US2119272A - Loudspeaker - Google Patents

Description

- May 31, 1938'.' ENGHOLM 2,119,272

LOUDSPEAKER Filed July 5, 1934 @54 Baa-4, X/4Z vim Sum/wen Patented May 31, 1938 c 1 q r UNi'iED STATES PATENT OFFIQE LOUDSPEAKER Bernard A. Engholm, Shaker Heights, Ohio, as-

signor to The Bola Company, Cleveland, Ohio, a corporation of Ohio Application July 5, 1934, Serial No. 733,757

2 Claims. (01. 179-4155) This invention relates to loud speakers, such opening 13 into which the tip of the inner pole for exampleas those, which utilize a moving coil piece extends, whereby an annular air gap is that operates in an air gap across a magnetic provided between the two pieces. A voice coil M field. Speakers, which have a magnetic field that is removably mounted on a support !5, within is produced by a permanent magnet usually comthe air gap, and the support in turn is attached prise a strip which is rectangular in cross secto a diaphragm l6, which is illustrated as being tion, and which has a width that is severaltimes substantially conical in form. The interconnected the thickness. The strip is generally arranged in support and diaphragm are shown as being atthe form of a U and supports an inner pole piece tached to a centering member I! which is rigidly on the intermediate portion, and an outer pole fastened at its inner periphery to the neck of 10 piece at the ends of the arms of the U. the diaphragm and at its outer periphery to the The inner pole piece, heretofore, so far as I clampin rings The clamping rings n turn am aware, has been a solid cylinder, the diammay be attached to astationary diaphragm houseter of which has been considerably smaller than ing 20, as by securing members 2 I.

it the width of the magnet. I have found however, I have found that if the inner pole piece is 15 that such construction is objectionable in that made solid and of uniform diameter throughout it restricts the extent to which the magnet can its length,and that if the diameter is less than be charged at the time of excitation. I believe the width of the permanent magnet, that the that the restriction is due to the fact that the magnet can be charged, but that the extent of pole piece, because of its small size becomes satit will be materially less than if the inner pole 20 urated before the magnet, and thereby prohibits piece were made in accordance with my inventhe introduction of suflicient flux at the time of tion. The invention therefore, comprises a excitation to saturate the magnet. As a result, structure in which the pole tip is circular in crossthe flux distribution in the magnet does not have section, within the regio 0f the a p ut is s the desired degree of uniformity, and the density fla ed ward y om s region until it is is greatly impaired. stantially equal to the width of the magnet.

An object of my invention therefore, is to make This is partic a ly ShOWn in @6011- a low reluctance pole structure, which when apomy of manufacture, I make the inner pole piece plied to a permanent magnet enables it to be of laminations and fasten'them rigidly together,

39 charged to a much greater degree than any conas by rivets. struction heretofore designed, and of which I The permanent magnetic field structure, which am aware. Furthermore, my invention is diis produced by my invention, as described, greatrected to a construction which, when the magnet 1y increases the charge that can be imparted to is in use will result in a field of greater intenthe magnet at the time of excitation, and prosity and of m r uniform fl x distribution, for duces a structure that has more uniform flux a net of a given S e, d W ch ca e made distribution over any type of pole structure hereeconomically and readily assembled. tofore used.

Referring now to the drawing, Fig. l'is a side I c1aim:- elevation, partly in section, of a loud speaker hav- 1 In a loud speaker having a permanent 40 mg Permenent field magnet; 2 is a real" netic structure comprising a one-piece U-shaped 40 View O the peaker shown in Fig. 1, but on a striphaving substantially uniform width throughreduced Scale, w pa t Of e magnet broken out its length, and having an inner pole piece fasaway to show the interior construction, and Fig. tened thereto, the inner pole piece comprising a 3 is a sectional v taken through the magnet plurality of flat plates which extend parallel to to show the inner pole piece in side elevation. each other and in the same direction as the arms 45 The loud speaker with which I have illusof the U, and having an outer pole piece attrated my invention has a permanent magnetic tached to the ends of the arms and having an field structure, which comprises a U-shaped opening that cooperates with the inner pole piece magnetic strip iii, towhich an inner pole piece to provide an annular air gap, one end portion mi N is rigidly connected, adjacent the midportion of the plates forming a cylinder and the interthereof, and to which an outer pole piece I2 is mediate portion of the plates being flared in connected at the ends thereof. Pole pieces are all planes which transversely cut the midportion preferably attached to the strip 58 by welding, of the U-shaped strip. although other forms of connection may be uti- 2. A magnetic structure for a loud speaker lized, if desired. The outer pole piece has an comprising a permanent magnetic one piece 55 nection thereto, the plates terminating at the opposite end in a reduced cylindrical tip which projects into the opening in the outer pole piece to provide an annular air gap.

BERNARD A. ENGHOLM.

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