Bending wave speaker

Abstract

This bending wave speaker comprises a diaphragm and an actuator that is disposed on the diaphragm and vibrates the diaphragm. The shape of the diaphragm is a parallelogram or an ellipse. When the diaphragm is a parallelogram, the ratio of the length of a first side, which is the longest side of the parallelogram, to the length in a direction perpendicular to the first side is an irrational number. When the diaphragm is an ellipse, the ratio of the major axis to the minor axis of the ellipse is an irrational number.

Description

bending wave speaker

[0001] The present invention relates to a bending wave speaker. This invention claims priority to U.S. Provisional Application No. 63 / 684,870, filed August 20, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, distributed mode loudspeakers (DMLs) have been proposed. DMLs generate bending waves on a thin panel by driving an electrodynamic exciter (vibrator) attached to the panel. For example, Non-Patent Document 1 discloses a configuration including a diaphragm, an exciter that drives the diaphragm, and a frame that supports the diaphragm. In Non-Patent Document 1, as an example of using one exciter, the exciter is positioned at a position where the lengths of the sides of the rectangular diaphragm are in a ratio of 3:4 or 4:5. Other exciter mounting positions are disclosed in Patent Document 1.

[0003] Patent No. 3763848

[0004] Distributed Mode Loudspeaker, Kazuhiko Kawahara, Journal of the Acoustical Society of Japan, Vol. 62, No. 11 (2006), pp. 798-801

[0005] Typically, speakers are required to have a distortion-free frequency response (a characteristic in which the amplitude response is flat within the target frequency band), while increasing the diffusion (the diffuse nature of the audible radiation) is more desirable than balancing the frequency response.

[0006] Therefore, an object of the present invention is to improve the diffusibility.

[0007] To solve the above problems, an aspect of the present disclosure has the following configuration: (1) A bending wave speaker according to an aspect of the present disclosure includes a diaphragm and an actuator disposed on the diaphragm and vibrating the diaphragm, the diaphragm having a shape of a parallelogram or an ellipse, and when the diaphragm is a parallelogram, the ratio of the length of a first side, which is the longest side of the parallelogram, to the length in a direction perpendicular to the first side is an irrational number, and when the diaphragm is an ellipse, the ratio of the major axis to the minor axis of the ellipse is an irrational number.

[0008] (2) In the bending wave speaker described in (1) above, the diaphragm may be the parallelogram, and the parallelogram may have two of the first sides and two second sides that are shorter than the first sides. When the length of the first sides is X, the length in the perpendicular direction is Y, the distance from the first sides to the actuator along the extension direction of the second sides is Y1, and the distance from the second sides to the actuator along the extension direction of the first sides is X1, the ratio Y1 / Y of Y1 to Y may be 60 / 139, and the ratio X1 / X of X1 to X may be 1 / 3.

[0009] (3) In the bending wave speaker described in (2) above, the diaphragm may be rectangular.

[0010] (4) In the bending wave speaker described in (3) above, X may be 450 mm, Y may be 278 mm, X1 may be 150 mm, and Y1 may be 120 mm.

[0011] (5) In the bending wave speaker described in (1) above, when the diaphragm is elliptical, and a parallelogram inscribed in the ellipse is drawn, the parallelogram has two long sides and two short sides, and when the length of the long sides is X, the length of the short sides is Y, the distance from the long sides to the actuator along the extension direction of the short sides is Y1, and the distance from the short sides to the actuator along the extension direction of the long sides is X1, the ratio Y1 / Y of Y1 to Y may be 60 / 139, and the ratio X1 / X of X1 to X may be 1 / 3.

[0012] (6) In the bending wave speaker described in (1) or (2) above, the diaphragm may be made of resin corrugated cardboard.

[0013] (7) In the bending wave speaker described in (6) above, the resin cardboard may have two liner sections arranged facing each other and approximately parallel to each other, and a buffer section arranged between the liner sections and connected to the liner sections, and the buffer section may have a rib structure arranged parallel and at equal intervals in one direction.

[0014] (8) In the bending wave speaker described in (6) above, the resin corrugated cardboard may be made of polypropylene.

[0015] (9) The bending wave speaker described in (1) above may further include a frame that is disposed on the diaphragm around the outer periphery of the diaphragm and supports the diaphragm.

[0016] (10) In the bending wave speaker described in (9) above, when the diaphragm is a parallelogram, the frame may have a parallelogram frame shape that follows the outer periphery of the parallelogram.

[0017] (11) In the bending wave speaker described in (10) above, the diaphragm may be the parallelogram, and the parallelogram may have two of the first sides and two second sides shorter than the first sides. When the dimension of the length of the first sides within the frame is X, the dimension of the length in the perpendicular direction within the frame is Y, the dimension of the distance from the first side to the actuator along the extension direction of the second side is Y1, and the dimension of the distance from the second side to the actuator along the extension direction of the first side is X1, the ratio Y1 / Y of Y1 to Y may be 48 / 115, and the ratio X1 / X of X1 to X may be 63 / 201.

[0018] (12) In the bending wave speaker described in (11) above, X may be 402 mm, Y may be 230 mm, X1 may be 126 mm, and Y1 may be 96 mm.

[0019] (13) In the bending wave speaker described in (9) above, the frame may be a wooden frame.

[0020] According to the above aspect, the diffusibility can be improved.

[0021] 1 is a perspective view of a bending wave speaker according to an embodiment; FIG. 2 is a side view of a diaphragm according to an embodiment; FIG. 3 is a diagram illustrating an example of an installation position of an actuator according to an embodiment; FIG. 4 is a diagram illustrating another example of an installation position of an actuator according to an embodiment; FIG. 5 is a diagram illustrating another example of an installation position of an actuator according to an embodiment; FIG. 6 is a diagram illustrating the frequency characteristics of a bending wave speaker according to an example (when the directivity angle is 0°); FIG. 7 is a diagram illustrating the frequency characteristics of a bending wave speaker according to an example (when the directivity angle is 45°); FIG. 8 is a diagram illustrating the frequency characteristics of a bending wave speaker according to an example (when the directivity angle is 90°); FIG. 9 is a diagram illustrating the frequency characteristics of a bending wave speaker according to an example (when the directivity angle is 135°); FIG. 10 is a diagram illustrating the frequency characteristics of a bending wave speaker according to an example (when the directivity angle is 180°); FIG. 11 is a diagram illustrating the dimensions of a manufactured BML; FIG. 12 is a diagram illustrating a completed BML; FIG. 13 is a diagram illustrating a measurement block diagram; FIG. 14 is a diagram illustrating the impulse response of a closed-type speaker (with level change); FIG. 15 is a diagram illustrating the impulse response of a closed-type speaker (without level change); FIG. 16 is a diagram illustrating the results of subjective evaluation of one speaker; FIG. 17 is a diagram illustrating the analysis results for subjects who answered the correct direction. 1 is a diagram showing the results of weighting according to response time. FIG. 2 is a perspective view of the bending wave speaker of the embodiment as seen from the front side. FIG. 3 is a perspective view of the bending wave speaker of the embodiment as seen from the back side. FIG. 4 is a perspective view of the bending wave speaker of the embodiment as seen from the side.

