Patent Publication Number: US-2022216810-A1

Title: Sound generator and sound apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Japanese Patent Application No. 2021-000737 filed on Jan. 6, 2021, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a sound generator and a sound apparatus. 
     Description of the Background 
     Recently, display apparatuses having improved sound performance for enhancing a sense of realism are being developed, and technology for enabling a display panel to function as a speaker is being developed. 
     As examples, Korean Patent Publication No. 10-2018-0077582 discloses a display apparatus including a display panel and an actuator, and Korean Patent Publication No. 10-2018-0077582 may be referred to as a display enabling sound apparatus which controls the actuator to vibrate the display panel to generate a sound. 
     SUMMARY 
     Accordingly, aspects of the present disclosure are directed to providing a sound generator and a sound apparatus that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     However, the related art needs the improvement of sound quality. 
     An aspect of the present disclosure is directed to providing a sound generator and a sound apparatus, which have enhanced sound quality. 
     Additional advantages and features of the disclosure will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the disclosure. Other advantages of the disclosure may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other aspects of the inventive concepts, as embodied and broadly described, a sound generator comprises a piezoelectric device; a first weight member disposed at a first portion of the piezoelectric device; a second weight member disposed at a second portion of the piezoelectric device; a first elastic member disposed at a third portion between the first portion and the second portion of the piezoelectric device; and a protection member configured to cover the piezoelectric device, the first weight member, the second weight member, and the first elastic member. 
     In another aspect of the present disclosure, a sound apparatus comprises a sound generator including a piezoelectric device, and an external frame configured to cover the sound generator, the external frame including an opening portion and a plurality of first vibration plates, the sound generator is disposed at the opening portion. 
     According to the aspects of the present disclosure, a sound generator and a sound apparatus with enhanced sound quality may be provided. 
     It is to be understood that both the foregoing general description and the following detailed description of the present disclosure are exemplary and explanatory and are intended to provide further explanation of the inventive concepts as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate aspects of the disclosure and together with the description serve to explain the principle of the disclosure. 
       In the drawings: 
         FIG. 1  is a diagram schematically illustrating a display apparatus; 
         FIG. 2  is a plan view illustrating a schematic configuration of piezoelectric devices; 
         FIG. 3  is a cross-sectional view taken along line A-A′ illustrated in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view illustrating in more detail a structure of a piezoelectric device; 
         FIG. 5  is a schematic diagram illustrating a deformation contracted in a horizontal direction when a voltage is applied to the piezoelectric device; 
         FIG. 6  is a schematic diagram illustrating a deformation expanded in a horizontal direction when a voltage is applied to the piezoelectric device; 
         FIG. 7  is a cross-sectional view illustrating a configuration of a piezoelectric device according to a comparative example; 
         FIG. 8  is a schematic diagram illustrating a vibration model according to the comparative example; 
         FIG. 9  is a schematic diagram illustrating a vibration model; 
         FIG. 10  illustrates a structure of a sound generator  100  according to an aspect of the present disclosure; 
         FIG. 11  is a cross-sectional view taken along line A-A′ illustrated in  FIG. 10 ; 
         FIG. 12  is a cross-sectional view taken along line B-B′ illustrated in  FIG. 10 ; 
         FIG. 13  illustrates an internal structure of a sound apparatus where the sound generator according to an aspect of the present disclosure; 
         FIG. 14  is a cross-sectional view taken along line A-A′ illustrated in  FIG. 13 ; 
         FIG. 15  is a cross-sectional view taken along line B-B′ illustrated in  FIG. 13 ; 
         FIG. 16  illustrates an internal structure of a sound apparatus where a sound generator according to a comparative example; 
         FIG. 17  is a characteristic diagram showing a result obtained by comparing a sound characteristic of the sound apparatus, illustrated in  FIG. 13 , with a sound characteristic of the sound apparatus illustrated in  FIG. 16 ; 
         FIG. 18  illustrates an internal structure of a sound apparatus according to a first modification aspect where the sound generator according to an aspect of the present disclosure; 
         FIG. 19  illustrates an internal structure of a sound apparatus according to a second modification aspect where the sound generator according to an aspect of the present disclosure is disposed. 
         FIG. 20  illustrates an internal structure of a sound apparatus according to a third modification aspect where the sound generator according to an aspect of the present disclosure; 
         FIG. 21  illustrates an internal structure of a sound apparatus according to a fourth modification aspect where the sound generator according to an aspect of the present disclosure; 
         FIG. 22  illustrates an internal structure of a sound apparatus according to a fifth modification aspect where the sound generator according to an aspect of the present disclosure; 
         FIG. 23  illustrates an internal structure of a sound apparatus according to a sixth modification aspect where the sound generator according to an aspect of the present disclosure; 
         FIG. 24  illustrates an internal structure of a sound apparatus according to a seventh modification aspect where the sound generator according to an aspect of the present disclosure; 
         FIG. 25  illustrates an internal structure of a sound apparatus according to an eighth modification aspect where the sound generator according to an aspect of the present disclosure; and 
         FIG. 26  illustrates an internal structure of a sound apparatus according to a ninth modification aspect where the sound generator according to an aspect of the present disclosure. 
     
    
    
     Throughout the drawings and the detailed description, unless otherwise described the same drawing reference numerals should be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to aspects of the present disclosure, examples of which may be illustrated in the accompanying drawings. In the following description, when a detailed description of well-known functions or configurations related to this document is determined to unnecessarily cloud a gist of the inventive concept, the detailed description thereof will be omitted. The progression of processing steps and/or operations described is an example; however, the sequence of steps and/or operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps and/or operations necessarily occurring in a particular order. Like reference numerals designate like elements throughout. Names of the respective elements used in the following explanations are selected only for convenience of writing the specification and may be thus different from those used in actual products. 
     Advantages and features of the present disclosure, and implementation methods thereof will be clarified through following aspects described with reference to the accompanying drawings. The present disclosure may, however, be embodied in different forms and should not be construed as limited to the aspects set forth herein. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Furthermore, the present disclosure is only defined by scopes of claims. 
     The shape, a size, a ratio, an angle, and a number disclosed in the drawings for describing aspects of the present disclosure are merely an example, and thus, the aspects of present disclosure are not limited to the illustrated details. Like reference numerals refer to like elements throughout. In the following description, when the detailed description of the relevant known function or configuration is determined to unnecessarily obscure the important point of the present disclosure, the detailed description will be omitted. When “comprise,” “have,” and “include” described in the present specification are used, another part may be added unless “only” is used. The terms of a singular form may include plural forms unless referred to the contrary. 
