Speaker system and thin display system

Abstract

To realize comfortable viewing of an image by suppressing occurrence of image blurring due to excitation of a displacement element so as to realize an excellent realistic feeling while realizing thinning of a display device.SOLUTION: A piezoelectric element is arranged on a back surface of an OLED display device so as to obtain a panel speaker, and also an electromagnetic speaker is added so as to obtain a speaker system. A cut-off frequency of a sound signal to be applied to the piezoelectric element of the panel speaker is defined as 500 Hz, and a frequency component equal to or less than the cut-off frequency is cancelled, so as to prevent image blurring. Besides, the sound of the cut low-frequency region equal to or less than 500 Hz is reproduced by the electromagnetic speaker, and an overlap band is allowed to be 2000 Hz to 3000 Hz, preferably to be 500 Hz to 3000 Hz, so as to obtain an excellent realistic feeling.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a thin display system such as a television receiver and a panel speaker used therefor, and more particularly to a speaker system suitable for a thin display device using organic EL (electroluminescence).

Background Art

[0002] In the field of display devices such as television receivers (hereinafter simply referred to as "televisions"), there has been a transition from a display device using a cathode ray tube to a thin display device using a plasma method or a liquid crystal method. In recent years, thin televisions employing ultra-thin display devices such as organic EL having a self-luminous display function have been widely recognized in the market, and cathode ray tube televisions have been discontinued by many television manufacturers.

[0003] In the process of such a transition, almost all of the cold cathode tubes that have been used as light-emitting devices for liquid crystal televisions have now changed to LEDs (light-emitting diodes). The original purpose of this transition is to make liquid crystal televisions thinner and lighter. By using a device with weight such as a cold cathode tube as an LED, an ideal wall-mounted television with the added value of weight reduction can be realized.

[0004] Particularly recently, display devices using organic EL have attracted attention. OLED (organic light-emitting diode) using organic EL is a self-luminous display device, and its thickness is as thin as 0.5 mm to 0.7 mm, and it does not require a light-emitting device such as an LED outside. Therefore, there is a possibility of realizing a television thinner than a conventional liquid crystal television. In addition, since there is no need for a space for mounting an LED, it has become possible to commercialize a narrow bezel type thin television. However, as described above, although OLED has an overwhelmingly advantageous point that its thickness is less than 1 mm, at present only narrow bezelization has been put into practical use, and the practical use of a thin television having a wall-mounted structure is still in the difficult range.

[0005] By the way, the basic functions of a TV are to display images and output sound. The former is realized by an OLED with the added value of a narrow bezel structure. On the other hand, regarding the latter, it is realized by mounting an electromagnetic speaker on the back of the TV cabinet. However, since there are irregularities in the thickness of the speaker, it is not necessarily suitable for thinning. It is said that the current thickness limit of a thin electromagnetic speaker is about 20 mm, and the minimum diameter required to realize the sound reproduction frequency necessary for a TV is about 25 mm. When a speaker of this size is mounted on the back of a TV, the merit of the thickness of less than 1 mm obtained by the OLED is offset, and the TV cabinet has to be thickened.

[0006] In addition, since convex portions due to electromagnetic speakers are generated on the back of the TV, it becomes difficult to realize a wall-mounted speaker also from the aspect of design. If the speaker is attached in the side direction of the screen, the back of the TV becomes flat, so wall mounting can be put into practical use. However, this time, the design of the narrow bezel is impaired.

[0007] By the way, in a movie theater where the sense of presence is the maximum added value, speakers are arranged facing the audience side behind a mesh screen with innumerable small holes, and sound is emitted from there toward the audience. With this method, since the sound that has passed through the mesh reaches the audience directly, the viewer can strongly feel the sense of presence, for example, feeling as if the voice of a character appears to be emitted from the screen, or the sound effects can be heard directly from the video. However, when a speaker is arranged behind the display screen like the TV described above, since the sound is not emitted directly toward the viewer, a spatial deviation occurs between the video and the sound, resulting in a video display lacking in a sense of presence.

[0008] On the other hand, Patent Document 1 below proposes a panel speaker that vibrates a thin plate panel with a vibration element to generate sound. According to this, by attaching and exciting a vibration element such as an electromagnetic solenoid or a piezoelectric ceramic that becomes a drive source to a thin plate-like member, sound is generated from the panel. According to this prior art, since sound is directly emitted from the display screen to the viewer side as in the above-mentioned movie theater, it is possible to reproduce video with a rich sense of presence. In this invention, proposals have been made to excite various objects to be vibrated, and in any case, a configuration is adopted in which sound is generated using a plurality of resonance modes (hereinafter referred to as "split vibration") of the object to be vibrated.

[0009] The magnitude P of the sound obtained from the object to be vibrated depends on the magnitude X of the amplitude, and generally the relationship P∝X holds. Further, regarding the relationship between the force F of the vibrating object and the rigidity K of the object to be vibrated, Hooke's law holds for the amplitude X, and X = F / K.