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. In the following description, a bending wave loudspeaker (BWL) will be described as an example, which is a panel speaker that utilizes bending waves of a diaphragm.

[0023] In the following description, expressions indicating relative or absolute arrangements, such as "parallel," "orthogonal," "center," and "coaxial," do not only mean such arrangements or states in the strict sense, but also include arrangements or states in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. In the drawings used in the following description, the scale of each component may be changed as appropriate to make each component recognizable.

[0024] <Bending Wave Speaker> Fig. 1 is a perspective view of a bending wave speaker 1 according to an embodiment. Fig. 2 is a side view of a diaphragm 2 according to an embodiment. Referring to Fig. 1 and Fig. 2 together, the bending wave speaker 1 includes a diaphragm 2, an actuator 3, and a frame 4.

[0025] <Vibration Plate> In this embodiment, the diaphragm 2 is a resin cardboard. In this embodiment, the resin cardboard includes two liner portions 2 a, 2 b arranged substantially parallel to each other and facing each other, and a buffer portion 2 c arranged between the liner portions 2 a, 2 b and connected to the liner portions 2 a, 2 b, and the buffer portion 2 c has a rib structure arranged parallel to one direction and at equal intervals. In this embodiment, the resin cardboard is made of polypropylene.

[0026] The two liner portions 2a, 2b are formed as parallel plates. The buffer portion 2c is disposed between the two liner portions 2a, 2b. The buffer portion 2c is connected to each of the two liner portions 2a, 2b. The buffer portion 2c has a rib structure that is arranged parallel to and at equal intervals in the in-plane direction (one direction) of the liner portions 2a, 2b.

[0027] In the embodiment, the shape of the diaphragm 2 is a parallelogram or an ellipse. When the diaphragm 2 is a parallelogram, the ratio of the length of the first side, which is the longest side of the parallelogram, to the length in the direction perpendicular to the first side is an irrational number. When the diaphragm 2 is an ellipse, the ratio of the major axis to the minor axis of the ellipse is an irrational number. In the example of FIG. 1 , the diaphragm 2 is a rectangle (an example of a parallelogram). Note that when the diaphragm 2 is a parallelogram (rectangle), the corners of the diaphragm 2 (at least some of the four corners) may be subjected to a process for rounding the corners or edges of a product, known as filleting (corner rounding).

[0028] The shape of the diaphragm 2 is not limited to a parallelogram or an ellipse, and may be a rectangle with parallel sides of different lengths. In this case, it is sufficient that the ratio of the length of the first side of the rectangle to the longest length among the lengths of the intersection of a line segment of the first side, which is perpendicular to the first side, and the intersection of a line segment of the second side opposite the first side, is an irrational number.

[0029] In addition, since it may not be possible to directly reflect the ratio of irrational numbers in the design, a tolerance of up to 1 mm is permitted in the actual design. The ratio of irrational numbers is not particularly limited, but is preferably the golden ratio.

[0030] <Actuator> The actuator 3 is a component that is disposed on the diaphragm 2 and vibrates the diaphragm 2. The actuator 3 is, for example, an electrodynamic exciter (vibrator). An electrodynamic exciter has the function of vibrating the surface (contact surface) of the diaphragm 2 to which it is attached.

[0031] <Frame> The frame 4 is a component that is disposed on the diaphragm 2 around the outer periphery of the diaphragm 2 and supports the diaphragm 2. In an embodiment, when the diaphragm 2 is a parallelogram, the frame 4 has a parallelogram-like frame shape that follows the outer periphery of the parallelogram. In an embodiment, the frame 4 is a wooden frame. The frame 4 may be formed by connecting adjacent portions of a plurality of (for example, four) rod-shaped members.

[0032] <Regarding the installation position of the actuator and the dimensional ratio of the diaphragm> Fig. 3 is a diagram showing an example of the installation position of the actuator 3 of the embodiment. Fig. 4 is a diagram showing another example of the installation position of the actuator 3 of the embodiment. Fig. 5 is a diagram showing another example of the installation position of the actuator 3 of the embodiment. Fig. 6 is a diagram showing another example of the installation position of the actuator 3 of the embodiment. For convenience, the frame 4 that supports the diaphragm 2 is not shown in Fig. 6. The installation position of the actuator 3 corresponds to the center position of the actuator 3 when viewed from a direction perpendicular to the surface of the diaphragm 2 on which the actuator 3 is attached (the thickness direction of the diaphragm 2).

[0033] Referring to both Figures 3 and 5, when the diaphragm 2 is a parallelogram (rectangle), the parallelogram has two first sides and two second sides shorter than the first sides, where X is the length of the first sides, Y is the length in the perpendicular direction, Y1 is the distance from the first sides to the actuator 3 along the extension direction of the second sides, and X1 is the distance from the second sides to the actuator 3 along the extension direction of the first sides. The ratio Y1 / Y of Y1 to Y is preferably 50 / 139 or more, and more preferably 55 / 139 or more. Furthermore, Y1 / Y is preferably 70 / 139 or less, and more preferably 65 / 139 or less. Furthermore, Y1 / Y is preferably 50 / 139 or more and 70 / 139 or less, and more preferably 55 / 139 or more and 65 / 139 or less. Most preferably, Y1 / Y is 60 / 139. The ratio of X1 to X, X1 / X, is preferably 13 / 45 or more, and more preferably 14 / 45 or more. X1 / X is preferably 17 / 45 or less, and more preferably 16 / 45 or less. X1 / X is preferably 13 / 45 or more and 17 / 45 or less, and more preferably 14 / 45 or more and 16 / 45 or less. X1 / X is most preferably 1 / 3.

