Patent Publication Number: US-6343128-B1

Title: Dual cone loudspeaker

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to acoustical loudspeakers and more particularly to acoustical loudspeakers with improved bass response. 
     2. Description of Related Art 
     My U.S. Pat. No. 4,595,801 discloses a dual cone loudspeaker with a primary speaker cone similar in function to a conventional dynamic loudspeaker mounted on a frame with a magnet structure. A secondary speaker cone mounts to a subframe on the back of the magnet structure and connects to the primary speaker cone through a rigid coupling device so the primary and secondary speaker cones move in unison. Sound waves from the secondary speaker cone travel through an orifice in a center pole piece of the magnet structure and through a hole in the center of the primary speaker cone radiating in the same direction as sound waves from the primary speaker cone. Consequently for a given excursion of the primary speaker cone my dual cone structure generates a sound having a greater sound volume than the primary cone alone by virtue of the simultaneous excursions of both the primary and secondary speaker cones that move a greater air volume for a given speaker cone displacement. 
     More specifically, the speaker disclosed in my patent includes a primary speaker cone with a frustoconical form with the center removed that attaches to a bobbin that carries a voice coil. The rigid coupling device includes a center link with radial spokes. The radially outer end of each spoke attaches directly to the secondary speaker cone at the voice coil bobbin. However, it is difficult to attach these outer ends of the radial spokes to the speaker cone or bobbin without distorting the voice coil. Moreover, adhesive or other techniques for bonding the ends of the radial spokes to the bobbin are subject to fatigue and ultimate failure. Stress concentrations at attachment points tend to force the bobbin out of round in operation contributing to a short life span for the speaker. It has also been found that this speaker is limited to operation at lower frequencies as a bass speaker. It would be helpful if the useful frequency range could be is extended to higher frequencies. 
     SUMMARY 
     Therefore it is an object of this invention to provide a dual cone loudspeaker with an improved linkage between the primary and secondary speaker cones. 
     Another object of this invention is to provide a coupled dual cone loudspeaker with a reliable construction. 
     Still another object of this invention is to provide improved linkage that enables a coupled dual cone loudspeaker to operate over an extended frequency range. 
     Yet another object of this invention is to provide a coupled dual cone loudspeaker that is easy to manufacture. 
     Yet still another object of this invention is to provide a coupled dual cone loudspeaker that is capable of broadcasting a wider range of frequencies with fidelity. 
     Still yet another object of this invention is to provide a coupled dual cone loudspeaker that can radiate a wide range of frequencies applied to a single voice coil. 
     Yet still another object of this invention is to provide a coupled dual cone loudspeaker capable of producing high frequency radiation independently of signals applied to a voice coil for a primary speaker cone. 
     In accordance with one aspect of this invention a coupled dual cone loudspeaker includes a first speaker cone resiliently suspended from a frame. A voice coil responds to first signals for displacing the first speaker cone relative to the frame. A second speaker cone is resiliently suspended from the frame and spaced from the first speaker cone. A ring attaches to the first speaker cone and an open support structure connects the ring to the second speaker cone whereby motion of the first speaker cone produces corresponding motion of the second speaker cone. 
     In accordance with another aspect of this invention, a dual-cone loudspeaker includes a loudspeaker frame, a first speaker cone resiliently suspended from the frame, voice coil for displacing the first speaker cone and a second speaker cone resiliently suspended from the frame and spaced from the first speaker cone. A link interconnects the first and second speaker cones whereby motion of the first speaker cone produce., 5  a corresponding motion of the second speaker cone. The loudspeaker additionally includes a high-frequency radiating structure attached to the link for producing high-frequency output signals in response to high-frequency signals applied to the voice coil. 
     In accordance with still another aspect of this invention, a dual-cone loudspeaker comprises a loudspeaker frame with a permanent magnet for defining a magnetic gap, a first speaker cone resiliently suspended from the frame, a second speaker cone resiliently suspended from the frame and spaced from the first speaker cone and a voice coil for being energized by an audio signal in electrical form. A cylindrical structure located in the magnetic field gap carries the voice coil and attaches to the first speaker cone whereby low frequency signals applied to the voice coil produce corresponding motion of the cylindrical structure. An open support structure formed centrally of the cylindrical structure includes a rigid link that connects to the second speaker cone whereby low frequency motion of the first speaker cone produces a corresponding motion of the second speaker cone. 
