Patent Publication Number: US-2015086030-A1

Title: Electronic device and method for controlling the same

Description:
The present application is a bypass continuation of international patent application PCT Application No. PCT/JP2013/064481, filed on May 24, 2013, entitled 
     “ELECTRONIC DEVICE”, which claims the benefit of Japanese Application No. 2012-122044, filed on May 29, 2012, entitled “ELECTRONIC DEVICE”. The disclosure of each of the above is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate to electronic devices, and more particularly relate to electronic devices transmitting sound to a user. 
     BACKGROUND ART 
     Various technologies have been conventionally proposed for electronic devices. 
     SUMMARY 
     An electronic device and methods are disclosed. A cover panel is located on a front surface of the electronic device. A piezoelectric vibration module configured to vibrate the cover panel. A drive module configured to vibrate the piezoelectric vibration module based on a sound signal. A pressure intensity acquiring module configured to acquire pressure intensity information. The pressure intensity information indicates an intensity at which an ear of a user is pressed onto the cover panel. A sound quality controller configured to control a sound quality of the sound signal based on the pressure intensity information. 
     In one embodiment, a method for controlling an electronic device comprising a cover panel vibrates the cover panel based on a sound signal. The method then acquires pressure intensity information indicating a pressure intensity at which an ear of a user is pressed onto the cover panel and controls a sound quality of the sound signal based on the pressure intensity information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view showing an external appearance of an electronic device. 
         FIG. 2  illustrates a front view showing the external appearance of the electronic device. 
         FIG. 3  illustrates a rear view showing the external appearance of the electronic device. 
         FIG. 4  illustrates a block diagram mainly showing an electrical configuration of the electronic device. 
         FIG. 5  illustrates a top view showing a structure of a piezoelectric vibration element. 
         FIG. 6  illustrates a side view showing the structure of the piezoelectric vibration element. 
         FIG. 7  illustrates a view showing a state where the piezoelectric vibration element produces flexural vibrations. 
         FIG. 8  illustrates another view showing the state where the piezoelectric vibration element produces flexural vibrations. 
         FIG. 9  illustrates a view showing a vertical cross-sectional structure of the electronic device. 
         FIG. 10  illustrates a plan view showing a cover panel viewed from an inner main surface side thereof. 
         FIG. 11  illustrates a view for describing air conducted sound and conduction sound. 
         FIG. 12  illustrates a block diagram showing a partial configuration of the electronic device. 
         FIG. 13  illustrates a diagram showing exemplary frequency characteristics of a sound signal after sound quality control. 
         FIG. 14  illustrates a flowchart showing operations of the electronic device. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     &lt;External Appearance of Electronic Device&gt; 
       FIGS. 1 to 3  illustrate a perspective view, a front view, and a rear view showing an external appearance of an electronic device  1  according to an embodiment, respectively. The electronic device  1  according to this embodiment is, for example, a mobile phone. As shown in  FIGS. 1 to 3 , the electronic device  1  comprises a cover panel  2  and a case part  3 . The cover panel  2  and the case part  3  are combined to constitute a device case  4  having a plate shape substantially rectangular in plan view. 
     The cover panel  2  has a substantially rectangular shape in plan view. The cover panel  2  forms a part in a front part of the electronic device  1  other than a peripheral part thereof. The cover panel  2  is formed of, for example, a transparent glass or a transparent acrylic resin. The case part  3  forms the peripheral part of the front part, a lateral part, and a rear part of the electronic device  1 . The case part  3  is formed of, for example, a polycarbonate resin. 
     The cover panel  2  is provided with a display part  2   a  on which various types of information such as characters, symbols, and diagrams are displayed. The display part  2   a  has, for example, a rectangular shape in plan view. A peripheral part  2   b  that surrounds the display part  2   a  in the cover panel  2  is black through, for example, application of a film. The peripheral part  2   b  accordingly serves as a non-display part on which no information is displayed. Attached to an inner main surface of the cover panel  2  comprises a touch panel  130 , which will be described below. The user can provide various instructions to the electronic device  1  by manipulating the display part  2   a  of the cover panel  2  with, for example, his/her finger. 
     A manipulation module  140  may be provided inside the device case  4 . The manipulation module  140  comprises a plurality of manipulation buttons  141 . Each manipulation button  141  is a so-called “hard key,” and the surface thereof is exposed from a lower-side end portion of an outer main surface  20  of the cover panel  2 . Made in the lower-side end portion of the cover panel  2  is a microphone hole  30 . Visible from an upper-side end portion of the outer main surface  20  of the cover panel  2  is an imaging lens  150   a  of a front-side imaging module  150 , which will be described below. Although three manipulation buttons  141  being “hard keys” are provided in the electronic device  1  according to this embodiment, the number of the manipulation buttons  141  may be appropriately changed. Alternatively, no manipulation button  141  may be provided. 
     As shown in  FIG. 2 , a piezoelectric vibration element  191  is provided inside the device case  4 . As shown in  FIG. 3 , speaker holes  40  are made in a rear surface  10  of the electronic device  1 , namely, in a rear surface of the device case  4 . Visible from the rear surface  10  of the electronic device  1  is an imaging lens  160   a  of a rear-side imaging module  160 , which will be described below. 
