Abstract:
An audio transducer for use in a loudspeaker system. The transducer includes a pair of flexible, curved diaphragms, with each diaphragm having a distal end and a proximal end. The curved diaphragms form hemi-cylindrical lobes being substantially tangent to one another at their proximal ends and are attached to energy absorbent dampers at their distal ends. The transducers can be employed in a line array as part of the loudspeaker system as well as some of the transducers facing forward while others rearward and, in doing so, their amplitudes and phases can be adjusted for fine tailoring the geometric coverage of acoustic energy radiating from the loudspeaker system.

Description:
[0001]    This application is a continuation of, and claims benefit of and priority to, U.S. application Ser. No. 11/324,652, filed on Jan. 3, 2006, and is entitled to that filing date for priority. The specification, drawings, and complete disclosure of U.S. application Ser. No. 11/324,652 are incorporated herein by reference for all purposes. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to audio transducers and specifically audio transducers having a pair of hemi-cylindrical lobes and loudspeaker systems employing such transducers in tailoring geometric coverage of acoustic radiation emanating from such a loudspeaker system. 
       BACKGROUND OF THE INVENTION 
       [0003]    The vast majority of audio transducers employ cylindrical diaphragms formed from flat sheets that are curved so that all lines normal to the curved surface remain perpendicular to the longitudinal axis of the diaphragm. Although such transducers are most common, there are many other forms of acoustic energy generating devices such as those disclosed in International Publication No. WO93-23967 and U.S. Pat. No. 5,249,237. 
         [0004]    A significant departure from those diaphragms created from flat sheets are those disclosed in U.S. Pat. No. 6,061,461, the disclosure of which is incorporated by reference herein. Transducers disclosed in the &#39;461 patent are especially useful as high frequency or tweeter transducers that are not necessarily limited to the reproduction of high frequencies. These transducers include a rigid frame and a permanent ring magnet mounted to the frame and a small bobbin, preferably formed of aluminum foil sized and arranged to fit within the open end of a magnetic gap while providing motion of the bobbin therein. A voice coil is wound on the bobbin and connectable to receive an audio signal similar to a conventional voice coil driver system. What is unique to the &#39;461 patented invention is the use of flexible, curved diaphragms disposed in a frame generally free to move except for the distal end of each diaphragm which is fixed to the frame of the transducer. The proximal ends of the diaphragms are connected together in a spaced relationship by a pliable decoupling pad, preferably formed of a closed-cell foam tape for decoupling the diaphragms from one another while enabling them to be driven with a single voice coil driver assembly. 
         [0005]    Although the transducers described in the &#39;461 patent provide excellent high frequency response and dispersion of acoustic energy, such transducers are not free of faults. In sum, the transducer to be described herein constituting the present invention is capable of smooth amplitude-frequency response, high electro acoustic conversion efficiency, wide dispersion of sound output and low distortion. Transducers of the present invention when operated above approximately 2 kHz represent a marked improvement over direct-radiator transducers which employ rigid diaphragms and are therefore, by necessity, very small. At high amplitudes the rigidity of such diaphragms usually fail in unpredictable modes and the result is non-uniform response in both amplitude and dispersion. As was the case with the &#39;461 transducer, the present invention makes use of the propagation of bending waves in a non-rigid material. In this type of transducer, the properties of the diaphragm material are exploited rather than design limitations to be overcome. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to an audio transducer comprising a rigid frame, a pair of flexible, curved diaphragms each having a distal end and a proximal end, said curved diaphragms forming a pair of hemi-cylindrical lobes being substantially tangent to one another at their proximal ends and a pair of energy absorbing dampers appended to said frame and connected to the distal end of the curved diaphragms. A cylindrical cup is provided located proximate the proximal ends of the curved diaphragms, the cylindrical cup housing a permanent magnet and a pole tip forming an annular gap at an open end of the cylindrical cup. A focusing magnet is further provided being mounted to the pole tip opposite the permanent magnet. A voice coil is wound on an aluminum form and placed within the gap for moving the pair of flexible curved diaphragms in response to audio frequency currents received by the audio transducer from a signal source. 
         [0007]    The audio transducer described above can be employed in a full range loudspeaker system preferably as the tweeter or high frequency transducer of such system although not necessarily so. Multiple such transducers can be arranged in a line-array while it is contemplated, as a preferred embodiment, that some of such transducers face forward and some rearward of the loudspeaker system cabinet whereby amplitudes and/or phase of these transducers can be selected to fine tailor geometric coverage of acoustic radiation emanating from the loudspeaker system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective cross-sectional view of the transducer of the present invention. 