[0034] In this embodiment, when the diaphragm 2 is a parallelogram (rectangle), the ratio of Y1 to Y, Y1 / Y, is 60 / 139, and the ratio of X1 to X, X1 / X, is 1 / 3. In this embodiment, when the diaphragm 2 is a parallelogram (rectangle), X is 450 mm, Y is 278 mm, X1 is 150 mm, and Y1 is 120 mm.

[0035] Referring also to FIG. 4 , when the diaphragm 2 is elliptical and a parallelogram inscribed in the ellipse is drawn, the parallelogram has two long sides and two short sides, with the length of the long sides being X and the length of the short sides being Y. The distance from the long side along the extension direction of the short sides to the actuator 3 is Y1, and the distance from the short side along the extension direction of the long sides to the actuator 3 is X1. The ratio Y1 to Y, Y1 / Y, is preferably 50 / 139 or more, and more preferably 55 / 139 or more. Furthermore, Y1 / Y is preferably 70 / 139 or less, and more preferably 65 / 139 or less. Furthermore, Y1 / Y is preferably 50 / 139 or more and 70 / 139 or less, and more preferably 55 / 139 or more and 65 / 139 or less. Most preferably, Y1 / Y is 60 / 139. The ratio of X1 to X, X1 / X, is preferably 13 / 45 or more, and more preferably 14 / 45 or more. X1 / X is preferably 17 / 45 or less, and more preferably 16 / 45 or less. X1 / X is preferably 13 / 45 or more and 17 / 45 or less, and more preferably 14 / 45 or more and 16 / 45 or less. X1 / X is most preferably 1 / 3.

[0036] In this embodiment, the diaphragm 2 is elliptical, and when a parallelogram inscribed in the ellipse is drawn, the ratio Y1 to Y is 60 / 139, and the ratio X1 to X is 1 / 3.

[0037] Referring also to FIG. 6 , in a configuration including a frame 4 supporting the diaphragm 2, if the diaphragm 2 is a parallelogram (rectangle), the parallelogram has two first sides and two second sides shorter than the first sides, where X denotes the dimension of the length of the first sides within the frame 4, Y denotes the dimension of the length of the perpendicular direction within the frame 4, Y1 denotes the dimension of the distance from the first side along the extension direction of the second side to the actuator 3 within the frame 4, and X1 denotes the dimension of the distance from the second side along the extension direction of the first side to the actuator 3 within the frame 4, the ratio Y1 / Y of Y1 to Y is preferably 38 / 115 or greater, more preferably 43 / 115 or greater. Furthermore, Y1 / Y is preferably 58 / 115 or less, more preferably 53 / 115 or less. Furthermore, Y1 / Y is preferably 38 / 115 or greater but 58 / 115 or less, more preferably 43 / 115 or greater but 53 / 115 or less. Furthermore, Y1 / Y is preferably 38 / 115 or greater but 58 / 115 or less, more preferably 43 / 115 or greater but 53 / 115 or less. Y1 / Y is most preferably 48 / 115. The ratio X1 / X of X1 to X is preferably 53 / 201 or more, more preferably 58 / 201 or more. X1 / X is preferably 73 / 201 or less, more preferably 68 / 201 or less. X1 / X is preferably 53 / 201 or more and 73 / 201 or less, more preferably 58 / 201 or more and 68 / 201 or less. X1 / X is most preferably 63 / 201.

[0038] In the embodiment, when the diaphragm 2 is a parallelogram (rectangle) in a configuration including a frame 4 supporting the diaphragm 2, the ratio of Y1 to Y, Y1 / Y, is 48 / 115, and the ratio of X1 to X, X1 / X, is 63 / 201. In the embodiment, when the diaphragm 2 is a parallelogram (rectangle) in a configuration including a frame 4 supporting the diaphragm 2, X is 402 mm, Y is 230 mm, X1 is 126 mm, and Y1 is 96 mm.

[0039] <Effects> As described above, the bending wave speaker 1 of the above embodiment includes the diaphragm 2 and the actuator 3 disposed on the diaphragm 2 to vibrate the diaphragm 2. The shape of the diaphragm 2 is a parallelogram or an ellipse. When the diaphragm 2 is a parallelogram, the ratio of the length of the first side, which is the longest side of the parallelogram, to the length in the direction perpendicular to the first side is an irrational number. When the diaphragm 2 is an ellipse, the ratio of the major axis to the minor axis of the ellipse is an irrational number. As a result of extensive research, the present inventors have found that when the shape of the diaphragm 2 in the bending wave speaker 1 is a parallelogram or an ellipse, and when the diaphragm 2 is a parallelogram, the ratio of the length of the first side, which is the longest side of the parallelogram, to the length in the direction perpendicular to the first side is an irrational number, or when the diaphragm 2 is an ellipse, the ratio of the major axis to the minor axis of the ellipse is an irrational number, the auditory diffuseness is greater than the frequency characteristics. That is, with this configuration, the diffusion (auditory diffusion properties) can be improved compared to when the diaphragm 2 of the bending wave speaker 1 is a parallelogram and the ratio of the length of the first side (the longest side) of the parallelogram to the length in the direction perpendicular to the first side is an integer, or when the diaphragm 2 is an ellipse and the ratio of the major axis to the minor axis of the ellipse is an integer. Therefore, the diffusion of the bending wave speaker 1 can be improved. For example, installing the bending wave speaker 1 in a commercial facility or public facility can prevent the speaker (sound source) from being difficult to determine its position or direction, which can lead to a blurry sound, and thus reduce the acoustic discomfort or unnaturalness that can occur. Furthermore, installing the bending wave speaker 1 in a train station or a location with a low ceiling can transmit necessary information while excluding unnecessary directional information when making announcements.

[0040] In the above embodiment, the diaphragm 2 is a parallelogram, and the parallelogram has two first sides and two second sides that are shorter than the first sides. The length of the first sides is X, the length in the perpendicular direction is Y, the distance from the first side to the actuator 3 along the extension direction of the second sides is Y1, and the distance from the second side to the actuator 3 along the extension direction of the first sides is X1. The ratio of Y1 to Y, Y1 / Y, is 60 / 139, and the ratio of X1 to X, X1 / X, is 1 / 3. After extensive research, the inventors found that when the diaphragm 2 is a parallelogram, by positioning the actuator 3 at a position that satisfies the above ratio, the auditory sense of diffusion is enhanced rather than the frequency characteristics. Therefore, the diffusion characteristics of the bending wave speaker 1 can be more effectively improved.

