Abstract:
A multiple voice-coil cone-driver for driving a loudspeaker includes a first voice-coil, and a second voice-coil coupled in parallel to the first voice-coil. Together, the first and second voice-coils in parallel are characterized by a baseline frequency response with an upper threshold frequency. In addition, at least one additional voice-coil (e.g., a third voice-coil) is coupled in parallel to the first and second voice-coils. The additional voice-coil(s), in conjunction with the first and second voice-coils, provide an enhanced frequency response in comparison to the baseline frequency response. One aspect of the enhanced frequency response is that it has an extended upper threshold frequency compared to the baseline frequency response, providing for more accurate reproduction of music and speech from a single speaker.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of loudspeakers. In particular, the invention relates to a multiple voice-coil cone-driver that may be incorporated into a loudspeaker. 
     2. Related Art 
     A loudspeaker typically includes a frame, a magnet assembly that provides a magnetic field across an air gap, a voice-coil, a former for supporting the voice-coil in the air gap, a diaphragm having an outer perimeter and an apex, and a surround coupled to the outer perimeter and the frame to support the outer perimeter from the frame. The voice-coil, supported by the former, is coupled to the apex of the diaphragm so that the current that flows through the voice-coil and causes the voice-coil to move in the air gap also causes the diaphragm to move. 
     In some settings, it is desirable to extend the upper threshold frequency (also known as “UTF”) of a loudspeaker so that the loudspeaker may more accurately reproduce a wider range of frequency content in speech, music, and the like. At the same time, many applications demand that the loudspeaker remain small in package size. Traditionally, designers extended the upper threshold frequency by decreasing the moving mass (i.e., the physical structure that moves when the voice-coil is energized), increasing the cone depth, or adding an additional cone (e.g., tailored to high frequency response). Unfortunately, these approaches are not always suitable. 
     For example, decreasing the moving mass often entails lightening the diaphragm, which typically increases distortion. As another example, increasing the cone depth may place the loudspeaker outside of acceptable packaging depth requirements. These requirements may be particularly stringent in, for example, automobile applications. 
     Therefore, there is a need for extending the upper threshold frequency of a loudspeaker while overcoming the disadvantages associated with decreasing the moving mass, increasing the cone depth and/or adding an additional cone. 
     SUMMARY 
     A multiple voice-coil cone-driver that drives a loudspeaker cone in an improved manner is described. Structurally, the multiple voice-coil cone-driver may include a first voice-coil, and a second voice-coil coupled in parallel to the first voice-coil. Together, the first and second voice-coils in parallel are characterized by a baseline frequency response with an upper threshold frequency. In addition, at least one additional voice-coil (e.g., a third voice-coil) may be coupled in parallel to the first and second voice-coils. All of the voice-coils may be supported by a single voice-coil former. 
     The multiple voice-coil cone-driver may be constructed by a process that includes mounting a first voice-coil on a voice-coil former and mounting in parallel a second voice-coil on the voice-coil former. As a result, a baseline frequency response is established with an upper threshold frequency. The process may also include the steps of mounting a third voice-coil on the voice-coil former and coupling the third voice-coil in parallel to the first voice-coil. The third voice-coil, in conjunction with the first and second voice-coils, provides an enhanced frequency response that extends beyond the upper threshold frequency of the baseline frequency response. 
     The additional voice-coils, in conjunction with the first and second voice-coils, provide an overall frequency response that is an enhanced version of the baseline frequency response. One aspect of the overall frequency response is that it has an extended upper threshold frequency compared to the baseline frequency response. In other words, the overall frequency response is enhanced at high frequencies. 
     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  shows an example implementation of a loudspeaker that includes a multiple voice-coil cone-driver. 
         FIG. 2  shows an impedance plot comparing the frequency response of a single coil cone-driver and a dual coil cone-driver with tri and quad voice-coil cone-drivers. 
         FIG. 3  shows a sound pressure level plot for a single, dual, tri, and quad voice-coil cone-drivers. 
         FIG. 4  shows an assembly drawing for an example implementation of a cone-driver as shown in  FIG. 1 . 
         FIG. 5  shows an example process for fabricating the multiple voice-coil cone-driver shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1  an example implementation of a loudspeaker  100  is shown. The loudspeaker  100  may include an enclosure  102  that supports one or more speakers  104 . The speaker  104  may include a magnet system  106  and a multiple voice-coil cone-driver (also referred to as a “cone-driver”)  108  that is operatively connected to a loudspeaker cone  110 . 
