US3296386A - Magnetic system for electrodynamic transducers - Google Patents

Description

Jan. 3, 1967 H. FANSELOW 3,296,386

MAGNETIC SYSTEM FOR ELECTRO'DYNAMIC TRANSDUCERS Filed Dec. 29, 1964 United States Patent Ofifice 3,295,386 Patented Jan. 3, 1967 3,296,386 MAGNETIC SYSTEM FOR ELECTRO- DYNAMIC TRANSDUCERS Heinrich Fanselow, Landshut, Bavaria, Germany, assignor to International Standard Electric Corporation Filed Dec. 29, 1964, Ser. No. 421,900 Claims priority, application Germany, Jan. 8, 1964, St 21,526 3 Claims. (Cl. 179-120) This invention relates in general to electro-dynamic transducers and in particular to telephone receivers. Magnetic systems equipped with cylindrical or annular-shaped magnetic insets of alloyed steel as carriers of the magnetic energy are used in such dynamic transducers. The iron parts of the magnetic system forming the magnetic circuit or flux path are shaped so that they leave an operating air gap in which a coil moves in the rhythm of the sound. In other known magnetic systems annular,

ceramic magnetic insets are used to carry the magnetic energy. The magnetic flux in such systems are led via pole plates and a pole core into the operating air gap.

A drawback of the above described magnetic systems used for dynamic transducers is their relatively high weight which, for example, is disadvantageous when the dynamic transducers with annular magnetic inserts are used in telephone receivers. A weight reduction can be obtained by using smaller magnetic rings and consequently, smaller pole plates. This reduction in weight, however, causes a loss of magnetic energy and correspondingly reduces the degree of the acoustic effect.

Thus, an object of the invention is to provide new and unique electro-dynamic transducers.

A related object is to provide light weight electrodynamic transducers having improved frequency characteristics.

A further object is to provide improved, relatively inexpensive, light weight transducers using magnetic elements made of sintered iron.

According to the invention the noted drawbacks are avoided in that the magnetically conductive parts, required to form an operating air gap in the magnetic system, such as pole plates and pole cores, consist of sintered iron and that these parts with the magnetic inset as carrier of the magnetic energy are composed by gluing or other composing methods known to the art. The reduced specific weight of such parts, made of sintered iron, results in a weight reduction compared with solid iron. In addition, the porosity of the sintered material aids in dampening the deleterious resonant peaks. Despite the smaller specific weight of parts made of sintered iron, the magnetic conductivity of said parts increases. This increase of the magnetic conductivity acts to further reduce the weight of the pole plates and the pole core according to a further embodiment of the invention by reducing the thickness of the pole plates towards the periphery and by allowing a cavity to be bored in the pole core, without undergoing a loss of magnetic energy. Due to an annular stud of little height around the pole core, the external diameter corresponds to the internal diameter of the ferrite ring. The magnetic losses which occur at the transition between the lower pole plate and the pole core, due to an increased scattering of the magnetic flux lines is further reduced, resulting in an increase of the air gap induction. Another advantage of the described annular stud of the pole plate is the saving of a center adjusting ring, when using sintered iron which has, besides the costs of material, no further expenses.

The use of sintered iron for the iron parts forming the magnetic circuit flux renders financial advantages despite the increased price for the base material, because a final treatment is not required.

The above mentioned and other features of this invention and the manner of obtaining them will become more apparent, and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing.

The accompanying drawing shows a preferred example of a dynamic transducer for telephone sets with the arrangement of such a magnetic system. An annular body 1 of ceramic magnetic material is provided to carry the magnetic energy. The top pole plate 2 has a cross-section decreasing in thickness towards the periphery and an annular study 2a which serves for centrally fixing of the basket-like diaphragm carrier 4. The bottom pole plate and the pole core 3 are manufactured in one production process. The annular study 3a around the pole core, provided for centering, is clearly seen on the drawing. The basket-like diaphragm carrier 4 can be connected with the top plate 2 by riveting. In the air gap 5, formed by the pole hole of the top pole plate 2 and the pole core 3, a coil freely oscillates. A cavity 6, obtained in this pole core, can be made a resonator, if the cover 7, which closes the opening airtight, and an attenuating disk 8 exist, which disk can be used as an acoustic filter for connecting the adjacent air spaces.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.

I claim:

1. A magnetic system for electro-dynamic transducers comprising a core of sintered magnetic material, a bottom pole plate which decreases in thickness towards the periphery thereof and is integral to said core, a top pole plate which decreases in thickness towards the periphery thereof and is fabricated of sintered magnetic material, said top pole plate associated with said core to form an operating air gap in said magnetic system, a stud centrally arranged around the air gap, a basket-like diaphragm support accommodated by said stud, and an inset of magnetic material located between said pole plates, surrounding said core.

2. The magnetic system of claim 1, wherein the lower pole plate is provided with a centrical stud around the pole core which serves to center said magnetic inset.

3. The magnetic system of claim 2, wherein a cavity is bored through said core, cover means are provided for closing off the bottom of said cavity and an attenuating disk is provided at the top of said cavity, whereby said closed cavity acts as a resonator.

References Cited by the Examiner UNITED STATES PATENTS relied upon.

KATHLEEN H. CLAFF Y, Primary Examiner. ROBERT H. ROSE, Examiner. F. N. CARTEN, Assistant Examiner.

Claims (1)

1. A MAGNETIC SYSTEM FOR ELECTRO-DYNAMIC TRANSDUCERS COMPRISING A CORE OF SINTERED MAGNETIC MATERIAL, A BOTTOM POLE PLATE WHICH DECREASES IN THICKNESS TOWARDS THE PERIPHERY THEREOF AND IS INTEGRAL TO SAID CORE, A TOP POLE PLATE WHICH DECREASES IN THICKNESS TOWARDS THE PERIPHERY THEREOF AND IS FABRICATED OF SINTERED MAGNETIC MATERIAL, SAID TOP POLE PLATE ASSOCIATED WITH SAID CORE TO FORM AN OPERATING AIR GAP IN SAID MAGNETIC SYSTEM, A STUD CENTRALLY ARRANGED AROUND THE AIR GAP, A BASKET-LIKE DIAPHRAGM SUPPORT ACCOMMODATED BY SAID STUD, AND AN INSET OF MAGNETIC MATERIAL LOCATED BETWEEN SAID POLE PLATES, SURROUNDING SAID CORE.

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