Patent Publication Number: US-7711138-B2

Title: Loudspeaker including a cone circumscribed by a stiffener

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional Application No. 60/672,378 entitled Carbon Ring Cone, filed Apr. 18, 2005, the contents of which are incorporated herein, be reference, in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     A loudspeaker for audio signals converts electrical energy into mechanical energy by vibrating a diaphragm. The vibrating diaphragm causes motion of the surrounding air, thus producing acoustic energy. 
     The most common form of diaphragm for low frequency and midrange loudspeakers is a cone. A voice coil immersed in a magnetic field is attached to the neck of the cone, and the cone is attached to a rigid frame by means of flexible members at both the neck and the outer edge of the cone. These flexible members (i.e. a “spider” at the neck, and a “surround” at the outer edge) allow the cone to move fore and aft within the frame while maintaining axial alignment (i.e. preventing the cone from tilting or rocking). 
     In order to maximize the efficiency of the loudspeaker, and also extend its frequency range upward, the cone should have as little mass as possible. In order to reduce distortion, the cone should be as rigid as possible. In order to achieve high output capacity, the cone should have high mechanical strength. In order to move a high volume of air, the cone should be as large as possible within the given frame size. In order to achieve high output at low frequencies the cone assembly needs to be capable of long excursions. 
     Conventional loudspeakers are limited in the amount of acoustic energy that can be produced with acceptably audio low distortion. The limit arises primarily from the structure of the surround, which limits the excursions of the cone, and the stiffness of the cone, which distorts under large excursions. 
     The prior art offers different solutions to stiffening the cone. By way of example, U.S. Pat. No. 2,513,171 issued to J. A. Hassan, Jun. 27, 1950 discloses methods of stiffening a loudspeaker cone using struts extending from the voice to the outer edge of the cone. 
     U.S. Pat. No. 2,641,329, issued to S. Levy &amp; A. Cohen, Jun. 9, 1953 deals with methods of stiffening a loudspeaker cone by attaching “transversely arched perforated plates bridging the central area of the diaphragm member” or by attaching a “horn shaped member secured at its smaller end to the junction of the dome cap and the diaphragm or directly to the dome cap, and secured at its larger end to the side of the diaphragm at a substantial distance from the smaller end. 
     U.S. Pat. No. 4,115,667, issued to B. Babb Sep. 19, 1978 discloses a method of stiffening a loudspeaker cone by means of a plurality of ribs extending along the surface of the dust cap and the surface of the cone. 
     U.S. Pat. No. 4,373,609 issued to C. D. Miller, February 1983, deals with a method of cone stiffening employing “a plurality of stiffener columns positioned in a plane to form a polygon essentially perpendicular to a central axis of the diaphragm with the ends of the columns being attached to the diaphragm intermediate the small end and the large end of the diaphragm. 
     Each of the aforementioned patents discloses a method of stiffening a cone which adds considerable mass to the cone, thus lowering the efficiency of the loudspeaker and reducing it&#39;s high frequency response. Accordingly, there is a need for a loudspeaker design which provides for delivering high volumes of air while simultaneously providing high electrical to acoustic efficiency, high frequency response and low distortion within a specified frame size. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated the present invention is a loudspeaker comprising a frame, a surround having a first end connected to the frame, and a cone having an outer edge in a shape of a reverse angle flange, where a front side of the flange is attached to a second end of the surround, and a reinforcing ring bonded to a back side of the flange. 
     Another aspect of the present invention is a loudspeaker comprising a frame, a cone having a first end and a second end, a surround connecting the first end of the cone to the frame, and a spider connecting the second of the cone to the frame, where the restoring force of the spider is greater than the restoring force of the surround. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
       In the drawings: 
         FIG. 1  is a sectional view of a loudspeaker according to a preferred embodiment of the present invention; 
         FIG. 2A  is a sectional view of a cone edge and a surround of the present invention in a rest position; 
         FIG. 2B  is a is a sectional view of a cone edge and a surround of a conventional loudspeaker in a rest position; 
         FIG. 3A  is a sectional view of a cone edge and a surround of the present invention in an extended position; 
         FIG. 3B  is a sectional view of a cone edge and a surround of the conventional loudspeaker in a rest position; and 
         FIG. 4  is a sectional view of the preferred embodiment of the loudspeaker showing a cone of the loudspeaker in extreme rearward excursion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1  there is shown in sectional view, a preferred embodiment of a loudspeaker  10  according to the present invention. The loudspeaker  10  comprises a diaphragm assembly  12 , and a driver assembly  14  that operates the diaphragm assembly  12  for producing acoustical output. 
     The diaphragm assembly  12  includes a frame  26 , a cone  16  attached with an adhesive or the like to a dome  18  to form a diaphragm  20 . An outer edge  38  of the cone  16  is connected to an upper end  24  of the frame  26  by a surround  22 . A lower end  28  of the cone  16  is connected to a voice coil former  30  which forms part of the driver assembly  14 . The voice coil former  30  (hereafter former) is in turn connected to the frame  26  through a flexible spider  32  that extends between the former  30  and a lower end  34  of the frame  26 . With the arrangement of the surround  22  and the spider  32 , the diaphragm  20  is free to move in an axial direction but is restrained from movement in a radial direction with respect to the frame  26 . 
     The driver assembly  14  includes a voice coil  36  mounted on the voice coil former  30  and a permanent magnet assembly  40  that cooperates with the voice coil  36  for driving the diaphragm  20 . The voice coil  36  is typically constructed of aluminum or copper wire and is attached to the voice coil former  30  by a conventional adhesive. The voice coil  36  is electrically connected to terminals of the loudspeaker through wires. 