     &lt;Electrical Configuration of Electronic Device&gt; 
       FIG. 4  illustrates a block diagram mainly showing an electrical configuration of the electronic device  1 . The electronic device  1  comprise a controller  100 , a wireless communication module  110 , a display panel  120 , the touch panel  130 , the manipulation module  140 , the front-side imaging module  150 , and the rear-side imaging module  160 . The electronic device  1  further comprises a receiver  190  configured with the piezoelectric vibration element  191  and the cover panel  2 , a microphone  180 , an external speaker  200 , and a battery  170 . These components of the electronic device  1  except for the cover panel  2  are housed in the device case  4 . 
     The controller  100  can control other components of the electronic device  1  to collectively manage the operation of the electronic device  1 . The controller  100  mainly comprises a CPU (central processing unit)  101 , a DSP (digital signal processor)  102 , and a storage module  103 . 
     The storage module  103  is configured with a non-transitory recording medium that can be read by the controller  100  (CPU  101  and DSP  102 ), such as a ROM (read only memory) and a RAM (random access memory). The storage module  103  can store a main program being a control program for controlling the operation of the electronic device  1 , specifically, the components such as the wireless communication module  110  and the display panel  120  included in the electronic device  1 , a plurality of application programs, and the like. The various functions of the controller  100  can be implemented by the CPU  101  and the DSP  102  executing the various programs in the storage module  103 . 
     The storage module  103  may include a computer-readable, non-transitory recording medium, except for the ROM and RAM. The storage module  103  may include, for example, a small hard disk drive, a small SSD (solid state drive), and the like. 
     The wireless communication module  110  can receive, through an antenna  111 , a signal from a mobile phone different from the electronic device  1  or a communication device such as a web server connected to the Internet via a base station. The wireless communication module  110  can perform amplification processing and down-conversion processing on the received signal and then outputs a resultant signal to the controller  100 . The controller  100  can perform modulation processing or other processing on a received signal that has been input, to thereby obtain, for example, a sound signal indicative of voice or music comprised in the received signal. Also, the wireless communication module  110  performs up-conversion processing and amplification processing on a transmission signal including the sound signal or the like that has been generated by the controller  100 , to thereby wirelessly transmit the processed transmission signal from the antenna  111 . The transmission signal from the antenna  111  is received, via the base station, by a mobile phone different from the electronic device  1  or a communication device connected to the Internet. 
     The display panel  120  comprises, for example, a liquid crystal display panel or an organic EL panel. The display panel  120  can display various types of information such as characters, symbols, and graphics under control of the controller  100 . The information, which is to be displayed on the display panel  120 , is displayed in the display part  2   a  of the cover panel  2  to be visible to the user of the electronic device  1 . 
     The touch panel  130  comprises, for example, a projected capacitive type touch panel. The touch panel  130  can detect the contact of an object with the display part  2   a  of the cover panel  2 . The touch panel  130  may be bonded to the inner main surface of the cover panel  2  and comprises two sheet-like electrode sensors disposed to face each other. The two electrode sensors are bonded together with a transparent adhesive sheet. 
     Formed in one of the electrode sensors are a plurality of elongated X electrodes that extend in the X-axis direction (for example, the horizontal direction of the electronic device  1 ) and are disposed parallel to one another. Formed in the other electrode sensor are a plurality of elongated Y electrodes that extend in the Y-axis direction (for example, the vertical direction of the electronic device  1 ) and are disposed parallel to one another. When the user&#39;s finger or the like comes into contact with the display part  2   a  of the cover panel  2 , a capacitance between the X electrode and the Y electrode located below the contact portion changes, so that the touch panel  130  detects the manipulation on (contact with) the display part  2   a  of the cover panel  2 . A change in the capacitance between the 
     X electrode and the Y electrode, which occurs in the touch panel  130 , is transmitted to the controller  100 . The controller  100  identifies, based on the capacitance change, the description of the manipulation made on the display part  2   a  of the cover panel  2 , and performs the operation corresponding to the identified description. 
     For each of the plurality of manipulation buttons  141 , when the user presses a manipulation button  141 , the manipulation module  140  outputs to the controller  100  a manipulation signal indicating that the manipulation button  141  has been pressed. The controller  100  identifies, based on the input manipulation signal, which manipulation button  141  of the plurality of manipulation buttons  141  has been manipulated and then performs the operation corresponding to the manipulation button  141  that has been manipulated. 
     The front-side imaging module  150  is configured with the imaging lens  150   a , an imaging element, and the like. The front-side imaging module  150  takes a still image and a moving image under the control of the controller  100 . As shown in  FIGS. 1 and 2 , the imaging lens  150   a  is provided on the front surface of the electronic device  1 . This allows the front-side imaging module  150  to take an image of the object located on the front side (cover panel  2  side) of the electronic device  1 . 
     The rear-side imaging module  160  comprises the imaging lens  160   a,  an imaging element, and the like. The rear-side imaging module  160  can take a still image and a moving image under the control of the controller  100 . As shown in  FIG. 3 , the imaging lens  160   a  is provided on the rear surface  10  of the electronic device  1 . The rear-side imaging module  160  can take an image of the object located on the rear surface  10  side of the electronic device  1 . 
     The microphone  180  can convert the sound input from the outside of the electronic device  1  into an electrical sound signal and then can output the electrical sound signal to the controller  100 . The sound from the outside of the electronic device  1  is taken inside the electronic device  1  through the microphone hole  30 , and the sound from the outside is input to the microphone  180 . The microphone hole  30  may be provided in the lateral surface of the electronic device  1  or may be provided in the rear surface  10 . 
