Abstract:
A linear loudspeaker motor. A flat, relatively thin, rigid elongate motor armature is disposed in a gap between the north pole of one elongate magnet and the south of another elongate magnet, or a gap between the north and south poles of the same, or effectively the same, magnet. Several alternative means are provided to suspend the armature in the gap. The armature includes an elongate electrically conductive, low impedance strip. When a current flows in the strip, a force is produced that tends to move the elongate armature in or out of the gap, thereby displacing a loudspeaker diaphragm to which it is attached.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicant claims priority to U.S. Provisional Application No. 61/785,918, filed Mar. 14, 2013 and entitled “Loudspeaker With Synthesized Wavefront Output,” and to U.S. Provisional Application No. 61/802,289, filed Mar. 14, 2013 and entitled “Linear Loudspeaker Motor,” the entire contents of both of which are hereby incorporated into the present patent application by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention disclosed herein relates to drive motors for acoustic transducers and particularly to linear drive motors for loudspeakers and other acoustic transducers. 
       BACKGROUND 
       [0003]    Loudspeakers typically comprise a diaphragm driven by a circular moving coil. This driver, or motor, technology has been perfected over many decades. Reasons for the dominance this type of motor technology in the loudspeaker marketplace include efficiency, concise design based on the circular coil of wire in a magnetic gap, and that it is particularly suitable for cone and dome diaphragms. 
         [0004]    However, as sound systems have become more miniaturized and embedded in products other than stand-alone music players, such as video and television products, a need for different form factors has arisen. Also, as speaker components have become smaller, the this dimensional spread of acoustic radiation has effectively become a point source. Consequently, it is common now to see multiple small loudspeakers arranged in a line to approximate a line source. This requires much expense and complexity of design. 
         [0005]    Accordingly, there is also a need for a more suitable, linear speaker motor in many applications. For example, such a motor can make possible many attractive loudspeaker, and combination video and loudspeaker, designs from both an acoustic and industrial design point of view. Indeed, a linear motor may be integrated with an amplifier and ancillary electronics to expand such design possibilities. 
       SUMMARY 
       [0006]    A motor is disclosed for producing planar motion, comprising an elongate first magnet having a north and south poles extending along the elongate dimension of the first magnet; an elongate second elongate magnet having a north and south poles extending along the elongate dimension of the second magnet; a support member for holding the first magnet in relation to the second magnet so that their elongate dimensions are substantially parallel, opposite poles of the first magnet and the second magnet face one another, respectively, and a gap exists there between; and a substantially planar armature disposed in the gap between the first magnet and the second magnet, the armature having a driving portion adjacent one edge thereof and a flat, electrically-conductive element having an elongate dimension extending substantially parallel to the elongate axes of the magnets, such that when an electric current is caused to flow in the elongate dimension of the electrically-conductive element, a force is exerted on the planar armature in a translational direction parallel to a surface of the armature and perpendicular to the elongate axes of the magnets. 
         [0007]    A method is disclosed for producing motion in a plane, comprising providing a U-shaped magnet having two sides separated by an elongate gap, having a north pole on one side the gap and a south pole on the other side of the gap; supporting an elongate substantially flat, rigid and movable armature within the gap; providing an elongate electrically-conductive strip disposed on the armature extending in the elongate dimension of the gap; and causing an electric current to flow in the strip so as to produce a magnetic field and concomitant force on the armature tending to move it in or out of the gap. 
         [0008]    It is to be understood that this summary is provided as a means for generally determining what follows in the drawings and detailed description, and is not intended to limit the scope of the invention. The foregoing and other objects, features, and advantages of the invention will be readily understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective of a first embodiment of a linear transducer motor according to principles disclosed herein, attached to a flat panel acoustic transducer diaphragm. 
           [0010]      FIG. 2  is a cross section of a second embodiment of a linear transducer motor according to the principles disclosed herein. 
           [0011]      FIG. 3  is a cross section of a third embodiment of a linear transducer motor according to the principles disclosed herein. 
           [0012]      FIG. 4  is a cross section of a fourth embodiment of a linear transducer motor according to the principles disclosed herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Various embodiments of a linear transducer motor that is particularly suitable for use with a stereo flat panel loudspeaker of the type shown in U.S. patent application Ser. No. 14/214,585 filed Mar. 14, 2014 and entitled Acoustic Transducer and Method for Driving Same (“Athanas 585”) are shown in  FIGS. 1 ,  2 ,  3  and  4 . This is because in that type of loudspeaker the goal is to produce linear transverse waves originating respectively from both the left and right edges of the panel, and concomitant approximately cylindrical longitudinal waves in the air. However, it is to be understood that the linear transducer disclosed herein may have application to other types of flat panel acoustics transducers and other devices as well. 
