US3112374A

US3112374A - Electromagnetic electroacoustic transducer

Info

Publication number: US3112374A
Application number: US155107A
Authority: US
Inventors: Gorike Rudolf
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-11-30
Filing date: 1961-11-27
Publication date: 1963-11-26
Anticipated expiration: 1980-11-26
Also published as: AT229386B; DE1176715B; GB995744A

Description

Nov. 26, 1963 R. GORIKE ELECTROMAGNETIC ELECTROACOUSTIC TRANSDUCER Filed Nov. 27, 1961 FIG 8 P6 INVENTOR'. RUDOLF GORIHE .BY AGENT M United States Patent 3,112,374 ELEQTRQMAGNETEQ ELECTROACUUFsTlL TRANDUCER Rudolf Giirike, 57c Sternwartestrasse, Vienna XVlll, Austria Filed Nov. 27, 1951, Ser. No. 155,167 Qlaims priority, application Austria Nov. 3t 1969 16 Claims. (Cl. 179-115) This invention relates to an electromagnetic electroacoustic transducer which constitutes a ring armature system. Such ring armature systems distinguish by a concentric arrangement so that they can easily be manufactured.

A ring armature system which has recently been disclosed and has mainly been developed as a ring armature earphone for telephone earphone units can be considered to represent the present state of the art in this field. It consists essentially of an annular pole piece, which defines with an annular permanent magnet 21 working air gap for the ring armature. The exciter coil is accommodated inside a U-shaped cavity, which is defined on one side by the annular pole piece and on the other side by a ring applied to the armature. The permanent magnetic flux passes from the cylindrical portion of the magnet through the disc-shaped portion of the magnet, then through the armature at right angles thereto and back through the pole piece.

Such a ring armature earphone has special advantages regarding its efiiciency because it delivers a large sound volume within a wide frequency range and with small non-linear distortions.

The design of other ring armature systems which have been disclosed in the patent literature is based substantially on the same principle as the ring armature earphone described hereinbefore. The magnetic system is always annular and so arranged that the transducer has a central cavity, which is closed by a diaphragm, which in most cases is slightly curved. Just as the ring armature earphone described first hereinbefore, the exciting coil is disposed in these systems in a U-shaped groove formed between the annular pole piece and the annular.

permanent magnet.

Although the acoustic properties of these transducers must generally be considered satisfactory, they have disadvantages regarding their design and manufacture. These disadvantages result in increased manufacturing costs and obstruct a general application of these transducers. Besides, the ring armature system cannot be made as small as desired because technological considerations prevent a manufacture of annular permanent magnets of relatively complex shape below a certain size.

The invention avoids these disadvantages. It provides a ring armature system which can be manufactured simply and without need for considerable adjustments and for expensive special molds for the permanent magnet so that a transducer embodying the invention can be made so small that it does not exceed dimensions, e.g., of 4 mm. x 7 mm. and still has a high efficiency.

The electroacoustic transducer according to the invention constitutes a ring armature system and is essentialiy characterized in that the permanent magnet which produces the permanent magnetic flux comprises a plug, e.g. of cylindrical shape, which is disposed at the center of the system and is contacted at its two end faces by pole plates the diameters of which are substantially equal, but exceed the diameter of the permanent magnet, and at least one external air gap is formed in the free space between the pole plates, in which air gap the armature having the shape of a circular ring (ring armature) of magnetic material is arranged with freedom of vibration, a diaphragm for radiating or receiving sound fat and consisting preferably of non-magnetic material is secured and the exciter winding is arranged inside the transducer and concentric with the axis thereof.

According to another feature of the invention, two air gaps may be provided, only one of which serves as a working air gap for the ring armature whereas the other gap disposed inside the transducer is arranged to receive the means for mounting the ring armature. Further features of the invention will be apparent from the following description.

FIGS. 1 to 3 and 5 to 7 show various embodiments of the electroacoustic transducer according to the invention. FiG. 4 shows a preferred embodiment of a ring armature used according to the invention and FIG. 8 shows by way of example a microphone according to the invention.

