Patent Publication Number: US-11647337-B2

Title: Display panel and display apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/767,673, filed on May 28, 2020, which is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/JP2018/043685, filed on Nov. 28, 2018, which claims the benefit of Japanese Priority Patent Application No. 2017-235533, filed in the Japanese Patent Office on Dec. 7, 2017, the disclosures of which are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a display panel and a display apparatus. 
     BACKGROUND ART 
     In recent years, flexible display panels have been actively developed. Among such display panels, for example, a thin and flexible display panel using, as a pixel, an organic EL (electro-luminescence) element called OLED (Organic Light Emitting Diode) has attracted attention. 
     SUMMARY OF THE INVENTION 
     Incidentally, a display panel and a display apparatus that utilize flexibility are demanded. It is therefore desirable to provide a display panel and a display apparatus that utilize flexibility. 
     A display panel according to an embodiment of the present disclosure includes a flexible organic electroluminescent panel, and one or a plurality of piezoelectric films provided on a rear surface of the organic electroluminescent panel and vibrating the organic electroluminescent panel as a flat speaker. 
     A display apparatus according to an embodiment of the present disclosure includes a display panel and a circuit substrate that drives the display panel. In this display apparatus, the display panel includes a flexible organic electroluminescent panel, and one or a plurality of piezoelectric films provided on a rear surface of the organic electroluminescent panel and vibrating the organic electroluminescent panel as a flat speaker. 
     The display panel and the display apparatus according to embodiments of the present disclosure include, one or a plurality of piezoelectric films that vibrates the organic electroluminescent panel as a flat speaker is provided on a rear surface of the organic electroluminescent panel. This makes it possible to provide the display panel with a sound device, while utilizing flexibility of the organic electroluminescent panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a perspective configuration example of a flexible display according to a first embodiment of the present disclosure. 
         FIG.  2    illustrates an example of a state in which the flexible display of  FIG.  1    is wound. 
         FIG.  3    illustrates a circuit configuration example of the flexible display of FIG. 
         FIG.  4    illustrates a circuit configuration example of a pixel of  FIG.  2   . 
         FIG.  5    illustrates a developed perspective configuration example of a display panel of  FIG.  1   . 
         FIG.  6    illustrates a perspective configuration example of a piezo film of  FIG.  5   . 
         FIG.  7    illustrates a perspective configuration example of the piezo film of  FIG.  5   . 
         FIG.  8    illustrates a developed perspective configuration example of the display panel of  FIG.  1   . 
         FIG.  9    illustrates a developed perspective configuration example of the display panel of  FIG.  1   . 
         FIG.  10    illustrates a developed perspective configuration example of the display panel of  FIG.  1   . 
         FIG.  11    illustrates a developed perspective configuration example of the display panel of  FIG.  1   . 
         FIG.  12    illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  13 A  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  13 B  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  13 C  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  14    illustrates a perspective configuration example of the piezo film of  FIG.  5   . 
         FIG.  15    illustrates a perspective configuration example of the piezo film of  FIG.  5   . 
         FIG.  16    illustrates a perspective configuration example of the piezo film of  FIG.  5   . 
         FIG.  17    illustrates a perspective configuration example of the piezo film of  FIG.  5   . 
         FIG.  18    illustrates a perspective configuration example of the piezo film of  FIG.  5   . 
         FIG.  19 A  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  19 B  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  19 C  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  20 A  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  20 B  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  20 C  illustrates a perspective configuration example of an adhesive layer that may be used in the display panel of  FIG.  1   . 
         FIG.  21    illustrates a perspective configuration example of a portion of the piezo film and a wiring layer of  FIG.  5   . 
         FIG.  22    illustrates a perspective configuration example of the piezo film and the wiring layer of  FIG.  5   . 
         FIG.  23    illustrates an example of wiring lines provided on the piezo films of  FIG.  16    to  FIG.  22   . 
         FIG.  24    illustrates a functional block example of a system circuit substrate of  FIG.  1   . 
         FIG.  25    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  26    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  27    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  28    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  29    illustrates an inner configuration example of a winding mechanism of  FIG.  28   . 
         FIG.  30    illustrates an example of a state in which the flexible display of  FIG.  28    is wound. 
         FIG.  31    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  32    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  33    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  34    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  35    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  36    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  37    illustrates an example of sound output in a state in which the display panel is wound by a winding mechanism. 
         FIG.  38    illustrates an example of sound output in a state in which the display panel is wound by a winding mechanism. 
         FIG.  39    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  40    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  41    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  42    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  43    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  44    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  45    illustrates a modification example of the perspective configuration of the flexible display of  FIG.  1   . 
         FIG.  46    illustrates a functional block example of the system circuit substrate of  FIG.  1   . 
         FIG.  47    illustrates a perspective configuration example of a microphone array that may be used in the display panel of  FIG.  1   , together with a piezo film. 
         FIG.  48    illustrates a circuit configuration example of a noise cancellation circuit that may be used in a flexible display provided with the microphone array of  FIG.  47   . 
         FIG.  49    illustrates an example of directionality of sound output when the flexible display of any of  FIG.  1   ,  FIG.  25    to  FIG.  28   ,  FIG.  31    to  FIG.  36   , and  FIG.  39    to  FIG.  45    is converted into a cylindrical shape. 
         FIG.  50    illustrates an example of directionality of sound output when the flexible display of any of  FIG.  1   ,  FIG.  25    to  FIG.  28   ,  FIG.  31    to  FIG.  36   , and  FIG.  39    to  FIG.  45    is converted into a cylindrical shape. 
         FIG.  51    illustrates an example of directionality of sound output when the flexible display of any of  FIG.  1   ,  FIG.  25    to  FIG.  28   ,  FIG.  31    to  FIG.  36   , and  FIG.  39    to  FIG.  45    is converted into a cylindrical shape. 
         FIG.  52    illustrates a perspective configuration example of a flexible display according to a second embodiment of the present disclosure. 
         FIG.  53    illustrates an example of a state in which the flexible display of  FIG.  52    is wound. 
         FIG.  54    illustrates a perspective configuration example of a display panel of  FIG.  52   . 
         FIG.  55    illustrates an inner configuration example of a winding mechanism of  FIG.  52   . 
         FIG.  56    illustrates a perspective configuration example of an actuator of  FIG.  52   , together with a perspective configuration example of a fixing member of the display panel of  FIG.  52   . 
         FIG.  57    illustrates an example of arrangement of actuators and support members when the flexible display of  FIG.  52    is converted into a cylindrical shape. 
         FIG.  58    illustrates an example of the arrangement of the actuators and the support members when the flexible display of  FIG.  52    is converted into a cylindrical shape. 
         FIG.  59    illustrates an example of a state in which the flexible display of  FIG.  52    is provided with a curved support member. 
         FIG.  60    illustrates an example of a state in which the flexible display of  FIG.  52    is provided with a support member including an elastic member. 
         FIG.  61    illustrates an example of a state in which the support member and the actuator in the flexible display of  FIG.  52    are provided as a stand separately. 
         FIG.  62    illustrates an example of a state in which the support member and the actuator in the flexible display of  FIG.  52    are provided as a stand separately. 
         FIG.  63    illustrates a modification example of the support members and the actuators in the flexible display of  FIG.  52   . 
         FIG.  64    illustrates a perspective configuration example of a flexible display according to a third embodiment of the present disclosure. 
         FIG.  65    illustrates an example of a state in which the flexible display of  FIG.  64    is wound. 
         FIG.  66    illustrates a perspective configuration example of a display panel of  FIG.  64   . 
         FIG.  67    illustrates a perspective configuration example of a flexible display according to a fourth embodiment of the present disclosure. 
         FIG.  68    illustrates an example of a state in which the flexible display of  FIG.  67    is wound. 
         FIG.  69    illustrates a perspective configuration example of a display panel of  FIG.  67   . 
         FIG.  70    illustrates a cross-sectional configuration example of a state in which the display panel of  FIG.  67    is fixed to a wall. 
         FIG.  71    illustrates a modification example of the perspective configuration of the flexible display of any of  FIG.  52   ,  FIG.  64   , and  FIG.  67   . 
         FIG.  72    illustrates an example of a state in which a sound-absorbing material is provided on a wall that faces a wall on which the flexible display of any of  FIG.  1   ,  FIG.  25    to  FIG.  28   ,  FIG.  31    to  FIG.  36   ,  FIG.  39    to  FIG.  45   ,  FIG.  52   ,  FIG.  64   , and  FIG.  67    is mounted. 
         FIG.  73    illustrates a perspective configuration example of a flexible display according to a fifth embodiment of the present disclosure, together with a wall. 
         FIG.  74    illustrates a perspective configuration example of a state in which a display panel depicted in  FIG.  73    is wound, together with the wall. 
         FIG.  75    illustrates a perspective configuration example of a flexible display according to a sixth embodiment of the present disclosure. 
         FIG.  76    illustrates a side configuration example of the flexible display of  FIG.  75   . 
         FIG.  77    illustrates a side configuration example of the flexible display of  FIG.  75   . 
         FIG.  78    illustrates a side configuration example of the flexible display of  FIG.  75   . 
         FIG.  79    illustrates a side configuration example of the flexible display of  FIG.  75   . 
         FIG.  80    illustrates a perspective configuration example of a flexible display according to a seventh embodiment of the present disclosure. 
         FIG.  81    illustrates a side configuration example of the flexible display of  FIG.  80   . 
         FIG.  82    illustrates an example of a sound control in the flexible display of  FIG.  80   . 
         FIG.  83    illustrates a perspective configuration example of a flexible display according to an eighth embodiment of the present disclosure. 
         FIG.  84    illustrates an example of a state in which the flexible display of  FIG.  83    is wound. 
         FIG.  85    illustrates a perspective configuration example of a display panel of  FIG.  83   . 
         FIG.  86    illustrates a perspective configuration example of microphones that may be used in the display panel of  FIG.  83   , together with speakers. 
         FIG.  87    illustrates a circuit configuration example of a noise cancellation circuit that may be used in a flexible display provided with the microphone of  FIG.  86   . 
         FIG.  88    illustrates a modification example of a perspective configuration of a display panel that may be used for the flexible display of any of  FIG.  1   ,  FIG.  25    to  FIG.  28   ,  FIG.  31    to  FIG.  36   ,  FIG.  39    to  FIG.  45   ,  FIG.  52   , and  FIG.  63   . 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     In the following, description is given in detail of some embodiments for carrying out the present disclosure with reference to the drawings. The following description is merely a specific example of the present disclosure, and the present disclosure is not limited to the following embodiments. Moreover, the present disclosure is not limited to arrangements, dimensions, dimensional ratios, and the like of respective components illustrated in the drawings. It is to be noted that the description is given in the following order. 