     In construing an element, the element is construed as including an error or tolerance range although there is no explicit description of such an error or tolerance range. 
     In describing a position relationship, for example, when a position relation between two parts is described as, for example, “on,” “over,” “under,” and “next,” one or more other parts may be disposed between the two parts unless a more limiting term, such as “just” or “direct(ly)” is used. 
     In describing a time relationship, for example, when the temporal order is described as, for example, “after,” “subsequent,” “next,” and “before,” a case that is not continuous may be included unless a more limiting term, such as “just,” “immediate(ly),” or “direct(ly)” is used. 
     In the description of aspects, when a structure is described as being positioned “on or above” or “under or below” another structure, this description should be construed as including a case in which the structures contact each other as well as a case in which a third structure is disposed therebetween. 
     It will be understood that, although the terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. 
     In describing elements of the present disclosure, the terms “first,” “second,” “A,” “B,” “(a),” “(b),” etc. may be used. These terms are intended to identify the corresponding elements from the other elements, and basis, order, or number of the corresponding elements should not be limited by these terms. The expression that an element is “connected,” “coupled,” or “adhered” to another element or layer, the element or layer can not only be directly connected or adhered to another element or layer, but also be indirectly connected or adhered to another element or layer with one or more intervening elements or layers “disposed,” or “interposed” between the elements or layers, unless otherwise specified. 
     The term “at least one” should be understood as including any and all combinations of one or more of the associated listed items. For example, the meaning of “at least one of a first item, a second item, and a third item” denotes the combination of all items proposed from two or more of the first item, the second item, and the third item as well as the first item, the second item, or the third item. 
     A size and a thickness of each component illustrated in the drawing are illustrated for convenience of description, and the present disclosure is not limited to the size and the thickness of the component illustrated. 
     Features of various aspects of the present disclosure may be partially or overall coupled to or combined with each other, and may be variously inter-operated with each other and driven technically as those skilled in the art can sufficiently understand. Aspects of the present disclosure may be carried out independently from each other, or may be carried out together in co-dependent relationship. 
     Hereinafter, aspects of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements having a common function, and repeated descriptions are omitted or will be briefly given. For convenience of description, a scale of each of elements illustrated in the accompanying drawings differs from a real scale, and thus, is not limited to a scale illustrated in the drawings. 
     [A Premise Technique] 
       FIG. 1  is a diagram schematically illustrating a display apparatus  1  according to a premise technique. 
     The display apparatus  1  may be electronic posters, digital bulletin boards, electronic advertisement signboards, computer image output devices, televisions, smart phones, or game machines, or the like, but aspects of the present disclosure are not limited thereto. 
     As illustrated in  FIG. 1 , the display apparatus  1  may include a piezoelectric device  10 , a display panel  20 , an elastic member  30 , a first controller  40 , a second controller  50 , a data driving circuit  60 , a gate driving circuit  70 . The display apparatus  1  may be an apparatus which displays an image by a display panel  20  based on RGB data or the like input thereto and generates a sound or a vibration based on a sound signal (or a vibration driving signal) or the like input thereto. Thus, the display apparatus  1  may be implemented as a sound apparatus. 
     The display panel  20  may include the plurality of pixels P arranged in a matrix. The pixel P may include a light emitting device including an organic light emitting diode or the like. When the display apparatus  1  is capable of displaying a color image, the pixel P may be a subpixel which displays one of a plurality of colors (for example, RGB) implementing a color image. 
     The piezoelectric device  10  may be an element where displacement occurs due to an inverse piezoelectric effect when a voltage is applied based on a sound signal input thereto. The piezoelectric device  10  may be an element where bent displacement occurs due to a voltage such as bimorph or unimorph. Because an input sound signal is an alternating current (AC) voltage, the piezoelectric device  10  may act as a vibration device which vibrates according to a sound signal input thereto. 
     The elastic member  30  may be a member configured by a material having elasticity. A material of the elastic member  30  may have an elastic modulus which is lower than the piezoelectric device  10  and the display panel  20 , and may be, for example, a material such as rubber or the like. A portion of the piezoelectric device  10  may be coupled or connected to a portion of the display panel  20  by the elastic member  30 , and thus, a vibration of the piezoelectric device  10  may be transferred to the display panel  20 , and the display panel  20  may generate a sound based on a sound signal input thereto. 
     A host system  2  may be a system including an apparatus or a plurality of apparatuses, which provide(s) an image signal such as RGB data or the like, a sound signal, and a timing signal to control the display apparatus  1 . The timing signal may include a vertical synchronization signal, a horizontal synchronization signal, and a data enable signal, or the like. The host system  2  may be, for example, a source sound reproduction apparatus, a local broadcast apparatus, a radio broadcast reproduction system, a television (TV) system, a set-top box, a navigation system, an optical disk player, a computer, a home theater system, and a video phone system, or the like. Also, the display apparatus  1  and the host system  2  may be an integrated apparatus, or may be configured as separate apparatuses. 
     The first controller  40  may provide a voltage to the piezoelectric device  10  based on a sound signal and a timing signal input from the host system  2 . The second controller  50  may control the data driving circuit  60  and the gate driving circuit  70  based on image data and a timing signal input from the host system  2 . The data driving circuit  60  may supply data voltages or the like to a plurality of pixels P through a driving line  61  disposed at each column of the plurality of pixels P. The gate driving circuit  70  may supply a control signal to the plurality of pixels P through a driving line  71  disposed at each row of the plurality of pixels P. Also, each of the driving line  61  and the driving line  71  may be provided in a plurality lines (or wiring lines). 
     Each of the first controller  40 , the second controller  50 , the data driving circuit  60 , and the gate driving circuit  70  may be configured by one semiconductor IC or a plurality of semiconductor ICs. Also, some or all of the first controller  40 , the second controller  50 , the data driving circuit  60 , and the gate driving circuit  70  may be configured as one semiconductor IC or one body (or a single body). 
       FIG. 2  is a plan view illustrating a schematic configuration of piezoelectric devices  10  according to a premise technique.  FIG. 3  is a cross-sectional views taken along line A-A′ illustrated in  FIG. 2 . In  FIG. 2 , a tetragonal (or a rectangular) border (or boundary) of a display panel  20  schematically illustrates an external frame or an external appearance or an external shape of the display panel  20 . 