     The external speaker  200  comprises, for example, a dynamic speaker (an electromagnetic speaker), and can convert an electrical sound signal from the controller  100  into sound and then outputs the sound. The sound output from the external speaker  200  is output to the outside through the speaker holes  40 . The user can hear the sound output through the speaker holes  40  in the place apart from the electronic device  1 . 
     The receiver  190  can transmit received sound to the user and comprises the piezoelectric vibration element  191  and the cover panel  2 . The receiver  190  can output sound with a volume lower than that of the external speaker  200 . The receiver  190  can output the sound high enough for the user to hear when the user brings his/her ear near or into contact with the cover panel  2 . The piezoelectric vibration element  191  is provided on the inner main surface of the cover panel  2  and is vibrated upon application of the drive voltage applied from the controller  100 . The controller  100  generates a drive voltage based on a sound signal, and then applies the drive voltage to the piezoelectric vibration element  191 . The piezoelectric vibration element  191  is vibrated based on a sound signal by the controller  100 , whereby the cover panel  2  vibrates based on the sound signal, transmitting the received sound to the user. 
     The battery  170  can output a power supply for the electronic device  1 . The power supply output from the battery  170  is supplied to the electronic components included in the controller  100 , the wireless communication module  110 , and the like of the electronic device  1 . 
     &lt;Details of Piezoelectric Vibration Element&gt; 
       FIGS. 5 and 6  illustrate a top view and a side view showing the structure of the piezoelectric vibration element  191 , respectively. As shown in  FIGS. 5 and 6 , the piezoelectric vibration element  191  is long in one direction. The piezoelectric vibration element  191  has an elongated plate shape rectangular in plan view. The piezoelectric vibration element  191  has, for example, a bimorph structure. The piezoelectric vibration element  191  comprises a first piezoelectric ceramic plate  191   a  and a second piezoelectric ceramic plate  191   b  bonded to each other with a shim material  191   c  therebetween. 
     In the piezoelectric vibration element  191 , a positive voltage is applied to the first piezoelectric ceramic plate  191   a  and a negative voltage is applied to the second piezoelectric ceramic plate  191   b,  so that the first piezoelectric ceramic plate  191   a  expands in the long-side direction and the second piezoelectric ceramic plate  191   b  contracts in the long-side direction. This causes, as shown in  FIG. 7 , the piezoelectric vibration element  191  to flex toward the first piezoelectric ceramic plate  191   a  in a convex manner. 
     In the piezoelectric vibration element  191 , meanwhile, a negative voltage is applied to the first piezoelectric ceramic plate  191   a  and a positive voltage is applied to the second piezoelectric ceramic plate  191   b,  so that the first piezoelectric ceramic plate  191   a  contracts in the long-side direction and the second piezoelectric ceramic plate  191   b  expands in the long-side direction. This causes, as shown in  FIG. 8 , the piezoelectric vibration element  191  to flex toward the second piezoelectric ceramic plate  191   b  in a convex manner. 
     The piezoelectric vibration element  191  alternately enters the state of  FIG. 7  and the state of  FIG. 8 , to thereby produce flexural vibrations. The controller  100  causes an AC voltage, which alternates between positive and negative voltages, to be applied between the first piezoelectric ceramic plate  191   a  and the second piezoelectric ceramic plate  191   b,  causing the piezoelectric vibration element  191  to produce flexural vibrations. 
     While the piezoelectric vibration element  191  shown in  FIGS. 5 to 8  is provided with a single structure configured with the first piezoelectric ceramic plate  191   a  and the second piezoelectric ceramic plate  191   b  that are bonded with the shim material  191   c  sandwiched therebetween, a plurality of the above-mentioned structures may be laminated. 
     &lt;Position at which Piezoelectric Vibration Element is Disposed&gt; 
       FIG. 9  illustrates a view showing the cross-sectional structure in the vertical direction (long-side direction) of the electronic device  1 .  FIG. 10  illustrates a plan view of the cover panel  2  when viewed from its inner main surface  21  side thereof. 
     As shown in  FIGS. 9 and 10 , the touch panel  130  is bonded to the inner main surface  21  of the cover panel  2 . The touch panel  130  faces the display part  2   a  of the cover panel  2 . The display panel  120  is disposed to face the cover panel  2  and the touch panel  130 . The touch panel  130  is thus located between the cover panel  2  and the display panel  120 . The part of the cover panel  2 , which faces the display panel  120 , serves as the display part  2   a.    
     A printed circuit board  250  is provided inside the device case  4 . Various components such as the CPU  101  and the DSP  102  are mounted on the printed circuit board  250 . The printed circuit board  250  is disposed to face the display panel  120  on the side closer to the rear surface  10  than the display panel  120 . As shown in  FIG. 10 , a plurality of holes  22  for respectively exposing the plurality of manipulation buttons  141  are made in the lower-side end portion of the cover panel  2 . 
     The piezoelectric vibration element  191  is bonded to the inner main surface  21  of the cover panel  2  with an adhesive  260  such as a double-sided tape. The piezoelectric vibration element  191  is disposed, on the inner main surface  21  of the cover panel  2 , at a position at which the piezoelectric vibration element  191  does not overlap the display panel  120  and the touch panel  130  in plan view of the cover panel  2  viewed from the inner main surface  21  side. In other words, when the cover panel  2  is viewed from the inner main surface  21  side in the thickness direction of the cover panel  2 , the piezoelectric vibration element  191  is disposed, on the inner main surface  21 , at a position at which the piezoelectric vibration element  191  does not overlap the display panel  120  and the touch panel  130 . Therefore, the touch panel  130  and the display panel  120  are not located between the cover panel  2  and the piezoelectric vibration element  191 . 