[0041] In the above embodiment, the diaphragm 2 is rectangular. This configuration allows for a higher yield rate than when the diaphragm 2 is oval, thereby reducing waste and enabling more efficient production.

[0042] In the above embodiment, when the diaphragm 2 is rectangular, X is 450 mm, Y is 278 mm, X1 is 150 mm, and Y1 is 120 mm. As a result of extensive research, the inventors have found that when the diaphragm 2 is rectangular, by setting the installation position of the actuator 3 to a position that satisfies the above dimensions, the audible diffusion properties are enhanced rather than the frequency characteristics. Therefore, the diffusion properties of the bending wave speaker 1 can be more effectively improved.

[0043] In the above embodiment, the diaphragm 2 is elliptical. When a parallelogram inscribed in the ellipse is drawn, the parallelogram has two long sides and two short sides. The length of the long sides is X, the length of the short sides is Y, the distance from the long side to the actuator 3 along the extension direction of the short sides is Y1, and the distance from the short side to the actuator 3 along the extension direction of the long sides is X1. The ratio of Y1 to Y, Y1 / Y, is 60 / 139, and the ratio of X1 to X, X1 / X, is 1 / 3. After extensive research, the inventors found that when the diaphragm 2 is elliptical, positioning the actuator 3 at a position that satisfies the above ratio enhances the audible diffusion characteristics rather than the frequency characteristics. Therefore, the diffusion characteristics of the bending wave speaker 1 can be more effectively improved.

[0044] In the above embodiment, the diaphragm 2 is made of resin corrugated cardboard. With this configuration, compared to when the diaphragm 2 is made of expanded polystyrene, it is possible to attenuate the vibration from the actuator 3 while appropriately deforming the diaphragm 2 in response to the movement of the actuator 3, and it is possible to appropriately increase the strength and rigidity of the diaphragm 2. Furthermore, since resin corrugated cardboard is generally inexpensive, it can be manufactured at low cost, which is preferable.

[0045] In the above embodiment, the resin cardboard comprises two liner sections 2 a, 2 b arranged substantially parallel to each other and facing each other, and a buffer section 2 c arranged between and connected to the liner sections 2 a, 2 b, with the buffer section 2 c having a rib structure arranged parallel to one direction and at equal intervals. This configuration makes it possible to damp vibrations from the actuator 3 while appropriately deforming the diaphragm 2 in response to the movement of the actuator 3, and is further advantageous in terms of appropriately increasing the strength and rigidity of the diaphragm 2.

[0046] In the above embodiment, the resin cardboard is made of polypropylene. This configuration allows the vibration plate 2 to be appropriately deformed in response to the movement of the actuator 3 while attenuating the vibration from the actuator 3, which is even more suitable for appropriately increasing the strength and rigidity of the vibration plate 2.

[0047] In the above embodiment, the bending wave speaker 1 further includes a frame 4 that is disposed on the diaphragm 2 around the outer periphery of the diaphragm 2 and supports the diaphragm 2. With this configuration, the frame 4 can appropriately increase the strength and rigidity of the bending wave speaker 1.

[0048] In the above embodiment, when the diaphragm 2 is a parallelogram, the frame 4 has a parallelogram frame shape that follows the outer periphery of the parallelogram. This configuration is preferable because it can maximize the area in which the diaphragm 2 vibrates (the area within the frame 4) when the diaphragm 2 is a parallelogram.

[0049] In the above embodiment, the diaphragm 2 is a parallelogram having two first sides and two second sides shorter than the first sides. The length of the first side within the frame 4 is X, the length in the perpendicular direction within the frame 4 is Y, the distance from the first side along the extension direction of the second side to the actuator 3 along the extension direction of the first side is Y1, and the distance from the second side along the extension direction of the first side to the actuator 3 along the extension direction of the first side is X1. The ratio of Y1 to Y, Y1 / Y, is 48 / 115, and the ratio of X1 to X, X1 / X, is 63 / 201. After extensive research, the inventors discovered that, in a configuration including a frame 4 supporting the diaphragm 2, by positioning the actuator 3 at a position that satisfies the above ratio, the auditory diffuseness is enhanced rather than the frequency characteristics. Therefore, the diffuseness of the bending wave speaker 1 can be more effectively improved. Furthermore, since the above ratio is set based on the area in which the diaphragm 2 vibrates (the area within the frame 4), it is highly beneficial in terms of more effectively increasing the diffusion of the bending wave speaker 1.

[0050] In the above embodiment, when the diaphragm 2 is a parallelogram in a configuration including a frame 4 supporting the diaphragm 2, X is 402 mm, Y is 230 mm, X1 is 126 mm, and Y1 is 96 mm. As a result of extensive research, the inventors have found that when the diaphragm 2 is a parallelogram in a configuration including a frame 4 supporting the diaphragm 2, by setting the installation position of the actuator 3 to a position that satisfies the above dimensions, the audible diffusion properties are enhanced rather than the frequency characteristics. Therefore, the diffusion properties of the bending wave speaker 1 can be more effectively improved.

[0051] In the above embodiment, the frame 4 is a wooden frame. This allows for a lighter weight bending wave speaker 1 compared to when the frame 4 is made of metal. Furthermore, wooden frames are generally inexpensive and can be manufactured at low cost, which is preferable.

[0052] <Modifications> In the above embodiment, the diaphragm is a parallelogram, and the parallelogram has two first sides and two second sides shorter than the first sides. The length of the first sides is X, the length in the perpendicular direction is Y, the distance from the first sides to the actuator along the extension direction of the second sides is Y1, and the distance from the second sides to the actuator along the extension direction of the first sides is X1. The ratio Y1 / Y of Y1 to Y is 60 / 139, and the ratio X1 / X of X1 to X is 1 / 3. However, this is not limited to this. For example, when the diaphragm is a parallelogram, the actuator may be installed at a position with a ratio different from the above ratio. The installation position of the actuator may be any position that can enhance the diffusion of sound in a bending wave speaker, and may be changed according to design specifications.