[0010] On the other hand, in the case of a liquid crystal panel using the above-described LED as a light source, when the backlight guide plate is included, the thickness as a display device is 3 mm to 4 mm. On the other hand, in the case of an OLED, as described above, it is 0.5 mm to 0.7 mm. The rigidity K of the plate of this display device, when the Young's modulus is E, the second moment of area is I, the width of the plate is a, and the thickness of the plate is h, I = ah 3 / 3 K = 48EI / L 3 = 16Eah 3 / L 3 It can be seen that the rigidity K of the plate thickness depends on the cube of the plate thickness h. Assuming that the plate thickness h in the OLED is 0.7 mm and the plate thickness h in the liquid crystal panel is 3 mm, (0.7 / 3) 3 ≒0.013, and the rigidity K differs greatly between the two. In the case of this example, it means that there is a difference of about 77 times in the force required to bend the OLED and the liquid crystal panel by the same amount.

[0011] To support such a relationship, Patent Document 2 below proposes a structure in which a vibration actuator is attached to the back surface of an OLED. The invention of this Patent Document 2 is basically similar to the structure of Patent Document 1. That is, from the above-described theoretical formula and the invention of the patent document, it can be seen that an OLED is a vibrated object with a display function that can generate large vibrations with a small force by a vibration element.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] As described above, when exciting with a vibration element to obtain a large sound, vibration must be applied to the OLED. However, the original purpose of the OLED is to display video and images. Nevertheless, there is a problem that when the display device vibrates, blurring occurs in the displayed video and images.

[0014] The present invention focuses on this point, and while realizing the thinning of the display device, suppresses the occurrence of blurring due to the excitation of the displacement element (vibration element), and realizes a good sense of presence and enables comfortable viewing of images. It aims to provide a speaker system and a thin display device.

Means for Solving the Problems

[0015] The speaker system of the present invention is a speaker system provided with a panel speaker in which a displacement element is attached to vibrate a display panel, and the display panel functions as a speaker, and among the frequency bands of the audio signal input to the displacement element, it is characterized in that low-frequency components are removed. According to one of the main forms, the low-pass cutoff frequency of the audio signal is set to 500 Hz, and frequency components below that are removed, which is characterized in that this can reduce image blurring.

[0016] According to another form, in addition to the panel speaker, an electromagnetic speaker separated from the display panel is provided, and the low-frequency components removed from the audio signal of the panel speaker are input to the electromagnetic speaker for reproduction. According to still another form, the high-pass cutoff frequency of the electromagnetic speaker is 2000 Hz to 3000 Hz, and audio signals in a frequency region higher than that are removed from the audio input of the electromagnetic speaker, and for audio signals in the frequency region from the low-pass cutoff frequency of the panel speaker to the high-pass cutoff frequency of the electromagnetic speaker, they are reproduced from both the panel speaker and the electromagnetic speaker, which is characterized in that preferably, the high-pass cutoff frequency is set to 500 Hz to 3000 Hz, which enables immersive audio reproduction.

[0017] According to still another form, a plurality of the displacement elements are attached to the display panel, and the plurality of displacement elements include displacement elements having different shapes. Further, as the displacement element, a unimorph type or bimorph type piezoelectric element is used, which is characterized in that.

[0018] According to the thin display system of the present invention, any of the above speaker systems is provided, and an OLED display device is used as the display panel, which is characterized in that the above and other objects, features, and advantages of the present invention will become clear from the following detailed description and the attached drawings.

Effects of the Invention

[0019] According to the present invention, the low-frequency components of the audio signal reproduced by the panel speaker below 500 Hz are removed to prevent picture jitter, and the high-frequency cutoff frequency of the audio signal reproduced by the electromagnetic speaker is set within the range of 2000 Hz to 3000 Hz, preferably within the range of 500 Hz to 3000 Hz, to remove higher-frequency components and ensure a sense of presence. Therefore, while realizing the thinning of the display device, the occurrence of picture jitter can be suppressed, a good sense of presence can be realized, and comfortable viewing of images can be achieved.

Brief Description of the Drawings

[0020]

Figure 1

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Figure 17

Embodiments for Carrying Out the Invention

[0021] Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples.

Examples

[0022] The display panel 10 to which this example is applied has a configuration in which a display device 14 using OELD is bonded to a glass substrate 12, as shown in FIG. 1(A), for example. The display device 14 has a configuration in which a transparent electrode layer, an organic light-emitting layer, and a reflective layer are laminated from the glass substrate 12 side. Then, a piezoelectric element 100 as a driving body is attached to the center of the back side (rear surface) of the display device 14 with, for example, an epoxy-based adhesive.