     The piezoelectric vibration element  191  is provided on the upper-side end portion  21   a  of the inner main surface  21  of the cover panel  2 . To be specific, as shown in  FIG. 10 , the piezoelectric vibration element  191  is provided on a center portion  21  aa in the horizontal direction (the short-side direction perpendicular to the long-side direction) at the upper-side end portion  21   a  of the inner main surface  21  of the cover panel  2 . 
     The piezoelectric vibration element  191  is disposed such that its long-side direction coincides with the horizontal direction of the cover panel  2 . The piezoelectric vibration element  191  is disposed at the center portion  21   aa  of the upper-side end portion  21   a  of the inner main surface  21  of the cover panel  2  such that the center in the long-side direction thereof coincides with the center in the horizontal direction at the upper-side end portion  21   a.    
     As shown in  FIGS. 7 and 8  described above, the piezoelectric vibration element  191  that produces flexural vibrations has the largest displacement amount at the center in the long-side direction thereof. Thus, disposing the piezoelectric vibration element  191  at the upper-side end portion  21   a  such that the center in the long-side direction thereof coincides with the center in the horizontal direction at the upper-side end portion  21   a  of the inner main surface  21  of the cover panel  2  allows the part of the piezoelectric vibration element  191 , which has the largest displacement amount of flexural vibrations, to coincide with the center in the horizontal direction at the upper-side end portion  21   a  of the inner main surface  21  of the cover panel  2 . 
     In the case where the touch panel  130  is located over the entire inner main surface  21  of the cover panel  2 , the piezoelectric vibration element  191  may be disposed on the inner main surface  21  of the cover panel  2  with the touch panel  130  therebetween. 
     While a clearance is provided between the touch panel  130  and the display panel  120  in the above-mentioned example as shown in  FIG. 9 , the touch panel  130  and the display panel  120  may be brought into contact with each other. A clearance, provided between the touch panel  130  and the display panel  120  as in this embodiment, can prevent the cover panel  2  from hitting the display panel  120  (more accurately, the touch panel  130  from hitting the display panel  120 ) even if the cover panel  2  flexes toward the display panel  120  by being pressed by the user with, for example, his/her finger. This prevents a display of the display panel  120  from being disturbed by the cover panel  2  hitting the display panel  120 . 
     &lt;Generation of Received Sound by Receiver&gt; 
     In the receiver  190  according to this embodiment, the piezoelectric vibration element  191  causes the cover panel  2  to vibrate, so that air conducted sound and conduction sound are transmitted to the user from the cover panel  2 . In other words, the vibrations of the piezoelectric vibration element  191  itself are transmitted to the cover panel  2 , allowing for the transmission of air conducted sound and conduction sound to the user from the cover panel  2 . 
     Herein, the air conducted sound is the sound recognized by the human brain when a sound wave (air vibrations), which has entered the external auditory meatus (so-called “earhole”), causes the eardrum to vibrate. Meanwhile, the conduction sound is the sound recognized by the human brain when the auricle is vibrated. The air conducted sound and conduction sound will now be described in detail. 
       FIG. 11  is a view for describing the air conducted sound and conduction sound.  FIG. 11  shows the structure of ear of the user of the electronic device  1 . In  FIG. 11 , a dashed line  400  indicates a conductive path of a sound signal (sound information) when the air conducted sound is recognized by the brain, and a solid line  410  indicates a conductive path of a sound signal when the conduction sound is recognized by the brain. 
     When the piezoelectric vibration element  191  mounted on the cover panel  2  is vibrated based on an electrical sound signal indicative of received sound, the cover panel  2  vibrates, whereby a sound wave is output from the cover panel  2 . When the user has the electronic device  1  in his/her hand and brings the cover panel  2  of the electronic device  1  near an auricle  300  of the user or presses the cover panel  2  of the electronic device  1  onto (brings the cover panel  2  of the electronic device  1  into contact with) the auricle  300  of the user, the sound wave output from the cover panel  2  enters an external auditory meatus  310 . The sound wave from the cover panel  2  travels through the external auditory meatus  310  and causes an eardrum  320  to vibrate. The vibrations of the eardrum  320  are transmitted to an auditory ossicle  330 , causing the auditory ossicle  330  to vibrate. Then, the vibrations of the auditory ossicle  330  are transmitted to a cochlea  340  and are then converted into an electrical signal in the cochlea  340 . The electrical signal is transmitted to the brain through an auditory nerve  350 , so that the brain recognizes the received sound. In this manner, the air conducted sound is transmitted from the cover panel  2  to the user. 
     When the user has the electronic device  1  in his/her hand and presses the cover panel  2  of the electronic device  1  onto the auricle  300  of the user, the auricle  300  is vibrated by the cover panel  2  vibrated by the piezoelectric vibration element  191 . As indicated by the solid line  410 , the vibrations of the auricle  300  are transmitted to the eardrum  320 , causing the eardrum  320  to vibrate. The vibrations of the eardrum  320  are transmitted to the auditory ossicle  330 , causing the auditory ossicle  330  to vibrate. The vibrations of the auditory ossicle  330  are then transmitted to the cochlea  340  and are then converted into an electrical signal in the cochlea  340 . Differently from the transmission through the conductive path indicated by the solid line  410 , in some cases, the vibrations of the auricle  300  are transmitted directly to the cochlea  340  without being transmitted to the eardrum  320 , and the vibrations are converted into an electrical signal in the cochlea  340 . The electrical signal obtained in the cochlea  340  is transmitted to the brain through the auditory nerve  350 , whereby the brain recognizes the received sound. In this manner, the conduction sound is transmitted from the cover panel  2  to the user.  FIG. 11  also shows an auricular cartilage  300   a  inside the auricle  300 . 
