragm.
Thus, it is achieved by simple means that by means of its trough portions—strictly speaking by means of the bottom walls of the trough portions—the intermediate diaphragm-zone, which is adapted to secure the voice coil of the transducer forms the actual mounting zone for securing the voice coil of the transducer. The mounting zone—as compared with a known mounting zone having the shape of an annular disc—is situated distinctly closer to the air gap of the magnet system of the transducer in accordance with the invention due to the trough shape of the trough portions, as a result of which the voice coil of a transducer in accordance with the invention can have a distinctly smaller height and is also disposed comparatively symmetrically with respect to the air gap of the magnet system. This provides a transducer having an improved sensitivity and a reduced susceptibility to nonlinear distortion as compared with a known transducer.
In a transducer in accordance with the invention having the characteristic features as defined above it has proved to be particularly advantageous if, in addition, viewed in a tangential direction, a first wedge portion adjoins each trough portion at one end and a second wedge portion at the other end, and each first wedge portion is bounded by a radial prolongation of the central zone of the diaphragm and by a tangential prolongation of the radially outer trough side wall of the adjacent trough portion, and each second wedge portion is bounded by a radial prolongation of the peripheral zone of the diaphragm and by a tangential prolongation of the radially inner trough side wall of the adjacent trough portion. The first wedge portions and the second wedge portions provide a distinct increase in stiffness of the annular intermediate zone, which is very advantageous in order to obtain a diaphragm having a maximal stiffness, the high stiffness of the diaphragm resulting in very good acoustic characteristics of such a transducer in accordance with the invention.
In a transducer in accordance with the invention having the characteristic features as defined above it has further proved to be advantageous if, in addition, the diaphragm has been manufactured by means of a deep-drawing process. With such a deep-drawing process the diaphragm of a transducer in accordance with the invention can be manufactured with a high precision, the deep-drawing process enabling even very small the diaphragm thicknesses of only a few hundredths of millimeters to be manufactured accurately and reproducibly, which is highly important particularly in the case of miniaturized electroacoustic transducers having only very small and thin diaphragms. It is to be noted that these measures can also be applied advantageously to a transducer in accordance with the invention having the characteristic features of the first and second wedge portions as defined above.
According to the invention, in order to achieve the afore-mentioned object with a diaphragm of the type defined in the second paragraph the annular intermediate zone has angularly spaced-apart trough portions which are substantially trough-shaped in cross-section and which are each bounded by a trough bottom wall and two trough side walls, of which trough side walls each radially inner trough side wall adjoins the central zone and each radially outer trough side wall adjoins the peripheral zone, and in each of these trough portions the trough bottom wall is connected to the trough side walls at those ends of the trough side walls which are remote from the free space in front of the diaphragm. In this way, advantages which correspond to the advantages desc
Frasl Ewald
Klein Erich
Biren Steven R.
Kuntz Curtis A.
Ni Suhan
U.S. Philips Corporation
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