[0053] In the above embodiment, an example was described in which X is 450 mm, Y is 278 mm, X1 is 150 mm, and Y1 is 120 mm when the diaphragm is a parallelogram, but this is not limiting. For example, when the diaphragm is a parallelogram, the actuator may be installed at a position with dimensions different from the above dimensions. The actuator may be installed at any position that can increase the diffusion of sound in the bending wave speaker, and may be changed according to the design specifications.

[0054] In the above embodiment, an example was described in which the diaphragm is elliptical, and when a parallelogram inscribed in the ellipse is drawn, the parallelogram has two long sides and two short sides, with the length of the long sides being X, the length of the short sides being Y, the distance from the long side along the extension direction of the short sides being Y1 to the actuator, and the distance from the short side along the extension direction of the long sides being X1, the ratio Y1 / Y of Y1 to Y is 60 / 139, and the ratio X1 / X of X1 to X is 1 / 3. However, this is not limited to this. For example, when the diaphragm is elliptical, the actuator may be installed at a position with a ratio different from the above. The installation position of the actuator may be any position that can enhance the diffusion of sound in a bending wave speaker, and may be changed according to design specifications.

[0055] In the above embodiment, the diaphragm is made of resin cardboard, but this is not limiting. For example, the diaphragm may be made of a carbon fiber plate. The diaphragm may be deformable in response to the movement of the actuator. Furthermore, it is preferable that the diaphragm has a configuration and material that can attenuate vibrations from the actuator. The shape of the diaphragm can be changed according to the design specifications.

[0056] In the above embodiment, an example was described in which the corrugated resin board includes two liner sections arranged substantially parallel to each other and facing each other, and a buffer section arranged between the liner sections and connected to the liner sections, and the buffer section has a rib structure arranged parallel and equally spaced in one direction. However, this is not limited to this. The configuration of the corrugated resin board is not particularly limited as long as it can deform in response to the movement of the actuator. Furthermore, it is preferable that the configuration of the corrugated resin board is capable of damping vibrations from the actuator. The form (configuration) of the corrugated resin board can be changed according to the design specifications.

[0057] In the above embodiment, the corrugated resin board is made of polypropylene, but the present invention is not limited to this. For example, the corrugated resin board may be made of polycarbonate. The material of the corrugated resin board is not particularly limited as long as it can deform in response to the movement of the actuator. Furthermore, it is preferable that the material of the corrugated resin board is a material that can attenuate vibrations from the actuator. The form (material) of the corrugated resin board can be changed according to the design specifications.

[0058] In the above embodiment, the bending wave speaker further includes a frame that is disposed on the diaphragm and supports the diaphragm. However, the present invention is not limited to this. For example, the frame does not have to be disposed on the diaphragm and around the diaphragm. The bending wave speaker may include a support member other than the frame. The installation mode of the frame can be changed according to design specifications.

[0059] In the above embodiment, when the diaphragm is a parallelogram, the frame has a parallelogram frame shape that follows the periphery of the parallelogram. However, this is not limited to this. For example, when the diaphragm is an ellipse, the frame may have an ellipse frame shape that follows the periphery of the ellipse. The shape of the frame is not particularly limited as long as it can support the diaphragm.

[0060] In the above embodiment, the diaphragm is a parallelogram, and the parallelogram has two first sides and two second sides shorter than the first sides. The length of the first side is defined as the dimension within the frame, the length in the perpendicular direction is defined as Y, the distance from the first side to the actuator along the extension direction of the second side is defined as Y1, and the distance from the second side to the actuator along the extension direction of the first side is defined as X1. The ratio Y1 / Y of Y1 to Y is 48 / 115, and the ratio X1 / X of X1 to X is 63 / 201. However, this is not limited to this. For example, in a configuration including a frame supporting the diaphragm, if the diaphragm is a parallelogram, the actuator may be installed at a position with a different ratio. The installation position of the actuator may be any position that enhances the diffusion of sound in a bending wave speaker, and may be changed according to the design specifications.

[0061] In the above embodiment, an example was described in which X is 402 mm, Y is 230 mm, X1 is 126 mm, and Y1 is 96 mm when the diaphragm is a parallelogram in a configuration including a frame supporting the diaphragm. However, this is not limited to this. For example, when the diaphragm is a parallelogram in a configuration including a frame supporting the diaphragm, the installation position of the actuator may be set to a position with dimensions different from the above dimensions. The installation position of the actuator may be any position that can increase the diffusion of the sound in the bending wave speaker, and may be changed according to the design specifications.

[0062] In the above embodiment, the frame is a wooden frame, but this is not limiting. For example, the frame may be made of metal. The material of the frame is not particularly limited as long as it can support the diaphragm.

[0063] Although the embodiments of the present invention have been described above, the present invention is not limited to these, and additions, omissions, substitutions, and other modifications to the configuration are possible within the scope of the spirit of the present invention, and the above-described embodiments can also be combined as appropriate.

[0064] The bending wave speaker according to the above embodiment of the present invention will be described in detail below with reference to examples. Note that the following examples are specific examples to which the present invention is applied, and are not intended to limit the present invention.

[0065] <Implementation Example of a Panel Speaker Utilizing Bending Waves of a Diaphragm> In the late 1990s, New Transducers Limited (NXT) of the UK proposed the Distributed Mode Loudspeaker (DML) (see Non-Patent Document 1). The DML was designed using a method registered in Japan as Patent No. 3763848 (see Patent Document 1). The inventor has had many opportunities to think about DML utilization technologies through industry-academia collaboration and other activities. Furthermore, research into speakers that radiate sound using bending waves of a diaphragm, including the DML, is ongoing.

[0066] In this study, we attempted to design and implement a panel speaker without relying on NXT's patents. During the design, we placed more emphasis on the auditory "diffuse properties of radiation" than on frequency characteristics. The diffuse properties of radiation have also been mentioned by Gontcharov et al. We will call the panel speaker implemented in this study, which emphasizes diffuse properties, a bending wave loudspeaker (BWL). In the following explanation, we will explain the design principles and report the measurement results of the amplitude-frequency characteristics in each direction as basic characteristics.