     The conduction sound described herein differs from bone-conducted sound (also referred to as “bone conduction sound”). The bone-conducted sound is the sound recognized by the human brain when the skull is vibrated and the vibrations of the skull directly stimulate the inner ear such as the cochlea. In  FIG. 11 , showing the case in which, for example, a mandibular bone  500  is vibrated, a plurality of arcs  420  indicate a transmission path of a sound signal when the bone conduction sound is recognized by the brain. 
     As described above, in the electronic device  1  according to this embodiment, the piezoelectric vibration element  191  appropriately vibrates the cover panel  2  on the front surface, so that the air conducted sound and conduction sound can be transmitted from the cover panel  2  to the user of the electronic device  1 . The structure of the piezoelectric vibration element  191  according to this embodiment is contrived to appropriately transmit the air conducted sound and conduction sound to the user. Various advantages can be achieved by configuring the electronic device  1  to transmit the air conducted sound and conduction sound to the user. 
     For example, the user can hear the sound by placing the cover panel  2  to his/her ear, and thus can have a telephone conversation without much consideration of the position where the user places his/her ear to the electronic device  1 . 
     For large ambient noise, the user can make it difficult to hear the ambient noise by pressing his/her ear strongly onto the cover panel  2  while turning up the volume of the conduction sound. This enables the user to appropriately have a telephone conversation even if the ambient noise is large. 
     Even while wearing earplugs or earphones in his/her ears, the user can recognize the received sound from the electronic device  1  by placing the cover panel  2  to his/her ear (more specifically, auricle). Alternatively, even while wearing headphones in his/her ears, the user can recognize the received sound from the electronic device  1  by placing the cover panel  2  to the headphones. 
     As described above, in the receiver  190  according to this embodiment, the piezoelectric vibration element  191  vibrated based on a sound signal vibrates the cover panel  2 , transmitting the sound to the user. This eliminates the need for providing a receiver hole (earpiece hole) to the cover panel  2 , unlike the case in which a dynamic speaker is used for the receiver  190 . 
     &lt;Sound Quality Control of Received Sound&gt; 
     As described above, in the receiver  190 , the piezoelectric vibration element  191  vibrates the cover panel  2 , causing the sound transmission from the cover panel  2  to the user. For this reason, compared with the sound output from, for example, the dynamic speaker used in the external speaker  200 , the sound transmitted from the receiver  190  to the user tends to have a minimum resonance frequency f 0  located at a high frequency side, resulting in that the level (sound pressure) of low frequency components tends to be low. The above-mentioned tendency holds true for the piezoelectric speaker as well. 
     Meanwhile, for the conduction sound transmitted from the cover panel  2  of the receiver  190  to the user, the low frequency components tend to be more easily transmitted to the user than high frequency components, compared with the air conducted sound transmitted from the cover panel  2  to the user. When the user presses his/her ear strongly onto the cover panel  2 , the volume of the conduction sound increases, and the minimum resonance frequency f 0  of the sound transmitted from the cover panel  2  to the user moves toward lower frequencies. This may result in that the level of low frequency components will become higher. For the sound transmitted from the cover panel  2  to the user, thus, the low frequency components tend to be more easily transmitted to the user in the case where the user strongly presses his/her ear onto the cover panel  2  than in the case where the user weakly presses his/her ear onto the cover panel  2 . 
     As described above, the sound transmitted from the receiver  190  to the user tends to have a lower level of low frequency components than the sound transmitted from a dynamic speaker, while low frequency components tend to be easily transmitted to the user when the user strongly presses his/her ear onto the cover panel  2 . 
     In the electronic device  1  according to this embodiment, therefore, the sound quality of the sound transmitted from the receiver  190  to the user is controlled based on the intensity of pressing the user&#39;s ear onto the cover panel  2  (intensity at which the user presses his/her ear onto the cover panel  2 ), to thereby improve the sound quality of the sound transmitted from the receiver  190  to the user. The sound quality control in the electronic device  1  will now be described in detail. In the following description, mere “pressure intensity” refers to the intensity of pressing the user&#39;s ear onto the cover panel  2 . 
       FIG. 12  illustrates a block diagram mainly showing the configuration for sound quality control in the electronic device  1 . As shown in  FIG. 12 , the electronic device  1  comprises a pressure intensity acquiring module  800 , a sound quality control module  810 , a volume control module  820 , and a drive module  830 . A drive module  800  can vibrate the piezoelectric vibration element  191 . 
     The pressure intensity acquiring module  800  can acquire the pressure intensity information. The pressure intensity indicates pressure intensity. The pressure intensity acquiring module  800  comprises the touch panel  130  and a contact area calculating module  801 . The contact area calculating module  801  may be a functional block to be formed in the controller  100 . The contact area calculating module  801  can calculate the contact area of the user&#39;s ear with the cover panel  2 . The contact area calculating module  801  can calculate the contact area based on the output signal from the touch panel  130 . The contact area increases with an increasing pressure intensity, and thus, it can be said that the contact area indicates pressure intensity. The contact area calculating module  801  outputs the determined contact area to the sound quality control module  810  as pressure intensity information. Hereinafter, mere “contact area” refers to the contact area of the user&#39;s ear with the cover panel  2 . 