     More specifically, the cone-driver  108  may include a voice-coil former  112 , a first, second, third, and fourth voice-coils  114 ,  116 ,  118 , and  120 , and a single source input  122 . The voice-coils  114 – 120  may be wound on and glued to the voice-coil former  112 . The voice-coils  114 – 120  are electrically connected (i.e., coupled) in parallel. There may be fewer (e.g., 3) voice-coils, or additional (e.g., 5) voice-coils. In addition, a protective collar  123  may be glued in place over both the combination of the former  112  and the voice-coils  114 – 120  and the loudspeaker cone  110 . 
     The voice-coil former  112  itself may reside in a magnetic field gap defined by the magnet system  106 . The loudspeaker cone  110 , cone-driver  108 , and magnet system  106  may take the form of a single cone assembly secured in place by a frame assembly (not shown) in the loudspeaker  100 . An external signal source  124  is coupled to the source input  122  to drive the loudspeaker  100 . The single source input  122  provides a connection point for a single source of external input signals (such as external signal source  124 ) to drive the loudspeaker  100 . The single source input  122  may be implemented as wire leads, wire terminals, solder points for wires that connect to external jacks, and the like. 
     The voice-coils  114 – 120  extend the upper threshold frequency of the speaker  104  beyond the upper threshold frequency that would be exhibited if only the first and second voice-coils  114 – 116  were present. More specifically, taking the first voice-coil  114  and the second voice-coil  116  together, those two voice-coils exhibit a baseline frequency response. The baseline frequency response has an upper threshold frequency (UTF) at the frequency where the sound pressure level (SPL) falls  3  decibels (db) below its nominal value. 
     When the third voice-coil  118  is added, the overall frequency response (i.e., the frequency response of the voice-coils  114 – 118  in parallel) is enhanced in comparison to the baseline frequency response provided by the two voice-coils  114 – 116  alone. In particular, the enhanced frequency response has an upper threshold frequency that extends beyond the upper threshold frequency of the baseline frequency response. Thus, the speaker  104  may more accurately reproduce a wider range of speech, music, and/or other types of sounds. Similarly, when the fourth voice-coil  120  is added, the overall frequency response is enhanced yet again. That is, the new frequency response has an upper threshold frequency that extends even further beyond the upper threshold frequency of the baseline frequency response. 
       FIG. 2  shows an impedance plot  200  of impedance in ohms versus frequency in Hertz (Hz). Plot  200  shows the effect on cone-driver  108  impedance magnitude assuming one, two, three, and four voice-coils. In  FIG. 2 , the impedance curve  202  shows the impedance magnitude of the cone-driver  108  when only the voice-coil  114  is present (the “single coil” design). The impedance curve  204  shows the impedance magnitude of the cone-driver  108  when the voice-coils  114  and  116  are present (the “dual coil” design). Similarly, the impedance curve  206  shows the impedance magnitude of the cone-driver  108  when the voice-coils  114 – 118  are present (the “tri coil” design). Finally, the impedance curve  208  shows the impedance magnitude of the cone-driver  108  when the voice-coils  114 – 120  are present (the “quad coil” design). 
     As shown in  FIG. 2 , after resonance (around 60 Hz) the impedance magnitudes drop, then start to rise again. However, the impedance magnitudes (particularly over the range of 20 to 20,000 Hz) of the tri coil and quad coil designs do not rise as quickly after approximately 1 KHz. The lower impedance magnitudes at higher frequencies yields an increase in SPL at those frequencies. Thus, the tri and quad coil designs provide an enhanced frequency response beyond the baseline frequency response given by the single or dual coil designs. 
       FIG. 3  shows an SPL plot  300  of SPL amplitude in decibels versus frequency for a cone-driver incorporating a single, dual, tri, or quad voice-coils. More particularly, the curve  302  shows the baseline frequency response for SPL of a single coil cone-driver. The curve  304  shows the baseline frequency response for SPL of a dual coil cone-driver. Similarly, the curve  306  shows an enhanced frequency response for SPL of a tri-coil cone-driver, while curve  308  shows an enhanced frequency response for SPL of a quad-coil cone-driver. 
     The upper threshold frequency or UTF is the frequency at which the SPL begins to roll off or diminish. It is generally regarded as the frequency where the SPL response is 3 db below its nominal value. For the physical constructions set forth below, the single coil design has an UTF of approximately 8,700 Hz, the dual coil design has an UTF of approximately 11,800 Hz, the tri coil design has an UTF of approximately 13,200 Hz, and the quad coil design has an UTF of approximately 12,900 Hz. 
     The physical construction of the coils is described next in detail with reference to  FIG. 4 . The cone-driver  400  shown in  FIG. 4  has the dimensions A–I, number of turns per voice-coil, DC resistance per coil (DCR), and wire type and size shown below in Table 1. Note that the DCR per coil increases when multiple voice-coils are employed in parallel in order to maintain a pre-selected overall DCR. For example, the DCR assuming a cone-driver with a single voice-coil is 2 ohms. When four voice-coils are employed, each has a DCR of 8 ohms, so that the four voice-coils in parallel result in an overall DCR of 2 ohms for the cone-driver. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Dimensions in millimeters (mm), 0.25 mm tolerance unless otherwise noted 
               