[0067] <Design Policy> This section describes the design policy for the bending wave speaker implemented in this study. When the diaphragm is rectangular and the ratio of the long side to the short side is a simple integer, the frequencies of the standing waves generated in the long side direction and the standing waves generated in the short side direction may coincide, resulting in degeneration of the modal frequency. When the modal frequency degenerates, the peak density of the amplitude frequency characteristics becomes sparse, and dips become more noticeable. In this study, to avoid such degeneration, the ratio of the long side to the short side was set to {(1 + √5) / 2}:1, the so-called golden ratio. The dimension of the long side was also set to 450 mm.

[0068] For the diaphragm, plastic cardboard was used as a durable material with moderate loss. Plastic cardboard is an anisotropic material. The grain direction (furrows) of the plastic cardboard was cut in the direction of the short side. This was done in the hope that bending waves would be more easily generated in the direction of the long side.

[0069] The driving position of the diaphragm was heuristically set to a position that maximized the perceived diffuseness rather than the frequency characteristics while conducting listening tests in a room such as a conference room. The dimensions of the diaphragm and driving position (actuator installation position) used in this study are shown in Figure 3. For implementation, the diaphragm was attached to a wooden frame 24 mm wide.

[0070] <Frequency Characteristics of the Implemented Bending Wave Speaker> The frequency characteristics of the implemented bending wave speaker were measured in an anechoic chamber in the Special Acoustics Building on the Ohashi Campus of Kyushu University. The directivity angle was measured every 45°. The 0° direction is perpendicular to the diaphragm. The results are shown in Figs. 7 to 11. Fig. 7 shows the frequency characteristics of the bending wave speaker of the example (when the directivity angle is 0°). Fig. 8 shows the frequency characteristics of the bending wave speaker of the example (when the directivity angle is 45°). Fig. 9 shows the frequency characteristics of the bending wave speaker of the example (when the directivity angle is 90°). Fig. 10 shows the frequency characteristics of the bending wave speaker of the example (when the directivity angle is 135°). Fig. 11 shows the frequency characteristics of the bending wave speaker of the example (when the directivity angle is 180°).

[0071] 7 to 11, it was confirmed that the 90° direction in the extension direction of the diaphragm exhibited unique characteristics from the amplitude-frequency characteristics for each direction. In directions other than the 90° direction, although there were slight changes in the peaks and dips of the characteristics, it was found that the characteristics were generally similar.

[0072] This example shows a concrete example of an attempt to design and implement a panel speaker without relying on NXT's patents. Furthermore, the results of measurements of directional amplitude-frequency characteristics as basic characteristics are shown. When designing the drive position, priority was given to the auditory sense of diffusion rather than balance of frequency characteristics, but as mentioned above, the overall characteristics of the frequency characteristics were similar regardless of direction.

[0073] <Study on the evaluation of speakers with different sound generation mechanisms based on critical distance in a diffuse sound field> This study outlines the characteristics of this study. Bending wave loudspeakers (BWL) have a unique sound generation mechanism that actively utilizes bending waves. As a result, they radiate sound with a distorted wavefront shape, driving a distinctive sound field. In this study, we defined this acoustic characteristic as "K" and analyzed the differences in "K" characteristics due to sound generation mechanisms, radiating area, and diaphragm materials, focusing on critical distance. For the analysis, we measured the impulse response of a reverberation room using a test speaker and compared critical distances using phase trend, group delay, and total energy methods. The results showed that bending wave loudspeakers, regardless of radiating area or material, have shorter critical distances than conventional speakers such as cone speakers. This suggests that the sound field driven by speakers with the "K" characteristic is dominated by reverberation.

[0074] <About BWL> This section explains the speaker used in the measurements in this study. While typical speakers use a cone-shaped diaphragm, bending wave speakers (BWL) use a flat panel diaphragm and generate sound waves by utilizing the bending waves of the diaphragm. Bending waves cause distortion in frequency characteristics. Therefore, cone speakers require a mechanism that prevents the generation of bending waves. However, BWL actively utilizes these bending waves. As a result, the wavefront does not radiate uniformly forward from the sound source, and the BWL's directivity does not have a main lobe. This allows for the sound energy to be distributed uniformly within the sound field, creating a distinctive, vague sound field. This characteristic of BWL is expected to enable its use in announcement broadcasts in public facilities where people gather, enabling the transmission of sound with the same sound pressure to many people in the space.

[0075] The bending wave speaker invented and designed by New Transducers Limited (NXT) in the UK is called the Distributed Mode Loudspeaker (DML), and in this study, the DML manufactured by Amonet Co., Ltd. was used for measurements. In this study, the bending wave speaker manufactured by Amonet is called the DML, and the bending wave speaker manufactured in the laboratory, which will be described later, is called the BWL.

[0076] <Definition of "characteristic K"> Let us explain the critical distance. Sound emitted from a sound source can be classified into direct sound, which arrives at the sound receiving point in a straight line over the shortest distance, and reverberant sound, which arrives at the sound receiving point after reflecting off the walls of the room and attenuating. The space where direct sound near the sound source is dominant is called the direct sound region, and the space other than that where reverberant sound is dominant is called the reverberant sound region. The boundary between these two regions is the point where the energy ratio between direct sound and reverberant sound is 1, and the distance from the sound source to this point is called the critical distance.

[0077] This section explains "coherence" in optics. Acoustics and optics, both fields that deal with the same wave phenomenon, often use analogies with each other. Below, we will explain "coherence" in optics, which is used in the analogy with acoustics, which will be discussed later. Light is also a wave phenomenon, so it can interfere like sound. The interference of light can be observed as interference fringes. Light that can create interference fringes is "coherent," or coherent. The condition for light to be coherent is that it has a constant amplitude and phase. Conversely, light with random phase and amplitude does not interfere, and is therefore "diffused."

[0078] Interference in optics is primarily classified into two types: "temporal coherence" and "spatial coherence." Simply put, the more similar the temporal or spatial waveforms of two superimposed beams of light are, the better the temporal or spatial coherence, which can be expressed by the autocorrelation function of the two waveforms. Spatial coherence relates to how little the light spreads and how parallel it is like a laser, while temporal coherence relates to how monochromatic the light is. Applying this classification of coherence in optics to sound, spatial coherence can be thought of as a property related to the directionality of the sound source and how close it is to a point source, while temporal coherence can be thought of as a property related to whether the sound source is a sine wave and whether the speaker is vibrating in a divided manner.