     The sound quality control module  810  can control the sound quality of a sound signal SS. The sound signal SS is used in controlling the vibrations of the piezoelectric vibration element  191  by the drive module  830 . The sound quality control module  810  can control the sound quality of a sound signal SS based on the pressure intensity information acquired in the pressure intensity acquiring module  800 . The sound quality control module  810  comprises an equalizer  811  and a to-be-used parameter determining module  812 . 
     The equalizer  811  can control the sound quality of the sound signal SS by controlling the frequency characteristics of the sound signal SS. The equalizer  811  can control the frequency characteristics based on a control parameter  840  stored in the storage module  103 . The frequency characteristics represent a signal level at each frequency. The to-be-used parameter determining module  812  can determine a control parameter  840  to be used by the equalizer  811 . The equalizer  811  is provided in the controller  100 . The to-be-used parameter determining module  812  may be a function block to be formed in the controller  100 . 
     The storage module  103  can store a plurality of types of control parameters  840 . The plurality of types of control parameters  840  have frequency characteristics of the sound signal SS different from one another, which are acquired by being controlled by the equalizer  811  based on a control parameter  840 . In other words, a plurality of types of control parameters  840  have sound qualities of the sound signal SS different from one another, which are acquired by being controlled by the equalizer  811  based on a control parameter  840 . The sound quality control module  810  can thus change the frequency characteristics of the sound signal SS to a plurality of types of frequency characteristics depending on a control parameter  840  to be used. The to-be-used parameter determining module  812  determines, based on the pressure intensity information acquired by the pressure intensity acquiring module  800 , a control parameter  840  to be used by the equalizer  811  from the plurality of types of control parameters  840  stored in the storage module  103 . The equalizer  811  controls the frequency characteristics of the sound signal SS based on the control parameter  840  determined to be used based on the pressure intensity information by the to-be-used parameter determining module  812 . In other words, the equalizer  811  controls the sound quality of the sound signal SS based on the control parameter  840 , whose use has been determined based on the pressure intensity information by the to-be-used parameter determining module  812 . The sound signal SS whose frequency characteristics have been controlled by the sound quality control module  810  is input to the volume control module  820 . 
     The volume control module  820  may be a functional block to be formed in the controller  100 . The volume control module  820  can control the volume of the sound signal SS whose sound quality has been controlled, based on a volume setting instruction from the user. For example, when the user manipulates the display part  2   a  and instructs the electronic device  1  to turn up the current volume of the sound from the receiver  190 , the volume control module  820  increases the signal level of the sound signal SS after the sound quality control, thereby turning up the volume of this sound signal SS. The sound signal SS whose sound quality and volume have been controlled is input to the drive module  830 . 
     The drive module  830  can vibrate the piezoelectric vibration element  191  of the receiver  190  based on the sound signal SS whose sound quality and volume have been controlled. This causes the cover panel  2  to vibrate based on the sound signal SS whose sound quality and volume have been controlled, so that the sound having desired frequency characteristics is transmitted from the cover panel  2  to the user. 
     The electronic device  1  according to this embodiment is configured such that the sound quality control module  810  increases the signal level of low frequency components comprised in the sound signal SS as the pressure intensity indicated by the pressure intensity information is lower. 
     In this embodiment, for example, in the case where the contact area is greater than a threshold (&gt;0), the frequency characteristics of the sound signal SS are controlled so as to obtain first frequency characteristics whose signal level is flat at the entire frequency band for the signal components comprised in the sound signal SS. 
     In the case where the contract area is greater than zero and not greater than the threshold, the frequency characteristics of the sound signal SS are controlled so as to obtain second frequency characteristics having a signal level of low frequency components that is higher than that of the first frequency characteristics. 
     In the case where the contact area is zero, as in the case where the user listens to the sound from the cover panel  2  without his/her ear being in contact with the cover panel  2 , the frequency characteristics of the sound signal SS are controlled so as to obtain third frequency characteristics having a signal level of low frequency components that is higher than that of the second frequency characteristics. 
       FIG. 13  illustrates a diagram showing exemplary first frequency characteristics FR 1 , second frequency characteristics FR 2 , and third frequency characteristics FR 3 . In this embodiment, the sound signal SS comprises signal components at audio frequency bands (20 Hz to 20 kHz). The first frequency characteristics FR 1  shown in  FIG. 13  have a flat (identical) signal level at all the frequency bands (20 Hz to 20 kHz) of the signal components comprised in the sound signal SS. The second frequency characteristics FR 2  shown in  FIG. 13  have signal levels higher than the first frequency characteristics FR 1  at all the frequency bands of the signal components comprised in the sound signal SS. Additionally, the second frequency characteristics FR 2  have higher signal levels at lower frequencies. The third frequency characteristics FR 3  shown in  FIG. 13  have signal levels higher than the second frequency characteristics FR 2  at all the frequency bands of the signal components comprised in the sound signal SS. Additionally, the third frequency characteristics FR 3  have higher signal levels at lower frequencies. 
