Abstract:
A transformer includes a bobbin having a cavity, a primary winding wound around the bobbin, and a secondary winding wound around the bobbin and magnetically coupled with the primary winding. In the transformer, at least one of the primary winding and the secondary winding is divided into at least two portions which include a portion wound at an inside region of the transformer and a portion wound at an outside region of the transformer. Also, at least a portion of the other one of the primary winding and the secondary winding is wound between said at least two portions obtained by dividing the one of the primary winding and the secondary winding, and at least a portion of the cavity of the bobbin is used as a space to dispose another member therein.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to transformers, loudspeaker devices, loudspeaker networks, and loudspeaker systems, and more specifically relates to a transformer included in a piezoelectric loudspeaker, and to a loudspeaker device, a loudspeaker network, and a loudspeaker system that include the above-described transformer. 
     2. Description of the Related Art 
     A transformer for a conventional piezoelectric loudspeaker is constructed such that a primary winding and a secondary winding are wound around a bobbin and a core is inserted into the bobbin. 
     In the above-described transformer for the conventional piezoelectric loudspeaker, the transformer is expensive as well as heavy due to the use of the core. Accordingly, the removal of the core has been contemplated to produce an inexpensive and light-weight transformer. However, the removal of the core decreases the magnetic coupling strength between the primary winding and the secondary winding. Moreover, to reduce the size of the piezoelectric loudspeaker, it is desirable to provide another member, such as a portion of the loudspeaker, within the above-described transformer of the conventional piezoelectric loudspeaker. These points also apply to a loudspeaker device, a loudspeaker network, and a loudspeaker system that include the transformer for the conventional piezoelectric loudspeaker. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems described above, preferred embodiments of the present invention provide an inexpensive, compact, and lightweight transformer which has strong magnetic coupling between a primary winding and a secondary winding, and which can hold another member therein. 
     Further, preferred embodiments of the present invention provide a loudspeaker device, a loudspeaker network, and a loudspeaker system which include a transformer that is inexpensive, compact, and lightweight, and that has strong magnetic coupling between a primary winding and a secondary winding, and which has another member disposed therein. 
     According to a first preferred embodiment of the present invention, a transformer including a bobbin having a cavity, a primary winding wound around the bobbin, and a secondary winding wound around the bobbin and magnetically coupled with the primary winding is provided. In the transformer, at least one of the primary winding and the secondary winding is divided into at least two portions which include a portion wound at the inside and a portion wound at the outside, at least a portion of the other one of the primary winding and the secondary winding is wound between said at least two portions obtained by dividing the one of the primary winding and the secondary winding, and at least a portion of the cavity of the bobbin is used as a space to accommodate another member therein. 
     According to another preferred embodiment of the present invention, a loudspeaker device includes a transformer as described in the previous paragraph, and a loudspeaker, connected to the transformer, and including a sound-producing body having a piezoelectric body. In the loudspeaker device, at least a portion of the loudspeaker is provided in the cavity of the bobbin. 
     In the loudspeaker device according to another preferred embodiment of the present invention, the loudspeaker has a horn for conducting sound waves transmitted from the sound-producing body, one end of the horn is inserted into the cavity of the bobbin, and the bobbin of the transformer is mounted on the horn. 
     According to another preferred embodiment of the present invention, a loudspeaker network includes a transformer having the features of the preferred embodiment described above and an impedance network connected to the transformer. 
     According to a further preferred embodiment of the present invention, a loudspeaker system includes a loudspeaker device according to a preferred embodiment described above, and a loudspeaker network according to the preferred embodiment described above. In the loudspeaker device, the transformer of the loudspeaker device includes the transformer of the loudspeaker network. 
     Since there is no core used in the transformer, the transformer is inexpensive as well as lightweight. 
     Furthermore, in the transformer according to preferred embodiments of the present invention, since at least one of the primary winding and the secondary winding is wound between at least two portions obtained by dividing the other one of the primary winding and the secondary winding, the magnetic coupling between the primary winding and the secondary winding of the transformer is stronger than a transformer constructed by winding the entire primary winding and the winding the entire secondary. 
     Also, in the transformer according to preferred embodiments of the present invention, since a portion of the cavity of the bobbin is used as a space for having another member disposed therein, another member, such as an end portion of the horn of the loudspeaker, can be disposed therein. 