[0079] We will now explain the characteristic K. Morse and Bolt [1] argued that the direct sound field is "coherent" and the reverberant sound field is "incoherent." NXT [2] also used the optical terms coherent and diffused to describe the acoustic characteristics of DML. As mentioned above, the wavefront shape of the sound generated by BWL, which uses bending waves, is distorted. Furthermore, because the directivity of BWL does not have a sharp main lobe, there is no sweet spot, and the sound is heard inconsistently within the sound field. In this study, we refer to the characteristic of a speaker with such "diffused" sound as K. The letter K was used because it was not commonly used as the initial letter of words in the Acoustics Dictionary [3].

[0080] <Research Background and Significance> In a study by Lende [4], a new index for expressing the acoustic characteristics of BWL, different from the evaluation index used in conventional speaker design, such as "high fidelity," was developed. The authors compared the critical distance distributions of speakers in a room from three perspectives: phase trend, group delay, and total energy method. Progress in this research is expected to enable the aforementioned speaker characteristic "K" to be expressed numerically. An evaluation index for this characteristic would enable comparison of two speakers to determine which has a better "K." It would also facilitate the expression of required performance depending on the intended use. For example, when using BWL in a certain location, knowing a guideline for the "K" required for a space of a certain size or reverberation characteristics would facilitate selecting the appropriate speaker. Furthermore, this evaluation index could serve as a guide for the development of new speakers. When developing a product for a specific intended use, knowing the aforementioned "K" guideline would allow the design to meet that guideline. This would also provide a clear guide for advancing BWL research and development. However, in the previously mentioned study [4], a microphone whose phase frequency characteristics had not been confirmed was used for the measurements, which was thought to be a problem in terms of accuracy. Also, previous studies have compared DML and cone speakers, but since the two differ not only in their sound-generating mechanisms but also in their radiating areas, it is necessary to confirm whether the differences in the results are due to the sound-generating mechanisms.

[0081] <Purpose of this study> In this study, we will examine methods for evaluating the "K" characteristic of speakers, focusing on critical distance. We predict that speakers with a higher "K" characteristic will have a shorter critical distance. For this reason, we selected closed-type cone speakers and bending wave speakers, which have different sound-generating mechanisms, as the speakers to be measured. We will also compare cone speakers and bending wave speakers, which have the same radiating area, to see if there are any differences in the critical distance. We will also check how the critical distance changes depending on the material used for the diaphragm of bending wave speakers.

[0082] Our laboratory is still in the trial and error stage of creating BWLs, and we are currently investigating the differences between materials and shapes. The diaphragm must vibrate smoothly and be durable enough to not tear. After considering a diaphragm material that was "thin, flexible, and strong," we determined that carbon fiber, which we had obtained in our laboratory, was suitable. This carbon fiber is formed into a sheet, and when rolled into a thin ball, it is strong enough to be used as a fishing rod. In this study, we used three methods to analyze the critical distance: phase trend, group delay, and total energy methods.

[0083] <Design and construction of BWL> In this experiment, we used BWLs with different diaphragms and sizes to confirm whether the critical distance differs depending on the shape of the speaker. Below, we will describe the design and construction of the speakers actually used in the measurements.

[0084] <The BWLs we created> We used two types of diaphragms, plastic cardboard and carbon sheet, and two sizes, large and small, with different combinations to create the following four BWLs: Plastic cardboard, small size; Plastic cardboard, medium size; Carbon, small size; Carbon, medium size

[0085] The design, manufacturing methods, and material selection were based on Iwata [7]. Iwata also used polystyrene board as the diaphragm material, but plastic cardboard showed a greater change in directivity depending on the frequency. Because of this, we decided to use plastic cardboard for the diaphragm in this experiment, as we thought it would better represent the "K" characteristic of the BWL mentioned above. As mentioned above, carbon fiber was used as the new diaphragm material in this experiment. Furthermore, in this study, we will use a BWL with the same dimensions as the BWL created by Iwata, which will be referred to as size M. As mentioned above, in this study, we will use a BWL with the same radiating area as the cone speaker used for comparison with the BWL, which will be referred to as size S.

[0086] The materials are explained below. (1) Wood (for medium size: 24mm x 45mm x 450mm x 2 pieces, 24mm x 45mm x 230.1mm x 2 pieces) (2) Wood (for small size: 24mm x 45mm x 194.2mm x 2 pieces, 24mm x 45mm x 146.2mm x 2 pieces) (3) Panels (plastic cardboard, carbon sheet (medium size: 450mm x 278.1mm, small size: 194.2mm x 194.2mm)) (4) Transducer (daytonaudio DAEX25) (5) Double-sided tape (butyric rubber cushion type) (6) Screws (8 pieces) (7) Adhesive

[0087] The dimensions will now be explained. The dimensions of the M and S size BWLs that were created are shown in Figure 12. Figure 12 is a diagram showing the dimensions of the manufactured BML. In Figure 12, the upper part corresponds to a view from above, and the lower part corresponds to a view from the side. In Figure 12, the dimensions are in mm.

[0088] The manufacturing method is explained below. (1) The wooden pieces are glued together as shown in Figure 12. (2) The wooden pieces are fixed in place with screws. (3) A panel is attached to one side of the wooden frame using double-sided tape. (4) A vibrator is attached to the panel. The completed BWL is shown in Figure 13 below. Figure 13 is a diagram showing the completed BWL. In Figure 13, the left is the M size and the right is the S size. In Figure 13, the left corresponds to the left in each of the figures (a) to (d), and the right corresponds to the right in each of the figures (a) to (d).

[0089] <Measurement of impulse response by distance> For the analysis of this experiment, we used impulse response data collected by gradually changing the distance between the sound source and the sound receiving point. The specific measurement conditions and procedures for the impulse response by distance are summarized below.

[0090] <Measurement> The measurement conditions are explained below. Measurement location: Reverberation room on the first floor of the special acoustic building at the Ohashi Campus of Kyushu University Equipment used: (1) Speakers: Closed full-range speakers (manufactured by the laboratory) DML (Amonet MONE01) BWL (S-size plastic cardboard) BWL (M-size plastic cardboard) BWL (S-size carbon sheet) BWL (M-size carbon sheet) (2) Amplifier (SONY STR-DH590) (3) Microphone (B & K 4191) (4) Microphone amplifier (ACO TYPE 6030) (5) Audio interface (RME Babyface Pro) (6) Matlab Impulse Response Measuring device on MacOS (48 kHz, 16-bit TSP signal)

[0091] The reverberation chamber used for the measurements had a volume of 154.71 m3, based on previous research [4]. ３ The reverberation time is 5.96 seconds, and the critical distance is 0.29 meters. The reverberation time was calculated by recording impulse responses for a total of 12 patterns, two sound source positions and six sound recording locations, and then averaging the reverberation times calculated from each response. The critical distance was calculated using equation (1).