     One main surface of the display panel  20  illustrated in  FIG. 3  may be an image display surface (or a first surface or a front surface)  20   a,  and the other main surface may be a rear surface (or a second surface or a backside surface)  20   b.  In coordinate axes illustrated in  FIGS. 2 and 3 , a horizontal direction of the image display surface  20   a  illustrates a x axis, a vertical direction of the image display surface  20   a  illustrates a z axis, and a depth direction of the image display surface  20   a  illustrates a y axis. Also, a direction from the rear surface  20   b  to the image display surface  20   a  may be a forward direction of the y-axis. 
     The shape of the piezoelectric device  10  may be a rectangular shape having a long-side direction (a z direction in  FIGS. 2 and 3 ) and a short-side direction (an x direction in  FIGS. 2 and 3 ) with respect to a plan view, and may be a flat plate shape. Accordingly, deformation which is bent to a cross-sectional surface (line A-A′) in the long-side direction may occur. A long-side direction of the piezoelectric device  10  may be disposed to be perpendicular to an end portion of the display panel  20 . 
     An elastic member  30  may be connected (or coupled) to a portion including a center of the piezoelectric device  10  in the long-side direction thereof. The center of the piezoelectric device  10  in the long-side direction thereof may be a portion which is an antinode of a vibration, and thus, a vibration may be efficiently transferred to the display panel  20 . 
     The piezoelectric device  10  illustrated in  FIG. 3  may include a main surface (or a first surface)  10   a  and a second main surface (or a second surface)  10   b.  The elastic member  30  may connect (or couple) the first surface  10   a  of the piezoelectric device  10  to a rear surface  20   b  of the display panel  20 . As described above, the piezoelectric device  10  and the elastic member  30  may be disposed at the rear surface  20   b  of the display panel  20  so as not to obstruction with image display of the image display surface  20   a.    
     The elastic member  30  may be connected (or coupled) to only a portion of the first surface  10   a  of the piezoelectric device  10 . Therefore, both end portions of the piezoelectric device  10  in a long-side direction thereof may be lifted, and thus, it may be suppressed the vibration of the piezoelectric device  10  at the both end portions, where a displacement of a bending vibration (or flexural vibration) is large of the piezoelectric device  10  in the long-side direction thereof. 
       FIG. 4  is a cross-sectional view illustrating in more detail a structure of a piezoelectric device  10  according to a premise technique.  FIG. 4  is a cross-sectional view taken along line A-A′ illustrated in  FIG. 2  like  FIG. 3  although a direction in which  FIG. 3  is rotated 90 degrees to the right. Also,  FIG. 4  schematically illustrates, by a circuit diagram, a connection relationship between electrodes included in the piezoelectric device  10 , for describing a method of inputting a sound signal to the piezoelectric device  10 . 
     The piezoelectric device  10  illustrated in  FIG. 4  may include a bimorph structure where two piezoelectric layers are stacked. The piezoelectric device  10  illustrated in  FIG. 4  may include a first electrode  11 , a first piezoelectric layer  12 , a second electrode  13 , a second piezoelectric layer  14 , and a third electrode  15 . The first electrode  11  may be disposed closest to the display panel  20  and may be connected to the elastic member  30 . The third electrode  15  may be disposed farthest from the display panel  20 . The second electrode  13  may be disposed between the first electrode  11  and the third electrode  15 . 
     The first piezoelectric layer  12  may be supported between the first electrode  11  and the second electrode  13 . The second piezoelectric layer  14  may be supported between the second electrode  13  and the third electrode  15 . Arrows represented inside the first piezoelectric layer  12  and the second piezoelectric layer  14  represent polarization directions, and the polarization direction of the first piezoelectric layer  12  may be the same as the polarization direction of the second piezoelectric layer  14 . 
     Also, a line (or wiring line) to apply a voltage to each electrode may be connected to the first electrode  11 , the second electrode  13 , and the third electrode  15 , but in  FIG. 4 , the illustration of the line is omitted. In addition, the line may be connected by soldering or the like, and aspects of present disclosure are not limited to a specific method. 
     A voltage applied to the piezoelectric device  10  may be based on a sound signal, and thus, may be an AC voltage corresponding to a frequency of a sound which is to be generated. In  FIG. 4 , the AC voltage is represented by a circuit sign for an AC power. In the AC power V, one terminal (or a first terminal) may be connected to the first and third electrodes  11  and  15 , and the other terminal (or a second terminal) may be connected to the second electrode  13 . For example, the voltage applied to the first electrode  11  and the voltage applied to the third electrode  15  may be the same phase (or in-phase), the voltage applied to the first electrode  11  and the voltage applied to the second electrode  13  may be opposite phases (or anti-phases), and the voltage applied to the second electrode  13  and the voltage applied to the third electrode  15  may be the same phase (or in-phase). Accordingly, the voltage applied to the first piezoelectric layer  12  and the voltage applied to the second piezoelectric layer  14  may be in opposite directions (or reverse directions). 
     Materials of the first and second piezoelectric layers  12  and  14  may be a piezoelectricity material, and aspects of present disclosure are not limited to a specific material. For example, the first and second piezoelectric layers  12  and  14  may include lead zirconate titanate (PZT) or the like. The PZT have high piezoelectricity, and thus, may have a large displacement amount with respect to the applied voltage. Also, although not illustrated in  FIG. 4 , an outer periphery (or an outer perimeter) of the piezoelectric device  10  may be covered by an insulator such as resin or the like so as to prevent an electrical short circuit between the piezoelectric device  10  and another member. 
       FIG. 5  is schematic diagrams illustrating a deformation contracted in a horizontal direction when a voltage is applied to the piezoelectric device  10  in the premise technique.  FIG. 6  is schematic diagrams illustrating a deformation expanded in a horizontal direction when a voltage is applied to the piezoelectric device  10  in the premise technique. As illustrated in  FIG. 4 , the polarization direction of the first piezoelectric layer  12  may be the same as the polarization direction of the second piezoelectric layer  12 . A direction of the voltage applied to the first piezoelectric layer  12  may be opposite to a direction of the voltage applied to the second piezoelectric layer  14 . For example, the voltages applied to the first and second piezoelectric layers  12  and  14  may have opposite phases. Accordingly, a stretching direction of the first piezoelectric layer  12  may be opposite or inverted (or reversed) to a stretching direction of the second piezoelectric layer  14 . 