           [0009]      FIG. 2  is a perspective view of the transducer of  FIG. 1 . 
           [0010]      FIG. 3  is a top plan view of the diaphragm film employed in constructing the transducer of the present invention. 
           [0011]      FIG. 4  is a perspective view of the frame or housing of the transducer of the present invention. 
           [0012]      FIG. 5  is a perspective view of the reticulated foam dampers employed in constructing the transducers of the present invention. 
           [0013]      FIG. 6  depicts the plan view of a portion of a loudspeaker cabinet showing the transducers of the present invention in line array. 
           [0014]      FIG. 7  shows a side plan view of a portion of a loudspeaker cabinet showing the present transducers positioned for ratio metric drive. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0015]    Turning first to  FIG. 1 , transducer  10  is depicted in cross-section in order to enable one to visualize its internal components. The present transducer is applied to a rigid frame which is shown as base plate  12  which can optionally be secured to vertically and horizontally extending housing components  13  and  14 , respectively. These latter elements can be part of the loudspeaker system that makes use of the presently described transducer  10 . 
         [0016]    In constituting the component parts of transducer  10 , reference is first made to magnetic permeable cup  11  housing, for example, a neodynium, iron boron high intensity primary magnet  15 . Magnet  15  causes a strong stationary magnetic field to exist in the gap formed between pole tip  16  and the upper end of magnetic permeable cup  11 . A voice coil is constructed and made a part of voice coil form  17  constructed ideally of copper-coated aluminum wire (for reduced mass compared to copper wire, alone). When alternating current from a signal source such as an audio amplifier is passed through the voice coil winding, the resulting magnetic field alternately draws the voice coil form  17  into cup  11  and pushes it out of cup  11 . The resulting reciprocating motion of the coil drives diaphragms  21  and  22 . In addition, focusing magnet  9  can be mounted to the pole tip opposite main magnet  15  in order to concentrate the flux in the gap. 
         [0017]    In again referring to  FIG. 1 , transducer  10  also includes spider  18  which is a flexible fabric circle with circumferential corrugations attached at its inner diameter to the voice coil and its outer diameter to spider/damper platform  19 . The spider/damper platform  19  is stationary and is mounted to the outside of magnetic permeable cup  11  and establishes the static elevation of the coil within voice coil form  17  and maintains is concentricity with pole tip  16  and therefore its centering within the gap. Further, the flexibility of spider/damper platform  19  permits axial movement of the voice coil. 
         [0018]    As an optional expedient, magnetic fluid can be introduced into the gap on both the inside and outside of voice coil form  17 , this magnetic fluid common to transducer fabrication and consists of a viscous fluid which contains magnetically active microscopic particles suspended in the fluid and captured by the magnetic flux in the gap. This prevents the migration of the fluid which is employed to assist in keeping voice coil form  17  centered within the gap and dampens unwanted lateral motions such as “rocking” of the voice coil and is also used to transfer heat from the voice coil during operation of the transducer. 
         [0019]    As noted previously, transducer  10  includes flexible diaphragms  21  and  22  having proximal ends  23  and distal ends  24 . Diaphragms  21  and  22  form two lobes which are connected at their distal ends to damper foam blocks  25  shown both in  FIGS. 1 and 5 . Damper foam blocks  25  absorb sound radiated from the back side of diaphragms  21  and  22 . As noted again in reference to  FIG. 1 , the surfaces of damper foam blocks  25  are not, throughout their outer edges, equidistant from the inner surfaces of diaphragms  21  and  22 . This design feature is intentional to spread out the frequency distribution of any residual reflections which might occur during imperfect absorbency of damper foam  25  to the acoustic energy generated on the back side of diaphragms  21  and  22 . Further, distal end  24  of diaphragms  21  and  22  are appended to damper foam  25  at interface  26  which is preferable to terminating distal ends  24  to base plate  12  because any remaining wave propagation in the diaphragm needs to be absorbed at distal end  24 . A hard termination, such as that suggested in the &#39;461 patent will reflect this energy back into diaphragms  21  and  22  causing undesirable vibrations in response. 
         [0020]    Once again referring to  FIG. 1 , it is noted that magnetic permeable cup  11  is mounted to base plate  12  as are the bottom surfaces of damper foam  25 . As such, the entire assembly is supported by base plate  12  which can be, as noted previously, appended to optional housing elements  13  and  14 . This is shown in  FIG. 2  whose component parts correspond to those described with regard to  FIG. 1 . 
