US3160716A - Transducer - Google Patents

Description

H. J. LUTH TRANSDUCER Filed Aug. 1, 1960 Dec. 8, 1964 United States Patent O 3,160,716 TRANSDUCER Hmoid i. Luth, Hai-Syd Chemicals, lne., Heiland, Mich. Filed Aug. l, 195i), Ser. No. 46,668 1 Claim. (Cl. i79-115.5)

This invention relates to devices utilizing a magnetic `field and more particularly to a conductor coil in a transducer.

It is common practice to operate a conductor coil in an air gap having a strong magnetic iield and to pass an electric current through the conductor coil causing it to move in the magnetic field, or to move the coil in the field to induce an electrical current in the coil. In some applications, the coil is moved from its neutral position by a momentary application of au electric current and is then returned to its neutral position by means of mechanical spring devices. Various types of solenoid switches, relays and transducers, such as microphones and loudspeakers operate in this manner.

More specifically and by way of example, in a moving coil or electrodynamic loudspeaker, a voice coil is affixed to the apex of a cone or diaphragm which is flexibly supported on a frame at the base diameter of the cone by an annular cloth ring called a surround, and is also supportedv at the voice coil connection by a smaller, ilexible annular ning called a spiden Thevoice coil is generally mounted with its axis at rightangles to magnetic lines of ux in a strong magnetic field, that is produced by a ring magnet and pole piece attached to the under side of the speaker frame. The surround and the spider centrally locate the voice coil and cone and hold them in a neutral axial position about the pole piece. An audio frequencyoutput from an Vamplifier is passed through the' voice coil and causes a force to be exerted in a direction of the axis of the coil, displacing the coil in the magnetic eld, the displacement varying with the magnitude of the current passing through the coil.

The exible nature of the supporting devices allows the coil movement and also supplies a spring or mechanical restoring force to move the coil back to its neutral position when the amplifier frequency is at zero. The coil and diaphragm move back and forth in an axial direction due to a variation in` the amplitude of the audio signal and produce audible sound.- Y The coil' restoring force should increase linearly with the displacement force in order to accurately reproduce the audio output of 'the amplifier, but an actual loudspeaker system, such restoring force is non-linear and such non-linearity increases rapidly as the displacement force is increased, causing serious distortion of the sound waves and undesirable resonances, especially when transient impulses of a high amplitude are impressed upon the voice coil. The same defect is found in a dynamic microphone.

A primary object of this invention is to provide a new and novel voice coil for an electrodynamic loudspeaker or other transducers that will allow them to respond to sound waves and transient impulses and transmit said waves and p impulses free from undesirableresonances and disortion.

Another object of this invention is to provide anonmechanical restoring force for a moving conductor in an electro-magnetic system.

Another object of this invention is to provide a magnetic ice `reluctance path to magnetic lines of ilux in an electromagnetic system which results in the linear return of a conductor that has been displacedin a magnetic eld to its original or neutral position, and which may be used in transient switching devices, remote positioning devices,

transducers and any electromagnetic device dependent upon a spring action for zero positioning.

Further objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a cross-sectional elevation of an electrodynamic loudspeaker' embodying the invention.

FIGURE 2 is an enlarged view of the voice coilcross section shown in FIGURE 1.

FIGURES 3 and 4 are traces as shown by an oscilloscope comparing the operation of applicants loudspeakers with that of la conventional speaker.

While this invention is susceptible to embodiments of different forms, there isV shown iu the drawings and Will herein be described in detail an embodiment of the invention With the understanding that the present disclosure is to be considered as an exempliiication of they principles of the invention, and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

Referring to the drawing, a suitable supporting structure for a loudspeaker is shown, including a permanent ring magnet 4 with a plate 5, having a centrally located hole 6 therein, mounted on itsV top surface, and a circular plate 7 with a centrally disposed cylindrical pole-piece 8, mounted on the bottom surface of magnet 4. The plates are'secured to ring magnet 4Aby a plurality of tie bolts 9. The pole piece S is smaller in diameter at its top portion than the hole 6 and extends axially upward through the ring magnet -4 and the hole 6 terminatnig near the top surface of the plate 5. A strong magnetic field is established by the'magnet- 4 in a circular air gap formed between the surface of hole 6 and the outer surface of pole piece 8. A plurality of upwardly and outwardly extending legs 10 originate at the outer periphery of plate 5 and terminate in an annular ring 11 to form the basket of the loudspeaker and a felt ring 11a is cemented to the top surface of ring 1l providing a cushion for mounting the loudspeaker.

The operating or moving lcomponents ot applicants 'Ilhe means lfor supporting the diaphragm and coil` consist of .an annular ring or surround 15 of cloth or other ilexible .material forming a flexible connection between the basket rim 11 and the base portion of the diaphragm l2. Additional support for the diaphragm and coil is provided Iby an annular ring or pider 16 of flexible sheet material atlxed to the voice coil adjacent its connection to the apex of the diaphragm and to the top plate 5, forming a exible connection therebetween.

The spider 16 which supports the voice coil 13 in Vthe speaker Aframe is made more tlexible in applicants loudspeaker than in a conventional loudspeaker for the purpose of utilizing the suspension device as centering means only, to keep the coil in axial alignment as it is moved in the air gap, and to afford very little, if any, opposition or restoring force to the movement of the coil.