     As illustrated in  FIG. 5 , the second piezoelectric layer  14  may be deformed in a direction expanding in a horizontal direction at a timing at which the first piezoelectric layer  12  is deformed to contract in the horizontal direction. Therefore, an end portion of the piezoelectric device  10  may be bent in a direction closer to the display panel  20 . For example, the display  20  may be deformed based on a stress applied thereto toward the piezoelectric device  10 . 
     As illustrated in  FIG. 6 , the second piezoelectric layer  14  may be deformed in a direction contracting in a horizontal direction at a timing at which the first piezoelectric layer  12  is deformed to expand in the horizontal direction. Therefore, the end portion of the piezoelectric device  10  may be bent in a direction distancing from the display panel  20 . For example, the display panel  20  may be deformed based on a stress applied thereto in a direction distancing from the piezoelectric device  10 . 
     When an AC voltage based on a sound signal is applied to the piezoelectric device  10 , a shape (or a form) illustrated in  FIG. 5  and a shape (or a form) illustrated in  FIG. 6  may be alternately repeated in a frequency of a sound. Thus, a vibration of the piezoelectric device  10  may be transferred to the display panel  20  to vibrate the display panel  20 . Accordingly, the display panel  20  may act as a speaker so that the display panel  20  generates a sound based on a sound signal. 
     In the premise technique, an effect obtained when a portion of a piezoelectric device  10  is connected to a display panel  20  by an elastic member  30  will be described.  FIG. 7  is a cross-sectional view illustrating a configuration of a piezoelectric device  10  according to a comparative example.  FIG. 8  is a schematic diagram illustrating a vibration model according to the comparative example. 
     In the comparative example illustrated in  FIG. 7 , a whole surface of the piezoelectric device  10  may be directly connected to the display panel  20 . Based on such a configuration, a displacement of the piezoelectric device  10  may be transferred to the display panel  20 , and thus, the display panel  20  may act as a speaker. The vibration model according to the comparative example illustrated in  FIG. 8 , a plurality of springs Si and S 2  may be connected to both ends of a mass point representing the piezoelectric device  10  and the display panel  20 . The piezoelectric device  10  having a mass m 1  may be directly connected to the display panel  20  having a mass m 2 . 
     The spring S 1  having a spring constant k 1  may be connected to the piezoelectric device  10 , and the spring S 2  having a spring constant k 2  may be connected to the display panel  20 . The spring S 1  may be implemented by modeling the elasticity of the piezoelectric device  10 . The spring S 2  may be implemented by modeling the elasticity of the display panel  20  or the elasticity of a member, which binds the display panel  20  such as a case or the like. Also, in the vibration model, both ends thereof may be a fixed end or a fixed member. 
     In the vibration model of the comparative example, the piezoelectric device  10  and the display panel  20  may be replaced with one mass point having a mass m 1 +m 2 . When a voltage is applied to the piezoelectric device  10 , a force generated by the piezoelectric device  10  may vibrate all of the display panel  20  and the piezoelectric device  10  having the mass m 1 +m 2 . For example, the mass m 1 +m 2  may be far greater than a mass m 1 . The force generated by the piezoelectric device  10  may affect an object having a very large mass, and thus, an acceleration applied to the piezoelectric device  10  and the first vibration member  20  by the force may be small. Accordingly, a displacement amount of the piezoelectric device  10  and the display panel  20  may be smaller, and in a configuration of the comparative example, the sound pressure of sound generated from the display panel  20  may be difficult to increase. 
       FIG. 9  is a schematic diagram illustrating a vibration model according to the premise technique. In the vibration model according to the premise technique illustrated in  FIG. 9 , a spring S 3  having a spring constant k 3  is connected between a mass point representing a display panel  20  and a piezoelectric device  10 . The spring S 3  may be implemented by modeling the elasticity of an elastic member  30 . The piezoelectric device  10  having a mass m 1  and the display panel  20  having a mass m 2  is connected to through the spring S 3 . 
     In the vibration model according to the premise technique, the piezoelectric device  10  and the display panel  20  are independently displaced from each other. A force, generated when a voltage is applied to the piezoelectric device  10 , vibrates the piezoelectric device  10  having the mass m 1 . For example, a mass of an object to which the force is applied may be less than the comparative example, and thus, an acceleration applied to the piezoelectric device  10  by the force may be greater than the comparative example. Therefore, the piezoelectric device  10  may be a resonance state with large displacement. Also, a displacement of the piezoelectric device  10  may be gradually transferred to the display panel  20  through the spring S 3 , and thus, like the comparative example, suppression of displacement by a mass of the display panel  20  may be difficult to occur. Accordingly, in an aspect of the premise technique, displacement may increase compared to the comparative example, and thus, a sound pressure level may be enhanced. 
     As described above, according to the premise technique, when the display panel  20  acts as a speaker, a sound pressure level of a sound generated by the display panel  20  may be enhanced. 
     Moreover, in the premise technique, a vibration source is the piezoelectric device  10 , but a sound generating source is the display panel  20  which is large in mass and is low in natural frequency. Therefore, in the premise technique, a sound pressure level of a low-pitched sound band may be more enhanced than that from a configuration, where the piezoelectric device  10  directly generates a sound, or a configuration where a sound is generated by a member which connects the piezoelectric device  10  to a separate small vibration plate differing from the display panel  20  and has a high natural frequency. 
     As described above, according to the premise technique, a sound pressure level of a low-pitched sound band may be enhanced, but it may be required to improve a sound pressure level of each of a middle-pitched sound band and a high-pitched sound band. In an aspect of the present disclosure, as described below, noise, a high frequency sound, and a sound pressure level difference between different pitched sound bands may be controlled. Also, in the following description, the low-pitched sound band may be defined as a sound having a frequency of 300 Hz or less, the middle-pitched sound band may be defined as a sound having a frequency which is higher than a frequency of 300 Hz and is lower than or equal to a frequency of 1 kHz or less, and the high-pitched sound band may be defined as a sound having a frequency which is higher than a frequency of 1 kHz, but not limited thereto. 
       FIG. 10  illustrates a structure of a sound generator  100  according to an aspect of the present disclosure.  FIG. 11  is a cross-sectional view taken along line A-A′ illustrated in  FIG. 10 .  FIG. 12  is a cross-sectional view taken along line B-B′ illustrated in  FIG. 10 . 