     In accordance with still another aspect of this invention, a dual-cone loudspeaker includes a loudspeaker frame with a permanent magnet means for defining a magnetic gap, a first speaker cone resiliently suspended from the frame and a second annular speaker cone resiliently suspended from said frame and spaced from said first speaker cone. A voice coil, energized by an audio signal in electrical form, is formed on a rigid cylindrical structure located in the magnetic field gap. The cylindrical structure is a component of a rigid link that interconnects the first and second speaker cones and that includes a rigid circular structure positioned in the opening through the second speaker structure and resiliently attached thereto about the periphery of the rigid circular structure and that includes a rigid element interconnecting the rigid cylindrical structure and the rigid circular structure. Low frequency signals applied to the voice coil produce corresponding motion of the first and second speaker cones and high frequency signals applied to the voice coil produce corresponding motion of the rigid circular structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which: 
     FIG. 1 is a view in cross-section of a dual cone loudspeaker constructed in accordance with this invention; 
     FIG. 2 is a perspective view of an open support structure constructed in accordance with this invention; 
     FIG. 3 depicts the detail of a single spoke in the open support structure of FIG. 2; 
     FIG. 4 depicts another embodiment of a dual cone loudspeaker constructed in accordance with this invention; 
     FIG. 5 depicts yet another embodiment of a dual cone loudspeaker constructed in accordance with this invention; 
     FIG. 6 details an alternative embodiment of an open support structure as shown in FIG. 2; 
     FIG. 7 depicts still yet another embodiment of a dual cone loudspeaker constructed in accordance with this invention; and 
     FIGS. 8,  9  and  10  depict certain details of the embodiment of FIG.  7 . 
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In this description FIGS. 1,  4  and  5  depict certain components that are common to each of these embodiments and to the coupled dual cone velocity driver speaker disclosed in my U.S. Pat. No. 4,595,801. Consequently, FIGS. 1,  4  and  7  use the same reference numerals to designate such components. 
     More specifically, a dual cone loudspeaker  100  shown in FIG.  1  and constructed in accordance with one aspect of this invention includes a rigid frame  1  to which a first speaker cone in the form of a primary speaker cone  2  is attached and a subframe  3  to which a second speaker cone in the form of a secondary speaker cone  4  is attached. Both frames  1  and  3  are mounted with a permanent magnet  5  to which pole pieces  6  are attached to form a magnetic field gap  7  into which a voice coil bobbin  8  with a voice coil  18  is placed. The voice coil bobbin  8  attaches to the base of the primary speaker cone  2  that is resiliently suspended from the frame  1  by a flexible surround  9  at its outer periphery and by a spider  10  at its bottom. A rigid link  11  that is constructed in accordance with one aspect of this invention and described more fully with respect to FIGS. 2 and 3, mechanically connects the voice coil structure  8  to the secondary speaker cone  4  by a center attachment  13  that may comprise a separate fastener or an adhesive material that bonds the link  11  to the secondary speaker cone  4 . 
     The secondary speaker cone  4  attaches to the subframe  3  through a flexible surround  9 ′. The secondary speaker cone  4  forms a second air piston that is pneumatically coupled to the primary speaker cone  2  through an orifice or aperture  14  through a center one of the pole pieces  6 . The aperture  14  is common to the closed chamber formed by the secondary speaker cone  4  and subframe  3  and the open chamber formed by the primary speaker cone  2 . The frame  1  may, in accordance with conventional construction, contain a plurality of mounting holes  15  therethrough. 
     As described in the foregoing patent, when a signal energizes the voice coil  18 , the interaction of the current in the voice coil  18  and the magnetic field in the magnetic field gap  7  causes the primary speaker cone  2  to displace in an alternating fashion at the frequency of the applied signal. As the rigid link  11  connects to both the primary speaker cone  2  and the secondary speaker cone  4 , the air in the closed chamber in the secondary speaker cone  4  pumps into and out of the open chamber of the primary speaker cone  2  through the orifice  14 . As a consequence a larger volume air flows than if there were only one primary speaker cone. The larger volume of air displaced results in a louder sound for a given cone excursion. However, the loudspeaker  100  occupies a cross-sectional area no bigger than a loudspeaker that has only a primary speaker cone. 
     FIG. 2 depicts the rigid coupling device or link  11  that constitutes one aspect of this invention in more detail as including an open support structure  19  and a thin ring  20 , that attaches by an adhesive or other method to the voice coil bobbin  8  that, in this embodiment provides increased rigidity to the ring  20 . For a given strength or rigidity the flared end portion  21  enables the construction of a very light weight ring  20 . The ring  20  also has a flared end portion  21 . The increased surface area between the ring  20  and voice coil bobbin  8  assures a more reliable attachment between the rigid link  11  and the bobbin  8 . Moreover, the open support structure  19  prevents the bobbin  21  from going out of round, especially when the ring  20  includes the flared end portion  21 . 