     The permanent magnet assembly  40  is generally annular in shape and is centrally located with respect to a central axis of the diaphragm assembly  12 . The permanent magnet assembly  40  includes a permanent magnet  50  disposed between a top plate  52  and a back plate  54 . The top plate  52  is rigidly connected to the frame  26 . A bumper  66  of soft rubber or other elastic material, is attached to a top surface of the top plate  52  proximate the second end of the cone  16 . As shown in  FIG. 4 , the bumper  66  is located such that the bumper  66  contacts the spider  32  near the lower end  28  of the cone  16  at extreme excursions of the cone  16  thus preventing the neck of the cone  16  from striking the top plate  52  and being damaged due to excessive rearward excursion. Preferably, the bumper  66  is in the shape of a ring surrounding the former  30  but need not totally surround the former  30 . 
     The top and back plates  52 ,  54  are constructed of a material capable of carrying magnetic flux, such as steel. A pole piece  56  of generally cylindrical shape is connected to the back plate  54  and extends generally toward the diaphragm  20 . The pole piece includes a pole vent  58  that is coincident with an opening  55  in the top plate  54 . A space or gap  68  is formed between the pole piece  56  and the top plate  52 , the permanent magnet  50 , and the back plate  54 . The voice coil  36  is positioned in the gap  68 . 
     In use, changing current is applied to the voice coil  36  through the terminals. The voice coil  36  in turn produces a magnetic field which interacts with the magnetic field produced by the permanent magnet assembly  40 . The interaction of the magnetic fields causes the voice coil  26  to oscillate linearly in accordance with the applied changing current. Oscillation of the voice coil  26  in turn pumps the diaphragm  20  linearly to generate sound. Movement of the diaphragm causes a change in volume of the airspace between the diaphragm assembly  12  and driver assembly  14 . When the diaphragm  20  moves away from the pole piece  56 , air is drawn toward the diaphragm  20  through the vent opening  55  of the bottom plate  54  and the pole vent opening  58  of the pole piece  56 . Likewise, when the diaphragm  20  moves toward the pole piece  56 , air is pushed through the pole vent  58  and opening  55 . 
     In the preferred embodiment, the outer edge  38  of the cone  16  is in the shape of a reverse angle flange  60 . The reverse angle flange  60  serves to stiffen the outer edge  38  of the cone  16 . Preferably, the width of the flange  60  ranges from 0.1 inch to 0.15 inch depending on the size of the cone  16  with 0.15 inches being more suitable for 12 inch and larger cones  16 . Preferably, the interior angle of the flange  60  is determined such that the force on the flange when the cone is at a maximum excursion is substantially in line with the plane of the flange  60 . In this manner, forces perpendicular to the face of the outer edge  38  of the cone  16  are avoided, thus reducing the tendency for the outer edge  38  of the cone  16  to crack under repeated extreme excursion conditions. In the preferred embodiment the interior angle of the flange  60  is approximately ninety degrees but the preferred angle of the flange  60  could be other than ninety degrees depending on the size of the extreme excursions of the cone  16 . 
     A reinforcing ring  62 , circumscribing the cone  16 , is bonded to a back side  60   b  of the flange  60 . The reinforcing ring  62  is preferably made of a high stiffness and low mass material. More preferably, the reinforcing ring  62  is made of uni-directional carbon fiber material bonded to the cone  16  with an adhesive. However other materials such as, for instance, Kevlar or glass fibers could also be used for the reinforcing ring  62 . The reinforcing ring  62  provides substantial additional stiffness and strength to the edge of the cone  16 . Additional reinforcing rings  64  which circumscribe the cone  16  may also be employed further down the body of the cone  16 , to further stiffen the cone  16  and reduce break-up of the cone  16  at higher frequencies. 
     Preferably, a front side  60   a  of the reverse angle flange  60  is connected to an upper end  24  of the frame  26  by a flexible suspension, referred to as the surround  22 . As shown in  FIG. 2A , the surround  22  comprises a plurality of wavelike pleats. Preferably the surround  22  is made of treated cloth but could be made of other materials, such as for instance, rubber or urethane. As further shown in  FIGS. 2A and 2B , the peak to peak heights of the pleats compared to the distance between the peaks is greater for the surround  22  than for a conventional surround. Preferably, the ratio of the peak to peak height of the surround  22  to the distance between the peaks of the surround  22  is approximately 0.7 when the surround is at rest. However, the ratio could be as low as 0.5 and still be within the scope of the invention. 
     The narrow width of the surround  22  compared to that of the conventional surround enables the diameter of the cone  16  to be larger for a specified frame size than the cone of a conventional loudspeaker, thus the loudspeaker  10  is able to move larger volumes of air for a specified frame size. For example, as shown in  FIGS. 2A and 2B , the outside diameter of the cone  16  of a 12″ cone assembly is increased from 9 inches for a conventional loudspeaker to 10.25 inches when using the inventive surround  22 . 
     The primary function of the surround  22  is to provide radial location of the cone and air seal. Accordingly, in the preferred embedment the restoring force of the surround  22  is made less than the restoring force of the spider  32 . Also, as shown in  FIG. 3A  the surround  22  is designed such when it is in an extended position, the force applied to the outer edge  38  of the cone  16  through the surround  22  is substantially in line with the plane of the flange  60 . This is in contrast to the surround of a conventional loudspeaker ( FIG. 3B ) where the surround exerts a force normal to the plane of the outer edge  38  of the cone  16  thus having the potential for causing the outer edge  38  of the cone  16  to crack. 
     As would be apparent to those skilled in the art, the combination of an edge of the cone  16  reinforced with the carbon fiber ring  62  and the narrow and tall surround  22  results in an improved loudspeaker capable of increased life/higher efficiency and lower distortion in a specified frame size than heretofore achieved with conventional loudspeakers. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.