     1. First Embodiment ( FIG.  1    to  FIG.  24   ) 
     2. Modification Examples of First Embodiment ( FIG.  25    to  FIG.  51   ) 
     3. Second Embodiment ( FIG.  52    to  FIG.  56   ) 
     4. Modification Examples of Second Embodiment ( FIG.  57    to  FIG.  63   ) 
     5. Third Embodiment ( FIG.  64    to  FIG.  66   ) 
     6. Fourth Embodiment ( FIG.  67    to  FIG.  70   ) 
     7. Modification Example Common to Respective Embodiments ( FIG.  71    and  FIG.  72   ) 
     8. Fifth Embodiment ( FIG.  73    and  FIG.  74   ) 
     9. Sixth Embodiment ( FIG.  75    to  FIG.  79   ) 
     10. Seventh Embodiment ( FIG.  80    to  FIG.  82   ) 
     11. Eighth Embodiment ( FIG.  83    to  FIG.  85   ) 
     12. Modification Example of Eighth Embodiment ( FIG.  86    and  FIG.  87   ) 
     13. Modification Example Common to First, Second and Eighth Embodiments ( FIG.  88   ) 
     1. First Embodiment 
     [Configuration] 
       FIG.  1    perspectively illustrates a schematic configuration example of a flexible display  1  according to a first embodiment of the present disclosure.  FIG.  2    illustrates an example of a state in which the flexible display  1  is wound.  FIG.  3    illustrates a circuit configuration example of the flexible display  1 . The flexible display  1  corresponds to a specific example of a “display apparatus” of the present disclosure. The flexible display  1  is a thin and flexible self-luminous display using, as a pixel, an organic EL (electro-luminescence) element called OLED (Organic Light Emitting Diode). 
     The flexible display  1  includes, for example, a display panel  10  having a display surface  1 A, and a frame  20  that protects an edge of the display panel  10  (a periphery of the display surface  1 A). The flexible display  1  further includes, for example, a system circuit substrate  30  that drives the display panel  10 , and an FPC (Flexible printed circuit)  30 A that electrically couples the display panel  10  and the system circuit substrate  30 . A plurality of pixels  11  are arranged in matrix on the display surface  1 A of the display panel  10 . The FPC  30 A is coupled to the edge of the display panel  10 . 
       FIG.  4    illustrates a circuit configuration example of the pixel  11  of the flexible display  1 . The display panel  10  includes, for example, a plurality of gate lines WSL and a plurality of power supply line DSL both extending in a row direction, and a plurality of data lines DTL extending in a column direction. The pixels  11  are provided in a manner corresponding to respective intersections of the data lines DTL and the gate lines WSL. Each of the data lines DTL, each of the gate lines WSL, and each of the power supply line DSL are electrically coupled to output ends of the system circuit substrate  30  via the FPC  30 A. 
     A scanning line WSL is used for selection of each pixel  11 , and supplies to each pixel  11  a selection pulse that selects each pixel  11  for each predetermined unit (e.g., pixel row). The signal line DTL is used for supplying to each pixel  11  a signal voltage corresponding to an image signal (a signal voltage Vimage described later), and supplies to each pixel  11  a data pulse including the signal voltage Vimage. The power supply line DSL supplies power to each pixel  11 . 
     Each pixel  11  is, for example, a pixel that emits red light, a pixel that emits green light, or a pixel that emits blue light. It is to be noted that each pixel  11  may be, for example, a pixel that emits another color (e.g., white, yellow, etc.). For example, a plurality of signal lines DTL are assigned to respective pixel columns on a line-by-line basis. For example, a plurality of scanning lines WSL are assigned to respective pixel rows on a line-by-line basis. For example, a plurality of power supply lines DSL are assigned to the respective pixel rows on a line-by-line basis. 
     Each pixel  11  includes a pixel circuit  11 - 1  and an organic EL element  11 - 2 . The pixel circuit  11 - 1  controls emission and extinction of the organic EL element  11 - 2 . The pixel circuit  11 - 1  has a function of holding a voltage (signal voltage Vimage) written into each pixel  11  by signal writing described later. The pixel circuit  11 - 1  further has a function of outputting a drive current of a magnitude corresponding to a magnitude of the voltage held to the organic EL element  11 - 2 . The pixel circuit  11 - 1  includes, for example, a drive transistor Tr 1 , a write transistor Tr 2 , and a holding capacitor Cs. 
     The write transistor Tr 2  controls application, to a gate of the drive transistor Tr 1 , of the signal voltage Vimage corresponding to an image signal. Specifically, the write transistor Tr 2  samples a voltage of the signal line DTL, and writes a voltage obtained by the sampling into the gate of the drive transistor Tr 1 . The writing of the voltage obtained by the sampling to the gate of the drive transistor Tr 1  is referred to as signal writing. The drive transistor Tr 1  is coupled in series to the organic EL element  11 - 2 . The drive transistor Tr 1  drives the organic EL element  11 - 2 . The drive transistor Tr 1  controls a current flowing through the organic EL element  11 - 2  in accordance with the magnitude of the voltage sampled by the write transistor Tr 2 . The holding capacitor Cs holds a predetermined voltage between the gate and a source of the drive transistor Tr 1 . The holding capacitor Cs serves to keep a gate-to-source voltage Vgs of the drive transistor Tr 1  constant during a predetermined period. It is to be noted that the pixel circuit  11 - 1  may have a circuit configuration in which various capacitors and transistors are added to the circuit of 2Tr1C described above, or may have a circuit configuration different from the circuit configuration of the 2Tr1C described above. 
     The gate of the write transistor Tr 2  is coupled to the scanning line WSL. A source or a drain of the write transistor Tr 2  is coupled to the signal line DTL. A terminal, of the source and the drain of the write transistor Tr 2 , that is not coupled to the signal line DTL is coupled to the gate of the drive transistor Tr 1 . The source or a drain of the drive transistor Tr 1  is coupled to the power supply line DSL. A terminal, of the source and the drain of the drive transistor Tr 1 , that is not coupled to the power supply line DSL is coupled to an anode of the organic EL element  11 - 2 . One end of the holding capacitor Cs is coupled to the gate of the drive transistor Tr 1 . The other end of the holding capacitor Cs is coupled to a terminal, of the source or the drain of the drive transistor Tr 1 , that is on side of the organic EL element  11 - 2 . 
       FIG.  5    illustrates a developed perspective configuration example of the display panel  10 . The display panel  10  includes, for example, a flexible OLED panel  12 , and a flexible piezo film  14  disposed on a rear surface of a heat-dissipating film  13  and vibrating the OLED panel  12  as a flat speaker. The display panel  10  further includes, for example, the flexible heat-dissipating film  13  disposed between the OLED panel  12  and the piezo film  14 . The OLED panel  12 , the heat-dissipating film  13 , and the piezo film  14  are stacked in this order with, for example, an adhesive in between. The display panel  10  is, for example, a stacked body including the OLED panel  12 , the heat-dissipating film  13 , and the piezo film  14 . The display panel  10  corresponds to a specific example of a “stacked body” of the present disclosure. The OLED panel  12  corresponds to a specific example of an “organic electroluminescent panel” of the present disclosure. The piezo film  14  corresponds to a specific example of a “piezoelectric film” of the present disclosure. 
     The OLED panel  12  is, for example, a panel in which the display surface  1 A is provided on a flexible base material  12   bd . The plurality of pixels  11  are arranged in matrix on the display surface  1 A. The base material  12   bd  is, for example, a flexible resin substrate. The base material  12   bd  corresponds to a specific example of a “first base material” of the present disclosure. 
     The heat-dissipating film  13  dissipates heat generated in the OLED panel  12  and the piezo film  14  to the outside. The heat-dissipating film  13  is preferably configured by a material that does not interfere with vibration of the piezo film  14  as much as possible. The heat-dissipating film  13  is configured by, for example, a foam material or a soft resin. 
     The piezo film  14  has a function of an actuator of a speaker. The piezo film  14  is, for example, a film in which one or a plurality of piezo elements is provided on a flexible base material  14   bd . The base material  14   bd  is, for example, a flexible resin substrate. For example, materials of the base material  12   bd  and the base material  14   bd  are different from each other. It is to be noted that the base material  12   bd  and the base material  14   bd  may be configured by a material common to each other. The base material  14   bd  is, for example, a flexible resin substrate. The base material  14   bd  corresponds to a specific example of a “second base material” of the present disclosure. The piezo film  14  vibrates a piezo element on the basis of a signal voltage (signal voltage Vsound described later) corresponding to a sound signal, and transmits the vibration to the OLED panel  12 . Accordingly, the OLED panel  12  function as a flat speaker. 
       FIG.  6    and  FIG.  7    each illustrate a perspective configuration example of the piezo film  14 . For example, as illustrated in  FIG.  6   , the piezo film  14  includes, on one base material  14   bd , one or a plurality of piezo elements  14   a  ( 14 R) provided on right side as viewed from the user and one or a plurality of piezo elements  14   a  ( 14 L) provided on left side as viewed from the user. For example, as illustrated in  FIG.  7   , the piezo film  14  includes, on one base material  14   bd , the one or the plurality of piezo elements  14   a  ( 14 R), the one or the plurality of piezo elements  14   a  ( 14 L), and one or a plurality of piezo elements  14   a  ( 14 C) provided at the front as viewed from the user. 
       FIG.  8    and  FIG.  9    each illustrate a developed perspective configuration example of the display panel  10 . For example, as illustrated in  FIG.  8   , the display panel  10  may include the heat-dissipating film  13  on side of a rear surface of the piezo film  14 . For example, as illustrated in  FIG.  9   , the display panel  10  may include the heat-dissipating film  13  not only on side of a front but also on the side of the rear surface of the piezo film  14 . 
       FIG.  10    and  FIG.  11    each illustrate a developed perspective configuration example of the display panel  10 . For example, as illustrated in  FIG.  10   , the display panel  10  may include a flexible separation layer  15  between the OLED panel  12  and the piezo film  14 . The separation layer  15  alleviates blocking of the vibration of the piezo film  14  caused by the OLED panel  12 . The separation layer  15  is formed by, for example, a foam material or a soft resin material. In a case where the display panel  10  includes a plurality of piezo films  14 , for example, as illustrated in  FIG.  11   , the separation layer  15  may be provided for each of the piezo films  14 . In this case, for example, the separation layer  15  and the piezo film  14  are alternately arranged in a direction away from the OLED panel  12 . 
     The display panel  10  includes, for example, an adhesive layer that adheres adjacent layers to each other. In the display panel  10 , for example, an adhesive layer  16  illustrated in  FIG.  12   ,  FIG.  13 A ,  FIG.  13 B , or  FIG.  13 C  may be provided between the OLED panel  12  and the heat-dissipating film  13  adjacent to each other. In addition, in the display panel  10 , for example, the adhesive layer  16  illustrated in  FIG.  12   ,  FIG.  13 A ,  FIG.  13 B , or  FIG.  13 C  may be provided between the heat-dissipating film  13  and the separation layer  15  adjacent to each other. In addition, in the display panel  10 , for example, the adhesive layer  16  illustrated in  FIG.  12   ,  FIG.  13 A ,  FIG.  13 B , or  FIG.  13 C  may be provided between the separation layer  15  and the piezo film  14  adjacent to each other. 
     The adhesive layer  16  is, for example, a sheet-like adhesive layer as illustrated in  FIG.  12   . The adhesive layer  16  may be, for example, a sheet-like adhesive layer having a plurality of perforations  16 A, as illustrated in  FIG.  13 A . The adhesive layer  16  may be, for example, a plurality of band-shaped adhesive layers  16 B separated from each other, as illustrated in  FIG.  13 B . Each of the band-shaped adhesive layers  16 B extends, for example, in a direction across each side of the display panel  10 . The adhesive layer  16  may be, for example, a lattice-shaped adhesive layer  16 C having a plurality of perforations, as illustrated in  FIG.  13 C . In the lattice-shaped adhesive layer  16 C, for example, a group of parallel lines constituting the lattice extends in a direction across each side of the display panel  10 . 