[0023] The piezoelectric element 100 is shown in FIGS. (B) to (D) of the same figure. FIG. (B) is a perspective view showing the whole, and FIG. (C) shows a view seen in the arrow direction along the line #1-#1 of the same figure. In these figures, the piezoelectric element 100 has a configuration in which external electrodes 120 and 130 are formed on the front and back surfaces of a piezoelectric body (piezoelectric ceramic plate) 110. The piezoelectric body 110 is obtained, for example, by using lead titanate zirconate as a piezoelectric material, laminating 20 sheets of 30-μm-thick sheets obtained by the green sheet method, and then performing pressure bonding and firing. The firing temperature is, for example, 1050°C. Then, a rectangular piezoelectric body 110 of 90 mm × 30 mm × 0.5 mm is obtained after firing.

[0024] Next, external electrodes 120 and 130 are printed on the front and back surfaces of the fired piezoelectric body 110, and then attached. At this time, a portion where the electrode layer is not applied is provided in a part of the external electrode 120. Then, another external electrode 132 that is not electrically connected to the external electrode 120 is simultaneously formed in a part of the external electrode 120, and the external electrode 132 is connected to the external electrode 130 on the opposite surface side by an electrode 134 that surrounds the side surface of the piezoelectric body 110 as shown in FIG. (C). The baking temperature of the electrodes 120, 130, 132, and 134 is, for example, 600°C. Then, as shown in FIG. (D), a high voltage is applied from a power source EP between the external electrodes 120 and 130 on the front and back surfaces to polarize the piezoelectric body 110 (see the arrow in the figure).

[0025] Next, as shown in FIG. 2(A), a lead wire 128 is connected to the external electrode 120 by solder 126. Further, a lead wire 138 is connected to the electrode 132 on the external electrode 120 side of the external electrode 130 by solder 136. By providing this piezoelectric element 100 on the back side of the display device 14 as shown in FIG. 1(A), it acts as a panel speaker. That is, when a driving voltage is applied between the lead wires 128 and 138 of the piezoelectric element 100, the piezoelectric body 110 expands, but the surface fixed with the epoxy adhesive is restricted by the display device 14 and thus cannot expand. For this reason, as shown in FIGS. 2(B) and (C), the display panel 10 undergoes bending deformation, generates air vibration, and sound is produced. Therefore, by applying, for example, an audio signal between the lead wires 128 and 138, sound is output from the surface (display surface) side of the display panel 10.

[0026] Next, an experiment was conducted on the relationship between the picture blur in the above panel speaker and the sense of presence experienced by viewers when using an electromagnetic speaker, and the conditions for preventing picture blur from the visual aspect when a self-luminous display device is vibrated to produce sound were considered. As described above, sound can be generated by attaching an actuator for excitation to a display device such as a liquid crystal and driving it. FIGS. 3(A) and (B) show measurement examples of vibration. The outer periphery of the rectangular glass plate GA was fixed with a fixing member GB, and the opposing surface of the glass plate GA was left free, and the primary and secondary resonance frequencies were measured by modal analysis. As a result, as shown in FIG. 3(C), it has split vibrations with many frequency components, and the split vibrations vibrate the air and are transmitted to the human ear as sound. The sound intensity I when the vibrating body generates a vibration displacement and produces an acoustic output is represented by the following Equation (1).

Equation

[0027] The density ρ and the speed of sound c of the gas vary slightly depending on the temperature and pressure of the gas (air), but here, the density ρ and the speed of sound c when released into the air under certain conditions are considered as a constant K. The sound intensity I in that case is represented by the following Equation (2).

Equation

[0028] On the one hand, the display device targeted by the present invention is a device that depicts images of a television. Therefore, if the display device itself generates large vibrations, the images being viewed will also shake significantly, resulting in a phenomenon where the image appears blurry (hereinafter referred to as the "image blur phenomenon"), which impairs the basic function of the television. For this reason, when generating sound using the vibrations of a display device for a television, it is not realistic to reproduce sounds in the entire frequency band from the low-frequency band to the high-frequency band by the vibrations of the display device.

[0029] Looking at it, as a speaker system for a television, a, a panel speaker that generates sound using a display device, b, an electromagnetic speaker that reproduces sounds in the low-frequency band to prevent image blur in the above-described low-frequency vibrations, it is desirable to efficiently drive both of them.

[0030] By the way, the screen sizes of televisions used in ordinary households are about 19 inches to 80 inches. If we assume that images are output by OLEDs for these sizes, the resonance frequencies of vibrations will be different for each size. Figure 4 shows the results obtained by calculating the resonance frequencies in display devices with sizes from 19 inches to 80 inches. In the figure, t represents the thickness of the display panel, X represents the horizontal length of the display device, and Y represents the vertical length. The above calculation uses the analysis model with the outer periphery of the OLED fixed by a line as shown in Figure 3, and shows the case where the thickness t is changed from 0.3 mm to 0.7 mm. As shown in the figure, it can be seen that the resonance frequency f of the display device depends on the screen sizes X, Y and the thickness t. Also, all the primary resonance frequencies are below 100 Hz. Even when assuming the reproduction frequency band of 100 Hz to 12 kHz of a general television speaker, it can be said that in the function of exciting only the OLED to reproduce sound, it is within a sufficient practical range.

