Abstract:
Several embodiments of the instant invention incorporate a loudspeaker design utilizing hard magnetic poles and yokes. The magnetic field of the loudspeaker is created and guided with a series of critically formed hard magnetic structures guiding the magnetic field from the primary magnet to the gap in a loop of hard magnetic material, replacing the soft magnetic materials normally used. Magnetization of the components of the hard magnetic loudspeaker driver with radial pole patterns—a yoke radial magnet, a washer pole magnet and a yoke upper ring magnet—is performed with these components in their final assembly relationships.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/088,683, filed Dec. 7, 2014, incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to loudspeakers. More particularly, the present invention relates to loudspeakers for ear phones. 
         [0003]    BACKGROUND 
         [0004]    The performance of dynamic loudspeakers and transducers incorporating moving coil or moving wire in a magnetic field spanning a gap between stationary structures (typically a pole and a yoke) is necessarily limited by the soft magnetic materials (typically iron) used in these stationary structures. Most loudspeakers use a mix of hard and soft magnetic materials to perform the function of guiding a magnetic field from a primary magnet through the gap of the transducer. 
         [0005]    In most standard loudspeaker designs, the magnetic flux from a fixed hard magnet or magnets is routed through soft magnetic material used in a pole piece and a yoke. The pole allows the field from the hard magnet to be routed to and focused in the gap between the pole and the yoke where the coil interacts with the field to transduce or convert a varying electrical signal passing through the coil into motion of the coil. The coil is fixed to a diaphragm and movement of the diaphragm produces sound. 
         [0006]    The use soft magnetic structures in a loudspeaker creates problems. The varying electrical currents in the transducer coils induce fluctuating magnetic fields in the soft magnetic pole and yoke structures, which can then cause the magnetic field in the gap to fluctuate. This flux modulation causes distortion in the sound produced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which: 
           [0008]    The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the detailed description, serve to explain the principles and implementations of the invention. 
           [0009]      FIG. 1A  shows an exploded view of an exemplary embodiment of a loudspeaker driver assembly. 
           [0010]      FIG. 1B  shows a perspective view of the loudspeaker driver assembly. 
           [0011]      FIG. 2A  shows a perspective view of the yoke. 
           [0012]      FIG. 2B  shows a top plan view of the yoke. 
           [0013]      FIG. 2C  shows a side cut-away view of the yoke. 
           [0014]      FIG. 3  shows a cut-away side view of the loudspeaker driver assembly. 
           [0015]      FIG. 4  shows a close-up of the pole-yoke gap in  FIG. 3 , showing magnetic lines of force in the pole-yoke gap. 
           [0016]      FIGS. 5 a  and 5 b    illustrate eddy current generation and mitigation. 
           [0017]      FIG. 6A  shows a cut-away view of the loudspeaker driver assembly and pole patterns of the magnets used. 
           [0018]      FIG. 6B  shows an overhead view of the yoke radial magnet. 
           [0019]      FIG. 6C  shows an overhead view of washer pole magnet. 
           [0020]      FIG. 6D  shows an overhead view of the yoke upper ring magnet. 
           [0021]      FIG. 7  shows a section view of a first fabrication set-up for fabricating the exemplary hard magnetic loudspeaker driver according to a first exemplary method of fabrication. 
           [0022]      FIG. 8  shows a section view of a second fabrication set-up for fabricating the exemplary hard magnetic loudspeaker driver according to a second exemplary method of fabrication. 
           [0023]      FIG. 9  shows a section view of a third fabrication set-up for fabricating the exemplary hard magnetic loudspeaker driver according to a third exemplary method of fabrication. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference materials and characters are used to designate identical, corresponding, or similar components in different figures. The figures associated with this disclosure typically are not drawn with dimensional accuracy to scale, i.e., such drawings have been drafted with a focus on clarity of viewing and understanding rather than dimensional accuracy. 
         [0025]    In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application and business related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
         [0026]    Use of directional terms such as “upper,” “lower,” “above,” “below”, “in front of,” “behind,” etc. are intended to describe the positions and/or orientations of various components of the invention relative to one another as shown in the various Figures and are not intended to impose limitations on any position and/or orientation of any embodiment of the invention relative to any reference point external to the reference. 
