US2961497A - Magnetic loudspeaker - Google Patents

Description

Nov. 22, 1960 E. A. HEPPNER 2,961,497

MAGNETIC LOUDSPEAKER Filed May 1, 1957 United States Patent MAGNETIC LOUDSPEAKER Elmore A. Heppner, Round Lake, Ill., assignor to Heppner Manufacturing Co., a corporation of Illinois Filed May 1, 1957, Ser. No. 656,289

4 Claims. (Cl. 179-114) This invention relates to a magnetic loudspeaker and in particular to loudspeakers utilizing a reed for vibrating the cone.

It is the principal object of the invention to provide a new and improved reed type inducer for use in a speaker wherein the reed is resiliently centered between opposed pole pieces.

Another object is to provide such an inducer wherein the reed is clamped at one end between a pair of magnets and the pole pieces are arranged to form with the reed and the magnets a pair of magnetic loops wherein the flux components in the reed tend to cancel each other.

A further object is to provide such an inducer having a fixed coil associated with the pole pieces and arranged around the reed to induce magnetic flux in the reed thereby to displace the reed from the centered position between the pole pieces as an incident to the passage of a signal current through the coil.

Still another object is to provide such an inducer wherein the coil is center-tapped for use with an audio frequency signal providing circuit, whereby direct current may be fed into the center tap to pass through opposed coil windings thereby to have a mutual counteracting eflect and preclude affecting the reed.

Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings wherein:

Fig. 1 is a rear view of a loudspeaker having an inducer embodying the invention;

Fig. 2 is, a side view thereof; and

Fig. 3 is a section view thereof taken approximately along the line 33 of Fig. 1.

In the exemplary embodiment of the invention as disclosed in the drawings, a loudspeaker generally designated is shown to comprise a frame 11 arranged to carry in the conventional manner a diaphragm or cone 12. The invention comprehended herein relates to the means for vibrating the cone to produce sounds corresponding to an electrical signal. More specifically, this means, herein referred to as transducer 13, comprises a magnetic reed device responsive to an input signal of audio frequency to produce a corresponding mechanical displacement of the cone 12.

Reference being had more specifically to Fig. 3, transducer 13 is seen to comprise a pair of magnets 14 and 15 between which one end 16a of an elongated, fiat reed 16 is clamped. The magnets are preferably of the bar type and are arranged so that the north pole of one magnet and the south pole of the other magnet are in abutment with reed end 16a. While it makes no difference which of the two possible arrangements is employed, for illustrative purposes I have shown the first magnet 14 as having its south pole 14a and the second magnet 15 as having its north pole 15a in opposed abutment with reed end 16a. Further, while magnets 14 and 15 may be alternatively of the permanent or electromagnetic type as desired, they are illustrated herein as comprising permanent magnets formed of a material having suitable high magnetic flux characteristics such as the alloy Alnico V. The means for clamping the magnets is shown to comprise a stud 17 which is arranged to be secured to a brace 18 carried on frame 11, for securing the entire transducer 13 to the frame.

. Reed 16 is preferably formed of a resilient or springy sheet material permitting high flux density. One example of a material found to be particularly satisfactory for such purposes is the iron-cobalt alloy manufactured under the trade name Permendur.

Extending from outer or north pole portion 14b of magnet 14 is a first pole piece 19 having an end 19a spaced a slight distance away from a second portion 16b of the reed. A similar second pole piece 20 extends from the outer or south pole portion 15b of magnet 15 with an end 20a spaced a slight distance from reed portion 16b opposite end 19a of the first pole piece. Thus, an air gap 21 is formed between pole piece ends 19a and 20a in which reed portion 16b is centered. Pole pieces 19 and 20 are preferably formed of a material such as soft iron having low reluctance. As best seen in Fig. 3 the pole pieces are secured to the magnets by means of stud 17.

The above described arrangement of the magnets, pole pieces and reed results in the formation of two magnetic circuits or loops. The first such loop is one wherein the fiux leaves the north pole 14b of the outer magnet 14, passes through pole piece 19, and through the reed from portion 16b to end portion 16a, and returns to the magnet at south pole 14a. The second loop is one wherein the flux leaves the north pole 15a of magnet 15, passes through reed 16 from end 16a to portion 16b thereof, and through pole piece 20, and returns to the magnet at south pole 15b thereof. Magnets 14 and 15 are of equal magnetic strength and thus the flux components in the reed cancel each other. The reed portion 16b is retained by its resiliency in a centered position between pole ends 19a and 20a in a magnetically neutral condition.