[0031] Next, the vibration frequencies of display devices that cause picture blur in human vision are considered. To evaluate whether picture blur is felt, viewers from their teens to their 60s were divided into six age groups, and 10 people were randomly selected from each group for an experiment in which they actually watched TV.

[0032] The devices and conditions for the experiment are as follows. (1) As shown in Fig. 5, the TV used in the experiment adopted an OLED with a thickness of 0.6 mm as the display device 900, and a general SMPTE color bar signal was used as the image signal to display the SMPTE color bar on the screen. On the back of the display device 900, an electromagnetic solenoid actuator (vibrator) 910 with a diameter of 50 mm and a thickness of 30 mm was attached to apply vibration so that the display device 900 functions as a panel speaker 902 to produce sound. (2) A sweep signal of a sine wave gradually decreasing from 10 kHz to 100 Hz is applied as an excitation signal to the display device 900 from the transmitter-equipped controller 912. (3) The distance L between the panel speaker 902 and the viewer 920 is changed to 0.5 m, 1.0 m, 2.0 m, and 5.0 m, and at these distances, while showing the above-mentioned SMPTE color bar to the viewer 920, the viewer 920 is made to listen to the sound of the excitation. (4) Then, during viewing at each position, the viewer is instructed to indicate the timing when blur occurs in the screen display of the display device 900, and the frequency of the sweep signal of the sound at that time is recorded. (5) Such an experiment on the frequency at which picture blur is felt was conducted for each display device 900 with screen sizes of 19 inches, 32 inches, 50 inches, 65 inches, and 80 inches, respectively. (6) Then, the data on the frequency at which picture blur is felt was tabulated for each age group of 10s, 20s, 40s, and 60s. Through such a series of experiments, it becomes possible to grasp the frequency at which image blur is felt for each age group and TV size.

[0033] Figure 6(A) shows the results of the above experiment for viewers in their teens. For all frequency data, the average values of 10 viewers are adopted. For example, when the distance from the TV is 1.5 m and the TV size is 19 inches, the frequency at which picture blur is felt is 303 Hz. According to this frequency data, the following trends can be seen. a, Regardless of the distance from the TV, as the TV size increases, the frequency at which picture blur is felt becomes higher. b, As the distance from the TV increases, the frequency at which picture blur is felt becomes lower.

[0034] When the frequency data in Figure 6(A) is graphed, it becomes as shown in Figure 6(B) of the same figure. In this figure, the horizontal axis is the screen size, the vertical axis is the frequency at which picture blur is felt, and the distance from the TV is used as a parameter. From this graph, it can be seen that, for example, even for a large TV such as 80 inches, picture blur is not felt at vibrations of generally 400 Hz or more.

[0035] Figure 6 shows the experimental results for the teenage group. However, by conducting similar experiments for each age group of 20s, 40s, and 60s, the graphs in Figures 7(A) to 7(C) were obtained respectively. Referring to these, the following trends can be seen. a, Basically, the same trends are shown regardless of the generation. b, The higher the age, the lower the frequency at which picture blur is felt. c, The teenage group is the most sensitive to picture blur.

[0036] When all the data in Figures 6 to 7 are overlaid, it becomes as shown in Figure 8. As shown in this figure, it can be seen that the area enclosed by the frame is the frequency area where picture blur is felt. Looking into it, it was found that when using OLED as the display device, most viewers can enjoy the video without feeling picture blur by driving at a frequency of 500 Hz or more.

[0037] However, even if only frequency components of 500 Hz or higher are reproduced as audio signals from the panel speaker, the volume of the bass will be insufficient, resulting in a sound that is not satisfactory. For example, low-frequency components are essential for reproducing music such as bass guitars and drums, and furthermore, frequencies in the range of 300 to 500 Hz are said to be necessary frequency bands for discriminating human voices. Therefore, in addition to the panel speaker that reproduces audio signals of 500 Hz or higher, it is necessary to configure a speaker system that simultaneously drives another speaker that compensates for audio signals of 500 Hz or lower.

[0038] By the way, when reproducing an audio signal of a low-frequency component using, for example, an electromagnetic speaker, if the electromagnetic speaker is installed at a position completely different from the video display device, there is generally no need to worry about picture blurring of the video due to sound generation. In addition, since an electromagnetic speaker has a wider reproduction frequency band than a panel speaker, in an extreme case, it can cover the entire audio reproduction frequency band of a TV. However, as described above, the sense of presence obtained in a movie theater is obtained by sound being emitted from the screen on which the video is displayed. Therefore, in order to obtain a sound with a sense of presence on a TV, audio reproduction using a panel speaker is essential.