         [0027]    Those skilled in the art will recognize that numerous modifications and changes may be made to the exemplary embodiment(s) without departing from the scope of the claimed invention. It will, of course, be understood that modifications of the invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the exemplary embodiment(s) is essential. Other embodiments are possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof. 
       Exemplary Embodiment 
       [0028]      FIG. 1A  shows an exploded view of an exemplary embodiment of a hard magnetic loudspeaker driver  100  and  FIG. 1B  shows a perspective view of the hard magnetic loudspeaker driver  100 . The hard magnetic loudspeaker driver  100  comprises a yoke  102 , a center pole  104 , and a washer pole magnet  106 . The center pole  104  is configured to nest within the yoke  102  and the washer pole magnet  106  is configured to nest within the yoke  102  on top of the center pole  104 . The yoke  102  and washer pole magnet  106  are sized, shaped, and positioned such that a pole-yoke gap  108  exists between them. 
         [0029]      FIG. 2A  shows a perspective view of the yoke  102 .  FIG. 2B  shows a top plan view of the yoke  102 .  FIG. 2C  shows a side cut-away view of the yoke  102 . The yoke  102  has a yoke gap  110  in one side to prevent large-scale eddy currents from occurring. The washer pole magnet  106  has a washer gap  112  that serves the same purpose.  FIGS. 5 a  and 5 b    illustrate eddy current  116  generation and mitigation. In the embodiment of  FIG. 5 a   , the yoke  102  does not have a yoke gap  110 . Eddy currents  116  induced into the yoke  102  can combine into a large net eddy current  116  around the yoke  102 . In  FIG. 5 b   , the washer pole magnet  106  has a washer gap  112  that prevents the eddy currents  116  induced into the washer pole magnet  106  from combining into a large net eddy current  116 . 
         [0030]      FIG. 3  shows a cut-away side view of the hard magnetic loudspeaker driver  100 .  FIG. 4  shows a close-up of the pole-yoke gap  108  in  FIG. 3 , showing magnetic lines of force  114  in the pole-yoke gap  108 . A voice coil  140  (see  FIG. 6A ) is configured to enter the pole-yoke gap  108  when current passing the through the voice coil  140  induces a magnetic field in the voice coil  140  that interacts with the magnetic lines of force  114  and draws the voice coil  140  to enter the pole-yoke gap  108 . The voice coil  140  moves according to signal variations in the current it is carrying, moving the speaker diaphragm  142 , which generates sound. 
         [0031]    In prior art embodiments, the center pole  104  comprises hard magnetic material (material that is difficult to magnetize, but once magnetized, is difficult to demagnetize) and the yoke  102  and washer pole magnet  106  comprise soft magnetic material (material that can be easily magnetized at low magnetic field). Since soft magnetic materials can be demagnetized at low magnetic field, coercivity H c  is low. As they can be easily magnetized, their permeability is high. Hard magnetic materials require a higher magnetic field to magnetize and have coercivity He that is usually high. The yoke  102  and the washer pole magnet  106  are shaped to focus the magnetic circuit that originates in center pole  104  into the pole-yoke gap  108 . This focused field is presumed to be stable—but in reality it is modulated by the signals reflection in the soft material of the yoke  102  and washer pole magnet  106 . This results in flux modulation distortion. Eddy currents  116  from a signal in the voice coil  140  can produce persistent phantom or sub poles in the soft magnetic materials used in the yoke  102 , and washer pole magnet  106 . Their relative strength and persistence is the product of magnetic, susceptibility, permeability and remanence. 
         [0032]    The first exemplary embodiment of the hard magnetic loudspeaker driver  100  uses hard magnetic material for some or all parts of the yoke  102  and washer pole magnet  106 . Hard magnets lack magnetic susceptibly and are not permeable thus they are stable poles once they are orientated and charged. Substituting uniquely formed magnetic axis aligned hard magnets for the normally used soft magnetic materials substantially eliminates flux modulation distortion. Uniquely constructed hard magnetic yoke  102  and washer pole magnet  106  are formed and charged to form a controlled axis pathway for magnetic lines of force  114  that are used in several ways to replace soft magnetic, high permeability pole materials (such as Iron or silicon steel). 