         [0014]    Turning to  FIG. 1 , a first embodiment of a linear motor according to the inventive concepts comprises an elongate U-shaped magnet  1  having a north pole  2 , a south pole  4 , and an interconnecting portion  6  forming a long, fixed gap  8  between the north and south poles. For explanatory purposes, the lateral dimension of the magnet will be referred to as the X axis of a Cartesian coordinate system, the elongate dimension of the magnet will be referred to as the Y axis of the coordinate system, and the Z axis of the coordinate system runs through the center of the gap between the north pole  2  and south pole  4  of the magnet. The motor also comprises a linear armature  10  that is relatively thin in the dimension of the X axis, elongate in the dimension of the Y axis and disposed in the gap between the two poles such that the armature can move in and out of the gap in the dimension of the Z axis. The armature comprises a non-magnetic relatively flat, thin and rigid body member and an elongate, electrically-conductive strip of material  12  disposed one each side of the elongate body member, respectively. The material may be gold, copper, aluminum or some other appropriate conductor. In this embodiment the armature is connected to the edge  16  of a flat panel speaker diaphragm  18 , described and explained in Athanas &#39;585, which holds the armature between the poles of the magnet  1 . 
         [0015]    When a current flows through the conductive strips  12 , the induced magnetic field interacts with the fixed magnetic field of magnet  1  to produce a force along the entire length of the armature  10  tending to push it out of or pull it into the gap  8 . This in turn displaces the edge  16  of the speaker diaphragm  18 , producing a transverse wave in the in the diaphragm originating at the edge  16 . 
         [0016]      FIG. 2  shows a second embodiment of a linear motor having unconnected magnets  20  and  22 , the north pole of magnet  20  being at the right side  24  of the magnet and the south pole of magnet  22  being at the left side  26  of the magnet, with the south and north poles respectively located on the opposite sides of the magnets. In this case an armature  28  is also disposed between the north pole of one magnet and the south pole of the other magnet, not necessarily connected to a speaker diaphragm. Also in this case the conductive metal strip  12  is sandwiched between two pieces of non-magnetic relatively flat, thin and rigid material to form the armature. The armature is supported by an upper suspension device  28  and a lower suspension device  30 , each of which is connected between the armature and the two magnets, to center the armature and keep ambient air pressure from leaking into the system. The magnets may be held in position by any appropriate mechanism that need not, but could, be a magnet flux conduction material. 
         [0017]    Each suspension device has a left flexible, curved suspension member  32  attached between the left side of the armature and the right side of the magnet  20 , and a right flexible, curved suspension member  34  attached between the left side of the armature and the right side of the magnet  20 . In the suspension members in the upper suspension device are preferably convex upwardly, while in the lower suspension device the suspension members are preferable convex downwardly so as two be mirror images of one another and to keep unwanted matter from getting caught in the suspension members. However, it is to be understood that it would be consistent with the inventive principles of this disclosure if one or both pairs of the suspension members were curved in the opposite direction, or stretchable and not curved at all. 
         [0018]    A further embodiment of a motor according to the inventive principles of this disclosure is shown in  FIG. 3 . This is like the embodiment of  FIG. 2 , except that the magnets  20  and  22  are held in place by a ferromagnetic frame  36 . In this case, multiple spaced apertures  38  are formed along the length of the frame to equalize the air pressure both above and below the suspension devices. 
         [0019]    Yet another, fourth embodiment of a motor according to the principles of this disclosure is shown in  FIG. 4 . Like the embodiment of  FIG. 22 , this embodiment comprises an elongate U-shaped magnet  40  having a north pole  44 , a south pole  46 , and an interconnecting portion  48  forming a long, fixed gap  50  between the north and south poles. The same Cartesian coordinate system used in  FIG. 22  is used here. This further embodiment also comprises a linear armature  52  like that used in the embodiments of  FIGS. 22-24 . This embodiment further comprises an upper armature suspension device  54  as used in the embodiments of  FIGS. 23 and 24 . However, this embodiment employs a ferrofluid  56  to levitate the conductive strip in the center of the magnetic circuit, maintain the lateral position of the armature in the gap between the north and south poles of the magnet  40 , cool the system and allow for much closer tolerances in the gap with increases efficiency. 
         [0020]    The ferrofluid preferably comprises microscopic ferromagnetic particles that collectively behave like a fluid, but will aggregate together under the influence of a magnetic field so as to assume a collective shape that minimizes potential energy. An example of a suitable ferrofluid is described in Athanas U.S. Pat. No. 5,335,287, the entire contents of which are hereby incorporated by reference. Consequently, the ferrofluid forms symmetric portions  58  and  60  on opposite sides of the armature  252  substantially midway between the top and bottom of the gap, adjacent the respective conductive strips  60  and  62 , thereby holding the armature in the center of the gap while it moves in the Z axis dimension in response to current flowing through the conductive strip  60  and  62 . To ensure that the pressure in the chambers  64  and  66  formed above the ferrofluid portions  56  and below the suspension device  54  is equal to the pressure in the chamber  68  formed below the ferrofluid and within the walls of the magnet, two pressure equalizing passageways  70  and  72  are formed in the magnet between the north-side upper chamber  56  and lower chamber  68 , and between the south-side upper chamber  66  and lower chamber  68 , respectively. 
         [0021]    The conductive strip in the motor embodiments of  FIGS. 1-4  would ordinarily have a low resistance, on the order of 1 ohm, and be used with a low output-impedance, low-voltage, high-current drive circuit, as would be understood by a person skilled in the art. 
         [0022]    It is to be understood that variations of the features of embodiments shown in  FIGS. 1   4  may be used to form other embodiments without departing from the inventive concepts discussed in this disclosure. It is also to be understood that the linear motor disclosed herein may be used in applications other than a loudspeaker or other acoustic transducer without departing from those inventive concepts. 
         [0023]    The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, to exclude equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.