A preferred form of applicants voice coil is shown in FIGURE 2 and comprises a cylindrical aluminum tube 2i? having its outer ysurface precoatedY with a silicone rubber 21. A cylindrical paper form 22 having a band of magnetic material 23 disposed on its outer surface extending from the edge to the center of the form is cemented concentrically about the tube 20, and a conductor 24 is wound in a double Alayer coil over the magnetic material. The ends ofthe conductor 24 are extended out to one of the legs and terminate in a connection 25.

In operation, the magnetic material 23 of the coil 13 offers a relatively low reluctance path for the magnetic lines of ilux in the air gap and as the coil is displaced axially upward or downward from its neutral position in the air gap, by an audio signal applied to the voice coil, Vthe magnetic tiux will follow the path of low reluctance offered by the magnetic material rather than the path of high reluctance oered by the air gap. YAs the `magnetic lines of flux fol-low the magnetic material, they Iare bent in the direction of coil movement and act to restore the coil to its neutral position when the displacement 'force is removed or reduced to zero. The ilux lines act as a magnetic spring producing a coil restoring force that is'completely linear to the'coil displacing force.

Various methods of coil construction may be resorted to in order to produce a magnetic material spacially coexistent with a conductor coil, and a few are enumerated in the following examples:

Example l Example I1 A self-supporting double layer cylindrical coiled conductor is cemented to the outside surface of a cylindrical aluminum tube and the outside surface of the coil coated with a catalyzed epoxy resin, dusted with iron powder and allowed to cure. Y

Example III Y An adhesive cement is made up with a low viscosity epoxy resin and iron powder, and used-for yfastening the turns .of a two-layer cylindrical conductor l'coiltogether as Well as to cement the coil to the outer surface of a cylindrical paper form.

Example l V A strip of paper coated on one side with a Iband of catalyzed resin has iron powder dusted onto and rolled into the band, as with a rubber roller, and allowed to cure. The paper is 'cemented to the outer surface of a cylindrical aluminum tube onto which a thin layer of silicone rubber has been precoated. A dou-ble layer of conductor coil is Wound about the magnetic band. The rubber coating acts as a yieldable surface between the tube and the conductor winding.

Example V A coil as in Example IV except that a double band of magnetic material is used, one on each side of the paper strip.

Example VI A magnetic iron conductor'is wound about the outer surface of a cylindrical paper form.

Example VII A lay-er of magnetic iron foi-l is formed about and aixed to the outer surface of a cylindrical paper form v and a conductor wound about the iron foil.

The above examples show that the voice coil of ap plicants invention can rbe made up in -many various ways. It should be noted that the greater the amount of magnetic material used in the construction of the coil, the lower the reluctance to the magnetic line of ilux.

The curves of FIGURES 3 and 4 show a comparison between the restoring forces operating on a loudspeaker coil having a magnetic material disposed coaxially with the coil conductor as described -in Example V and an identical speaker coil but without the magnetic material, as measured on an oscilloscope. In each instance, the coils were placed on a magnetic structure and fastened with a spider except that the spider used with the magnetic coil was of a larger diameter in order to form a more liexible Imounting and relegato its function to centering purposes only. The coils were raised a fixed distance aboverthe gap and released. It can be said that if there werel no inductance in the coil, and no initial forces or gravitational forces that the trace would be .a straight line. The trace shown in FIGURE 3 is the result obtained from the magnetic coil and it can be seen that the restoring force is completely linear. In FIGURE 4, the trace obtained by the non-magnetic coil shows a'slow take-off which is due to the restriction offered lby the spider and a non-linear restoring force -where considerable bouncing took placeldue to the spiden It is apparent trom viewing the two curves that Vthe restoring force offered by the magnetic spring effect is superior to the mechanical spider device since the restoring force of the magneticspring is completely Y linear to the coil displacing force.

Utilizing applicants invention in a loudspeaker results in excellent time constants when transient impulses are imposed on the voice coil. Because of the linear restoring force provided by the magnetic spring effect, ap plications for applicants invention include, any `device dependent upon lspring Iaction for zero positioning, such as meters, relays, transient switching devices and remote positioning devices.

I claim:

' A transducer comprising: a voice coil consisting of a cylindrical non-magnetic form with a current conductor wound about its outer surface and having a magnetic materialand a thin layer of yieldable material interposed between said conductor and said outer surfacega cylindrical pole piece having lines of magnetic ilux extending radially outward therefrom; means for mounting said voice coil concentric with and about said pole piece so that said coil is free to move in its axial direction from a 5 5 Y n neutral position; means for moving said voice coil in a 2,522,859 9/50 Carbonneau 179-1155 direction at right angles to said lines of magnetic iux; and 2,53 8,691 1/ 51 Kim 179-1155 means for bending said ux lines in the direction of coil 2,590,554 3/52 Lukacs 179-1155 movement including `a low reluctance path to said flux 2,352,059 11/58 Marchand et al 179-1155 lines oered by said magnetic material and which serves 5 FOREIGN PATENTS 1zlintlhte principal force 'to return the co11 to its neutral posr- 447,846 5/36 Great Britain.

119,719 5 30 Austria.

References Cited by the Examiner 253159 6/26 Great Britain 4 UNTTED STATES PATENTS lo ROBERT H. ROSE, Primary Examiner.

1,921,924 8/33 Hunter 179-1155 L. MILLER ANDRUS,WILL1AM C. COOPER, 1,962,012 6/34 Grossmann 179-1155 Examiners.

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