         [0033]    The use of hard magnetic yoke  102  and washer pole magnet  106  components increases linearity of the loudspeaker motor dramatically reduces flux modulation and phase distortion. The reduction of these factors makes the hard magnetic loudspeaker driver  100  utilizing this technology uniquely suited for in ear monitors (IEMS), hearing aids or other applications that require a low distortion linear broadband transducer. 
         [0034]      FIG. 6A  shows a cut-away view of the hard magnetic loudspeaker driver  100  and pole patterns of the magnets used. The hard magnetic loudspeaker driver  100  a voice coil  140  attached to a speaker diaphragm  142 , which is attached to a diaphragm retainer  144 . The voice coil  140  is positioned directly over the pole-yoke gap  108  and configured to enter within when drawn in by currents within the voice coil  140  generating magnetic fields that interact with those in the pole-yoke gap  108 . The yoke  102  comprises a yoke radial magnet  120 , a yoke lower ring magnet  122  and a yoke upper ring magnet  124 . In  FIG. 6A  these three components of the containment structure yoke  102  are separate components, but in some embodiments, the yoke  102  is a single monolithic part and these three components are conceptual parts of the yoke  102 . The yoke radial magnet  120  has a pole pattern with a north pole in the center and a south pole on the circumference. The yoke lower ring magnet  122  has a pole pattern with a north pole facing the south pole of the yoke radial magnet  120  and a south pole at the upper end near the yoke upper ring magnet  124 . The yoke upper ring magnet  124  has a pole pattern with a north pole on the outer circumference and a south pole on the inner circumference. The washer pole magnet  106  has a pole pattern with a south pole in the center and a north pole around the circumference. These patterns are illustrated in  FIG. 6B , which shows an overhead view of the yoke radial magnet  120 , in  FIG. 6C , which shows an overhead view of washer pole magnet  106  and in  FIG. 6D , which shows an overhead view of the a yoke upper ring magnet  124 . In other embodiments, the magnets of the hard magnetic loudspeaker driver  100  could have exactly opposite polarities. For example, the washer pole magnet  106  could have a pole pattern with a north pole in the center and a south pole at the circumference, with the yoke radial magnet  120 , yoke lower ring magnet  122 , and yoke upper ring magnet  124  having reversed polarities as well. 
         [0035]    In alternative embodiments, some, but not all of the yoke radial magnet  120 , yoke lower ring magnet  122 , and yoke upper ring magnet  124 , and washer pole magnet  106  are of hard magnetic materials and the remainder are comprised of soft magnetic materials. 
       First Exemplary Method of Fabrication 
       [0036]      FIG. 7  shows a section view of a first fabrication set-up  160  for fabricating the exemplary hard magnetic loudspeaker driver  100  according to a first exemplary method of fabrication. The center pole  104 , the yoke radial magnet  120 , the washer pole magnet  106  and the yoke upper ring magnet  124  are made from hard magnetic material in their designed shapes, using known manufacturing techniques such as sintering or casting. These component are initially made without imparting any magnetization to them. These components are made separately and then assembled in the first fabrication set-up  160  as shown in  FIG. 7  with a non-magnetic yoke lower ring  152  substituted for the yoke lower ring magnet  122 . A magnetization coil  150  is placed around the non-magnetic yoke lower ring  152 . Current is passed through the magnetization coil  150 , magnetizing the center pole  104 , the yoke radial magnet  120 , the washer pole magnet  106  and the yoke upper ring magnet  124 . The direction of the current determines the orientation of the poles in these components. These components are then removed from the magnetization coil  150  and the yoke lower ring magnet  122  placed inside the magnetization coil  150 . Current is then passed through the magnetization coil  150  in an opposite direction from the current used in magnetizing the other components of the hard magnetic loudspeaker driver  100 . The yoke lower ring magnet  122  is then removed from the magnetization coil  150 . Now magnetized with substantial residual magnetism, the components of the hard magnetic loudspeaker driver  100  are assembled as described and shown in  FIG. 6A . 
         [0037]    Hard magnetic materials that may be used include alnico alloys, alloys of neodymium (such as Nd 2 Fe 14 B) and alloys of strontium. If the materials used are anisotropic, the center pole  104 , the washer pole magnet  106  and the yoke radial magnet  120  should be fabricated with the hard magnetic properties oriented in radial directions and soft magnetic properties oriented circumferentially and along cylindrical axes. 
