US2894182A

US2894182A - Electro-acoustic transducer

Info

Publication number: US2894182A
Application number: US541436A
Authority: US
Inventors: Siegfried J Zuerker; Benjamin J Saggese
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1955-10-19
Filing date: 1955-10-19
Publication date: 1959-07-07
Anticipated expiration: 1976-07-07

Description

July 7, 1959 5. J. ZUERKER ET AL 9 ELECTRO-ACOUSTIC TRANSDUCER Filed Oct. 19, 1955 F\G.l.

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INVENTORSI SIEGFRIED J. ZUERKER, BENJAMIN J. SAGGESE,

, THEIR ATTORNEY.

United States Patent ELECTRO-ACOUSTIC TRANSDUCER Siegfried J. Zuerker, Pennellville, and Benjamin J. Saggese, Liverpool, N.Y., assignors to General Electric Company, a corporation of New York Application October 19, 1955, Serial No. 541,436

2 Claims. (Cl. 317-201) This invention relates to an improved structure for the magnetic component of a transducer device.

It is an object of this invention to provide a novel magnetic structure for a transducer, such as a loudspeaker which permits fabrication at a reduced cost.

It is another object of this invention to provide a novel magnetic structure for loudspeakers, which structure has a configuration permitting it to be molded out of a powdered magnetic material.

It is still another object of this invention to provide a novel magnetic structure for loudspeakers, wherein the magnetic structure may be assembled to the rest of the speaker assembly by the use of a portion of the magnetic structure itself so that the cost of assembly is reduced.

In the prior art wherein one component of magnetic material has been soldered to another, it has been found necessary to first coat the components with a suitable base before applying the solder. This method of bonding results in a relatively thick effective air gap between the two members and a consequent increase of reluctance in the circuit. Therefore, it is a further object of this invention to provide a novel method of bonding magnetic materials so that the effective air gap between the materials is minimized.

It is still a further object of this invention to provide a novel means and method of bonding components of magnetic structures to one another so that the cost of assembly of these components is reduced and the sensitivity of the structures are increased.

Briefly, the objects of this invention are achieved in one form by the provision of a unitary structure forming a portion of the magnetic circuit of a loudspeaker, which unitary structure has provided thereon an integral means supporting the magnetic structure on the speaker basket. A second portion completes the magnetic circuit and is assembled to the remainder of the magnetic structure by the use of a bonding material which reduces the equivalent air gap normally existing between the second portion and the rest of the magnetic structure and thereby cuts down the consequent flux loss and yields a more sensitive instrument.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, both as to its structure and method of assembly, will best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

Figure 1 is a cross-sectional side view of a speaker embodying our invention; and

Figure 2 is a rear view of the speaker illustrated in Figure 1.

Referring now to Figure l of the drawing, it may be seen that the speaker is constituted by the supporting frame or basket 1. At the outer periphery of the basket a flange 2 supports the outer edge of a frusto-conical diaphragm 3. If desired, a spacing or securing ring, such ice as shown at 4, may be provided at the outer edge of the cone. At the center of the cone 3 there is provided a substantially tubular voice coil form 5 which is coupled to and drives the speaker cone 3 in the manner well known in the art. Also, in the manner well known in the art, we provide a flexible spider 6, which is secured at its outer periphery to the basket as shown at 7. A moving or voice coil 8 is wound on the voice coil form 5 and drives the diaphragm 3 in accordance with the varying electrical signals representing sound intelligence impressed thereon. The construction described is substantially that construction well known in the art and constitutes no part of our invention.

In accordance with our invention, we provide a permanent magnet 9 which may have a cylindrical configuration aud is disposed, as illustrated in the drawing, just to the rear of the basket 1. The magnet may, if desired, be constituted by an electro-magnet or may be a permanent magnet formed from the material known by the trade name Alnico V which is commonly used in the art for this purpose. A pole plate 10 of magnetic ma terial may be secured by any suitable means to the front of the magnet 9 or may be held by the action of the magnet itself and provides a path to carry magnetic flux to a region surrounding the voice coil 8. Alternatively the pole plate 10 may be eliminated and the magnet 9 extended to the region occupied by the pole plate. A cup or yoke structure 11, which is formed as a tube and which may have a circular cross-section, encompasses the magnet 9 and also constitutes a portion of the magnetic circuit of the device. The remainder of the magnetic circuit is completed by the bottom plate 12 which may be formed from a soft steel or other magnetic material and is secured to the rear end of the magnet 9 and engages the inner surface of the larger inner diameter end of the cup. A forward portion of the cup 11 is provided with a portion extending radially inward as shown at 13 and presents a smaller inner diameter. In combination with the pole plate 10, the portion 13 forms an air gap 14 in which the voice coil 8 is situated, whereby the electrical conductors constituting this coil may be traversed by the magnetic fiux emanating from the magnet 9. The extent of the inwardly directed portion is selected in accordance with the principle well known in the art so that the required spacing between the outer periphery of the magnet 9 and the inner wall of the cup 11 is at an optimum to maintain fringe flux losses between these two members at a minimum. The forward end of the portion 13 is provided with a means whereby the cup may be secured to the basket 1 by positioning extension 13, in an opening in the rear portion 15 of the basket 1 and peening it over to engage the frame in the manner indicated by reference numeral 16.