       FIG.  14   ,  FIG.  15   ,  FIG.  16   ,  FIG.  17    and  FIG.  18    each illustrate a perspective configuration example of the piezo film  14 . For example, as illustrated in  FIG.  14   , the piezo film  14  is configured by a plurality of base materials  14   d  separated from each other. The base material  14   d  corresponds to a specific example of a “third base material” of the present disclosure. 
     The piezo film  14  includes one or a plurality of piezoelectric elements on each base material  14   d . For example, as illustrated in  FIG.  14   , the piezo film  14  includes the piezo element  14   a  ( 14 R) provided on the right side as viewed from the user on one base material  14   d  provided on the right side as viewed from the user. For example, as illustrated in  FIG.  14   , the piezo film  14  further includes the piezo element  14   a  ( 14 L) provided on the left side as viewed from the user on one base material  14   d  provided on the left side as viewed from the user. 
     For example, as illustrated in  FIG.  15   , the piezo film  14  includes the piezo element  14   a  ( 14 R) on one base material  14   d  provided on the right side as viewed from the user. For example, as illustrated in  FIG.  15   , the piezo film  14  further includes the piezo element  14   a  ( 14 L) on one base material  14   d  provided on the left side as viewed from the user. For example, as illustrated in  FIG.  15   , the piezo film  14  further includes the piezo element  14   a  ( 14 C) provided at the front as viewed from the user on one base material  14   d  provided at the front as viewed from the user. At this time, these three base materials  14   d  each have, for example, a band shape extending in a direction parallel to one side of the display panel  10 . Further, these three base materials  14   d  are arranged in a direction orthogonal to the extending direction of the base material  14   d , for example. 
     For example, as illustrated in  FIG.  16   , the piezo film  14  includes the plurality of base materials  14   d  in a band shape extending in a direction parallel to one side of the display panel  10 . The plurality of base materials  14   d  are arranged in a direction orthogonal to the extending direction of the base material  14   d . For example, as illustrated in  FIG.  16   , the piezo film  14  includes the piezo element  14   a  on each base material  14   d.    
     For example, as illustrated in  FIG.  17   , the piezo film  14  may include the plurality of base materials  14   d  extending in a direction across each side of the display panel  10 . At this time, the plurality of base materials  14   d  are arranged, for example, in a direction orthogonal to the extending direction of the base material  14   d . For example, as illustrated in  FIG.  18   , the piezo film  14  may include the plurality of base materials  14   d  in a rectangular shape. At this time, the plurality of base materials  14   d  are arranged in matrix, for example. 
     In a case where the piezo film  14  is configured by the plurality of base materials  14   d  separated from each other, the adhesive layer  16  may be sized to come into contact with a portion of a surface of one base material  14   d  (a surface on side of the OLED panel  12 ), as illustrated in  FIG.  19 A ,  FIG.  19 B , and  FIG.  19 C , for example. At this time, the adhesive layer  16  has, for example, a circular shape as illustrated in  FIG.  19 A . The adhesive layer  16  may have a star shape, for example, as illustrated in  FIG.  19 B . The adhesive layer  16  may have a square shape, for example, as illustrated in  FIG.  19 C . 
     In a case where the piezo film  14  is configured by the plurality of base materials  14   d  separated from each other, the adhesive layer  16  may be sized to span the plurality of base materials  14   d  as illustrated in  FIG.  20 A ,  FIG.  20 B , and  FIG.  20 C , for example. At this time, the adhesive layer  16  has, for example, a circular shape as illustrated in FIG.  FIG.  20 A ,  FIG.  20 B , and  FIG.  20 C . The adhesive layer  16  may have a star shape or a square shape, for example. 
       FIG.  21    and  FIG.  22    each illustrate a perspective configuration example of the piezo film  14 . The piezo film  14  includes, for example, a wiring layer  14   b  electrically coupled to the piezo element  14   a  in a layer common to the piezo film  14 , as illustrated in  FIG.  21   . The wiring layer  14   b  is, for example, a resin layer including a wiring line L 1  electrically coupled to the piezo element  14   a . For example, as illustrated in  FIG.  22   , the piezo film  14  may include a wiring layer  17  electrically coupled to the piezo element  14   a  in a layer different from the piezo film  14 . The wiring layer  17  is, for example, a wiring substrate in which the wiring line L 1  electrically coupled to the piezo element  14   a  is formed on a resin layer. In the wiring layer  14   b  or the wiring layer  17 , the wiring line L 1  may be configured to allow for active matrix driving of the plurality of piezo elements  14   a  for respective groups Gp, for example, as illustrated in  FIG.  23   . 
       FIG.  24    illustrates a functional block example of the system circuit substrate  30 . The system circuit substrate  30  includes, for example, a reception circuit  31 . The reception circuit  31  has a configuration corresponding to the type of signals to be received. For example, in a case where the reception circuit  31  receives a television broadcast signal, the reception circuit  31  includes, for example, an antenna terminal, a digital tuner, and a demultiplexer. 
     The antenna terminal is a terminal to which a television broadcast signal received at a receiving antenna (not illustrated) is inputted. For example, the digital tuner processes a television broadcast signal inputted to the antenna terminal, and outputs a predetermined transport stream corresponding to a channel selected by a user. The demultiplexer extracts a partial TS (Transport Stream) corresponding to the channel selected by the user, for example, from the transport stream obtained by the digital tuner, and outputs the extracted partial TS to a processor  32 . 
     For example, in a case where the reception circuit  31  receives an IP (Internet Protocol) signal via an Internet line, the reception circuit  31  receives the IP signal via the Internet line, and performs standard protocol processing in an IP network, for example, on the received IP signal. The reception circuit  31  further extracts the partial TS corresponding to the channel selected by the user from the signal subjected to the protocol processing, and outputs the extracted partial TS to the processor  32 . 
     The system circuit substrate  30  further includes, for example, the processor  32 . The processor  32  controls operations of respective components of the flexible display  1 . For example, the processor  32  transmits the partial TS obtained at the reception circuit  31  to a decoder  33 . The system circuit substrate  30  further includes, for example, the decoder  33 , an image signal processing circuit  34 , a graphics generation circuit  35 , an OLED panel driver  36 , a sound signal processing circuit  37 , and a sound device driver  38 . 
     For example, the decoder  33  performs decoding processing on an image PES (Packetized Elementary Stream) packet included in the partial TS obtained at the reception circuit  31  to thereby obtain image data. In addition, the decoder  33  performs, for example, decoding processing on a sound PES packet included in the partial TS obtained at the reception circuit  31  to thereby obtain sound data. 
     The image signal processing circuit  34  and the graphics generation circuit  35  perform, for example, multi-image processing, graphics data superimposition processing, and the like on image data obtained at the decoder  33  as necessary. The image signal processing circuit  34  performs predetermined processing on the image data, and outputs image data subjected to the predetermined processing to the graphics generation circuit  35 . The graphics generation circuit  35  generates, for example, a UI (User Interface) screen to be used when displaying the screen. The OLED panel driver  36  drives the OLED panel  12  on the basis of, for example, image data outputted from the graphics generation circuit  35 . 
     The sound signal processing circuit  37  performs, for example, processing such as D/A conversion on sound data obtained at the decoder  33 . For example, the sound device driver  38  amplifies a sound signal subjected to processing according to an operation command inputted from the processor  32 , and supplies the amplified sound signal to the piezo film  14 . 
     [Effects] 
     Next, description is given of effects of the display panel  10  and the flexible display  1  according to the present embodiment. 
     In recent years, flexible display panels have been actively developed. Among such display panels, for example, a thin and flexible display panel using, as a pixel, an organic EL element called OLED has attracted attention. Therefore, a display panel utilizing flexibility has been demanded. 
     In the present embodiment, one or a plurality of piezo films  14  that vibrate the display panel  10  as a flat speaker is provided on a rear surface of the display panel  10 . This makes it possible to provide the display panel  10  with a sound device, while utilizing the flexibility of the display panel  10 . Accordingly, it is possible to provide the display panel  10  and the flexible display  1  that utilize the flexibility. 
     In the present embodiment, a plurality of pixels  11  each including the organic EL element  11 - 2  may be provided on the base material  12   bd , and the one or the plurality of piezo elements  14   a  may be provided on the base material  14   bd . At this time, the materials of the base material  12   bd  and the base material  14   bd  are different from each other. This causes internal loss of the display panel  10  to be increased, thus improving sound quality at a high-pitched sound. Accordingly, it is possible to achieve an improvement in the sound quality by utilizing the flexibility. 
     In the present embodiment, the base material  14   bd  may be configured by the plurality of base materials  14   d  separated from each other, and the one or the plurality of piezo elements  14   a  may be provided for respective base materials  14   d . This lowers rigidity of the display panel  10 , thus making it easier to wind the display panel  10 . Accordingly, it is possible to achieve an improvement in the sound quality without impairing the flexibility. 
     In the present embodiment, the separation layer  15  that alleviates blocking of the vibration of the piezo film  14  caused by the OLED panel  12  may be provided between the OLED panel  12  and the piezo film  14 . Here, the separation layer  15  impairs no flexibility because of the nature thereof. Accordingly, it is possible to achieve an improvement in the sound quality without impairing the flexibility. 
     In the present embodiment, the adhesive layer  16  is provided that fixes the piezo film  14  to the OLED panel  12 , and the adhesive layer  16  may be the sheet-like adhesive layer having the plurality of perforations  16 A, the plurality of band-shaped adhesive layers  16 B separated from each other, or the lattice-shaped adhesive layer having the plurality of perforations. Thus, the rigidity of the display panel  10  is not excessively increased by the adhesive layer  16 , which makes it easier to wind the display panel  10 ; in addition, no vibration of the piezo film  14  is blocked. Accordingly, it is possible to achieve an improvement in the sound quality without impairing the flexibility. 
     In the present embodiment, the wiring layer  14   b  electrically coupled to the piezo element  14   a  may be provided in a layer common to the piezo film  14 . Thus, the rigidity of the display panel  10  is not excessively increased by the wiring layer  14   b , which makes it easier to wind the display panel  10 ; in addition, no vibration of the piezo film  14  is blocked. Accordingly, it is possible to achieve an improvement in the sound quality without impairing the flexibility. 
     In the present embodiment, the wiring layer  17  electrically coupled to the piezo element  14   a  may be provided in a layer different from the piezo film  14 . This makes it possible to improve durability when rewinding the flexible display  1  many times. In addition, by adopting, for the resin layer inside the wiring layer  17 , a material different from that of the resin substrate of the piezo film  14 , the internal loss of the display panel  10  is increased, thus improving the sound quality at a high-pitched sound. Accordingly, in such a case, it is possible to improve the sound quality. 
     In the present embodiment, for example, as illustrated in  FIG.  16    to  FIG.  18   , each of the base material  14   d  may have a band shape extending in a direction parallel to one side of the display panel  10 , and the plurality of base materials  14   d  may be arranged in a direction orthogonal to the extending direction of the base material  14   d . In such a case, it is possible to achieve an improvement in the sound quality without impairing the flexibility of the display panel  10 . 
     In the present embodiment, for example, as illustrated in  FIG.  19   , each of the base materials  14   d  may have a band shape extending in a direction across each side of the display panel  10 , and the plurality of base materials  14   d  may be arranged in a direction orthogonal to the extending direction of the base material  14   d . In such a case, it is possible to achieve an improvement in the sound quality without impairing the flexibility of the display panel  10 . 