     Referring again to FIG. 2, the open support structure  19  in the embodiment that attaches to the ring  20  includes a plurality of equiangularly spaced spokes  22 . As shown more clearly in FIG. 3 each spoke  22  has a first end portion  23 , a second end portion  24  and an intermediate body portion  25 . A tab  26  extends from the first end portion  23  about a distance equal to the thickness of a spoke  22 . A slot  27  extends through the first end portion for receiving a tab. The tab  26  from one spoke  22 , such as a spoke designated as  22 ( 1 ) in FIG. 2, engages the slot  27  in an adjacent spoke, designated  22 ( 4 ) in FIG.  2 . When all four spokes are assembled in this fashion, they form a hub  30  as shown in FIG. 2 that has a square aperture extending through the open support frame  12 . 
     The second end  24  of each spoke  22  terminates in a radially outward facing transverse notch or channel  31  that enables the spoke  22  to engage the ring  20 . Alternatively the ring might be found with slots and the spokes terminated with corresponding tabs. To conserve weight, the spokes  22  have a maximum dimension at the hub  30  where maximum strength is needed and a minimum dimension at the second end  24 . The spokes  22  and the ring  20  form a rigid circular structure and, as previously indicated, prevent distortion of the bobbin  21  shown in FIG.  1 . 
     Referring again to FIG. 1, in this embodiment the open support structure  19  additionally carries a rigid rod-like member  32  that extends from the hub  30  to the attachment  13 . The combination of the ring  20  and open support structure  19  including the rigid member  32  provide a rigid link between the primary speaker cone  2  and the secondary speaker cone  4  that is more reliable than found in the prior art. 
     The open support structure  19  including any or all of ring  20 , the spokes  22  and the link  31  can be made of metal or plastic so long as the structure remains rigid axially and lightweight. What is important is that the rigid link  11  including the ring  20 , optimal flared end portion  21  and the open support structure  19  provides sufficient rigidity so that the second speaker cone  4  replicates any displacement of the first speaker cone  2 . 
     FIG. 4 depicts another embodiment of a loudspeaker  101  constructed in accordance with this invention to enhance its frequency response. This embodiment utilizes the same rigid link  11  as described with respect to FIGS. 1,  2  and  3 . I have found however, that notwithstanding the low frequency characteristic of the speaker shown in my patent, the bobbin  8  and voice coil  18  tend to vibrate at the composite driving frequency of the applied signal. This composite signal will have frequency components ranging from the low-bass to the high-treble regions of the audio spectrum. However, the mass of the primary speaker cone  2  and the secondary speaker cone  4  rapidly damp out any higher frequency components so that the primary speaker cone  2  and secondary speaker cone  4  do not radiate any significant energy at the higher frequencies. Consequently, the basic speaker in FIG. 1 is characterized by having a high frequency roll off. While in many applications this roll off is desirable, there are other applications in which the loudspeaker of FIG. 1 could benefit if it could operate with a frequency range extended into the mid-range and treble frequency ranges. 
     The increased strength and rigidity of the link  11  shown in FIG. 1 allows a further advantage of enabling the introduction of a high frequency radiating structure or radiator to enhance the frequency response of the loudspeaker, such as the loudspeaker  101  in FIG.  4 . More specifically, a high frequency radiator  40  is positioned proximate the spokes  22  of the open support structure  12 . The radiator  40  is rigid and spherical in shape. In one embodiment, a neck  41  attaches to the rigid member  32 . An adjacent portion  42  of the radiator  40  is sectored to form gaps that allow this portion of the radiator to pass over the spokes  22 . A surface portion  43  of the radiator  40  would be continuous and rigid to form a forward directed radiating surface housing having a semi-spherical shape. 
     The neck  41  and portion  42  flare from a narrow dimension at a lower end  44  facing the secondary speaker cone  4  to a maximum diameter at a position  45  adjacent the open web structure  19  of the primary speaker cone  2 . The curved surface of the portion  42  smoothly directs any air flow to a location outside the high frequency radiator  40  thereby to minimize any turbulence that the high frequency radiator might otherwise introduce into the low frequency sound emanating from the secondary speaker cone  4 . In another approach, the ring  20 , spokes  22 , radiator  40  and link  32  could be found as a molded structure with the central portion of the open structure  19  internally of the radiator being eliminated and the portions of the spokes  22  externally of the radiator  40  being formed as extensions of the radiator  40 . 
