Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2002-08-06
2004-11-16
Ni, Suhan (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S398000, C381S423000, C381S433000
Reexamination Certificate
active
06819773
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electro-dynamic loudspeaker comprising a chassis, a translatable body with a three-dimensional diaphragm extending within the chassis, the diaphragm comprising a front part and a back part, and an electromagnetic actuator for displacing said body with respect to the chassis along a translation axis extending from said front part to said back part of the diaphragm, said actuator comprising a stationary actuator element fixed to the chassis and a translatable actuator element connected to the translatable body proximate to the back part of the diaphragm, said actuator elements being capable of magnetically co-operating with each other over an air gap, while a first flexible connecting means is present proximate to the front part of the diaphragm for movably journaling the translatable body with respect to the chassis, and a second flexible connecting means is present proximate to the back part of the diaphragm for movably journaling the translatable body with respect to the chassis.
2. Description of the Related Art
A dynamic loudspeaker comprising a conical diaphragm, a loudspeaker housing with a loudspeaker basket and an electromagnetic driver is known from German Gebrauchsmuster DE-U 75 02 568. The driver is accommodated in the housing, outside the diaphragm, and has a driving coil arranged on a coil former secured to the diaphragm, as well as a magnetic system secured to the loudspeaker basket. The diaphragm, which is within the loudspeaker basket, is fixed on its front side to the loudspeaker basket via a flexible suspension rim, and on its rear side via a centering means. In the known loudspeaker, the driver is situated in an area outside the loudspeaker basket so that the loudspeaker has a relatively large axial dimension. This has the drawback that the depth of the housing in practical embodiments is relatively large with respect to the front dimensions of the loudspeaker. Consequently, the known loudspeaker occupies a relatively large space of the volume constituted by the housing, which leads to relatively high system resonances, and thus, to a relatively high lower limit of the frequency range associated with a given volume.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a compact loudspeaker that can be subjected to a high load. According to the invention, this object is achieved with the loudspeaker which is characterized in that the air gap, which extends between the stationary actuator element and the translatable actuator element, is present outside the space enclosed and defined by the contours of the diaphragm and within an area between the first flexible connecting means and the second flexible connecting means.
Due to the characteristic feature described above, the loudspeaker according to the invention has only a limited axial dimension in spite of its three-dimensional diaphragm, so that it has a small build-in depth. Such a loudspeaker built in a housing therefore occupies a comparatively small volume, resulting in a low system resonance. The loudspeaker according to the invention is therefore eminently suitable for use in subwoofer systems in which compact, shallow housings are desired. The diaphragm used preferably has a conical central portion.
It is to be noted that European Patent Application No. EP 0806883, corresponding to U.S. Pat. No. 5,898,786, discloses a loudspeaker in which the electromagnetic drive of the diaphragm is situated within the space enclosed and defined by the contours of the diaphragm. In such a “wafer” loudspeaker, the available space within the diaphragm is, however, too small to build a sufficiently powerful magnetic system which complies with the high load requirements. Apart from the available space, the thermal load of the magnetic material of the magnetic system is also a limiting factor in this type of loudspeaker. Notably with modern magnetic material such as neodymium-iron-boron alloys, the maximum allowable temperatures are relatively low. For these reasons, a loudspeaker of this type is only suitable for loudspeaker systems having a relatively small power.
In a practical embodiment of the loudspeaker according to the invention, the stationary actuator element is at least largely, and preferably completely, present within a zone situated between the first flexible connecting means and the second flexible connecting means of the loudspeaker.
A preferred embodiment of the loudspeaker according to the invention is characterized in that the stationary actuator element comprises an annular permanent magnet, and the translatable actuator element comprises a magnet coil, also referred to as voice coil, the magnet coil being situated in a field surrounding the magnet, i.e., the magnetic field of the magnet.
In this embodiment, annular magnet coils having large coil diameters are possible. Such drive coils have large cooling faces and offer ample possibilities of ventilation so that they can be subjected to high loads. Consequently, the coil temperature remains relatively low during use, also in the case of high loads, and only a limited transfer of heat to the other parts, such as the permanent magnet of the actuator, takes place. This embodiment, therefore, has a favorable thermal household. It has been found that the temperature of the coil and the magnet remains within acceptable limits, also at higher powers. Modern magnetic materials, such as neodymium-iron-boron alloys, can, therefore, be used without any problem.
It is to be noted that International Patent Application No. WO-A 97/32451, corresponding to U.K. Patent Application No. GB 2,325,373A, discloses a loudspeaker unit which is provided with a damper fixed to a diaphragm. A coil former, with a coil extending in a magnetic gap surrounding a plate on a magnet, is fixed to the diaphragm, this gap extending outside the area bounded by the suspensions of the diaphragm. The magnet, which is situated at a maximum distance from the diaphragm, is fixed to a bottom part of the unit.
In a practical embodiment of the loudspeaker according to the invention, the first flexible connecting means has a flexible structure with an undulation or wrinkle, this first flexible connecting means being fixed to the chassis at one end and to the translatable body at the other end. In principle, the second flexible connecting means may be formed similarly.
To allow relatively large and accurately defined axial displacements of the translatable body with respect to the chassis, a preferred embodiment of the loudspeaker according to the invention is characterized in that the second flexible connecting means comprises a set of at least three leaf spring elements positioned around the translation axis, each leaf spring element comprising two leaf springs arranged in a slanting position with respect to a plane oriented transversely to the translation axis, the leaf springs of each leaf spring element being each provided with two peripheral parts each extending parallel to said plane, while one of the leaf springs is fixed to the chassis proximate to one of its peripheral parts and the other of its peripheral parts is fixed to the translatable body proximate to one of its peripheral parts, the leaf springs of each leaf spring element being interconnected proximate to their other peripheral parts. This embodiment of the second flexible connecting means allows a large axial displacement of the diaphragm, and is, therefore, suitable for applications where loudspeakers having a high sound-radiating power are desired.
The flexible connecting device used as the second flexible connecting means described hereinbefore, is essentially without friction and guarantees an accurate alignment of the translatable body and, hence, of the diaphragm with respect to the chassis. Embodiments of this connecting device are described and elucidated in European Patent Application No. EP-A 1036485, corresponding to U.S. Pat. No. 6,385,327, herein incorporated by reference. In this respect, it is only noted that the leaf
Goodman Edward W.
Koninklijke Philips Electronics , N.V.
Ni Suhan
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