     In the present embodiment, for example, as illustrated in  FIG.  20   , each of the base materials  14   d  may have a rectangular shape, and the plurality of base materials  14   d  may be arranged in matrix. In such a case, it is possible to achieve an improvement in the sound quality without impairing the flexibility of the display panel  10 . 
     In the present embodiment, the base material  14   bd  is configured by the plurality of base materials  14   d  separated from each other, and the one or the plurality of piezo elements  14   a  may be provided for the respective base materials  14   d . In such a case, it is possible to achieve an improvement in the sound quality without impairing the flexibility of the display panel  10 . 
     In the present embodiment, circuits that drive the plurality of piezo elements  14   a  independently for the respective groups Gp may be provided in the system circuit substrate  30 . In such a case, it is possible to partially output a sound from the display panel  10  and to simultaneously output sounds different from each other from the display panel  10 . Accordingly, it is possible to achieve various sound outputs. 
     2. Modification Examples of First Embodiment 
     Next, description is given of modification examples of the first embodiment. 
     Modification Example A 
     In the flexible display  1 , the display panel  10  functions as a diaphragm of a speaker. Therefore, a degree of deflection of the display panel  10  has a large influence on the sound quality. Accordingly, it is desirable that desired tension be generated with respect to the display panel  10 . In order to generate desired tension with respect to the display panel  10 , it is desirable to provide a means for pulling the display panel  10  in the foregoing embodiment. In the following, description is given of various means for pulling the display panel  10 . 
       FIG.  25   ,  FIG.  26   ,  FIG.  27    and  FIG.  28    each illustrate a perspective configuration example of the flexible display  1 . For example, as illustrated in  FIG.  25   , the display panel  10  includes a support member  21  (a first support member) fixed close to an upper end of the display panel  10 , and a support member  21  (a second support member) fixed close to a lower end of the display panel  10 . The support member  21 , which is the first support member, is fixed close to an upper end of the rear surface of the display panel  10 , for example. In addition, the support member  21 , which is the second support member, is fixed close to a lower end of the rear surface of the display panel  10 , for example. 
     The support member  21  has, for example, a rod shape extending in a horizontal direction of the display panel  10 . For example, when the support member  21  close to the upper end of the display panel  10  is fixed to a wall, the display panel  10  is pulled downward due to an own weight of the support member  21  close to the lower end of the display panel  10 . This generates tension in the display panel  10 , thus reducing the deflection of the display panel  10 . It is to be noted that, for example, as illustrated in  FIG.  26   , the display panel  10  before being pulled by the support member  21  may have a shape having constriction in a vertical direction. In this case, the display panel  10  may be pulled by the support member  21  to thereby cause the display panel  10  to be deformed into a rectangular shape, for example, as illustrated in  FIG.  25   . It is to be noted that the support member  21  fixed close to the lower end of the display panel  10  may be fixed to the wall, together with the support member  21 . In this case, the two the support members  21  are fixed to the wall to allow the display panel  10  to be pulled in the vertical direction. 
     For example, as illustrated in  FIG.  27   , the display panel  10  may include the support member  21  fixed close to the upper end of the display panel  10 , and a support mechanism  22  (a second support member) fixed close to the lower end of the display panel  10 . The support mechanism  22  includes, for example, a rod-shaped support member  22 A extending in the horizontal direction of the display panel  10 , and one or a plurality of elastic members  22 B provided between the support member  22 A and the lower end of the display panel  10 . The support member  22 A is fixed to the wall, for example, together with the support member  21 . The one or the plurality of elastic members  22 B are coupled to the support member  22 A and the lower end of the display panel  10 . The elastic member  22 B is, for example, a spring coupled to the support member  22 A and the lower end of the display panel  10 . In this case, the display panel  10  is pulled downward by the elastic member  22 B, and thus tension is generated in the display panel  10 , thus reducing the deflection of the display panel  10 . 
     For example, as illustrated in  FIG.  28   , the display panel  10  may include a winding mechanism  23  (a first support member) fixed close to the upper end of the display panel  10 , and a support member  24  (a second support member) fixed close to the lower end of the display panel  10 . The support member  24  is fixed close to the lower end of the rear surface of the display panel  10 , for example. The support member  24  has, for example, a rod shape extending in the horizontal direction of the display panel  10 . Thus, the display panel  10  is pulled downward due to an own weight of the support member  24 , which generates tension in the display panel  10 , thus reducing the deflection of the display panel  10 . 
     For example, as illustrated in  FIG.  29   , the winding mechanism  23  includes a winding core  23 B that winds the display panel  10 , and a box  23 A that accommodates the display panel  10  in a state of being wound around the winding core  23 B. For example, as illustrated in  FIG.  29   , the winding mechanism  23  may further include an opening/closing door  23 C that opens and closes a lower surface of the box  23 A. Closing the opening/closing door  23 C causes an inner space of the box  23 A to be a closed space. Winding the display panel  10  using the winding mechanism  23  causes the flexible display  1  to have, for example, a rod shape as illustrated in  FIG.  30   . 
     In the present modification example, the support member  21  or the winding mechanism  23  is fixed close to the upper end of the display panel  10 , and the support member  21 , the support mechanism  22 , or the support member  24  is fixed close to the lower end of the display panel  10 . This generates tension in the display panel  10 , thus reducing the deflection of the display panel  10 . This makes it possible to achieve an improvement in the sound quality. 
     In the present modification example, the winding mechanism  23  includes the winding core  23 B that winds the display panel  10 , and the box  23 A that accommodates the display panel  10  in a state of being wound around the winding core  23 B. This makes it possible to perform the winding operation of the display panel  10  in a state in which tension is generated in the display panel  10 . Accordingly, it is possible to perform the winding operation of the display panel  10  without lowering the sound quality. 
     Modification Example B 
     In the flexible display  1  according to the foregoing embodiment and the modification example thereof, a speaker may be provided separately from the OLED panel  12 . For example, as illustrated in  FIG.  31   , one or a plurality of low-range speakers  23 D may be provided in the box  23 A. At this time, the one or the plurality of low-range speakers  23 D may be provided at both ends of the winding core  23 B. This enables the box  23 A and the opening/closing door  23 C to be used as a housing of the low-range speaker  23 D, thus making it possible to improve the low-range sound quality, while avoiding an increase in size of the flexible display  1 . 
     In Modification Example B, for example, as illustrated in  FIG.  32   , a bass reflex duct  23 E may be provided in the middle part of the box  23 A. The shape of the bass reflex duct  23 E is, for example, a rectangular shape or a circular shape.  FIG.  32    exemplifies a case where the shape of the bass reflex duct  23 E is a rectangular shape. This enables the box  23 A and the opening/closing door  23 C to be used as a housing of the bass reflex duct  23 E, thus making it possible to improve the low-range sound quality, while avoiding an increase in size of the flexible display  1 . 
     In Modification Example B, for example, as illustrated in  FIG.  33   , respective bass reflex ducts  23 F may be provided one by one in the vicinities of both ends of the box  23 A. The shape of the bass reflex duct  23 F is, for example, a rectangular shape or a circular shape.  FIG.  33    exemplifies a case where the shape of the bass reflex duct  23 F is a rectangular shape. This enables the box  23 A and the opening/closing door  23 C to be used as a housing of the bass reflex duct  23 F, thus making it possible to improve the low-range sound quality, while avoiding an increase in size of the flexible display  1 . 
     In Modification Example B, for example, as illustrated in  FIG.  34   , the one or the plurality of low-range speakers  23 D may be provided close to the lower end of a front surface of the display panel  10 . At this time, a box  27  may be further provided that accommodates the one or the plurality of low-range speakers  23 D provided close to the lower end of the front surface of the display panel  10 , and is fixed to the lower end of the front surface of the display panel  10 . This generates tension in the display panel  10  due to an own weight of the box  27 , thus reducing the deflection of the display panel  10 . This makes it possible to achieve an improvement in the sound quality. In addition, it is possible to use the box  27  as a housing of the one or the plurality of low-range speakers  23 D, thus making it possible to improve the low-range sound quality, while avoiding an increase in size of the flexible display  1 . 
     In Modification Example B, for example, as illustrated in  FIG.  35   , the box  23 A may be omitted. At this time, the winding core  23 B may have a tubular shape, and the respective low-range speakers  23 D may be provided one by one at both ends of the winding core  23 B. At this time, for example, as illustrated in  FIG.  36   , respective bass reflex ducts  23 G may be further provided one by one at both ends of the winding core  23 B. The shape of the bass reflex duct  23 G is, for example, a rectangular shape or a circular shape.  FIG.  36    exemplifies a case where the shape of the bass reflex duct  23 G is a rectangular shape. This enables the winding core  23 B to be used as a housing of the bass reflex duct  23 G, thus making it possible to improve the low-range sound quality, while avoiding an increase in size of the flexible display  1 . 
     Modification Example C 
     In the flexible display  1  according to the foregoing embodiment and the modification example thereof, it is assumed that the piezo film  14  is configured by the plurality of base materials  14   d  separated from each other and that the piezo elements  14   a  are provided on the respective base materials  14   d . Further, in the flexible display  1  according to the foregoing embodiment and the modification example thereof, it is assumed that the winding mechanism  23  is provided close to the upper end of the display panel  10  and that the display panel  10  is wound by the winding mechanism  23 . In this case, for example, the system circuit substrate  30  may independently drive the plurality of piezo elements  14   a  for the respective groups Gp separated by the base materials  14   d , and may drive the plurality of piezo elements  14   a  inside the groups Gp present in the frontmost layer of the display panel  10  in a state in which the display panel  10  is wound around the winding core  23 B. In such a case, for example, as illustrated in  FIG.  37   , a sound is outputted from the frontmost layer of the wound display panel  10 , and no sound is outputted from a layer other than the frontmost layer (i.e., an inner layer) of the wound display panel  10 . As a result, generation of a noise due to the vibration of the display panel  10  is suppressed, thus making it possible to improve the sound quality as compared with the case of outputting a sound from the entire display panel  10 . 
     Modification Example D 
     For example, as illustrated in  FIG.  38   , the flexible display  1  according to the foregoing embodiment and the modification example thereof may include a vibration-damping film  28  which may be wound by the winding mechanism  23 , while being in contact with a surface of the display panel  10  (specifically, the OLED panel  12 ). In such a case, the system circuit substrate  30  may drive all the piezo elements  14   a  simultaneously, for example, even in a state in which the display panel  10  is wound around the winding core  23 B. When all the piezo elements  14   a  are driven, a layer other than the frontmost layer (i.e., the inner layer) of the wound display panel  10  is clamped by the vibration-damping film  28 . Accordingly, a sound is outputted only from the frontmost layer of the wound display panel  10 , and no sound is outputted from the layer other than the frontmost layer (i.e., the inner layer) of the wound display panel  10 . As a result, the generation of a noise due to the vibration of the display panel  10  is suppressed, thus making it possible to improve the sound quality as compared with the case of outputting a sound from the entire display panel  10 . 