     FIG. 5 depicts another embodiment  102  of a loudspeaker with an improved bass response modified to provide an enhanced high frequency response. In this embodiment the center portion of the secondary speaker cone  4  is replaced with a stiff high frequency radiator  50  attached to the annular speaker cone  4  by a surround  51 . An attachment  13  as described in the other embodiments connects the high frequency radiator  50  to a rigid coupling device  52  carried by the open support structure  19 . This rigid coupling device  52  includes a piezoelectric transducer  53  attached to the spokes  22  and hub and energized by a separate source (not shown). A rigid member  54  attaches to the output of piezoelectric transducer  53  and the attachment  13 . 
     At low frequencies, the rigid coupling device  52  moves the primary speaker cone  2  in the same manner as occurs in the embodiments of FIGS. 1 and 4. The piezoelectric transducer  53  only receives high frequency signals from a crossover, phase or other adjustment network. As the transducer  53  receives only high frequency signals, at low frequencies the piezoelectric transducer  53 , the member  54 , the attachment  13  and the high frequency radiator  50  act as a rigid structure so that low frequency excursions of the voice coil  18  and bobbin  21  produce like excursions of the secondary speaker cone  4 . Consequently, at low frequencies the composite of the speaker cone  4  and radiator  50  still act as a low frequency driver. 
     When higher frequencies energize the transducer  53 , the transducer  53  drives the member  54  relative to the open support structure  12  and thereby displaces the high frequency radiator  50  at that same higher frequency. The surround  51  is constructed to enable this high frequency reciprocating motion of the high frequency radiator  50  to occur without impacting the motion of the secondary speaker cone  4 . 
     In certain applications the signal applied to the high frequency radiator  50  may produce a signal that is out of phase with the signal from the primary cone  2  due to the distance between the primary speaker cone  2  and the high frequency radiator  50 . The transducer  53  provides a tool for allowing a phase adjustment to compensate any such phase error. 
     Thus the loudspeaker  102  in FIG. 5 provides the advantages of improved bass response provided by the structure in FIG. 1 and, in addition, provides an enhanced frequency response by enabling the same basic structure to produce high frequency output. Depending on the nature of the physical size of the piezoelectric transducer  53 , it may be desirable to include a streamlining structure in the embodiment of FIG. 5 comparable to the streamlining structure  41  shown in FIG.  4 . 
     FIG. 6 depicts still another loudspeaker  103  in which the ring  20  shown in FIGS. 1,  4  and  5  is modified to provide a cylindrical structure that includes an integral elongated cylinder  60 . This cylinder  60  performs both the stiffening and attachment functions of the ring  20  with respect to the spokes  22  and serves as a bobbin for the voice coil  10 . The upper end of the cylinder  60  terminates in a conical upper end portion  61  that flares outwardly from the bobbin portion  62  like the flared end  21  in FIGS. 1 and 2. In addition to improving the strength of the ring portion, the flared portion  61  provides a surface for attachment of the primary speaker cone  2  and the spider  10  to produce a structure with even greater reliability than as shown in FIGS. 1,  4  and  5 . Moreover, if the cylinder  60  is constructed of a lightweight metal or rigid plastic material, the overall weight of the cylinder  60  can be reduced thereby lowering the inertia of this structure to enhance frequency response further. Eliminating the ring-to-bobbin attachment minimizes a potential failure point. It has also been found that this structure is easy to manufacture. 
     FIGS. 7 through 10 depict still another loudspeaker embodiment having the same general construction as shown in FIGS. 1 and 4 through  6 . Referring specifically to FIG. 7, this loudspeaker embodiment  104  includes a rigid frame  1  that carries a primary speaker cone  2 . A subframe  3  carries a secondary speaker cone  4 . Both the first and second cones  2  and  4  are annular in shape. A surround  9  connects the primary speaker cone  2  to the frame  1 . A surround  9 ′ connects the second annular speaker cone  4  to the subframe  3 . A permanent magnet  5  with pole pieces  6  defines an air gap  7  for a voice coil  18 . The pole pieces  6  also form a passage or orifice  14  from the chamber formed by the subframe  3  and second speaker cone  4  through the primary speaker cone  2 . 
     In this embodiment the connection between the primary speaker cone  2  and the second cone  4  is constituted by a rigid link  70  that has three basic components. These include a cylindrical section  71 , a circular section  72  and a rigid element  73 . 
     Now referring to FIGS. 7 through 9, the cylindrical section  71  includes a cylinder  74  with a center portion  75 . A flared end portion  76  extends from one end of the center portion  75  to provide a surface to which the first speaker cone  2  and the spider  10  can connect in a manner similar to that disclosed with respect to FIG. 5. A channel portion  77  is formed on the other side of the center portion  75 . As shown particularly in FIG. 9, a channel is formed by an offset  80 , a base portion  81  and a lower lip  82 . The resulting channel provides an axially constrained bobbin on which a single or multi-turn voice coil  18  can be wound. An adhesive is applied to the voice coil  18  to adhere it to the base portion  81  according to normal practice. As known, it is possible for this adhesive to fail in use and to allow the coil to unwrap. The channel  77  in the cylindrical structure  71  provides physical containment of the voice coil  18  that should minimize the unraveling even by sliding axially if the adhesive fails. 