     With reference to  FIGS. 10 to 12 , the sound generator  100  may include a first weight member  101 , a first elastic member  102 , a second weight member  103 , a second elastic member  104 , and a piezoelectric device  105  having a rectangular shape, and a protection member  106 . For example, the first and second weight members  101  and  103  may each be a weight, a balance weight, a mass, a mass member, or a vibration amplification member, but aspects of the present disclosure are limited thereto. The protection member  106  may be an elastic protection member or a flexible protection member, but aspects of the present disclosure are limited thereto. 
     The piezoelectric device  105  may have a rectangular shape including a long-side and a short-side. For example, the piezoelectric device  105  may include a first portion (or a second vibration area or a second sound area), a second portion (or a first vibration area or a first sound area), and a third portion (or a third vibration area or a third sound area) between the first portion and the second portion, with respect to a long-side direction, and the first to third portions may respectively generate sounds of different pitched sound bands. 
     The first weight member  101  may be a member which is provided at the first portion of the piezoelectric device  105  in the long-side direction and is provided for amplifying a vibration of the piezoelectric device  105 . The second weight member  103  may be a member which is provided at the second portion of the piezoelectric device  105  in the long-side direction and is provided for amplifying a vibration of the piezoelectric device  105 . The first elastic member  102  may include an elastic material and may include a material which is more difficult to deform than the second elastic member  104 , and for example, may be an aggregation element where a material of the protection member  106  is solidly hardened. The second elastic member  104  may include an elastic material and may include an elastic material which is easier to deform than the first elastic member  102  or may include an elastic material which has a lower density than the first elastic member  102 , and for example, may be a sponge. 
     The piezoelectric device  105  may correspond to the piezoelectric device  10  according to the premise technique and may be a device which, when a voltage based on a sound signal input thereto is applied thereto, may be displaced by an inverse piezoelectric effect to generate a sound in the sound generator  100 . 
     The protection member  106  may be a member which has elasticity and covers the first weight member  101 , the first elastic member  102 , the second weight member  103 , and the piezoelectric device  105  in the sound generator  100 , and for example, may include silicon, rubber, silicon rubber, or the like, but aspects of the present disclosure are limited thereto. The protection member  106  may be a case which includes, for example, silicon rubber, and may include a notch (or a slit) which is provided at a portion thereof. The protection member  106  may cover or surround each of the first weight member  101 , the first elastic member  102 , the second weight member  103 , and the piezoelectric device  105  which are inserted thereinto through the notch. For example, the first weight member  101 , the first elastic member  102 , the second weight member  103 , and the piezoelectric device  105  may be provided as one body (or a single body) and may be inserted into the case (or the protection member  106 ) through the notch, and thus, may cover or wholly surround each of the first weight member  101 , the first elastic member  102 , the second weight member  103 , and the piezoelectric device  105 . 
     The first portion, where the first weight member  101  is disposed, of the piezoelectric device  105  in the long-side direction may be a high-pitched sound band generating portion which generates a sound having a high frequency (or a first frequency band). The second portion, where the second weight member  103  is disposed, of the piezoelectric device  105  in the long-side direction may be a low-pitched sound band generating portion which generates a sound having a low frequency (or a second frequency band). A portion where the first elastic member  102  is disposed may be a middle-pitched sound band generating portion which generates a sound having a middle frequency (or a third frequency band) between a sound generated by the high-pitched sound band generating portion and a sound generated by the low-pitched sound band generating portion. Also, the second elastic member  104  may be disposed at the low-pitched sound band generating portion, but aspects of the present disclosure are not limited thereto. Also, as illustrated in  FIG. 10 , in the sound generator  100 , the low-pitched sound band generating portion may have a size (or an area) which is relatively greater than each of the high-pitched sound band generating portion and the middle-pitched sound band generating portion. 
       FIG. 13  illustrates an internal structure of a sound apparatus  200  where the sound generator  100  according to an aspect of the present disclosure is disposed.  FIG. 14  is a cross-sectional view taken along line A-A′ illustrated in  FIG. 13 .  FIG. 15  is a cross-sectional view taken along line B-B′ illustrated in  FIG. 13 . 
     With reference to  FIGS. 10 and 13 to 15 , the sound apparatus  200  according to an aspect of the present disclosure may include the sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame (or a first frame)  203  including an opening portion  202 , and an internal frame (or a second frame)  204 . The sound apparatus  200  may be supported between two vibration plates  203   a.    
     The middle-pitched sound band generating portion of the sound generator  100  may be connected or fixed to the two vibration plates  203   a  through the first elastic member  102  at a position which is closer to the first portion, where the first weight member  101  is provided, of the piezoelectric device  105  in the long-side direction than a center of the piezoelectric device  105  in the long-side direction. The elastic member  201  may include an elastic material, and for example, may be the same sponge as the second elastic member  104 . The elastic member  201  may be disposed outward from the external frame  203 . 
     The external frame  203  may output a sound, generated by the sound generator  100 , to the outside. The external frame  203  may include a high-pitched sound band generating portion (or a first portion) which generates a high-pitched sound band, a low-pitched sound band generating portion (or a second portion) which generates a low-pitched sound band, and a middle-pitched sound band generating portion (or a third portion) which generates a middle-pitched sound band between the high-pitched sound band generating portion (or the first portion) and the low-pitched sound band generating portion (or the second portion). 
     Moreover, the two vibration plates  203   a  may be included in the external frame  203 , or may be provided as two or more. The sound generator  100  may be disposed at at least one of the opening portion  202  disposed at the first portion of the external frame  203  and the third portion of the external frame  203 . The external frame  203  with the opening portion  202  provided therein and the internal frame  204  may be provided as one body (or a single body), but aspects of the present disclosure are not limited thereto. 
     The internal frame  204  may be configured so that each of a sound generated by the middle-pitched sound band generating portion and a sound generated by the low-pitched sound band generating portion is introduced into a space formed in a portion of an inner portion of the sound apparatus  200  and reverberated. 
     In the sound generator  100 , the first elastic member  102  may be attached to a vibration plate of the external frame  203  at an adhesive surface  1020  provided inside the middle-pitched sound band generating portion (or the third portion), and may be attached to a vibration plate of the external frame  203  at an adhesive surface  1040  provided inside the low-pitched sound band generating portion (or the second portion). A vibration plate  203   a  of a portion (or a third portion) of the adhesive surface  1020  may be a first vibration plate and a vibration plate  203   a  of a portion (or a second portion) of the adhesive surface  1040  may be a second vibration plate, and thus, the vibration plate  203   a  may be configured by a plurality of vibration plates. 