     Modification Example E 
     For example, as illustrated in  FIG.  39   ,  FIG.  40   ,  FIG.  41   ,  FIG.  42   ,  FIG.  43   ,  FIG.  44   , and  FIG.  45   , the flexible display  1  according to the foregoing embodiment and the modification example thereof may include a sound-absorbing material  29  on a rearmost surface of the display panel  10 . For example, the sound-absorbing material  29  may be formed on the entire rearmost surface of the display panel  10 , or may be formed only on a location, of the rearmost surface of the display panel  10 , that is not covered with the support member  21 , the winding mechanism  23 , or the support member  24 . When the display panel  10  is mounted on a wall, a pillar, a window, etc., the sound-absorbing material  29  may come in contact with the wall, the pillar, the window, etc. on which the display panel  10  is mounted. 
     Modification Example F 
     In the flexible display  1  according to the foregoing embodiment and the modification example thereof, for example, as illustrated in  FIG.  46   , the system circuit substrate  30  may further include a tension detection circuit  39  that detects pulling force or a corresponding physical quantity applied to the display panel  10 . The tension detection circuit  39  detects the pulling force or the corresponding physical quantity applied to the display panel  10 , for example, from an amount of displacement assumed for a predetermined input given to each of the piezo elements  14   a  and a difference from the actual amount of displacement. In this case, the tension detection circuit  39  outputs detection results to the sound signal processing circuit  37 . The sound signal processing circuit  37  corrects sound data on the basis of the detection results inputted from the tension detection circuit  39 . This causes sound data corresponding to the pulling force applied to the display panel  10  to be inputted to the sound device driver  38 , thus making it possible to reduce an influence of the deflection of the display panel  10  on the sound quality. 
     Modification Example G 
     In the flexible display  1  according to the foregoing embodiment and the modification example thereof, it is assumed that the piezo film  14  is configured by the plurality of base materials  14   d  separated from each other and that the one or the plurality of piezo elements  14   a  are provided on the respective base materials  14   d . In this case, for example, as illustrated in  FIG.  47   , the display panel  10  may further include a microphone array  19  in which one or a plurality of microphones  19   a  are assigned to the respective base materials  14   d  of the piezo film  14  on side of the front surface of the display panel  10 . At this time, for example, as illustrated in  FIG.  48   , the system circuit substrate  30  may include a circuit (a noise cancellation circuit  40 ) that suppresses a noise of the display panel  10  using a sound signal obtained by a microphone  19   a . The noise cancellation circuit  40  outputs, to the piezo element  14   a  of the piezo film  14 , a signal obtained by inverting a phase of the sound signal obtained by the microphone  19   a , for example. This makes it possible to suppress the noise of the display panel  10 . 
     Modification Example H 
     In the flexible display  1  according to the foregoing embodiment and the modification example thereof, for example, as illustrated in (A) of  FIGS.  49 A  and (B) of  FIG.  49   , the display panel  10  may have a cylindrical shape. (A) of  FIG.  49    illustrates a perspective configuration example of the flexible display  1  in Modification Example H. (B) of  FIG.  49    illustrates a top configuration example of the flexible display  1  in Modification Example H. In Modification Example H, when the display panel  10  has a cylindrical shape, the system circuit substrate  30  may drive each of the piezo elements  14   a  to allow a sound to be outputted 360 degrees in all directions. In Modification Example H, when the display panel  10  has a cylindrical shape, the system circuit substrate  30  may output a common sound signal to each of the piezo elements  14   a , for example. 
     In Modification Example H, for example, as illustrated in (A) of  FIGS.  50    and (B) of  FIG.  50   , when the display panel  10  has a cylindrical shape, the system circuit substrate  30  may drive the piezo elements  14   a  independently for the respective groups Gp separated by the base materials  14   d  to allow a sound to be outputted only in a predetermined angular direction. (A) of  FIG.  50    illustrates a perspective configuration example of the flexible display  1  in Modification Example H. (B) of  FIG.  50    illustrates a top configuration example of the flexible display  1  in Modification Example H. This enables only a person in a specific direction to hear a sound selectively. 
     In Modification Example H, for example, as illustrated in  FIG.  51   , when the display panel  10  has a cylindrical shape, the system circuit substrate  30  may drive the piezo elements  14   a  independently for the respective group Gp separated by base materials  14   d  to allow a sound outputted from the upper part of the display panel  10  and a sound outputted from the lower part of the display panel  10  to be different from each other. This makes it possible, for example, to simultaneously output a sound to be heard by an adult and a sound to be heard by a child from the display panel  10 , while preventing the adult from hearing the sound to be heard by the child and preventing the child from hearing the sound to be heard by the adult. 
     3. Second Embodiment 
     [Configuration] 
     Next, description is given of a flexible display  2  according to a second embodiment of the present disclosure.  FIG.  52    perspectively illustrates a schematic configuration example of the flexible display  2 .  FIG.  53    illustrates an example of a state in which the flexible display  2  is wound. The flexible display  2  is a thin and flexible self-luminous display using, as a pixel, an organic EL element called OLED. 
     The flexible display  2  includes, for example, a display panel  50  having a display surface and a rear surface  2 B, and a frame  20  that protects an edge of the display panel  50  (a periphery of the display surface). The flexible display  2  further includes, for example, the system circuit substrate  30  that drives the display panel  50 , and the FPC  30 A that electrically couples the display panel  50  and the system circuit substrate  30 . The display panel  50  includes, on the display surface thereof, the plurality of pixels  11  arranged in matrix. The FPC  30 A is coupled to the edge of the display panel  50 . 
       FIG.  54    illustrates a perspective configuration example of the display panel  50 . The display panel  50  includes, for example, an OLED panel  51 . The OLED panel  51  has a configuration similar to that of the OLED panel  12  according to the foregoing embodiment. 
     The flexible display  2  is provided on the rear surface of the display panel  50  (the OLED panel  51 ), for example, and includes one or a plurality of actuators  26  that vibrate the display panel  50  (the OLED panel  51 ) as a flat speaker, and a support member  25  that supports the actuator  26 . 
     The flexible display  2  further includes, for example, the winding mechanism  23  fixed close to the upper end of the display panel  50 . Here, the support member  25  is supported by the winding mechanism  23 , for example. For example, as illustrated in  FIG.  52    and  FIG.  53   , the support member  25  has a rod shape, and, for example, the end of the support member  25  is movably supported by the winding mechanism  23 . For example, as illustrated in  FIG.  55   , one end of the support member  25  is inserted into an opening  23 H of the opening/closing door  23 C, and the end of the support member  25  is provided with a protrusion in an extent not to be fallen off from the opening  23 H, for example. This makes it possible to dispose the support member  25  along the winding mechanism  23 , for example, as illustrated in  FIG.  53   . 
     The one or the plurality of actuators  26  incorporates, for example, a magnet having a magnetic pole in an orientation as illustrated in  FIG.  56    in a bobbin  26 A. It is to be noted that the one or the plurality of actuators  26  may incorporate, for example, a magnet having a magnetic pole in an orientation opposite to that of the magnetic pole illustrated in  FIG.  56   . For example, as illustrated in  FIG.  56   , the display panel  50  includes a fixing member  50   a  configured by a magnet having a magnetic pole in an orientation opposite to the orientation of the magnetic pole of the actuator  26 . The fixing member  50   a  is disposed at a position, of the rear surface  2 B of the display panel  50 , that faces the one or the plurality of actuators  26 . The bobbin  26 A is formed by a metal material such as iron. The bobbin  26 A has such a length that, when the tip of the bobbin  26 A and the fixing member  50   a  are brought into contact with each other by magnetic force, the magnetic force of the magnet included in the fixing member  50   a  does not interfere with driving of the one or the plurality of actuators  26 . 
     It is to be noted that the fixing member  50   a  may include, instead of the magnet, a member that is able to fix the display panel  50  and the actuator  26  to each other. The fixing member  50   a  may include, for example, a detachable viscous layer instead of the magnet. 
     [Effects] 
     In the present embodiment, the one or the plurality of actuators  26  and the support member  25  that supports the one or the plurality of actuators  26  are provided on the rear surface of the display panel  50  including the OLED panel  51  (the OLED panel  51 ). The one or the plurality of actuators  26  are detachably fixed to the rear surface of the display panel  50  (the OLED panel  51 ). This makes it possible to provide the display panel  50  with a sound device, while utilizing the flexibility of the display panel  50 . Accordingly, it is possible to provide the display panel  50  and the flexible display  2  which utilize the flexibility. 
     In the present embodiment, the winding mechanism  23  is fixed close to the upper end of the display panel  50  (the OLED panel  51 ), and the winding mechanism  23  includes the winding core  23 B that winds the display panel  50  and the box  23 A that accommodates the display panel  50  in a state of being wound around the winding core  23 B. This makes it possible to perform the winding operation of the display panel  50  in a state in which tension is generated in the display panel  50 . Accordingly, it is possible to perform the winding operation of the display panel  50  without lowering the sound quality. 
     In the present embodiment, the display panel  50  is provided with the fixing member  50   a  including a magnet having a magnetic pole in an orientation opposite to the orientation of the magnetic pole of the one or the plurality of actuators  26 . This causes the bobbin  26 A of the one or the plurality of actuators  26  and the fixing member  50   a  to be fixed to each other by magnetic force. Furthermore, the bobbin  26 A has a predetermined length, thus making it possible to prevent the driving force of the one or the plurality of actuators  26  from being weakened due to the influence of the magnetic force of the magnet included in the fixing member  50   a.    
     4. Modification Examples of Second Embodiment 
     Next, description is given of modification examples of the second embodiment of the present disclosure. 
     Modification Example I 
     In the flexible display  2  according to the foregoing second embodiment, the display panel  50  may have, for example, a cylindrical shape as illustrated in (A) of  FIG.  57   . At this time, the flexible display  2  may include a plurality of support members  41  and  42  instead of the support member  25 , as illustrated in (B) of  FIGS.  57    and (C) of  FIG.  57   , for example. Further, for example, as illustrated in (B) of  FIGS.  57    and (C) of  FIG.  57   , the flexible display  2  according to Modification Example I may include one or a plurality of actuators  43  instead of the one or the plurality of actuators  26 . The actuator  43  is, for example, a magnetic actuator or a solid-state piezo actuator. It is to be noted that (A) of  FIG.  57    exemplifies a perspective configuration of the flexible display  2  according to Modification Example I. (B) of  FIGS.  57    and (C) of  FIG.  57    each exemplify the plurality of support members  41  and  42  and the plurality of actuators  43  in the flexible display  2  according to Modification Example I. 
     The support member  41  is disposed, for example, at a location through which a center axis of the cylindrical display panel  50  passes, and has a rod shape parallel to the center axis of the cylindrical display panel  50 . The support member  42  has, for example, a rod shape extending in a direction orthogonal to the support member  41 . In each support member  42 , one end is fixed to the support member  41 , and the other end is fixed to the actuator  43 . The support members  41  and  42  support each of actuators  43  from inside the cylindrical display panel  50 , and press each of the actuators  43  against an inner surface (rear surface) of the cylindrical display panel  50 . This enables the system circuit substrate  30 , when the display panel  50  has a cylindrical shape, to drive each of the actuators  43  independently to allow a sound to be outputted 360 degrees in all directions, for example. 
     In Modification Example I, when the display panel  50  has a cylindrical shape, for example, the system circuit substrate  30  may drive each of the actuators  43  independently to allow a sound to be outputted only in a predetermined angular direction. This enables only a person in a specific direction to hear a sound selectively. 