         [0038]    In some alternative embodiments, the center pole  104  may be fabricated and magnetized separately to achieve a customized level of magnetization. In such embodiments, the center pole  104  may be substituted with a soft magnetic pole during the magnetization of the washer pole magnet  106 , the yoke radial magnet  120 , and the yoke upper ring magnet  124 . After all these components are magnetized, the center pole  104  is assembled with the other components of the hard magnetic loudspeaker driver  100 . 
       Second Exemplary Method of Fabrication 
       [0039]      FIG. 8  shows a section view of a second fabrication set-up  162  for fabricating the exemplary hard magnetic loudspeaker driver  100  according to a second exemplary method of fabrication. The second method of fabrication is similar to the first method of fabrication, differing only in the fabrication set-ups used. The second fabrication set-up  162  is similar to the first fabrication set-up  160 , the primary difference being the placement of a soft magnetic collar  156  around the magnetization coil  150  and configured to provide a path for magnetic lines of force  114  from the yoke upper ring magnet  124  to the yoke radial magnet  120  during magnetization. With the soft magnetic collar  156 , better magnetization and pole patterns can be created in the yoke upper ring magnet  124  and yoke radial magnet  120 . Also, less energy is required for the same amount of magnetization. The same soft magnetic collar  156  may be used for magnetization of the yoke lower ring magnet  122 , or a different soft magnetic collar may be used with different geometries to provide better magnetization and pole patterns for the yoke lower ring magnet  122 . 
       Third Exemplary Method of Fabrication 
       [0040]      FIG. 9  shows a section view of a third fabrication set-up  162  for fabricating the exemplary hard magnetic loudspeaker driver  100  according to a third exemplary method of fabrication. The third method of fabrication is similar to the first method of fabrication, with some differences in the fabrication set-up and the methodology as follows. 
         [0041]    As in the first fabrication set-up  160 , the third fabrication set-up  164  has a magnetization coil  150 . In some embodiments, soft magnetic collar  156  may be included the third fabrication set-up  164  and used in a similar manner as in the second exemplary method of fabrication, but in other embodiments, no soft magnetic collar  156  is used, as in the first exemplary method. 
         [0042]    As in the first exemplary method, the center pole  104 , the yoke radial magnet  120 , the washer pole magnet  106  and the yoke upper ring magnet  124  are made from hard magnetic material in their designed shapes, using known manufacturing techniques such as sintering or casting. At least the yoke radial magnet  120 , the washer pole magnet  106  and the yoke upper ring magnet  124  are initially made without imparting any magnetization to them. However, unlike in the first exemplary method, here the yoke lower ring magnet  122  is magnetized separately. These components are then assembled as in the third fabrication set-up  164  as shown in  FIG. 9 . However, unlike the first fabrication set-up  160 , no non-magnetic yoke lower ring  152  is substituted for the yoke lower ring magnet  122 . The magnetization coil  150  is placed around the yoke lower ring magnet  122 . Current is passed through the magnetization coil  150 , magnetizing the center pole  104 , the yoke radial magnet  120 , the washer pole magnet  106  and the yoke upper ring magnet  124 . The magnetic lines of force  114  will pass through the yoke lower ring magnet  122  in a direct opposite the magnetization of the yoke lower ring magnet  122 . This could potentially reverse the polarity of magnetization of the yoke lower ring magnet  122 , which would not be desirable. However, if the current in the coils is kept below a level calculated to keep the magnetic field intensity below the coercivity Hc, the yoke lower ring magnet  122  should maintain its original polarity and most of its previous residual magnetism. The third exemplary method then has a disadvantage over the other two in that the magnetization of the components will probably not be as strong. However, the third exemplary method has the advantages of simplicity and that the magnetization of the components of the hard magnetic loudspeaker driver  100  with radial pole patterns—the yoke radial magnet  120 , the washer pole magnet  106  and the yoke upper ring magnet  124 —is performed with all the yoke  102  and center pole  104  components in their final assembly. This will likely make a better alignment of pole patterns between the various components than if they were magnetized separately.