       FIG. 16  illustrates an internal structure of a sound apparatus  200   a  where a sound generator  100   a  according to a comparative example is disposed. The sound apparatus  200   a  may include the sound generator  100   a  including a piezoelectric device, an elastic member  201 , and an external frame  203 . The sound generator  100   a  may include two second weight members  103 , two second elastic members  104 , and a piezoelectric device  105 . In the sound generator  100   a,  the two second weight members  103  and the two second elastic members  104  may be provided at both portions (or a first portion and a second portion) of the piezoelectric device  105  in a long-side direction. 
       FIG. 17  is a characteristic diagram showing a result obtained by comparing a sound characteristic of the sound apparatus  200 , illustrated in  FIG. 13 , with a sound characteristic of the sound apparatus  200   a  illustrated in  FIG. 16 . In  FIG. 17 , the abscissa axis represents a frequency, and the ordinate axis represents an amplitude. In the characteristic diagram of  FIG. 17 , a first enlarged view, a second enlarged view, and a third enlarged view illustrate the enlargements of three portions. In the first enlarged view, the second enlarged view, and the third enlarged view, a characteristic in a middle-pitched sound band or a high-pitched sound band is shown, but in all enlarged views, a sound pressure level may increase (particularly, a sound pressure level in a high-pitched sound band may increase) and a sound pressure level difference between the middle-pitched sound band and the high-pitched sound band may be reduced. Also, in the second enlarged view and the third enlarged view, it may be seen that, as an increase or a reduction in amplitude of a variation of a frequency in the high-pitched sound band is reduced, a high frequency sound is reduced and noise in the high-pitched sound band is reduced. As illustrated in  FIG. 17 , in the sound apparatus  200  illustrated in  FIG. 13 , noise in the high-pitched sound band may be reduced, the high frequency sound may be reduced, and a sound pressure level difference between the middle-pitched sound band and the high-pitched sound band may be reduced. 
     Moreover, a sound apparatus according to an aspect of the present disclosure is not limited to a configuration (or a structure) illustrated in  FIGS. 13 to 15 , and a modification aspect of the sound apparatus according to an aspect of the present disclosure will be described below. 
       FIG. 18  illustrates an internal structure of a sound apparatus  200   a  according to a first modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 18 , the sound apparatus  200   a  according to the first modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202 , and a plurality of internal frames  204  and  204 a. Comparing with the sound apparatus  200  according to an aspect of the present disclosure, the sound apparatus  200   a  according to the first modification aspect of the present disclosure has a difference in that the internal frame  204   a  is additionally provided in the sound apparatus  200 , and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     Two internal frames  204   a  may be disposed at an area of a low-pitched sound band and may be configured so that a path of a sound generated by the sound generator  100  narrows in a direction distancing from an area of the middle-pitched sound band and is reverberated in an area distancing from the area of the middle-pitched sound band. According to a configuration illustrated in  FIG. 18 , a sound pressure level characteristic of the low-pitched sound band may be enhanced. 
       FIG. 19  illustrates an internal structure of a sound apparatus  200   b  according to a second modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 19 , the sound apparatus  200   b  according to the second modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202 , and an internal frame  204   b.  Comparing with the sound apparatus  200  according to an aspect of the present disclosure, the sound apparatus  200   b  according to the second modification aspect of the present disclosure has a difference in that the internal frame  204   b  is provided instead of the internal frame  204  of the sound apparatus  200 , and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     The internal frame  204   b  may be disposed at an area of the middle-low-pitched sound band and may be configured so that a path of a sound generated by the sound generator  100  bypasses an area of the middle-low-pitched sound band at least once and is reverberated at the area of the middle-pitched sound band. According to a configuration illustrated in  FIG. 19 , a sound pressure level characteristic of the low-pitched sound band may be enhanced. 
       FIG. 20  illustrates an internal structure of a sound apparatus  200   c  according to a third modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 20 , the sound apparatus  200   c  according to the first modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202  and a port  205 , and an internal frame  204 a. Comparing with the sound apparatus  200   b  according to the second modification aspect of the present disclosure, the sound apparatus  200   c  according to the third modification aspect of the present disclosure has a difference in that the port  205  is provided at the external frame  203 , and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     The port  205  may be provided for enhancing a sound pressure level of a low-pitched sound band. In a closed type speaker, a rear surface (or a backside) of the speaker may be closed and an air room may be provided, but when a port (or a hole) is formed at the closed air room, a resonance frequency may be adjusted based on a capacity of the air room, a cross-sectional area of an opening of the port  205 , and a length of a duct provided at the air room of the port  205 , and thus, a speaker where a low-pitched sound band is emphasized may be implemented. Therefore, the port  205  may be configured at the external frame  203  to communicate with a space (or an air room) surrounded by the external frame  203  and two vibration plates  203 a. For example, a shape of the opening of the port  205  is not limited to a specific shape and may be circular or oval or may be tetragonal or polygonal. The port  205  may be configured at the external frame  203  of an area of a middle-low-pitched sound band so as to enhance a sound pressure level of a low-pitched sound band. For example, the resonance frequency may be adjusted by the port  205 , and thus, the sound pressure level of the low-pitched sound band may be enhanced. In a configuration illustrated in  FIG. 20 , a sound pressure level characteristic of the low-pitched sound band may be enhanced. 
       FIG. 21  illustrates an internal structure of a sound apparatus  200   d  according to a fourth modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 21 , the sound apparatus  200   d  according to the fourth modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202 , and an internal frame  204   c.  Comparing with the sound apparatus  200  according to an aspect of the present disclosure, the sound apparatus  200   d  according to the fourth modification aspect of the present disclosure has a difference in that the internal frame  204   c  is provided instead of the internal frame  204  of the sound apparatus  200 , and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     The internal frame  204   c  may be disposed at each of an area of the middle-pitched sound band and an area of the low-pitched sound band and may be configured so that a path of a sound generated by the sound generator  100  is reverberated to the area of the middle-pitched sound band and the path of the sound bypasses to the area of the low-pitched sound band and is reverberated at an area distancing from the area of the middle-pitched sound band. According to a configuration illustrated in  FIG. 21 , a sound pressure level of a middle-pitched sound band and a sound pressure level of a low-pitched sound band may be enhanced. 