[0039] However, unlike a surround system that increases the number of speakers to generate a three-dimensional sound or a system that outputs a signal with phase manipulation to obtain a pseudo surround effect, there are individual differences in the sense of presence felt by viewers when sound directly comes out from the TV screen in the same way as in a movie theater. Therefore, the following experiment was conducted to investigate how the sense of presence is felt.

[0040] The experimental apparatus and conditions are as follows. (1) The experimental apparatus is shown in Fig. 9(A). As shown in the figure, an OLED configured to apply vibration by attaching the electromagnetic solenoid actuator 910 shown in Fig. 5 and emit sound from the panel speaker 902 is used as a TV for viewing. Here, TVs with sizes of 19 inches, 50 inches, and 80 inches were used. (2) Assume a scenario where the viewer watches the TV from a position that is three times the height (vertical width) of its screen. Note that the distance between this TV and the viewer is considered to be the ideal position for watching the TV (for example, http: / / www.enjoy.ne.jp / ~k-ichikawa / TV_distance.html Refer to). (3) At the ideal distance, install the microphone 930 at the height of the central part of the screen of the display device 900. (4) Install the electromagnetic speaker 932 on the lower side of the TV screen, facing the viewer. (5) Input pink noise to the panel speaker 902 and the electromagnetic speaker 932 separately. (6) Then, measure the noise level with the microphone 930, and adjust the input magnitude of each speaker 902, 932 so that the noise levels of the panel speaker 902 and the electromagnetic speaker 932 are equal. (7) Next, construct the drive circuit shown in FIG. 9(B). Convert the left and right channel signal outputs of the DAP (Digital Audio Processor) 950 into analog signals with the D / A converters 952L, 952R respectively, amplify them with the audio amplifier 954, extract the high-frequency components with the HPF (high-pass filter) 956L, 956R, and apply them to the piezoelectric elements of the panel speaker 902. If the cut-off frequency at this time is set to 500 Hz described above, no picture blur will occur in the display device 900. (8) On the other hand, apply the low-frequency components from the LPF (low-pass filter) 958 to the electromagnetic speaker (SUB WOOFER) 932. Here, the cut-off frequency of the LPF 958 is configured to be variable below 10 kHz. (9) Then, supply a video signal to the display device 900, and simultaneously input an audio signal to the panel speaker 902 and the electromagnetic speaker 932 from the drive circuit of FIG. 9(B). As a result, audio will be output from the panel speaker 902 and the electromagnetic speaker 932 in synchronization with the video on the display device 900. (10) Next, 10 people were randomly selected from those in their 20s, 40s, and 50s, and these viewers were made to watch videos and listen to audio using the above system. Here, in the sample videos, they were made to watch the battle scenes of the movie "STAR WARS" (registered trademark), the live performance of a musician, and the sports relay of the "World Cup" (registered trademark) soccer game, respectively. (11) Under the above viewing conditions, the cut-off frequency of the LPF958 connected to the electromagnetic speaker 932 was gradually decreased from 10 kHz to 100 Hz one by one. Basically, the higher the cut-off frequency, the more dominant the sound emitted by the electromagnetic speaker 932 becomes compared to the sound emitted by the panel speaker 902. Conversely, by decreasing the cut-off frequency, the influence of the sound of the panel speaker 902 becomes dominant. (12) Ask the viewers to indicate the frequency at which they feel a sense of presence as the cut-off frequency changes. By conducting such an experiment, the relationship between the cut-off frequency of the electromagnetic speaker 932 and the degree of dependence of the sense of presence given to the viewers can be grasped.

[0041] The above experimental results are shown in Fig. 10. Figures (A) to (C) in the same figure show the cases where the screen sizes are 19 inches, 50 inches, and 80 inches, respectively. The numbers on the vertical axis indicate 10 viewers. For example, in Fig. (A), the first viewer in their 20s who watched the 19-inch screen felt a sense of presence when the cut-off frequency of the LPF958 was 2700 Hz while watching the movie. Looking at Figs. (A) to (C) as a whole, although there is a tendency to depend on the genre being watched, it can be seen that regardless of age, the cut-off frequency is generally around 2000 Hz to 3000 Hz or less when feeling a sense of presence.

[0042] When combining the above two experimental results, in a speaker system that simultaneously drives the panel speaker 902, which causes the display device 900 to vibrate and produce sound by vibrating the piezoelectric element attached to the self-luminous display device 900, and the electromagnetic speaker 932 separated from the display device 900, it was found that if the overlap band of the panel speaker 902 and the electromagnetic speaker 932 is from 500 Hz to 3000 Hz, it is a condition that can prevent image blurring and obtain a sense of presence.