As is shown in FIG. 1, the cylindrical permanent magnet 1 forms the core of the transducer. At each of its two surface-ground end faces, it carries a

pole plate

2, 3, which may consist of a flat plate or may have a different shape, e.g., similar to a pot. Whereas the term plate is not really appropriate for the last-mentioned plate, it is more desirable for a clear description to define a comp nent only by its function irrespective of its shape. For this reason a pot-shaped plate is also referred to as a pole plate, sometimes as a pot-shaped pole plate.

In FIG. 1, the upper pole plate 2 consists of a fiat plate whereas the opposite plate 3 is potshaped. Its upturned rims define with the pole plate 2 an air gap 5, which receives the ring armature f. The diameter of the ring armature slightly exceeds that of the pole plate 2 so that the rim of the armature extends beyond the periphery of the driving system. This is necessary because the preferably slightly curved, sound radiating diaphragm 6 of non-magnetic material is secured to the rim, e.g., by being fitted, adhesively connected or flange-connected with application of heat. This arrangement has the advantage that more than the entire diameter of the transducer is available for a radiation of sound. This is of decisive significance in the case of small systems. In the illustrative embodiment shown in this figure, the excited winding 7 concentrically surrounds the cylindrical permanent magnet. The exciter winding 7 may either be directly wound on the magnet, e.g., with insulating paper interposed, or it may be wound on a separate coil body. The ring armature 4 is supported at its inside .perimherv at 9 by a non-magnetic sleeve 14-.

The illustrative embodiment according to FIG. 2 difiers from that according to FIG. 1 in that two pot-shaped pole plates 3, ltd having different diameters and arranged one in the other are provided on one side. This arrangement results in the formation of two air gaps, the outer air gap 5 constituting the working air gap for the ring armature 4- whereas the inner air gap 9 serves for securing or mounting the ring armature 4. In this embodiment the exciter coil is arranged on the cylindrical outside wall of the inner pot-shaped pole plate. To intensify the magnetic flux through the workingair gap, the upper pole plate 2 is offset at its rim so that the air gap 5 is smaller than the inner air gap 9.

In this connection it may be stated in general that the term air gap refers also to gaps in which the clearance between the pole faces is filled by nonmagnetic materials. These nonmagnetic materials serve for retaining the diaphragm.

In order to simplify the manufacture of the transducer according to the invention, it may be suitable under certain circumstances to use two fiat pole plates 2. and 3 and to mount a pole piece 8 consisting of a channel section bent in the form of a ring on one pole plate 3. Such an embodiment is shown in FIG. 3. The intermediate web portion of the channelshaped pole piece is in firm engagement with the pole plate 3, and its free ends define with the other pole plate 2 two annular air gaps and the outer one of which serves again as a working air gap whereas the ring armature 4 is mounted in the inner air gap. Just as the arrangements described hereinbefore, this arrangement comprises according to the invention the cylindrical permanent magnet at the center of the transducer. As is shown in FIG. 4, the ring armature used in all embodiments may have radial slots, which reduce the stiffness of the armature and reduce the eddy current losses to some extent. The slots 11 need not be radial but may be inclined, as is shown in FIG. 4 at 13.

FIG. 5 shows an embodiment of the invention comprising two

exciter coils

7 and 7a. The ring armature 4- is held between two

sleeves

14 and 14a of nonmagnetic material. Two pot-shaped pole plates 2', 3 are symmetrically arranged and the exciter coil is divided, the two half-

windings

7, 7a being disposed on opposite sides of the ring armature.

FIG. 6 shows an embodiment which comprises also two

exciter coils

7 and 7a but two

air gaps

5 and 9, the gap 5 constituting a working air gap whereas the inner air gap 9 accommodates the ring armature 4.

For this purpose, at least one of the

pole plates

2, 3 is formed at its rim with a channel section. The free space around the permanent magnet may communicate through bores 30 with the air cushion behind the diaphragm and with the outside air or a larger air chamber.

FIG. 7 shows another embodiment of the means for mounting the armature. The pole plate 3 is formed at its rim with a channel section, which accommodates the exciter winding. The ring armature 4 is mounted between a cylindrical sleeve 14 and a ring 14a, both of which consist of nonmagnetic material.