       FIG. 22  illustrates an internal structure of a sound apparatus  200   e  according to a fifth modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 22 , the sound apparatus  200   e  according to the fifth modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202  and a plurality of ports  205  and  205   a,  and an internal frame  204   c.  Comparing with the sound apparatus  200   d  according to the fourth modification aspect of the present disclosure, the sound apparatus  200   e  according to the fifth modification aspect of the present disclosure has a difference in that the ports  205  and  205   a  are provided at the external frame  203  and the other elements are the same, and thus, repetitive descriptions of the same elements are omitted. 
     The port  205  (or a first port) may be configured at the external frame  203  of an area of the low-pitched sound band so as to enhance a sound pressure level of a low-pitched sound band, and the port  205   a  (or a second port) may be configured at the external frame  203  of an area of the middle-pitched sound band so as to enhance a sound pressure level of a middle-pitched sound band. For example, the port  205  may be configured identically to the port  205  illustrated in  FIG. 20 . Except for that the port  205   a  is provided at the external frame  203  adjacent to the opening portion  202 , the port  205   a  may be configured identically to the port  205 . According to a configuration illustrated in  FIG. 22 , a sound pressure level of the middle-pitched sound band and a sound pressure level of the low-pitched sound band may be enhanced. 
       FIG. 23  illustrates an internal structure of a sound apparatus  200   f  according to a sixth modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 23 , the sound apparatus  200   f  according to the sixth modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202  and a port  205 , and a plurality of internal frames  204  and  204   d.  Comparing with the sound apparatus  200  according to an aspect of the present disclosure, the sound apparatus  200   f  according to the sixth modification aspect of the present disclosure has only a difference in that the internal frame  204   d  is added and the port is provided at the external frame  203 , and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     The internal frame  204   d  may be disposed at an area of the low-pitched sound band, may be disposed in approximately parallel with the internal frame  204  provided at the area of the low-pitched sound band, and may be configured so that a path of a sound generated by the sound generator  100  bypasses the area of the low-pitched sound band so as to face a corner portion of the external frame  203  and is reverberated at an area distancing from an area of the middle-pitched sound band. According to a configuration illustrated in  FIG. 23 , a sound pressure level of a low-pitched sound band may be enhanced. 
       FIG. 24  illustrates an internal structure of a sound apparatus  200   g  according to a seventh modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 24 , the sound apparatus  200   g  according to the seventh modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202  and a port  205 , and a plurality of internal frames  204 ,  204   d,    204   e,  and  204   f.  Comparing with the sound apparatus  200   f  according to the sixth modification aspect of the present disclosure, the sound apparatus  200   g  according to the seventh modification aspect of the present disclosure has only a difference in that the internal frames  204   e  and  204   f  are additionally provided, and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     The internal frame  204   e  may be disposed at an area of the low-pitched sound band. A portion of the internal frame  204   e  may be configured to block a path of a sound passing through a region between the internal frame  204  and the internal frame  204   d  so that a path of a sound generated by the sound generator  100  bypasses and reverberates, and another portion of the internal frame  204   e  may be configured to be approximately parallel to a portion of the internal frame  204   d  disposed at the area of the low-pitched sound band. The internal frame  204   f  may be provided in approximately parallel with another portion of the internal frame  204   e  so that a path of a sound generated by the sound generator  100  bypasses and reverberates. The port  205  may be provided at the external frame  203  of the area of the low-pitched sound band, thereby enhancing a sound pressure level of a low-pitched sound band. According to a configuration illustrated in  FIG. 24 , the sound pressure level of the low-pitched sound band may be enhanced. 
       FIG. 25  illustrates an internal structure of a sound apparatus  200   h  according to an eighth modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 25 , the sound apparatus  200   h  according to the eighth modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202 , and an internal frame  204   g.  Comparing with the sound apparatus  200  according to an aspect of the present disclosure, the sound apparatus  200   g  according to the eighth modification aspect of the present disclosure has a difference in that the internal frame  204   g  is provided instead of the internal frame  204  of the sound apparatus  200 , and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     The internal frame  204   g  may be disposed at an area of the middle-pitched sound band and may be configured so that a path of a sound generated by the sound generator  100  bypasses along the external frame  203  and is reverberated. According to a configuration illustrated in  FIG. 25 , a sound pressure level characteristic of a middle-pitched sound band and a sound pressure level characteristic of a low-pitched sound band may be enhanced. 
       FIG. 26  illustrates an internal structure of a sound apparatus  200   i  according to a ninth modification aspect where the sound generator  100  according to an aspect of the present disclosure is disposed. 
     With reference to  FIG. 26 , the sound apparatus  200   i  according to the ninth modification aspect of the present disclosure may include a sound generator  100  including a piezoelectric device, an elastic member  201 , an external frame  203  including an opening portion  202  and a port  205   a,  and an internal frame  204   g.  Comparing with the sound apparatus  200   h  according to the eighth modification aspect of the present disclosure, the sound apparatus  200   i  according to the ninth modification aspect of the present disclosure has only a difference in that the port  205   a  is provided at the external frame  203  of the sound apparatus  200   h,  and the other elements are the same. Therefore, repetitive descriptions of the same elements are omitted. 
     The port  205   a  may be configured to enhance a sound pressure level characteristic of a middle-pitched sound band and a sound pressure level characteristic of a low-pitched sound band. For example, the port  205   a  may be provided at the external frame  203  adjacent to the opening portion  203 . According to a configuration illustrated in  FIG. 26 , a sound pressure level characteristic of a middle-pitched sound band and a sound pressure level characteristic of a low-pitched sound band may be enhanced. 
     Moreover, in the configurations illustrated in  FIGS. 18 to 26 , a sound pressure level may be enhanced for each pitched sound band, and thus, the balance of each pitched sound band may be adjusted. As described above, an aspect and modification aspects of the present disclosure may implement a sound apparatus which may adjust noise, a harmonic distortion sound, and a sound pressure level difference between different sound bands and may enhance sound quality. 
     A sound generator and a sound apparatus according to the present disclosure will be described below. 