[0043] As described above, according to this embodiment, a. By providing a piezoelectric element on the back surface of the OLED display device to form a panel speaker, a simple structure can achieve a significant reduction in thickness. b. By setting the cut-off frequency of the audio signal applied to the piezoelectric element of the panel speaker to 500 Hz and removing frequency components below that, image blurring can be prevented. c. By adding an electromagnetic speaker to the panel speaker and setting the high-pass cut-off frequency of the electromagnetic speaker to 2000 Hz - 3000 Hz, preferably 500 Hz - 3000 Hz, and removing frequency components above that, a good sense of presence can be obtained.

Embodiment

[0044] Next, with reference to FIGS. 11 to 12, an example of a speaker system suitable for the above-described conditions will be described. FIG. 11(A) shows the panel speaker 200 according to this embodiment. The display panel 10 by OLED has a configuration in which the display device 14 by OLED is bonded to the glass substrate 12 as described above. The display device 14 has a structure in which a transparent electrode layer, an organic light-emitting layer, and a reflective layer are laminated from the glass substrate 12 side. In this embodiment, as the display device 14, one with a size of 420 mm in width × 240 mm in height × 0.7 mm in thickness is used. Then, piezoelectric elements 210 and 220 as driving bodies are provided on the back side of the display device 14 to act as a panel speaker. As the piezoelectric elements 210 and 220, those having the structures shown in FIGS. 1 and 2 described above are used.

[0045] Here, when measuring the frequency characteristics of the sound pressure when only the piezoelectric element 210 is provided as shown in FIG. 1, the result was as shown in FIG. 12(A). The measurement was performed by fixing the display panel 10 to a stand (not shown) and inputting a sine wave sweep signal to the piezoelectric element 210 with the drive circuit shown in FIG. 9(B). At that time, HPF956L and 956R were short-circuited, and the sound pressure was measured with the microphone 930 at a distance of 1 m as shown in FIG. (A), resulting in a graph as shown by the solid line in FIG. 12(A). According to this, effective sound is obtained from around 300 Hz to around 6 kHz.

[0046] However, in this frequency characteristic, the high-frequency sound pressure is insufficient, and the audible sound is somewhat stuffy. This is due to the fact that the resonance frequency of the bending vibration of the display panel 10 shown in FIG. 2(C) is caused by the dimensions of the piezoelectric element 210, and the larger the element dimensions, the lower the resonance frequency.

[0047] Therefore, in this embodiment, a piezoelectric element 220 having dimensions different from those of the piezoelectric element 210 was attached to the back surface of the display device 14 as shown in FIG. 11(A). The dimensions of the piezoelectric element 220 are 45 mm × 15 mm × 0.5 mm. When measuring the sound pressure frequency characteristics when driving this piezoelectric element 220 in the same manner as described above, a graph shown by a dotted line in FIG. 12(A) was obtained. According to this, the characteristics at low frequencies are almost the same as the graph of the solid line in the figure, but the sound pressure is increased in the high band of 5 kHz to 10 kHz. Also, audibly, the high-frequency sound became a clear and extended sound. However, since effective sound is emitted at 400 Hz, picture blur in the display device 14 can be confirmed. Therefore, when using HPF956L and 956R shown in FIG. 9(B) to cut the frequencies below 500 Hz at 6 dB / Oct for the signals applied to the piezoelectric elements 210 and 220, the occurrence of picture blur disappeared.

[0048] Next, as described above, when sound is generated only by the panel speaker 200, low-frequency sound cannot be heard. Therefore, in this embodiment, an electromagnetic woofer 300 is used for low-frequency correction. The electromagnetic woofer 300 is attached to the lower surface side of the television housing 400, for example, as shown in FIG. 11(B). In this embodiment, a bass-reflex type speaker system as shown in FIG. (C) of the same figure is used as the electromagnetic woofer 300. The woofer 300 used is a moving coil type woofer with an impedance of 8 Ω and a diameter of 160 mm. A speaker 310 and a port 320 are provided in the housing 302, and a duct 330 is provided between the port 320 and the speaker 310, having a general configuration.

[0049] FIG. 12(B) shows the frequency characteristics of the electromagnetic woofer 300. This characteristic is measured at a position 1 m from the front of the speaker. The original characteristic is shown by the solid line in the figure. However, in order to obtain a sense of presence, the input to the electromagnetic woofer 300 is gain-controlled by the LPF958 shown in FIG. 9, and attenuation of -6 dB / Oct is performed from 1 kHz, and it is adjusted to be almost equal to the sound pressure near 1 kHz in the frequency characteristic of the panel speaker 200 shown by the solid line in FIG. 12(A). The reproduction band of the electromagnetic woofer 300 generally has characteristics of 20 Hz to 10 kHz.