     In the example of  FIG. 13 , the second frequency characteristics FR 2  have higher signal levels than the first frequency characteristics FR 1  at all the frequency bands of the signal components comprised in the sound signal SS. Alternatively, only the signal levels of the low frequency components may be higher than those of the first frequency characteristics FR 1 . For example, for the second frequency characteristics FR 2 , only the signal levels in the range from 20 Hz to the first third of the range from 20 Hz to 20 kHz (range from 20 Hz to 6.68 kHz) may be higher than those of the first frequency characteristics FR 1 . Similarly, for the third frequency characteristics FR 3 , only the signal levels of low frequency components may be higher than those of the second frequency characteristics FR 2 . 
     The storage module  103  stores a control parameter  840  corresponding to the first frequency characteristics FR 1  (hereinafter, referred to as “first control parameter  840 ”), a control parameter  840  corresponding to the second frequency characteristics FR 2  (hereinafter, referred to as “second control parameter  840 ”), and a control parameter  840  corresponding to the third frequency characteristics FR 3  (hereinafter, referred to as “third control parameter  840 ”). In the sound quality control module  810 , the to-be-used parameter determining module  812  reads the first control parameter  840  from the storage module  103  and then inputs the first control parameter  840  to the equalizer  811  in the case where the pressure intensity information acquired by the pressure intensity acquiring module  800 , namely, the contact area is greater than the threshold. The equalizer  811  controls the frequency characteristics (sound quality) of the sound signal SS based on the input first control parameter  840 . As a result, the controlled frequency characteristics for the sound signal SS turn into the first frequency characteristics FR 1 . 
     The to-be-used parameter determining module  812  reads the second control parameter  840  from the storage module  103  and then inputs the second control parameter  840  to the equalizer  811  in the case where the pressure intensity information acquired by the pressure intensity acquiring module  800 , namely, the contact area is greater than zero and is not greater than the threshold. The equalizer  811  controls the frequency characteristics (sound quality) of the sound signal SS based on the input second control parameter  840 . As a result, the controlled frequency characteristics for the sound signal SS turn into the second frequency characteristics FR 2 . 
     The to-be-used parameter determining module  812  reads the third control parameter  840  from the storage module  103  and then inputs the third control parameter  840  to the equalizer  811  in the case where the pressure intensity information acquired by the pressure intensity acquiring module  800 , namely, the contact area is zero. The equalizer  811  controls the frequency characteristics (sound quality) of the sound signal SS based on the input third control parameter  840 . As a result, the controlled frequency characteristics for the sound signal SS turn into the third frequency characteristics FR 3 . 
     In this embodiment, as described above, the signal levels of the low frequency components comprised in the sound signal SS become higher as the contact area is smaller, that is, the pressure intensity indicated by the pressure intensity information is lower. As described above, for the sound transmitted from the cover panel  2  of the receiver  190  to the user, the level of the low frequency components tends to be low compared with the sound transmitted from the dynamic speaker, while the low frequency components are tend to be easily transmitted to the user when the user strongly presses his/her ear onto the cover panel  2 . Thus, the levels of the low frequency components comprised in the sound signal SS to be used in controlling the vibrations of the cover panel  2  are increased as the pressure intensities indicated by the pressure intensity information become lower, so that the sound with a desired sound quality can be transmitted from the cover panel  2  to the user even if the user does not strongly press his/her ear onto the cover panel  2 . In other words, the signal levels of the low frequency components comprised in the sound signal SS to be used in controlling the vibrations of the cover panel  2  are reduced as the pressure intensities indicated by the pressure intensity information become higher, so that the sound with a desired sound quality can be transmitted from the cover panel  2  to the user irrespective of an intensity at which the user presses his/her ear onto the cover panel  2 . In this example, the desired frequency characteristics for the sound transmitted to the user are the frequency characteristics whose level is flat at all the frequency bands. This allows the sound having frequency characteristics whose level is flat at all the frequency bands to be transmitted from the cover panel  2  to the user by controlling the sound quality of the sound signal SS based on the pressure intensity information, irrespective of the intensity at which the user presses his/her ear onto the cover panel  2 . 
     Description will now be given of a series of operations of the electronic device  1  when the sound quality of the sound signal SS is controlled based on the pressure intensity information, and then the piezoelectric vibration element  191  is vibrated based on the sound signal SS having the controlled sound quality so that the sound from the cover panel  2  is transmitted to the user.  FIG. 14  is a flowchart showing the series of operations.  FIG. 14  shows the operations of the electronic device  1  when the electronic device  1  has a voice conversation with a communication partner device. 
     As shown in  FIG. 14 , in Step s 1 , the electronic device  1  starts a voice conversation with the communication partner device when the user manipulates a conversation button displayed on the display part  2   a  of the cover panel  2 . Upon start of the voice conversation by the electronic device  1 , the user brings or presses his/her ear near or onto the cover panel  2  to listen to the sound from the cover panel  2 . 
     After the electronic device  1  starts a conversation, in Step s 2 , in the pressure intensity acquiring module  800 , the contact area calculating module  801  determines the contact area of the user&#39;s ear with the cover panel  2  based on the output signal from the touch panel  130 , and then, outputs the resultant as pressure intensity information. If the user merely brings his/her ear near the cover panel  2  and does not bring his/her ear into contact with the cover panel  2 , the contact area is zero, that is, the pressure intensity is zero. 
     Then, in Step s 3 , in the sound quality control module  810 , the to-be-used parameter determining module  812  determines a control parameter  840  to be used by the equalizer  811  based on the pressure intensity information (contact area) acquired in Step s 2  as described above. 
     Then, in Step s 4 , the equalizer  811  controls the frequency characteristics of the sound signal SS based on the control parameter  840  whose use has been determined by the to-be-used parameter determining module  812 , thereby controlling the sound quality of the sound signal SS. 