    
    
     Other features, characteristics, arrangements and advantages of the present invention will become more apparent from the detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration showing one example of a loudspeaker system according to a preferred embodiment of the present invention; 
     FIG. 2 is an illustration showing a loudspeaker device of the loudspeaker system shown in FIG. 1; 
     FIG. 3 is a sectional view showing a vibrator of a piezoelectric loudspeaker included in the loudspeaker system shown in FIG. 1; 
     FIG. 4 is a circuit diagram of the loudspeaker system shown in FIG. 1; 
     FIG. 5 is a graph showing frequency characteristics of the boost ratio of a loudspeaker network used in the loudspeaker system shown in FIG. 1; 
     FIG. 6 is a graph showing frequency characteristics of the impedance of the loudspeaker network used in the loudspeaker system shown in FIG. 1; 
     FIG. 7 is a graph showing frequency characteristics of the sound pressure of the loudspeaker system shown in FIG. 1; and 
     FIG. 8 is a perspective view of another preferred embodiment of a loudspeaker system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is an illustration showing one example of a loudspeaker system according to a preferred embodiment of the present invention. FIG. 2 is an illustration showing a loudspeaker device of the loudspeaker system. A loudspeaker system  10  shown in FIG. 1 preferably includes a substantially cylindrical casing  12  made of synthetic resin, or other suitable material. One end of the casing  12  is open while the other end has a disk-shaped lid  14  adhered thereto. 
     The casing  12  has a piezoelectric loudspeaker  20  mounted therein as a tweeter. The piezoelectric loudspeaker  20  includes a disk-shaped supporting member  22  as shown in FIG. 2. A hole  22   a , serving as a so-called “air vent” is provided at the approximate center of the supporting member  22 . One major surface of the supporting member  22  has a substantially hemispherical vibrator  24  with a diameter of about 20 mm attached thereto. The vibrator  24  functions as a sound-producing body and includes a substantially hemispherical vibrating body  26  which is made of a piezoelectric material, such as a piezoelectric ceramic, or other suitable piezoelectric material, polarized in the thickness direction, as shown in FIG.  3 . Electrodes  28   a  and  28   b  are provided on the internal surface and external surface of the vibrator  24 , respectively. 
     As shown in FIG. 2, input terminals  30   a  and  30   b  each have one end thereof soldered to the electrodes  28   a  and  28   b  of the vibrator  24 , respectively. Furthermore, a horn  32  made of a synthetic resin, or other suitable material, is mounted around the supporting member  22 . 
     The horn  32  is configured so that the width thereof gradually increases from one end  34  towards the other end  36 . The end  34  of the horn  32  includes a step and the other end  36  of the horn  32  includes a flange. The end  34  of the horn  32  is adhered to the surrounding of the supporting member  22 , thus securing the input terminals  30   a  and  30   b  between the end  34  of the horn  32  and the surrounding of the support member  22 , as shown in FIG.  2 . The other end  36  of the horn  32  is adhered to one end of the casing  12  as shown in FIG. 1, and supports the piezoelectric loudspeaker  20  in the casing  12 . In this piezoelectric loudspeaker  20 , by inputting a signal across the input terminals  30   a  and  30   b , the vibrator  24  vibrates, and a sound is produced from the horn  32 . 
     Furthermore, the loudspeaker system  10  includes a loudspeaker network  40 . The loudspeaker network  40  includes a transformer  50  and an impedance network  70 . 
     As shown in FIG. 2, the transformer  50  includes a substantially cylindrical bobbin  52  made of a synthetic resin, or other suitable material. The bobbin  52  has a cavity  52   a  in the approximate center thereof. The nose of the end  34  of the horn  32  of the piezoelectric loudspeaker  20  is inserted into the cavity  52   a  of the bobbin  52 . Thus, the bobbin  52  is fixedly adhered around the end  34  of the horn  32 . In this case, not only the end  34  of the horn  32  but also the supporting member  22  of the piezoelectric loudspeaker  20  and middle portions of the input terminals  30   a  and  30   b  are provided in the cavity  52   a  of the bobbin  52 . A primary winding  54  and a secondary winding  56  are wound around this bobbin  52 . In this case, the secondary winding  56  is divided into two portions  56   a  and  56   b . The portion  56   a  of the secondary winding  56 , the primary winding  54 , and the portion  56   b  of the secondary winding  56  are wound in that order around the bobbin  52 , such that the primary winding  54  is sandwiched between portions  56   a  and  56   b  of the secondary winding  56 . Furthermore, in the secondary winding  56 , one end of the portion  56   a  is connected to the input terminal  30   a  of the piezoelectric loudspeaker  20 , the other end of the portion  56   a  is connected to one end of the portion  56   b , and the other end of the portion  56   b  is connected to the input terminal  30   b  of the piezoelectric loudspeaker  20 . That is, the ends of the secondary winding  56  are connected to the corresponding input terminals  30   a  and  30   b  of the piezoelectric loudspeaker  20 . The ends of the primary winding  54  are connected to corresponding terminals  58   a  and  58   b . These terminals  58   a  and  58   b  are mounted via an insulating tape  60  on the portion  56   b  of the secondary winding  56 . 
     As described above, the loudspeaker device is constructed by combining the piezoelectric loudspeaker  20  and the transformer  50 . 