[0050] Then, when the panel speaker 200 and the electromagnetic woofer 300 are simultaneously driven by the drive circuit in FIG. 9 to measure the frequency characteristic of the sound pressure, the result as shown in FIG. 12(C) is obtained. According to this, a characteristic that is generally flat from 20 Hz to 10 kHz is obtained. In addition, when a video signal including audio is added to this panel speaker system and visually confirmed, there is no picture blur, and a viewing full of a sense of presence can be performed.

[0051] As described above, according to this embodiment, a. Two piezoelectric elements with different dimensions are provided on the back of the OLED display device to form a panel speaker, and an electromagnetic speaker is added to form a speaker system. b. The high-frequency range of the piezoelectric element with a large dimension is supplemented by the output of the piezoelectric element with a small dimension. c. Set the low-pass cutoff frequency of the audio signal applied to the piezoelectric element of the panel speaker to 500 Hz, and remove the frequency components below that frequency to prevent picture jitter. b. Set the high-pass cutoff frequency of the electromagnetic speaker to 2000 Hz - 3000 Hz, and remove the frequency components above that frequency to obtain a good sense of presence.

Example

[0052] Next, Example 3 of the present invention will be described with reference to FIGS. 13 to 14. In the panel speaker 500 of this example, as shown in FIG. 13, piezoelectric elements 510, 512, 520, and 522 are arranged at equal intervals on the back side of the display panel 10 in which the display device 14 using an OLED is bonded to the glass substrate 12. That is, the piezoelectric elements 510, 512, 520, and 522 are attached at the positions that divide each of the long side direction and the short side direction of the display device 14 into three equal parts. In this example, since a display device 14 having large dimensions of 1770 mm × 996 mm × 0.7 mm is used, the number of piezoelectric elements is also increased to four.

[0053] When the frequency characteristics of such a panel speaker 500 were measured, the result was as shown in FIG. 14(A). Compared with Example 1, the area of the display device 14 is larger and the air exclusion volume is increased, so the overall sound pressure has increased. Also, the reproduction frequency band has dropped to around 300 Hz. When a video signal containing a music signal was input to this panel speaker 500 and reproduced, picture jitter was confirmed. Therefore, similar to Example 1, when the frequencies of 500 Hz or less of the audio signal applied to the piezoelectric elements 510, 512, 520, and 522 were cut at 6 dB / Oct by HPF956L and 956R, the occurrence of picture jitter disappeared.

[0054] Next, similar to the above-described Example 1, when only the panel speaker 500 generates sound, the sound in the low-frequency range cannot be heard. Therefore, the bass-reflex type electromagnetic woofer 300 shown in FIG. 11(C) is used for low-frequency correction. When the frequency characteristics of the bass-reflex type electromagnetic woofer 300 shown in this example are shown, it becomes as shown in FIG. 14(B). The original characteristics are shown by the solid line in the figure. However, in order to obtain a sense of presence, the input to the electromagnetic woofer 300 is gain-controlled by the LPF958 shown in FIG. 9, and attenuation of -6 dB / Oct is performed from 1 kHz as shown by the dotted line in FIG. 14(B), so that it is adjusted to be almost equal to the sound pressure near 1 kHz in the frequency characteristics of the panel speaker 200 shown in FIG. 14(A).

[0055] Then, when the panel speaker 500 and the electromagnetic woofer 300 were simultaneously driven by the drive circuit in FIG. 9 to measure the frequency characteristics of the sound pressure, the results shown in FIG. 14(C) were obtained. According to this, a substantially flat characteristic from 20 Hz to 10 kHz was obtained, and it became clear that even when the display device 14 using a large-sized OLED was used, it was possible to enjoy a video with a rich sense of presence without picture blur.

[0056] As described above, according to this example, since a plurality of piezoelectric elements having different dimensions are provided according to the size of the display device using an OLED, even when a large-sized display device is used, there is no picture blur and a good sense of presence can be obtained.

Example

[0057] Next, referring to FIGS. 15 to 17, Example 4 will be described. This example is an example in which a bimorph type piezoelectric element is used instead of the unimorph type piezoelectric element described above. First, the piezoelectric element 600 shown in FIG. 15 shows the appearance in FIG. 15(A), and as shown in the cross section viewed in the arrow direction along the #15-#15 line in the figure, external electrodes 620 and 630 are provided on the front and back surfaces of the piezoelectric body 610, respectively. Then, as shown in FIG. 15(C), a high voltage is applied from the power supply EP between the external electrodes 620 and 630 on the front and back surfaces to polarize the piezoelectric body 610 (see the arrow F15 in the figure).