     A sound generator according to an aspect of the present disclosure may include a piezoelectric device, a high-pitched sound band generating portion provided at one end of the piezoelectric device in a long-side direction, a low-pitched sound band generating portion provided at the other end of the piezoelectric device in the long-side direction, a middle-pitched sound band generating portion provided between the high-pitched sound band generating portion and the low-pitched sound band generating portion, a first weight member provided at the high-pitched sound band generating portion, a second weight member provided at the low-pitched sound band generating portion, a first elastic member provided at the middle-pitched sound band generating portion, and a protection member which covers the piezoelectric device, the first weight member, the second weight member, and the firs elastic member. 
     According to some aspects of the present disclosure, the sound generator may further include a second elastic member provided at the low-pitched sound band generating portion. 
     According to some aspects of the present disclosure, the low-pitched sound band generating portion may be greater than each of the high-pitched sound band generating portion and the middle-pitched sound band generating portion. 
     A sound apparatus according to an aspect of the present disclosure may include a sound generator including a piezoelectric device, and an external frame which covers the sound generator and includes an opening portion and a plurality of first vibration plates, and the sound generator may be disposed at the opening portion. 
     According to some aspects of the present disclosure, the external frame may include a first portion generating a high-pitched sound band, a second portion generating a low-pitched sound band, and a third portion generating a middle-pitched sound band between the first portion and the second portion. 
     According to some aspects of the present disclosure, the opening portion may be disposed at the first portion. 
     According to some aspects of the present disclosure, the first vibration plate may be disposed at the third portion. 
     According to some aspects of the present disclosure, the sound generator may be disposed at the opening portion and the third portion. 
     According to some aspects of the present disclosure, the external frame may include a plurality of second vibration plates and may be disposed at the second portion. 
     The sound apparatus according to an aspect of the present disclosure may be a sound apparatus including a sound generator generating a sound on the basis of a vibration of a piezoelectric device having a rectangular shape, and the sound generator, including a high-pitched sound band generating portion including a weight member disposed at one end of a piezoelectric device in a long-side direction, a middle-pitched sound band generating portion fixed to two vibration plates through a first elastic member at a position closer to the one end of the piezoelectric device in the long-side direction than a center of the piezoelectric device in the long-side direction, a low-pitched sound band generating portion including a weight member disposed at the other end of the piezoelectric device in the long-side direction, and a protection member covering the piezoelectric device and covering the first elastic member or provided as one body with the first elastic member, may be surrounded by an external frame and two vibration plates. 
     According to some aspects of the present disclosure, the low-pitched sound band generating portion may be fixed to the two vibration plates through the second elastic member. 
     According to some aspects of the present disclosure, an internal frame may be disposed at an area surrounded by the external frame, and the internal frame may be configured so that at least one of a sound generated by the middle-pitched sound band generating portion and a sound generated by the low-pitched sound band generating portion is introduced into a space formed in a portion of a space surrounded by the external frame and the two vibration plates and reverberated. 
     A sound generator according to an aspect of the present disclosure may include a piezoelectric device, a first weight member disposed at a first portion of the piezoelectric device, a second weight member disposed at a second portion of the piezoelectric device, a first elastic member disposed at a third portion between the first portion and the second portion of the piezoelectric device, and a protection member configured to cover the piezoelectric device, the first weight member, the second weight member, and the first elastic member. 
     According to some aspects of the present disclosure, the piezoelectric device may generate sounds of different sound bands at the first to third portions, respectively. 
     According to some aspects of the present disclosure, the piezoelectric device may generate a high-pitched sound band at the first portion, generates a low-pitched sound band at the second portion, and may generate a middle-pitched sound band between the high-pitched sound band and the low-pitched sound band at the third portion. 
     According to some aspects of the present disclosure, the sound generator may further comprise a second elastic member disposed at the second portion of the piezoelectric device. 
     According to some aspects of the present disclosure, the second elastic member may comprise an elastic material which differs from a material of the first elastic member. 
     According to some aspects of the present disclosure, the second elastic member may comprise an elastic material having a lower density than a density of the first elastic member. 
     According to some aspects of the present disclosure, the second portion may have a size which is greater than a size of each of the first portion and the third portion. 
     According to some aspects of the present disclosure, the protection member may comprise an elastic material and wholly surround the piezoelectric device, the first weight member, the second weight member, and the first elastic member. 
     A sound apparatus according to an aspect of the present disclosure may comprise a sound generator including a piezoelectric device, and an external frame configured to cover the sound generator and configured to include an opening portion and a plurality of first vibration plates, the sound generator may be disposed at the opening portion. 
     According to some aspects of the present disclosure, the external frame may comprise a first portion generating a high-pitched sound band, a second portion generating a low-pitched sound band, and a third portion generating a middle-pitched sound band between the first portion and the second portion. 
     According to some aspects of the present disclosure, the opening portion may be disposed at the first portion. 
     According to some aspects of the present disclosure, the first vibration plate may be disposed at the third portion. 
     According to some aspects of the present disclosure, the sound generator may be disposed at the opening portion and the third portion. 
     According to some aspects of the present disclosure, the external frame may comprise the plurality of second vibration plates and is disposed at the second portion. 
     According to another aspect of the present disclosure, the sound generator may comprises a piezoelectric device, a first weight member disposed at a first portion of the piezoelectric device, a second weight member disposed at a second portion of the piezoelectric device, a first elastic member disposed at a third portion between the first portion and the second portion of the piezoelectric device, and a protection member configured to cover the piezoelectric device, the first weight member, the second weight member, and the first elastic member. 
     According to some aspects of the present disclosure, the third portion of the piezoelectric device may be configured to be fixed between two vibration plates through the first elastic member, and the sound generator may be configured to be surrounded by the external frame and the two vibration plates. 
     According to some aspects of the present disclosure, the second portion of the piezoelectric device may be configured to be fixed between the two vibration plates through a second elastic member. 
     According to some aspects of the present disclosure, the sound apparatus may further comprise an internal frame disposed at an area surrounded by the external frame, the internal frame may be configured so that at least one of a sound generated by the third portion of the external frame and a sound generated by the external frame is introduced into a space formed at a portion of a space surrounded by the external frame and the two vibration plates and reverberated. 
     According to some aspects of the present disclosure, the sound apparatus may further comprise a port provided in the external frame to communicate with a space surrounded by the external frame and the two vibration plates. 
     According to some aspects of the present disclosure, the sound apparatus may further comprise another port provided in the external frame adjacent to the opening portion to communicate with a space surrounded by the external frame and the two vibration plates. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the spirit or scope of the disclosures. Thus, it is intended that the present disclosure covers the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.