The construction of the magnetic portion of the speaker is such that the yoke or cup 13 may be molded using any suitable material capable of carrying magnetic flux. Thus, it is possible to utilize a powdered iron material for this portion of the assembly which may be fabricated by molding so as to considerably reduce the cost of this portion of the device. This particular advantage is gained by providing that the forward reduced inner diameter portion 13 of the cup constitutes the element completing the air gap, necessary for the operation of the voice coil.

As pointed out above, the magnetic circuit is completed by the bottom plate 12. The bottom plate, in addition to completing the magnetic circuit, also functions to make possible the use of material having a relatively low saturation value, and consequently relatively inexpensive materials, as it reduces the flux density by providing a path of ever increasing cross-section from its center to its periphery where it engages the cup 11. Thus, a powdered iron material is capable of transmitting the required flux without incurring high losses due to high flux density.

A further feature of our invention is the manner in which the bottom plate 12 and the pole plate are secured to the permanent magnet 9. It has been the custom in the prior art to solder such assemblies. The soldering operation has been carried out by coating the members with a base such as cadmium and by depositing pellets of solder and flux between the surfaces of the two members after the coating. Heat is then applied and the solder disperses over the two surfaces. However, the structure which thereby results is subject to the disadvantage of what amounts to a fairly large air gap exists between the two members 9 and 12. This air gap may be on the order of 0.002 of an inch and the resulting flux losses serve to reduce the sensitivity of the device.

In accordance with our invention, we provide that the opposing surfaces of the pole plate 10, bottom plate 12 and the magnet 9 shall each be cleaned by the application of a suitable cleansing agent and then coated with a relatively thin coat of tin-zinc, It has been found that a tinzinc composition of from 73 %83% tin and from 27%- 17% zinc, by weight, yields a bond of sufiicient strength to hold the members together. Within this range, a composition of 78% tin and 22% Zinc, by weight, appears to yield a bond of optimum strength characteristics. We have found that electroplating is the most effective method for forming a coating of tin-zinc on the surfaces to be joined. The members 9, 10, and 12 are then subjected to heat. The tin-zinc forms, upon cooling, a strong bond to hold the members 9, 10 and 12 together. The equivalent air gap between these members is far less than that obtained by other methods such as noted above and the consequent losses are avoided. The air gaps, obtainable by the use of this method, are on the order of 0.0002 of an inch and an overall increase in speaker sensitivity is obtained. Such an advantage permits either the construction of a more sensitive speaker or, if sensitivity comparable to competing speakers is desired, a smaller magnet with its consequent cost reducing feature may be used. We have found that if a further decrease in the equivalent air gap is de sired, pressure may be exerted on the elements 9, 10 and 12 to force out Whatever bubbles or undue thickness of plating material may be present.

The bonding technique, described above, has particular utility in forming structures constituting a magnetic circuit wherein it is desirable to avoid flux losses. However, it is not limited in its application to loudspeaker magnetic structures, but obviously has general utility in fabricating magnetic devices of diverse characteristics.

While the present invention is described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. We therefore, aim in the appended claims to cover all such variations as come within the true spirit and scope of the foregoing disclosure.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic assembly comprising a cup of one magnetic material, one end of said cup defining a first opening, the other end of said cup defining a second opening, a bottom plate of another magnetic material mounted on said cup so as to close said second opening, a magnet mounted on said bottom plate inside said cup and extending in the direction of said first opening, the magnetic material of said cup being such that it would be saturated by flux emanating from an end of said magnet, and the material of said bottom plate being such that it can carry the flux produced at the end of said magnet without saturating.

2. A magnetic structure as defined in claim 1 wherein the cup is made of molded magnetic material.

References Cited in the file of this patent UNITED STATES PATENTS 2,047,361 Dijksterhuis July 14, 1936 2,110,200 Clarke Mar. 8, 1938 2,397,400 Barwich Mar. 26, 1946 2,398,449 Ranci Apr. 16, 1946 2,705,263 Schoenberg Mar. 29, 1955 2,786,983 Hill Mar. 26, 1957 FOREIGN PATENTS 586,500 Great Britain Mar. 20, 1947 1,052,050 France Jan. 20, 1954