         [0021]    As noted in reference to  FIG. 3 , diaphragms  21  and  22  can be constructed from a single rectangular die-cut film constructed with three holes  31 ,  32  and  33  and two small slots  34  and  35  where diaphragms  21  and  22  extend tangentially to one another at their proximal ends. In order to maintain the folded film in the form shown herein, a two mil closed-cell foam tape can be applied to the inside of the fold at proximal end  23 . The 2 mil spacer provided by the tape prevents any possibility of diaphragms  21  and  22  touching one another during operation which could cause “buzzing.” The resulting stiff structure at proximal end  23  is the point in which diaphragms  21  and  22  are driven by the voice coil. The two small slots match the diameter of the voice coil and are engaged by it and secured with activated cyanoacrylate adhesive. The two diaphragms  21  and  22  then curve backwards and their distal ends  24  are attached to damper foam blocks  25  ( FIG. 1 ) either by pressure sensitive adhesive or by activated cyanoacrylate or other suitable adhesive. As a preferred embodiment, diaphragms  21  and  22  are made from polyetheramide film, typically 3 mils thick. For appearance, a matt finish can be applied to the front side of diaphragms  21  and  22 . 
         [0022]    It should be pointed out that holes  31 ,  32  and  33  take on the appearance of notches when the rectangular film producing diaphragms  21  and  22  is laid flat before folding. Holes  31 ,  32  and  33  serve two purposes, namely, to remove moving mass near the proximal ends of diaphragms  21  and  22 , in other words, at their point of drive to improve high frequency response and to slightly weaken the mechanical beam which is produced by the fold at proximal end  23  and the foam tape. This causes slight flexure when diaphragms  21  and  22  are driven and causes the driving force to be imparted to the film isophasically. In turn, this causes wave propagation in the film to be slightly disorganized, or chaotic, which causes the radiation to be slightly diffuse. The beneficial consequence of this is that the vertical dispersion is wider than would occur if the film were vibrating isophasically. Other means of creating isophasic vibration could also be employed besides configuring holes  31 ,  32  and  33  at proximal ends  23  and their employment is considered to be part of the present invention. 
         [0023]      FIG. 4  depicts a typical rigid frame  40  for receiving the various functional components described above. As noted, various holes  41  can be tapped within frame  40  for receiving suitable audio frequency currents from an audio amplifier (not shown) employed for driving the present transducer. Holes  42  can also be provided for attaching frame  40  to a suitable loudspeaker. 
         [0024]    As noted previously,  FIG. 5  depicts damper foam  25  described previously with reference to  FIG. 1 . Suitably, damper foam  25  can consist of reticulated urethane foam although other materials could be employed which have the necessary structural rigidity and acoustical wave absorbing characteristics preferable exhibited for the purposes described above. 
         [0025]    Reference is next made to  FIG. 6 . In employing transducer  10  in a loudspeaker system, the transducer can be ideally employed to provide high frequency output (above approximately 2 kHz) or could be used to convey other frequencies within the audio spectrum. In either case, because present transducers  15  are maintained on base plate  12  ( FIG. 1 ), they can be placed quite close to one another in a line array. This configuration is illustrated in  FIG. 6  showing the line array of transducers  51 ,  52 , etc. within loudspeaker housing  50 . When so arranged, an effectively unbroken vertical diaphragm having an arbitrary length is possible which closely approaches a true line source. 
         [0026]    Reference is now made to  FIG. 7  showing speaker enclosure  60  from its side view. As noted, transducer  61  and  63  can be placed upon surface  65  facing a listener while transducers  62  and  64  can be configured upon surface  67  away from a listener. Any number of transducers can be so employed and driven in various ways to accomplish certain design criteria sought after herein. Specifically, transducer  61 ,  62 ,  63  and  64  etc. can be driven with equal in-phase signals to enable loudspeaker  60  to closely approach a perfectly omni directional radiation pattern in a horizontal plane. When this degree of omni directionality is not required (or desired) it is possible to drive, for example, transducer  61  and  63  within phase voltages with transducer  62  and  64  but with different amplitudes. This will result in a radiation pattern in the horizontal plane which is very broad but still possesses some preferential directivity. Alternately, introducing either pure delay or frequency-dependent phase shift between the electrical signals provided to transducers  61  and  63  as compared to those provided to transducers  62  and  64  can produce a wide range of directional characteristics according to the system design requirements. 
         [0027]    Thus, it should be understood that the embodiments and examples described herein have been chosen and described in order to best illustrate the principles of the invention and its practical applications to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited for particular uses contemplated. Even though specific embodiments of this invention have been described, they are not to be taken as exhaustive. There are several variations that will be apparent to those skilled in the art.