The ring armature need not be of uniform thickness but may be enlarged in certain zones, e.g. in the region of the alternating magnetic flux. This may be effected by the application of a second ring having a larger inside diameter to the gripped thinner ring. These two rings may be connected by spot welding. Alternatively, a covering of magnetic material in the form of a circular ring may be applied to the thinner armature ring, e.g., by means of an adhesive.

FIG. 8 shows an illustrative embodiment of a microphone according to the invention. The magnet 1 has a bore, through which a hollow rivet 15 extends, which serves for the fixation of the

pole plates

2 and 3. The diaphragm 6 is provided with a rim zone 16, which is of conical or similar shape and which terminates in elastic corrugations 17. The diaphragm is mounted on the housing 19 at 18. To modify the vibrations of the diaphragm in a manner known per se, a curved member 213 and a member 21 are provided to define a low air chamber behind the diaphragm. The sound waves can enter the large chamber 26 of the housing 19 through the hollow rivet 15, which may accommodate clamping means 22 and 23, and through openings 24 in the member 21. The openings 24 may also be covered with damping means 25. A tube 27 extends in a manner known per se in the chamber 26 and leads at 23 into the free sound field. A guard screen 29 is disposed before the diaphragm. When the sound transducer is inserted in a housing, e.g., a telephone receiver, the pole plates may suitably be formed with openings 3%), as is shown in FIG. 6. This will reduce the restoring force of the small air chambers behind the diaphragm and will utilize the hollow space of the housing.

Through these openings the rear side of the diaphragm may be exposed to the external sound field so that a transducer for a directional reception or radiation of sound is provided.

This is not the only application of the transducer according to the invention. The same can be manufactured in any size, c.g., in miniature size for hearing aids or in a size suitable for incorporation in telephone handsets. The large diameter of the diaphragm will ensure to an excellent acoustic efiiciency as well as an excellent frequency response with minimum distortions whereas the manufacturing costs are much less than those of the previously usual transducers.

The invention is not restricted in its application to electroacoustic transducers but may be used, e.g., as a receiver or transmitter for vibrations if the ring armature protruding from the magnetic system is connected to the inert mass of the vibration-receiving means or to the coupling means provided for the transmission of force.

Similarly, the invention may be applied to all devices in which a driving force in a circular distribution is provided.

What is claimed is:

1. An electromagnetic electroacoustic transducer, which comprises a central plug of permanent-magnetic material generating a permanent magnetic flux and having two mutually opposite end faces, pole means comprising two pole plates, each of which contacts one of said end faces and the diameters of which are substantially equal to them selves and larger than the diameter of said plug, said pole plates defining between themselves a free space, said pole means defining an outer air gap and an inner air gap, an armature of magnetic material in the shape of a circular ring extending through said outer air gap with freedom of vibration therein and having an inner rim disposed in said inner air gap, said transducer comprising further annular armature retaining means of nonmagnetic material engaging said inner rim of said armature on both sides thereof in said inner air gap to retain said armature, said armature having an outer rim disposed radially outwardly of the periphery of said pole means, said transducer comprising further a diaphragm secured to said outer rim of said armature and adapted to vibrate at sound frequencies, and an exciter winding which is disposed in the interior of said transducer and concentric with the axis thereof and adapted to generate an alternating magnetic flux permeating said armature where it extends through said outer air gap.

2. A transducer as set forth in claim 1, in which said plug is cylindrical.

3. A transducer as set forth in claim 1, in which said diaphragm consists of nonmagnetic material.

4. A transducer as set forth in claim 1, in which said armature is formed with slots.

5. A transducer as set forth in claim 1, in which said pole means comprise a channel-shaped pole piece which concentrically surrounds said plug and has a web directly secured to one of said pole plates and two free edges defining said outer and inner air gaps, respectively.

6. A transducer as set forth in claim 5, in which the other of said pole plates is substantially fiat and has an orTset marginal zone defining said outer air gap.