An input electrical signal is caused to act upon reed 16 by means of a coil 22 extending freely around the reed and disposed between the pole piece ends 19a and 20a and the magnets. The coil is carried on a suitable bobbin 22a which s slightly smaller internally in a direction perpendicular to the fiat plane of the reed than the distance between pole piece ends 19a and 20a. Thus the reed movement through gap 21 is limited by abutment of the reed with the bobbin, thereby precluding the reed from contacting either pole piece end. When an electrical signal such as an audio frequency current passes through coil 22, it magnetizes the reed in a manner corresponding to the amplitude and direction of the current. The varying magnetic flux induced in portion 16b of the reed reacts with the magnetic field between ends 19a and 20a of the pole pieces to cause the reed to be drawn alternatively to one or the other of the pole pieces and away from the centered position. At the outer end of the reed, a pin 23 is provided to connect fixedly the apex 12a of cone 12 and the reed. Thus the movement of reed portion 16b in the gap 21 causes end 16c of the reed to move pin 23 and the cone 12 at the frequency of and in correspondence with the amplitude of the input signal.

While coil 22 may be of any suitable type proper for use with the specific audio frequency signal supply circuit to be used, in the illustrated embodiment, the coil comprises a continuous coil having a first end connection 22b, a center-tap connection 22c and a second end connection 22d. Thus direct current from the power supply may be fed into the coil center-tap connection 22c from which it may flow in opposite directions to each of the end connections 22a and 220. Resultingly, the magnetizing effect of the direct current on reed 16 is canceled out and only the alternating, audio frequency current which is supplied through end connections 22b and 22d affects the reed. Sucha coil arrangement is advantageous where push-phil circuits are employed for "providing the audio frequency current. V

While Ihave shown and descrihed cet'tain embodiments of my invention, it is to be understood that iscapable of many modifications. Changes, ther'efot e, ii1 theconstruction and arrangement may be iriade without departing from the spirit and scope of the'i'nvention as defined in the appended claims.

I claim: V p

1. A transducer comprising: a reed bf readily nag netizable material; a pair of pole pieces spaced on appesite sides ofone 'portion of the reed; apair of magnets for inducing flux in said pole pieces to form opposite poles therein adjacent the feed, said magnets and pole pieces extending in a series relationship to place another portion of the reed in a magnetically neutral condition; and a coil forindu'cing in said reed a magnetic flux corresponding to an alternating current signal, said coil being center tapped for distributing direct current through opposite halves of the coil in opposite directions to nullify magnetic effect thereof on said reed.

2. A transducer comprising: an elongated reed of resilient material having a high permeability; a firstrnagn'et having a north pole abutting a first portion of the reed; a first pole piece extending from the south pole of said magnet to an end spaced slightly from a second portion of the reed to form with the reed and first magnet a first magnetic loop; a second magnet similar to the first magnet and having a south pole abutting said first portion of the reed opposite the north pole of said first magnet, whereby said first portion is clamped therebetween; a second pole piece extending from the north pole of the second magnet to an end spaced slightly from said second reed portion opposite the end of the first pole piece to form with the reed and second magnet a second magnetic loop, the resiliency of said reed acting to urge said second portion of the reed to a centered position in an air gap formed between said ends of the pole pieces; and a coil around said reed to magnetize said second portion in conformity With electrical current therein, to cause corresponding displacement of said second portion relative to said centered position, said coil having opposing portions for carrying a direct current component of the signal in opposite directions to nullify its effect on said reed.

3. A speaker comprising: a reed of resilient material adapted to have high flux saturation; at first permanent magnet having a north pole adjacent a first portion of the reed; a first soft iron pole piece extending from the south pole of said magnet to an end spaced slightly from a second portion of the reed to form with the reed and first magnet a first magnetic loop; a second permanent magnet similar to the first magnet and having a south pole adjacent said first portion of the reed opposite the north pole of said first magnet; a second soft iron pole piece extending from the north pole of the second magnet to an end spaced slightly from said second portion opposite the end of the first pole piece to form with the reed and second magnet a second magnetic loop, whereby the fluxes in the reed cancel each other out, said second portion of the reed being urged to a centered position intermediate said ends of the pole pieces by the resiliency of the reed; a coil around said reed to magnetize said second portion in conformity with an audio frepuency electrical signal, to cause said magnetized second portion to react with said pole piece ehds and be displaced relative to said centered position, said coil being center tapped to permit direct current to be fed therethrough without effecting the reed; a speaker diaphragm; and means connecting the reed to the diaphragm to move said diaphragm with said second portion.

4. A transducer comprising: pole pieces forming a pair of spaced magnetic poles of opposite polarity; a magnetic reed extending freely through the space between said poles and having a portion projecting therefrom; a coil carried on an annular bobbin around said portion for inducing a magnetic flux in the element as a result of passage of audio frequency c'urrent through the coil, said flux coacting with "the flux of the magnetic poles to reciprocate the element toward and from respective poles, said bobbin being internallysmaller ina direction parallel to a line between the poles than the distance betweenthc pole pieces thereby limiting the extentof reciprocation of the element to preclude contact of the'reed with each of said polepiece's.

References Cited in the file of this patent UNITED STATES PATENTS 1,153,593 Baldwin a Sept. 14, 1915 2,241,107 Woodru'g May 6, 1941 2,300,638 Wente Nov. 3, 1942 2,551,114 Lavery June 13, 1950 2,582,942 Baker Jan. 22, 1952 2,588,327 Roberts 'et a1. Mar. 4, 1952 2,692,918 Berger t Oct. 26, 1954

Images