     Now referring to FIGS. 7 and 8, the circular section  72  is rigid to serve as a high-frequency radiator. As previously indicated the second speaker cone  4  has an annular structure that defines a central aperture  78  with a central speaker cone periphery  79 . Looking specifically at FIG. 7, the second speaker cone  4  has a predetermined shape in cross-section. The circular section  72  preferably has a corresponding or complementary cross-section with is peripheral edge  72 A adjacent and slightly overlapping the central speaker cone periphery  79 . 
     Referring now to the detail of FIG. 10, a peripheral edge  72 A comprises bifurcated arms  83  and  84  interconnected by a base  85 . This produces a circumferentially extending channel  86  that overlaps and receives the periphery of the second speaker cone  4 . An elastomer adhesive  87  fills the channel  86  and encapsulates the periphery of the second speaker cone  4  thereby to provide an elastic bond between the circular section  72  and the second speaker cone  4 . Any number of elastomer materials can be provided. Such a material should provide a reliable bond for the environment in which the loudspeaker will be used and should enable the circular section  62  to oscillate at higher audio frequencies with a minimal transfer of that motion to the speaker cone  4  while allowing low frequency excursions of the circular section  62  to be reliably transferred to the speaker cone  4  with minimal attenuation in the magnitude of the excursions. 
     Referring again to FIG. 8, the rigid element  73  includes an open central structure  90  formed by a plurality of equiangularly spaced, thin planar spokes. In this specific embodiment a plurality of four spokes  91  through  94  extend from a common juncture  95  located on a vertical axis V. Each of the spokes is identical so that the following discussion is limited to spoke  92 . 
     Spoke  92  tapers from a maximum diameter that forms a radial arm  96  between the common juncture  95  and the center portion  75 . The spoke  92  tapers to a minimum dimension at a position  97  that is proximate the circular section  72 , but spaced slightly therefrom to enable an additional portion of the spoke  92  to provide a transition  98  into the circular section  72 . The rigid element  73 , by virtue of the intersecting spokes  91  through  94 , forms an axially and radially rigid structure. Arms, such as the arm  96  provide stability in the transverse dimension of the cylindrical section  71  so that the voice coil  18  remains in a round configuration. The flared attachment at  98  further provides positional stability between the rigid element  73  and the circular section  72  so that the circular section  72  does not tilt or yaw about the axis V during excursions of the voice coil  18 . 
     The rigid link  70  can be formed as a lightweight, strong integral structure with axial and radial stiffness. This construction minimizes the number of potential adhesive failure points to the attachment points for the primary speaker cone  2 , the spider  10  and the second speaker cone  4 . At each of these attachment points the rigid link  00  provides a more reliable connection thereby to minimize any failure potential. The result is a loudspeaker that has an improved bass response, an extended upper frequency response and a reliable construction. 
     Thus in accordance with several objects of this invention, the rigid coupling device  11  shown in FIGS. 1 through 6 with its ring  20  and spokes  22  and the rigid link  70  in FIG. 7 provide rigid, lightweight structures that have an improved ability to attach to primary and secondary speaker cones and thereby increase the overall reliability of a dual cone loudspeaker and facilitate the manufacture of such loudspeakers. Moreover, these improved rigid couplings or rigid links provide a platform for a high frequency radiating structure to enhance the overall operating frequency range and allow the broadcast of a wider range of frequencies with good fidelity. 
     This invention has been described in terms of certain specific embodiments. It will be apparent to those of ordinary skill in that art that a number of modifications could be made. For example, in one embodiment the improved rigid coupling structure  12  is formed of aluminum. Other metallic and nonmetallic materials such as titanium or plastics could also be utilized. The open support structure  11  is shown with four equiangularly spaced spokes  22  extending out and circumscribed by the ring  20 . It will be apparent that any other number of spokes, preferably three or five or more, could be substituted as well as being modified to produce an equivalent structure in an alternate fashion. Finally, this invention has been disclosed in terms of a specific speaker structure with a particular frame and magnet configuration. It will be apparent that the invention is readily adapted to speakers having other frame and magnet configuration. Therefore, it is the intent of the appended claims to cover all such variations and modifications as come within the true spirit and scope of this invention.