             
          
           
               
                   
                 Single voice-coil 
                 Dual voice-coil 
                 Tri voice-coil 
                 Quad voice-coil 
               
               
                   
                   
               
             
          
           
               
                 A 
                 25.910 +− 0.030 
                 25.910 +− 0.030 
                 25.910 +− 0.030 
                 25.910 +− 0.030 
               
               
                 B 
                 27.20 
                 26.97 
                 26.85 
                 26.77 
               
               
                 C 
                 25.04 
                 25.04 
                 25.04 
                 25.04 
               
               
                 D 
                 10.65 
                 11.00 
                 10.16 
                  9.39 
               
               
                 E 
                 13.0 
                 13.0 
                 13.0 
                 13.0 
               
               
                 F 
                  0.80 
                  0.80 
                  0.80 
                  0.80 
               
               
                 G 
                 60.0 
                 60.0 
                 60.0 
                 60.0 
               
               
                 H 
                  9.60 +− 2.50 
                  9.60 +− 2.50 
                  9.60 +− 2.50 
                  9.60 +− 2.50 
               
               
                 I 
                 25.54 +− 0.50 
                 25.54 +− 0.50 
                 25.54 +− 0.50 
                 25.54 +− 0.50 
               
               
                 Turns 
                 70 
                 45 
                 32 
                 25 
               
               
                 Wire 
                 Japan Industrial 
                 JIS20 
                 JIS17 
                 JIS15 
               
               
                   
                 Standard (JIS) 25 
               
               
                 DCR 
                  2.0 ohms +− 0.15 
                  4.0 ohms +− 0.15 
                 6.0 ohms +− 0.15 
                 8.0 ohms +− 0.15 
               
               
                   
               
             
          
         
       
     
     The voice-coils  114 – 120  may be wound in multiple layers (e.g., two layers). Additionally, any of the voice-coils  114 – 120  may by wound in a BiFiler, TriFiler, or QuadFiler winding process in which multiple voice-coils are wound simultaneously. For example, using the TriFiler winding process, the three voice-coils  114 – 118  may be wound at the same time onto the former  112 . As one example, a winding mandrel approximately 25.90 mm in diameter may be employed to wind the voice-coils, while a baking mandrel approximately 25.86 mm in diameter may be employed to bake cure the voice-coils (e.g., for 45 minutes at 375 degrees F.) after gluing. The former  112  may be made from 0.08 mm Kapton™ material, for example, while the collar  123  may be made from CeQuin™ material available from QUIN-T Corporation of Tilton, N.H. 
     Turning next to  FIG. 5 , that figure summarizes an example process (i.e., method) for constructing or fabricating a voice-coil for driving the loudspeaker cone  110  shown in  FIG. 1 . The example method may include mounting a first voice-coil (for example, voice-coil  114 ) on a voice-coil former  112  (Step  502 ). Next, the method mounts a second voice-coil (for example, voice-coil  116 ) on the voice-coil former  112  (Step  504 ) and couples the first voice-coil  114  to the second-voice coil  116  (Step  506 ). As a result, as noted above, the first and second voice-coils  114 – 116  coupled in parallel provide a baseline frequency response with an upper threshold frequency. 
     Subsequently, the example method may also include mounting a third voice-coil (for example, voice-coil  118 ) on the voice-coil former  112  (Step  508 ). The third voice-coil  118  may be coupled in parallel to the first and second voice-coils  114 – 116 , thereby providing an enhanced frequency response that extends beyond the upper threshold frequency of the baseline frequency response (Step  510 ). In a similar manner, a fourth voice-coil (for example, voice-coil  120 ) may be mounted on the voice-coil former  112  (Step  512 ) and coupled in parallel to the first voice coil  114 , resulting in an further enhanced frequency response (Step  514 ). Therefore, the voice-coils  114 – 120  may be mounted by winding them onto the voice-coil former  112 . As examples, the voice-coils  114 – 120  may be individually wound and soldered or otherwise coupled together, or they may be simultaneously wound using a BiFiler, TriFiler, or QuadFiler winding process. 
     In summary, either or both of the voice-coils  118 – 120  may be employed to extend the upper threshold frequency of the speaker  104  beyond what would be exhibited if only the first and second voice-coils  114 – 116  were present. The extension in upper threshold frequency allows the speaker  104  to more accurately reproduce a wider range of speech, music, and/or other sounds. 
     While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of this invention.