     Then, in Step s 5 , the volume control module  820  controls the volume of the sound signal SS whose sound quality has been controlled, based on the current volume setting value. After that, in Step s 6 , the drive module  830  vibrates the piezoelectric vibration element  191  based on the sound signal SS whose sound quality and volume have been controlled. This allows the transmission of the sound having desired frequency characteristics, in this example, frequency characteristics whose level is flat at all the frequency bands, from the cover panel  2  to the user. 
     While the electronic device  1  is in a voice conversation, the processes of Steps s 2  to s 6  described above are repeated regularly or irregularly. As a result, even if the pressure intensity varies while the electronic device  1  is in a voice conversation, the sound quality of the sound signal SS can be controlled appropriately. 
     In the example above, the sound quality of the sound signal SS to be used in controlling the vibrations of the cover panel  2  is controlled such that the frequency characteristics of the sound transmitted from the cover panel  2  to the user turn into the frequency characteristics whose level is flat at all the frequency bands. Alternatively, the sound quality of the sound signal SS may be controlled so as to have other frequency characteristics. 
     As described above, in this embodiment, the sound quality of the sound signal SS to be used in controlling the vibrations of the cover panel  2  is controlled based on the pressure intensity information indicating pressure intensity, allowing the transmission of the sound with a desired sound quality from the cover panel  2  to the user irrespective of pressure intensity. Therefore, the sound quality of the sound transmitted from the electronic device  1  to the user is improved. 
     &lt;Modifications&gt; 
     Although the storage module  103  stores the first control parameter  840  to the third control parameter  840  in the example above, the storage module  103  may store only the third control parameter  840  thereamong. In this case, for a contact area greater than zero and not greater than a threshold, the to-be-used parameter determining module  812  changes the third control parameter  840  to generate a control parameter  840  corresponding to the second control parameter  840 , and then inputs the resultant to the equalizer  811  as the control parameter  840  to be used. Then, for a contact area of zero, the to-be-used parameter determining module  812  changes the third control parameter  840  to generate a control parameter  840  corresponding to the first control parameter  840 , and then, inputs the resultant to the equalizer  811  as the control parameter  840  to be used. 
     The storage module  103  may store only the first control parameter  840  among the first control parameter  840  to the third control parameter  840 . In this case, for a contact area greater than zero and not greater than a threshold, the to-be-used parameter determining module  812  changes the first control parameter  840  to generate a control parameter  840  corresponding to the second control parameter  840 , and then, inputs the resultant to the equalizer  811  as the control parameter  840  to be used. For a contact area greater than the threshold, the to-be-used parameter determining module  812  changes the first control parameter  840  to generate a control parameter  840  corresponding to the third control parameter  840 , and then, inputs the resultant to the equalizer  811  as the control parameter  840  to be used. 
     Although the sound quality of the sound signal SS is adjustable by three levels according to pressure intensity in the example above, the sound quality of the sound signal SS may be adjustable by two levels according to pressure intensity, or the sound quality of the sound signal SS may be adjustable by four or more levels according to pressure intensity. 
     Although the pressure intensity acquiring module  800  is configured with the touch panel  130  and the contact area calculating module  801  in the example above, the pressure intensity acquiring module  800  may have other configuration. As an example, the pressure intensity acquiring module  800  may be configured with a pressure sensor formed of a piezoelectric element or the like, which detects the pressure applied to the cover panel  2 . In this case, an output signal (output voltage) from the pressure sensor is the pressure intensity information indicating pressure intensity. 
     The volume control module  820  may turn up the volume of the sound signal SS as the pressure intensity indicated by the pressure intensity information is lower. As described above, the volume of the conduction sound from the cover panel  2  increases as the user presses his/her ear onto the cover panel  2  more strongly, whereby the volume of the sound transmitted from the cover panel  2  to the user becomes lower as the intensity at which the user presses his/her ear onto the cover panel  2  becomes lower. As in this example, therefore, by turning up the volume of the sound signal SS as the pressure intensity indicated by the pressure intensity information becomes lower, the sound having an appropriate volume can be transmitted from the cover panel  2  to the user irrespective of pressure intensity. 
     As described above, in the case where the volume of the sound signal SS is controlled based on pressure intensity information, for example, the volume of the sound signal SS that is set for a contact area greater than zero and not greater than a threshold is set to be higher than the volume of the sound signal SS that is set for a contact area larger than a threshold. Also, the volume of the sound signal SS that is set for a contact area of zero is set to be higher than the volume of the sound signal SS that is set for a contact area greater than zero and not greater than a threshold. 
     The receiver  190  may have other configuration. As an example, the receiver  190  may be configured with a dynamic receiver similarly to the external speaker  200  or may be configured with a piezoelectric speaker. 
     Although the examples above have been given of the case where the embodiments of the present disclosure are applied to a mobile phone, the embodiments of the present disclosure are also applicable to electronic devices other than mobile phones. 
     The electronic device  1  has been described in detail, but the above-mentioned description is illustrative in all aspects and the embodiments of the present disclosure are not intended to be limited thereto. The examples described above are applicable in combination as long as they do not contradict each other. Various modifications not exemplified are construed to be made without departing from the scope of the present disclosure. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           1  electronic device 
           2  cover panel 
           191  piezoelectric vibration element 
           800  pressure intensity acquiring module 
           810  sound quality control module 
           820  volume control module 
           830  drive module