[0058] As shown in Fig. 16(A), the piezoelectric element 600 as described above is adhered to both sides of a metal plate (thin metal plate) 650 with a conductive adhesive while aligning the polarization directions, thereby forming a bimorph-type piezoelectric element 700. When the switch SQ is turned ON and the DC power supply EQ is energized to this element as shown in Fig. (B) of the same figure, the upper piezoelectric element 600A contracts and the lower piezoelectric element 600B expands. Due to these actions, the metal plate 650 undergoes a bending deformation. In the illustrated example, it bends downward in the figure. This deformation bends in the opposite direction by reversing the polarity of the applied voltage by the DC power supply EQ. Then, as shown in Fig. (C) of the same figure, when an AC voltage is applied by the AC power supply ER via the switch SR, the upper and lower piezoelectric elements 600A and 600B repeatedly expand and contract in different directions, causing the entire element to undergo vertical bending vibration. As shown in Figs. 17(A) and (B), both ends of the metal plate 650 of such a bimorph-type piezoelectric element 700 are fixed to the support member 660. Thereby, as shown in Fig. (C) of the same figure, the vertical bending vibration of the piezoelectric element 700 can be achieved without any hindrance by the support member 660. When the support member 660 is joined to the back surface of the display device 14 as shown in Fig. (D) of the same figure and a drive signal is supplied to the piezoelectric elements 600A and 600B, the bending vibration of the piezoelectric element 700 is transmitted from the back surface to the front surface of the display device 14 via the support member 660, and sound is output from the display device 14, functioning as a panel speaker.

[0059] <Other Embodiments> Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, the following are also included. (1) The shapes and dimensions shown in the above embodiments are merely examples, and may be appropriately changed as needed to achieve similar functions. (2) In the above embodiments, the present invention is applied to an OLED as a self-emissive display device, but it can be applied to various other thin display devices. (3) The number of piezoelectric elements attached to the display device may be appropriately increased or decreased as needed. (4) In the above embodiment, a piezoelectric element is used, but it does not prevent the use of other displacement elements, such as magnetostrictive elements or electromagnetic elements. (5) In the above embodiment, an OLED is shown as a thin display device, but various other display devices may be used.

Industrial Applicability

[0060] According to the present invention, the low-frequency components of the audio signal reproduced by the panel speaker below 500 Hz are removed to prevent picture blur, and the frequency of the audio signal reproduced by the electromagnetic speaker is set to 2000 Hz to 3000 Hz, preferably 500 Hz to 3000 Hz, to remove the high-frequency components above that to ensure a sense of presence. Therefore, while realizing the thinning of the display device, the occurrence of picture blur is suppressed, a good sense of presence is realized, comfortable viewing of images can be realized, and it is suitable for thin TVs and the like.

Explanation of Reference Numerals

[0061] 10: Display panel 12: Glass substrate 14: Display device 100: Piezoelectric element 110: Piezoelectric body 120, 130, 132, 134: Electrodes 126, 136: Solder 128, 138: Lead wires 200: Panel speaker 210, 220: Piezoelectric elements 300: Electromagnetic woofer 302: Housing 310: Speaker 320: Port 330: Duct 400: Housing 500: Panel speaker 510, 512, 520, 522: Piezoelectric elements 600: Piezoelectric element 600A, 600B: Piezoelectric elements 610: Piezoelectric body 620, 630: External electrodes 650: Metal plate 660: Support member 700: Piezoelectric element 900: Display device 902: Panel speaker 910: Electromagnetic solenoid actuator 912: Controller with transmitter 920: Viewer 930: Microphone 932: Electromagnetic speaker 950: DAP (Digital Audio Processor) 952L, 952R: D / A converter 954: Audio amplifier 956L, 956R: HPF (High Pass Filter) 958: LPF (Low Pass Filter) EP: Power supply EQ: DC power supply ER: AC power supply GA: Glass plate GB: Fixing member L: Distance SQ, SR: Switch

Claims

1. A speaker system comprising a panel speaker in which a displacement element is attached to vibrate a display panel, and the display panel functions as a speaker, wherein a low-frequency component in the frequency band of the audio signal input to the displacement element is removed.

2. The speaker system according to claim 1, wherein the cut-off frequency of the audio signal is 500 Hz, and frequency components below that are removed.

3. In addition to the panel speaker, an electromagnetic speaker separated from the display panel is provided, and the low-frequency component removed from the audio signal of the panel speaker is input to the electromagnetic speaker for reproduction.

4. The high-frequency cut-off frequency of the electromagnetic speaker is 500 Hz to 3000 Hz, and audio signals in a frequency region higher than that are removed from the audio input of the electromagnetic speaker, and for audio signals in the frequency region from the low-frequency cut-off frequency of the panel speaker to the high-frequency cut-off frequency of the electromagnetic speaker, reproduction is performed from both the panel speaker and the electromagnetic speaker.

5. The speaker system according to claim 1, wherein a plurality of the displacement elements are attached to the display panel, and the plurality of displacement elements include displacement elements having different shapes.

6. The speaker system according to claim 1, wherein a unimorph-type or bimorph-type piezoelectric element is used as the displacement element.

7. A thin display system comprising the speaker system according to any one of claims 1 to 6, wherein an OLED display device is used as the display panel.

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