7. A transducer as set forth in claim 5, in which said exciter winding is disposed inside said channel-shaped pole piece.

8. A transducer as set forth in claim 5, in which the interior of said channel-shaped pole piece is entirely occupied by said exciter winding.

9. A transducer as set forth in claim 1, in which said pole plates comprise a fiat pole plate and two pot-shaped pole plates having different diameters and arranged one in the other, said pot-shaped pole plates defining with said flat pole plate said outer and inner air gaps.

10. A transducer as set forth in claim 9, in which said two pot-shaped pole plates define between them a free space containing said exciter winding.

11. A transducer as set forth in claim 10, in which said two pot-shaped pole plates comprise an inner pole plate having a cylindrical outside surface, on which said exciter winding is mounted.

:12. A transducer as set forth in claim 1, in which at least one of said pole plates has a rim formed with a channel section defining said air gaps.

13. A transducer as set forth in claim 12, which comprises means defining'an air cushion with the rear side of said diaphragm and means confining with said plug a free space surrounding said plug, said last-mentioned means being formed with bores establishing a communication from said space to said air cushion and the outside air.

14. A transducer as set forth in claim 12, which oomprises means defining an air cushion with the rear side of said diaphragm, means confining with said plug a free space surrounding said plug, said last-mentioned means being formed with bores, and means defining an air chamber larger than said free space around said plug, said bores establishing a communication from said free space around said plug to said air cushion and to said air chamber.

15. A transducer as set forth in claim 12, in which said plug and pole means are symmetric with respect to a plane, in which said armature extends.

16. A transducer as set forth in claim 12, in which said channel section contains sa-id exciter winding and in which said armature retaining means comprises a cylindrical sleeve and a ring, both of which surround said plug and retain said armature between them.

References Cited in the file of this patent UNITED STATES PATENTS 1,822,095 High Sept. 8, 1931

Claims

1. AN ELECTROMAGNETIC ELECTROACOUSTIC TRANSDUCER, WHICH COMPRISES A CENTRAL PLUG OF PERMANENT-MAGNETIC MATERIAL GENERATING A PERMANENT MAGNETIC FLUX AND HAVING TWO MUTUALLY OPPOSITE END FACES, POLE MEANS COMPRISING TWO POLE PLATES, EACH OF WHICH CONTACTS ONE OF SAID END FACES AND THE DIAMETERS OF WHICH ARE SUBSTANTIALLY EQUAL TO THEMSELVES AND LARGER THAN THE DIAMETER OF SAID PLUG, SAID POLE PLATES DEFINING BETWEEN THEMSELVES A FREE SPACE, SAID POLE MEANS DEFINING AN OUTER AIR GAP AND AN INNER AIR GAP, AN ARMATURE OF MAGNETIC MATERIAL IN THE SHAPE OF A CIRCULAR RING EXTENDING THROUGH SAID OUTER AIR GAP WITH FREEDOM OF VIBRATION THEREIN ADN HAVING AN INER RIM DISPOSED IN SAID INNER AIR GAP, SAID TRANSDUCER COMPRISING FURTHER ANNULAR ARMATURE RETAINING MEANS OF NONMAGNETIC MATERIAL ENGAGING SAID INNER RIM OF SAID ARMATURE ON BOTH SIDES THEREOF IN SAID INNER AIR GAP TO RETAIN SAID ARMATURE, SAID ARMATURE HAVING AN OUTER RIM DISPOSED RADIALLY OUTWARDLY OF THE PERIPHERY OF SAID POLE MEANS, SAID TRANSDUCER COMPRISING FURTHER A DIAPHRAGM SECURED TO SAID OUTER RIM OF SAID ARMATURE AND ADAPTED TO VIBRATE AT SOUND FREQUENCIES, AND AN EXCITER WINDING WHICH IS DISPOSED IN THE INTERIOR OF SAID TRANSDUCER AND CONCENTRIC WITH THE AXIS THEREOF AND ADAPTED TO GENERATE AN ALTERNATING MAGNETIC FLUX PERMEATING SAID ARMATURE WHERE IT EXTENDS THROUGH SAID OUTER AIR GAP.