     In Modification Example I, for example, when the display panel  50  has a cylindrical shape, the system circuit substrate  30  may drive each of the actuators  43  independently to allow a sound outputted from the upper part of the display panel  50  and a sound outputted from the lower part of the display panel  50  to be different from each other. This makes it possible, for example, to simultaneously output a sound to be heard by an adult and a sound to be heard by a child from the display panel  50 , while preventing the adult from hearing the sound to be heard by the child and preventing the child from hearing the sound to be heard by the adult. 
     In Modification Example I, for example, as illustrated in (A) of  FIG.  58   , (B) of  FIG.  58   , and (C) of  FIG.  58   , the flexible display  2  may further include one or a plurality of dampers  44  that comes into contact with a surface, of the inner surface of the cylindrical display panel  50 , between two adjacent actuators  43 . In such a case, vibrations of the display panel  50  caused by the two actuators  43  adjacent to each other are separated by the dampers  44 . Thus, the vibrations of the display panel  50  caused by the respective actuators  43  enable sounds separated from each other to be outputted from the display panel  50 . As a result, it is possible to cause people in different directions to hear different sounds, for example. 
     Modification Example J 
     In the flexible display  2  according to the foregoing second embodiment, for example, as illustrated in  FIG.  59   , the support member  25  may be fixed to the display panel  50  in a curved state. For example, as illustrated in  FIG.  59   , a holding part  45  including a clip, a nipper, or the like is used to fix the support member  25  to the display panel  50 . In such a case, the display panel  50  is pulled, with the actuator  26  as a fulcrum, by force of the support member  25  to return straight. This generates tension in the display panel  50 , thus reducing deflection of the display panel  50 . As a result, it is possible to achieve an improvement in the sound quality. 
     Modification Example K 
     In the flexible display  2  according to the foregoing second embodiment, for example, as illustrated in  FIG.  60   , the support member  25  may include an elastic member  46  that tends to extend in a direction that reduces the deflection of the display panel  50 . In such a case, the display panel  50  is pulled by the force of the support member  25  to extend. This generates tension in the display panel  50 , thus reducing the deflection of the display panel  50 . As a result, it is possible to achieve an improvement in the sound quality. 
     Modification Example L 
     In the flexible display  2  according to the foregoing second embodiment, the support member  25 , the actuator  26 , and the holding part  45  may be removed from the display panel  50 . In this case, for example, as illustrated in  FIG.  61    and  FIG.  62   , a stand  400  in which the support member  25 , the actuator  26  and the holding part  45  are supported by a leg part  47  may be provided separately from the display panel  50 . It is to be noted that  FIG.  61    exemplifies a state in which respective holding parts  45  are provided one by one at both ends of one support member  25 , with the actuator  26  being provided at the middle of the support member  25 , and one end of the support member  25  being supported by the leg part  47 . In addition,  FIG.  62    exemplifies a state in which two support members  25  are fixed to each other in an intersecting manner, and respective holding parts  45  are provided one by one at both ends of one support member  25 , with respective actuators  26  being provided one by one at both ends of the other support member  25 , and one end of the one support member  25  being supported by the leg part  47 . 
     In this manner, in Modification Example L, the stand  400  is provided separately from the display panel  50 . This enables the display panel  50  to be mounted on various places, other than a wall, a window, or a pillar. 
     Modification Example M 
     For example, as illustrated in  FIG.  63   , the flexible display  2  according to the foregoing second embodiment may include a vibration mechanism  49  instead of the support member  25 , the actuator  26 , and the support member  24 . The vibration mechanism  49  is provided close to the lower end of the display panel  50 , and includes one or a plurality of actuators  49 B that vibrates the display panel  50  as a flat speaker, and a support member  49 A that supports the one or the plurality of actuators  49 B. The actuator  49 B is, for example, a magnetic actuator or a solid-state piezo actuator. The support member  49 A is fixed to, for example, a wall, a window, a column, and the like. 
     In this manner, in Modification Example M, the lower end of the display panel  50  is vibrated with the one or the plurality of actuators  49 B to thereby cause the display panel  50  to function as a flat speaker. This eliminates the necessity of providing a structure such as a speaker on the rear surface of the display panel  50 , thus making it easier to wind the display panel  50 . As a result, it is possible to provide the display panel  50  with a sound device, while utilizing the flexibility of the display panel  50 . Thus, it is possible to provide the display panel  50  and the flexible display  2  which utilize the flexibility. 
     In Modification Example M, the winding mechanism  23  is fixed close to the upper end of the display panel  50 , and the vibration mechanism  49  is fixed close to the lower end of the display panel  50 . This generates tension in the display panel  50 , thus reducing the deflection of the display panel  50 . This makes it possible to achieve an improvement in the sound quality. 
     5. Third Embodiment 
     [Configuration] 
     Next, description is given of a flexible display  3  according to a third embodiment of the present disclosure.  FIG.  64    perspectively illustrates a schematic configuration example of the flexible display  3 .  FIG.  65    illustrates an example of a state in which the flexible display  3  is wound. The flexible display  3  is a thin and flexible self-luminous display using, as a pixel, an organic EL element called OLED. 
     The flexible display  3  includes, for example, a display panel  60  having a display surface  3 A, and a frame  20  that protects an edge of the display panel  60  (a periphery of the display surface). The flexible display  3  further includes, for example, the system circuit substrate  30  that drives the display panel  60 , and the FPC  30 A that electrically couples the display panel  60  and the system circuit substrate  30 . The display panel  60  includes, on the display surface  3 A, the plurality of pixels  11  arranged in matrix. The FPC  30 A is coupled to the edge of the display panel  60 . 
       FIG.  66    illustrates a perspective configuration example of the display panel  60 . The display panel  60  includes, for example, a flexible OLED panel  61 . The OLED panel  61  has a configuration similar to that of the OLED panel  12  according to the foregoing embodiment. The OLED panel  61  corresponds to a specific example of an “organic electroluminescent panel” of the present disclosure. 
     The display panel  60  further includes one or a plurality of Heil drivers  62  at edges (e.g., both left and right ends) of the OLED panel  61 . The one or the plurality of Heil drivers  62  is formed on a protrusion  61 A provided at the edge of the OLED panel  61 , for example. The Heil driver  62  includes, for example, a wave-shaped electrode  62 A having irregularities in a normal direction of the display panel  60 , and further includes an electrode formed by arranging a magnet  62 B around the wave-shaped electrode  62 A. For example, the system circuit substrate  30  causes a current to flow through the electrodes of Heil driver  62  to thereby cause a crest and a trough of the wave-shaped electrode  62 A to be opened and closed and to inhale and exhale the air, thus generating an acoustic wave. 
     [Effects] 
     In the present embodiment, the one or the plurality of Heil drivers  62  is provided at the edge of the display panel  60  including the OLED panel  61  (the OLED panel  61 ). 
     This makes it possible to provide the display panel  60  with a sound device, while utilizing the flexibility of the display panel  50 . Thus, it is possible to provide the display panel  60  and the flexible display  3  which utilize the flexibility. 
     In the present embodiment, the winding mechanism  23  is fixed close to the upper end of the display panel  60 , and the support member  24  is fixed close to the lower end of the display panel  60 . This generates tension in the display panel  60 , thus reducing the deflection of the display panel  60 . This makes it possible to achieve an improvement in the sound quality. 
     6. Fourth Embodiment 
     [Configuration] 
     Next, description is given of a flexible display  4  according to a fourth embodiment of the present disclosure.  FIG.  67    perspectively illustrates a schematic configuration example of the flexible display  4 .  FIG.  68    illustrates an example of a state in which the flexible display  4  is wound. The flexible display  4  is a thin and flexible self-luminous display using, as a pixel, an organic EL element called OLED. 
     The flexible display  4  includes, for example, a display panel  70  having a display surface and a rear surface  4 B, and a frame  20  that protects an edge of the display panel  70  (a periphery of the display surface). The flexible display  4  further includes, for example, the system circuit substrate  30  that drives the display panel  70 , and the FPC  30 A that electrically couples the display panel  70  and the system circuit substrate  30 . The display panel  70  includes, on the display surface thereof, the plurality of pixels  11  arranged in matrix. The FPC  30 A is coupled to the edge of the display panel  70 . 
       FIG.  69    illustrates a perspective configuration example of the display panel  70 . The display panel  70  includes, for example, a flexible OLED panel  71 . The OLED panel  71  has a configuration similar to that of the OLED panel  12  according to the foregoing embodiment. The OLED panel  71  corresponds to a specific example of an “organic electroluminescent panel” of the present disclosure. 
     The display panel  70  further includes one or a plurality of coils  72  on the rear surface  4 B of the OLED panel  71 . The one or the plurality of coils  72  is provided, for example, on the rear surface  4 B of the OLED panel  71 , and vibrates the OLED panel  71  as a flat speaker. For example, as illustrated in  FIG.  70   , the flexible display  4  is fixed to a wall  100  configured by a magnet sheet, with the winding mechanism  23  and the support member  24  in between. In such a state, for example, the system circuit substrate  30  causes a current to flow through the one or the plurality of coils  72  to thereby cause, for example, the one or the plurality of coils  72  and the wall  100  to be magnetically coupled through a gap G, thereby generating a vibration in the one or the plurality of coils  72 . This causes the display panel  70  to vibrate as well and to output a sound. 
     [Effects] 
     In the present embodiment, the one or the plurality of coils  72  is provided on the rear surface  4 B of the OLED panel  71 . This makes it possible to provide the display panel  70  with a sound device, while utilizing the flexibility of the display panel  70 . Thus, it is possible to provide the display panel  70  and the flexible display  4  which utilize the flexibility. 
     In the present embodiment, the winding mechanism  23  is fixed close to the upper end of the display panel  70 , and the support member  24  is fixed close to the lower end of the display panel  70 . This generates tension in the display panel  70 , thus reducing the deflection of the display panel  70 . This makes it possible to achieve an improvement in the sound quality. 
     7. Modification Example Common to Respective Embodiments 
     In the second, third, and fourth embodiments and the Modification Examples thereof, for example, as illustrated in  FIG.  71   , the one or the plurality of low-range speakers  23 D may be provided close to the lower end of the front surface of the display panel  50 ,  60 , or  70 . At this time, the box  27  may be further provided that accommodates the one or the plurality of low-range speakers  23 D provided close to the lower end of the front surface of the display panel  50 ,  60 , or  70 , and is fixed to the lower end of the front surface of the display panel  50 ,  60 , or  70 . This generates tension in the display panel  50 ,  60 , or  70  due to an own weight of the box  27 , thus reducing the deflection of the display panel  50 ,  60 , or  70 . This makes it possible to achieve an improvement in the sound quality. In addition, it is possible to use the box  27  as a housing of the one or the plurality of low-range speakers  23 D, thus making it possible to improve the low-range sound quality, while avoiding an increase in size of the flexible display  2 ,  3 , or  4 . 
     In addition, for example, as illustrated in  FIG.  72   , a wall  300  facing a wall  200  provided with any of the flexible displays  1  to  4  according to the foregoing first, second, third, and fourth embodiments and the Modification Examples thereof may be provided with a sound-absorbing material  310  that absorbs a highly directional sound outputted from any of the flexible displays  1  to  4  according to the first, second, third, and fourth embodiments and the modification example thereof. This makes it possible to suppress reflection of a highly directional sound by the wall  300 , thus making it possible to improve the sound quality. 