     As shown in FIG. 1, the impedance network  70  includes a capacitor  72  of about 2 μF and a resistor  74  of about 6.7 kΩ, or other suitable capacitance and resistance. One end of the capacitor  72  and one end of the resistor  74  are connected to the two terminals  58   a  and  58   b  of the transformer  50 , respectively. The other end of the capacitor  72  and the other end of the resistor  74  are connected to two external terminals  76   a  and  76   b , respectively. These external terminals  76   a  and  76   b  are mounted so as to penetrate the lid  14  of the casing  12 . 
     Therefore, this loudspeaker system  10  includes a circuit shown in FIG.  4 . 
     Since there is no core provided in the transformer  50  of the loudspeaker network  40 , the loudspeaker system  10  is inexpensive as well as lightweight. 
     Since the primary winding  54  is wound between the two portions  56   a  and  56   b  obtained by dividing the secondary winding  56  of the transformer  50  of this loudspeaker system  10 , the magnetic coupling between the primary winding  54  and the secondary winding  56  is stronger than the magnetic coupling between a primary winding and a secondary winding of a transformer constructed by winding the primary winding and the secondary winding in that order, such that the primary winding is not sandwiched between two portions of the secondary winding. 
     Furthermore, in this loudspeaker system  10 , the cavity  52   a  of the bobbin  52  of the transformer  50  is effectively used as a space for disposing the supporting member  22  and the input terminals  30   a  and  30   b  of the piezoelectric loudspeaker  20 , and the end  34  of the horn  32 . 
     In this loudspeaker system  10 , as shown by frequency characteristics of the boost ratio of the loudspeaker network  40  in FIG. 5, the boost ratio is high in the high frequency band. Accordingly, this loudspeaker system  10  produces an outstanding tweeter because high sound pressure is obtained from the piezoelectric loudspeaker  20  in the high frequency band. 
     In this loudspeaker system  10 , the frequency characteristics of the impedance of the loudspeaker network  40  as shown in FIG. 6 illustrate that the impedance is high at portions of the low frequency band. Accordingly, when this loudspeaker system  10  is connected in parallel with another loudspeaker, such as a woofer, this loudspeaker system  10  performs very well because it does not practically affect a signal in the low frequency band. Frequency characteristics of sound pressures concerning this loudspeaker system  10 , another loudspeaker system, and the loudspeaker system obtained by connecting these systems in parallel are shown in FIG.  7 . According to the frequency characteristics shown in FIG. 7, the other loudspeaker system does not have a very high sound pressure in the high frequency band. However, by connecting the loudspeaker system  10  in parallel with the other loudspeaker system, the sound pressure is increased in the high frequency band while it is not substantially affected in the low frequency band. 
     In this loudspeaker system  10 , the end  34  of the horn  32  of the piezoelectric loudspeaker  20  is a node of the piezoelectric loudspeaker  20 . Since the loudspeaker device is constructed by mounting the transformer  50  at the end  34 , a loudspeaker device having a compact structure is produced, in which the transformer  50  does not substantially affect the vibration of the piezoelectric loudspeaker  20  and the space of the air-core unit of the transformer  50  (the cavity  52   a ) can be effectively utilized. 
     In this loudspeaker system  10 , since a core is not used in the transformer  50 , the inductance of the transformer  50  is greatly reduced, and the desired inductance is obtained in the high frequency band. Accordingly, the transformer  50  is well-suited for use in the loudspeaker network  40 . 
     FIG. 8 is a perspective view showing another preferred embodiment of the loudspeaker system according to the present invention. A loudspeaker system  10  shown in FIG. 8 has the piezoelectric loudspeaker  20  and the loudspeaker network  40 , along with a midrange  90  and a woofer  100 , mounted in one casing  80 . 
     In the above described loudspeaker system  10 , unlike in the transformer  50  of the loudspeaker network  40  where the primary winding  54  is wound between the two portions  56   a  and  56   b  of the secondary winding  56 , the secondary winding  56  can be wound between two portions of the primary winding  54 . Alternatively, portions obtained by dividing each of the primary winding  54  and the secondary winding  56  into at least two portions may be alternately wound from among the primary winding portions and the secondary winding portions. 
     Although in the above-described loudspeaker system  10 , the supporting member  22  and the input terminals  30   a  and  30   b  of the piezoelectric loudspeaker  20  and the one end of the horn  32  are provided within the cavity  52   a  of the bobbin  52  of the transformer  50 , other members may also be disposed therein. 
     In the above-described loudspeaker system  10 , although the impedance network  70  including the capacitor  72  and the resistor  74  is provided, another impedance network may be used. 
     In the above-described loudspeaker system  10 , although the piezoelectric loudspeaker  20  is used, another type of loudspeaker may be used. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skill in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit of the invention.