     8. Fifth Embodiment 
     [Configuration] 
     Next, description is given of a flexible display  5  according to a fifth embodiment of the present disclosure.  FIG.  73    perspectively illustrates a schematic configuration example of the flexible display  5 , together with the wall  200 .  FIG.  74    illustrates a perspective configuration example of a state in which the display panel  50  of the flexible display  5  illustrated in  FIG.  73    is wound. The flexible display  5  is a thin and flexible self-luminous display using, as a pixel, an organic EL element called OLED. 
     The flexible display  5  includes, for example, the display panel  50 , the winding mechanism  23  disposed close to the upper end of the display panel  50 , and the support member  24  disposed close to the lower end of the display panel  50 . The flexible display  5  further includes, for example, a vibration-transmitting member  52  provided on the rear surface of the display panel  50  and transmitting vibrations of one or a plurality of actuators  210  embedded in the wall  200  to the display panel  50 . The vibration-transmitting member  52  is provided in contact with a location, of the rear surface of the display panel  50 , that is not covered with the winding mechanism  23  and the support member  24 . The vibration-transmitting member  52  is configured by, for example, a detachable viscous layer that is highly adherent to the wall  200 . 
     In the present embodiment, the vibration-transmitting member  52  that transmits the vibrations of the one or the plurality of actuators  210  embedded in the wall  200  to the display panel  50  is provided on the rear surface of the display panel  50 . Thus, even in a case where the flexible display  5  itself is not provided with the actuator, the utilization of the one or the plurality of actuators  210  embedded in the wall  200  enables the display panel  50  to function as a flat speaker. 
     9. Sixth Embodiment 
     [Configuration] 
     Next, description is given of a flexible display  6  according to a sixth embodiment of the present disclosure.  FIG.  75    perspectively illustrates a schematic configuration example of the flexible display  6 .  FIG.  76    illustrates a side configuration example of the flexible display  6  depicted in  FIG.  75   . The flexible display  6  is a thin and flexible self-luminous display using, as a pixel, an organic EL element called OLED. In addition, the flexible display  6  is a self-luminous display having a roll towel structure. 
     The flexible display  6  includes, for example, a tubular display panel  80  having a display surface  8 A, and a frame  90  that protects an edge of the tubular display panel  80  (a periphery of the display surface  8 A). The flexible display  6  further includes, for example, two rotary parts  110  that rotatably support the tubular display panel  80 . The two rotary parts  110  are inserted into a void surrounded by the display panel  80 , and are in contact with an inner surface (rear surface) of the display panel  80 . When the two rotary parts  110  are rotated in a common direction, the display surface  8 A of the display panel  80  is displaced. 
     The flexible display  6  further includes, for example, a support member  111  fixed to one rotary part  110 , and one or a plurality of actuators  112  fixed to the support member  111 . The support member  111  supports the actuator  112 . The actuator  112  is, for example, a magnetic actuator or a solid-state piezo actuator. The one or the plurality of actuators  112  is disposed in contact with an inner surface (rear surface) of the display panel  80 , and vibrates the display panel  80  as a flat speaker. A pair of flat surfaces  8 B 1  and  8 B 2  is present on the inner surface (rear surface) of the display panel  80 . The one or the plurality of actuators  112  is in contact with one flat surface  8 B 1  of the inner surface (rear surface) of the display panel  80 . Thus, a region, of the display surface  6 A of the display panel  80 , that faces the flat surface  8 B 1  is vibrated by vibrations of the one or the plurality of actuators  112  to output a sound. 
     For example, as illustrated in  FIG.  77   , the flexible display  6  may further include not only the one or the plurality of actuators  112  in contact with the one flat surface  8 B 1 , but also one or a plurality of actuators  112  in contact with another flat surface  8 B 2 , out of the inner surface (rear surface) of the display panel  80 . Thus, not only the region facing the one flat surface  8 B 1 , but also the region facing the other flat surface  8 B 2 , out of the display surface  8 A of the display panel  80 , is vibrated by the vibrations of the one or the plurality of actuators  112  to output a sound. 
     For example, as illustrated in  FIG.  78   , the flexible display  6  may include one or a plurality of actuators  112  in contact with the rotary part  110 . This causes vibrations of the one or the plurality of actuators  112  to be transmitted to the rotary part  110  in contact with the one or the plurality of actuators  112 , causing a vibration of the rotary part  110  to be transmitted to the display panel  80 , thus causing a sound to be outputted from the display panel  80 . 
     For example, as illustrated in  FIG.  79   , the flexible display  6  may include the one or the plurality of actuators  112  in contact with the rotary part  110 , and may further include one or a plurality of actuators  113  in contact with the one or the plurality of actuators  112 . The actuator  113  is, for example, a magnetic actuator or a solid-state piezo actuator. The one or the plurality of actuators  113  vibrates at a frequency lower than that of the one or the plurality of actuators  112 . For example, in a case where the display panel  80  is pressed with a pen or the like, the system circuit substrate  30  causes, in order to prevent damage to the display panel  80 , the one or the plurality of actuators  113  to vibrate at a low frequency of about several hundred Hertz, for example, to bring the display panel  80  into deflection. 
     In the present embodiment, the one or the plurality of actuators  112  vibrates the display surface  8 A of the display panel  80  having the roll towel structure to cause a sound to be outputted from the display surface  8 A. Accordingly, it is possible to provide the display panel  80  and the flexible display  6  which utilize the flexibility. 
     10. Seventh Embodiment 
     [Configuration] 
     Next, description is given of a flexible display  7  according to a seventh embodiment of the present disclosure.  FIG.  80    perspectively illustrates a schematic configuration example of the flexible display  7 .  FIG.  81    illustrates a side configuration example of the flexible display  7  illustrated in  FIG.  80   . The flexible display  7  is a thin and flexible self-luminous display using, as a pixel, an organic EL element called OLED. In addition, the flexible display  7  is a self-luminous display having the roll towel structure. 
     The flexible display  7  includes, for example, a tubular display panel  120  having a display surface  120 A, and a frame  130  that protects an edge of the tubular display panel  120  (a periphery of the display surface  120 A). The flexible display  7  further includes, for example, the two rotary parts  110  that rotatably support the tubular display panel  120 . The two rotary parts  110  are inserted in a void surrounded by the display panel  120 , and are in contact with an inner surface (rear surface) of the display panel  120 . A pair of flat surfaces  120 A 1  and  120 A 2  is present on the display surface  120 A of the display panel  120 . When the two rotary parts  110  are rotated in a common direction, the display surface  120 A of the display panel  80  is displaced. 
     The display panel  120  has a configuration common to that of that of the display panel  10  according to the foregoing embodiment. Specifically, the display panel  120  is a stacked body including, for example, the OLED panel  12 , the heat-dissipating film  13 , and the one or the plurality of piezo films  14  in this order. The display panel  120  may further include, for example, the separation layer  15  and the adhesive layer  16 . In the display panel  120 , the piezo film  14  includes the plurality of base materials  14   d  as illustrated in  FIG.  18   ,  FIG.  19   , or  FIG.  20   , for example. The piezo film  14  includes the piezo elements  14   a  on the respective base materials  14   d  as illustrated in  FIG.  18   ,  FIG.  19   , or  FIG.  20   , for example. Accordingly, a vibration due to the piezo film  14  is transmitted to the OLED panel  12 , thus causing a sound to be outputted from the OLED panel  12 . 
       FIG.  82    illustrates an example of a sound control in the flexible display  7 . The system circuit substrate  30  rotates the two rotary parts  110  to thereby rotate an image displayed on the display surface  120 A of the display panel  120 . At this time, for example, in a case where there is an image beginning to be displayed on the flat surface  120 A 1 , the system circuit substrate  30  drives the piezo element  14   a  (e.g., a piezo element  14   a  at a position B) to allow a sound volume corresponding to the image to gradually increase. In addition, for example, in a case where there is an image beginning to deviate from the flat surface  120 A 1 , the system circuit substrate  30  drives the piezo element  14   a  (e.g., a piezo element  14   a  at a position A) to allow a sound volume corresponding to the image to gradually decrease. 
     In the present embodiment, the piezo film  14  vibrates the display surface  120 A of the display panel  120  having the roll towel structure to cause a sound to be outputted from display surface  120 A. Accordingly, it is possible to provide the display panel  120  and the flexible display  7  which utilize the flexibility. 
     11. Eighth Embodiment 
     [Configuration] 
     Next, description is given of a flexible display  8  according to an eighth embodiment of the present disclosure.  FIG.  83    perspectively illustrates a schematic configuration example of the flexible display  8 .  FIG.  84    illustrates an example of a state in which the flexible display  8  is wound. The flexible display  8  is a thin and flexible self-luminous display using, as a pixel, an organic EL element called OLED. 
     The flexible display  8  includes, for example, a display panel  81  having a display surface and a rear surface  8 B, and a frame  20  that protects an edge of the display panel  81  (a periphery of the display surface). The flexible display  8  further includes, for example, the system circuit substrate  30  that drives the display panel  81 , and the FPC  30 A that electrically couples the display panel  81  and the system circuit substrate  30 . The display panel  81  includes, on the display surface thereof, the plurality of pixels  11  arranged in matrix. The FPC  30 A is coupled to the edge of the display panel  81 . 
       FIG.  85    illustrates a perspective configuration example of the display panel  81 . The display panel  81  includes, for example, an OLED panel  82 , and a plurality of speakers  83  on a rear surface (the rear surface  8 B) of the OLED panel  82 . The OLED panel  82  has a configuration similar to that of the OLED panel  12  according to the foregoing embodiment. 
     [Effects] 
     In the present embodiment, the plurality of speakers  83  is provided on the rear surface of the display panel  81 . This makes it possible to provide the display panel  81  with a sound device, while utilizing the flexibility of the display panel  81 . Accordingly, it is possible to provide the display panel  81  and the flexible display  8  which utilize the flexibility. 
     12. Modification Example of Eighth Embodiment 
     In the foregoing eighth embodiment, for example, as illustrated in  FIG.  86   , the display panel  81  may further include a microphone array in which one or a plurality of microphones  84  are assigned to the respective speakers  83 . At this time, for example, as illustrated in  FIG.  87   , the system circuit substrate  30  may include a circuit (the noise cancellation circuit  40 ) that suppresses a noise of the speaker  83  using a sound signal obtained by the microphone  84 . The noise cancellation circuit  40  outputs, to the speaker  83 , a signal obtained by inverting a phase of the sound signal obtained by the microphone  84 . This makes it possible to suppress the noise of the speaker  83 . 
     13. Modification Example Common to First, Second and Eighth Embodiments 
     In the foregoing  13 . first, second, and eighth embodiments, for example, as illustrated in  FIG.  88   , the display panel  12 ,  51 , or  82  may include, on an outer edge of the display panel  12 ,  51 , or  82 , an acoustic transmission part  85 , and the plurality of speakers  83  at positions facing the acoustic transmission part  85 . The acoustic transmission part  85  has, for example, a plurality of through-holes penetrating the display panel  12 ,  51 , or  82 . The acoustic transmission part  85  may have, for example, a non-woven fabric shape. This allows a sound from each of the speakers  83  to propagate in front of the display panel  12 ,  51 , or  82  through the acoustic transmission part  85 . Accordingly, it is possible to achieve an improvement in the sound quality. 
     Although the description has been given of the present disclosure with reference to the plurality of embodiments, the present disclosure is not limited to the foregoing embodiments, and may be modified in a variety of ways. It is to be noted that effects described herein are merely examples. Effects of the present disclosure are not limited to the effects described herein. The present disclosure may have effects other than the effects described herein. 
     Moreover, for example, the present disclosure may have the following configurations. 
     (1) A display panel including: 
     a flexible organic electroluminescent panel; and 
     one or a plurality of piezoelectric films provided on a rear surface of the organic electroluminescent panel, and vibrating the organic electroluminescent panel as a flat speaker. 
     (2) The display panel according to (1), in which 
     the organic electroluminescent panel includes, on a first base material, a plurality of pixels each including an organic electroluminescent element, 
     the piezoelectric film includes one or a plurality of piezoelectric elements on a second base material, and 
     materials of the first base material and the second base material are different from each other. 
     (3) The display panel according to (2), in which 
     the second base material is configured by a plurality of third base materials separated from each other, and 
     the one or the plurality of piezoelectric elements are provided for the respective third base materials. 
     (4) The display panel according to any one of (1) to (3), further including a separation layer provided between the organic electroluminescent panel and the piezoelectric film, the separation layer alleviating blocking of a vibration of the piezoelectric film caused by the organic electroluminescent panel. 
     (5) The display panel according to any one of (1) to (4), further including an adhesive layer that fixes the piezoelectric film to the organic electroluminescent panel, in which 
     the adhesive layer includes a sheet-like adhesive layer having a plurality of perforations, a plurality of band-shaped adhesive layers separated from each other, or a lattice-shaped adhesive layer. 
     (6) The display panel according to (3), further including a wiring layer electrically coupled to the piezoelectric element in a layer common to the piezoelectric film or in a layer different from the piezoelectric film. 
     (7) The display panel according to any one of (1) to (6), further including: 
     a stacked body including the organic electroluminescent panel and the one or the plurality of piezoelectric films; 
     a first support member fixed close to an upper end of the stacked body; and 
     a second support member fixed close to a lower end of the stacked body. 
     (8) The display panel according to (7), in which the first support member includes a winding core that winds the stacked body, and a box that accommodates the stacked body in a state of being wound around the winding core. 
     (9) The display panel according to (8), in which the first support member further includes a low-range speaker in the box. 
     (10) The display panel according to (7), in which the first support member includes a winding core that winds the stacked body. 
     (11) The display panel according to (10), in which the first support member further includes a low-range speaker incorporated in each of both ends of the winding core. 
     (12) The display panel according to any one of (7) to (11), in which the second support member includes an elastic member that pulls the stacked body downward. 
     (13) The display panel according to any one of (7) to (12), in which the stacked body includes a sound-absorbing material on a rearmost surface. 
     (14) A display apparatus including: 
     a display panel; and 
     a circuit substrate that drives the display panel, 
     the display panel including 
     a flexible organic electroluminescent panel, and 
     one or a plurality of piezoelectric films provided on a rear surface of the organic electroluminescent panel, and vibrating the organic electroluminescent panel as a flat speaker. 
     (15) The display panel according to (3), in which 
     each of the third base materials has a band shape extending in a direction parallel to one side of the display panel, and 
     the plurality of third base materials are arranged in a direction orthogonal to the extending direction of each of the third base materials. 
     (16) The display panel according to (3), in which 
     each of the third base materials has a band shape extending in a direction across each side of the display panel, and 
     the plurality of third base materials are arranged in a direction orthogonal to the extending direction of each of the third base materials. 
     (17) The display panel according to (3), in which 
     each of the third base materials has a rectangular shape, and 
     the plurality of third base materials are arranged in matrix. 
     (18) The display panel according to (9), in which the box includes a bass reflex duct. 
     (19) The display panel according to (11), in which the winding core has a tubular shape and includes a bass reflex duct. 
     (20) The display panel according to (7), in which the second support member includes a low-range speaker and a box that accommodates the low-range speaker. 
     (21) The display panel according to any one of (1) to (6), further including: 
     a tubular stacked body including the organic electroluminescent panel and the one or the plurality of piezoelectric films; and 
     a rotary part that rotatably supports the tubular stacked body. 
     (22) The display apparatus according to (14), in which 
     the organic electroluminescent panel includes, on a first base material, a plurality of pixels each including an organic electroluminescent element, 
     the piezoelectric film includes one or a plurality of piezoelectric elements on a second base material, and 
     materials of the first base material and the second base material are different from each other. 
     (23) The display apparatus according to (22), in which 
     the second base material is configured by a plurality of third base materials separated from each other, and 
     the one or the plurality of piezoelectric elements are provided for the respective third base materials. 
     (24) The display apparatus according to (23), in which 
     the display panel includes a stacked body including the organic electroluminescent panel and the plurality of piezoelectric films, 
     the stacked body further includes a microphone array in which one or a plurality of microphones are assigned for the respective third base materials, and 
     the circuit substrate includes a circuit that suppresses a vibration of the piezoelectric film on side of a rearmost surface of the stacked body using a sound signal obtained by the microphone array. 
     (25) The display apparatus according to (23), in which the circuit substrate includes a circuit that drives the plurality of piezoelectric elements independently for respective groups separated by the third base materials. 
     (26) The display apparatus according to (23), in which 
     the display panel includes
         a stacked body including the organic electroluminescent panel and the plurality of piezoelectric films, and   a winding core fixed close to an upper end of the stacked body, and winding the stacked body, and       

     the circuit substrate drives the plurality of piezoelectric elements independently for respective groups separated by the third base materials, and drives the plurality of piezoelectric elements in the groups present in a frontmost layer of the stacked body in a state in which the stacked body is wound around the winding core. 
     (27) The display apparatus according to (23), in which, when the stacked body has a cylindrical shape, the circuit substrate drives the plurality of piezoelectric elements independently for respective groups separated by the third base materials to allow a sound to be outputted only in a predetermined angular direction. 
     (28) The display apparatus according to (23), in which, when the stacked body has a cylindrical shape, the circuit substrate drives the plurality of piezoelectric elements independently for respective groups separated by the third base materials to allow a sound outputted from an upper part of the stacked body and a sound outputted from a lower part of the stacked body to be different from each other. 
     (29) The display apparatus according to (23), in which 
     the display panel includes a tubular stacked body including the organic electroluminescent panel and the one or the plurality of piezoelectric films, and includes a rotary part that rotatably supports the tubular stacked body, 
     the circuit substrate drives the plurality of piezoelectric elements to cause a sound volume to gradually increase, the piezoelectric elements belonging to the groups that begin to enter the display surface in association with rotation of the stacked body by the rotary part, and 
     the circuit substrate drives the plurality of piezoelectric elements to cause the sound volume to gradually decrease, the piezoelectric elements belonging to the groups that begin to deviate from the display surface in association with rotation of the stacked body by the rotary part. 
     (30) A display panel including: 
     a flexible organic electroluminescent panel; 
     one or a plurality of magnetic actuators or solid-state piezo actuators provided on a rear surface the organic electroluminescent panel, and vibrating the organic electroluminescent panel as a flat speaker; and 
     a first support member that supports the magnetic actuator or the solid-state piezo actuator. 
     (31) The display panel according to (30), further including a second support member fixed close to an upper end of the organic electroluminescent panel, in which 
     the second support member includes
         a winding core that winds the organic electroluminescent panel, and   a box that accommodates the organic electroluminescent panel in a state of being wound around the winding core, and       

     the first support member is supported by the box. 
     (32) The display panel according to (30) or (31), in which the organic electroluminescent panel includes a magnet having a magnetic pole in an orientation opposite to an orientation of a magnetic pole of the magnetic actuator. 
     (33) The display panel according to (30), in which 
     the stacked body has a cylindrical shape, and 
     the first support member supports the magnetic actuator or the solid-state piezo actuator from inside the cylindrical stacked body. 
     (34) The display panel according to (33), further including a vibration-damping member interposed in contact between two of the magnetic actuators adjacent to each other or between two of the solid-state piezo actuators adjacent to each other, out of an inner surface of the stacked body. 
     (35) The display panel according to (33), in which the first support member is fixed to the organic electroluminescent panel in a curved state. 
     (36) The display panel according to (33), in which the first support member includes an elastic member that tends to extend in a direction that reduces deflection of the organic electroluminescent panel. 
     (37) A display panel including: 
     a flexible organic electroluminescent panel; and 
     one or a plurality of Heil drivers provided at an edge of the organic electroluminescent panel. 
     (38) The display panel according to (37), including a support member fixed close to an upper end of the organic electroluminescent panel, in which 
     the support member includes 
     a winding core that winds the organic electroluminescent panel, and 
     a box that accommodates the organic electroluminescent panel in a state of being wound around the winding core. 
     (39) A display panel including: 
     a flexible organic electroluminescent panel; and 
     one or a plurality of coils provided on a rear surface of the organic electroluminescent panel, and vibrating the organic electroluminescent panel as a flat speaker. 
     (40) The display panel according to (39), including a support member fixed close to an upper end of the organic electroluminescent panel, in which 
     the support member includes 
     a winding core that winds the organic electroluminescent panel, and 
     a box that accommodates the organic electroluminescent panel in a state of being wound around the winding core. 
     (41) A display panel including: 
     a flexible organic electroluminescent panel; 
     one or a plurality of actuators provided close to a lower end of the organic electroluminescent panel, and vibrating the organic electroluminescent panel as a flat speaker; and 
     a first support member that supports the one or the plurality of actuators. 
     (42) The display panel according to (41), including a second support member fixed close to an upper end of the organic electroluminescent panel, in which 
     the second support member includes 
     a winding core that winds the organic electroluminescent panel, and 
     a box that accommodates the organic electroluminescent panel in a state of being wound around the winding core. 
     (43) The display panel according to (8), further including a vibration-damping film that is windable around the winding core in a state of being in contact with a surface of the organic electroluminescent panel. 
     (44) The display apparatus according to (14), in which the circuit substrate includes a tension detection circuit that detects pulling force or a corresponding physical quantity applied to the organic electroluminescent panel. 
     (45) A display panel including: 
     a flexible organic electroluminescent panel; 
     one or a plurality of magnetic actuators or solid-state piezo actuators provided on a rear surface of the organic electroluminescent panel, and vibrating the organic electroluminescent panel as a flat speaker; 
     a first support member that supports the magnetic actuator or the solid-state piezo actuator; and 
     a second support member fixed close to a lower end of the organic electroluminescent panel, 
     the second support member including a low-range speaker and a box that accommodates the low-range speaker. 
     (46) A display panel including: 
     a flexible organic electroluminescent panel; 
     one or a plurality of Heil drivers provided at an edge of the organic electroluminescent panel; and 
     a second support member fixed close to a lower end of the organic electroluminescent panel, 
     the second support member including a low-range speaker and a box that accommodates the low-range speaker. 
     (47) A display panel including: 
     a flexible organic electroluminescent panel; 
     one or a plurality of coils provided on a rear surface of the organic electroluminescent panel, and vibrating the organic electroluminescent panel as a flat speaker; and 
     a second support member fixed close to a lower end of the organic electroluminescent panel, 
     the second support member including a low-range speaker and a box that accommodates the low-range speaker. 
     According to the display panel and the display apparatus according to the embodiments of the present disclosure, it is possible to provide the display panel with a sound device, while utilizing the flexibility of the organic electroluminescent panel, thus making it possible to provide the display panel and display apparatus which utilize the flexibility. It is to be noted that effects of the present disclosure are not necessarily limited to the effects described herein, and may be any of the effects described herein. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.