[0092]

[0093] The measurement method will be explained. For the measurement, an Impulse Response Measurer was used on MacOS. A 48 kHz, 16-bit TSP signal was used. The block diagram used for the measurement is shown in Figure 14. Figure 14 shows the block diagram used for the measurement.

[0094] The specific measurement procedure is explained below. A TSP signal was played from the speaker under measurement, and sound was collected by a microphone. The measurement points and speaker output levels were set with reference to Lende [4]. The distance from the sound source to the measurement points and the number of points vary depending on the analysis method of the measurement results. For the phase trend and group delay, sound was collected at a total of 17 points, with the distance varying by a factor of √2 between 0.01 m and 2.56 m. For the total energy method, sound was collected at a total of 11 points, with the distance varying by a factor of √2 between 0.112 m and 3.584 m.

[0095] We will now explain the S / N ratio. In this study, we will analyze the impulse response by distance using three methods: phase trend, group delay, and total energy method. Phase trend analyzes the gradient of the amplitude characteristics of the transfer function obtained from the impulse response, while group delay analyzes the phase change of the transfer function. For this reason, it is desirable to adjust the speaker output level and perform measurements so that a constant S / N ratio is achieved at each measurement point. Therefore, the impulse response by distance used in the analysis of phase trend and group delay was measured by adjusting the microphone gain so that the S / N ratio at each measurement point fell within a certain range.

[0096] On the other hand, the total energy method analyzes the change in sound pressure of the impulse response at different distances. Therefore, measurements were taken at all measurement points with the same speaker sound pressure and microphone gain, without adjusting the microphone gain. A different measurement interval was set for this data set from the other two analyses. This was to prevent a large difference in the S / N ratio when the sound source-receiving point distance was at its minimum and maximum.

[0097] <Measurement Results> Below are some of the impulse response results measured using a closed-type speaker.

[0098] The case where the microphone gain is changed will be explained. The impulse response for analysis using phase trend and group delay was measured while adjusting the microphone gain as described above. Figure 15 shows a portion of the impulse response of a reverberation room measured using a closed-type speaker. These time waveforms are normalized with the maximum value set to 1. Figure 15 shows the impulse response of a closed-type speaker (with level change).

[0099] The case where the microphone gain was not changed will now be described. As described above, the impulse response for analysis using the total energy method was measured without adjusting the microphone gain. A portion of the impulse response of a reverberation room measured using a closed-type speaker is shown in Figure 16. Figure 16 shows the impulse response of a closed-type speaker (without level change).

[0100] <Evaluation of Diffusion (Diffusional Properties of Radiation Auditory Sensation)> Diffusion (Diffusional Properties of Radiation Auditory Sensation) was evaluated through experiments. In the first experiment, multiple speakers were placed at intervals in an ordinary room, and multiple subjects were blindfolded and asked to raise their hands in the direction they thought a speaker was facing. Ordinary speakers were used for this experiment. As a result of the subjects' responses, the number of subjects who could not identify the direction of the speaker (number of people who gave incorrect answers) was three.

[0101] The subjective evaluation of one speaker will now be described. In the second experiment, a subjective evaluation of one speaker was performed. In the second experiment, a conventional loudspeaker (comparative example) and a bending wave speaker (example) were used as speakers.

[0102] The conventional loudspeaker (comparison example) used was the distributed mode loudspeaker (DML) disclosed in the aforementioned Non-Patent Document 1. The comparative DML is configured with a diaphragm, an exciter that drives the diaphragm, and a frame that supports the diaphragm. The comparative DML is equipped with one exciter, and the exciter position is set at a position where the lengths of the sides of the rectangular diaphragm are in a ratio of 3:4 or 4:5.

[0103] The bending wave speaker (Example) used the bending wave speaker in the above-described embodiment. The bending wave speaker of the Example was configured to include a diaphragm, an actuator disposed on the diaphragm to vibrate the diaphragm, and a frame disposed on the diaphragm around the periphery of the diaphragm to support the diaphragm. The bending wave speaker of the Example had a diaphragm shaped like a parallelogram (rectangle), and the ratio between the length of the first side, which is the longest side of the rectangle, and the length in the direction perpendicular to the first side was an irrational number. In the bending wave speaker of the example, a rectangle is composed of two first sides and two second sides that are shorter than the first sides, and the dimension within the frame of the length of the first sides is X, the dimension within the frame of the length in the perpendicular direction is Y, the dimension within the frame of the distance from the first side along the extension direction of the second side to the actuator is Y1, and the dimension within the frame of the distance from the second side along the extension direction of the first side to the actuator is X1, where the ratio of Y1 to Y is Y1 / Y is 48 / 115, the ratio of X1 to X is X1 / X is 63 / 201, X is 402 mm, Y is 230 mm, X1 is 126 mm, and Y1 is 96 mm.

[0104] In the second experiment, three subjects (those who gave incorrect answers) from the first experiment were excluded. The results of the second experiment are shown in FIG.

[0105] Figure 17 shows the results of subjective evaluations of a single speaker. As shown in Figure 17, the bending wave speaker (Example) had a more dispersed distribution than the conventional loudspeaker (Comparative Example), and it was confirmed that many subjects took a relatively long time to respond. This is thought to be because the direction of the bending wave speaker (Example) was not clearly identified, which led to a longer response time. The vertical axis of Figure 17 also shows the error between the response direction and the installation position. The larger this error, the more the speaker's position was misidentified.

[0106] The answer trends will now be explained. In this analysis, we analyzed the subjects who answered the correct speaker direction with an accuracy of ±2° in the second experiment. Seven subjects (only those who answered correctly) were used in this analysis. The results of this analysis are shown in Figure 18.

[0107] 18 shows the analysis results for subjects who answered the correct direction. As shown in FIG. 18, it was confirmed that, even though subjects took longer to answer in the Example than in the Comparative Example, there was a large error between the answered direction and the installation position. It was also confirmed that subjects made mistakes even though they answered faster in the Example than in the Comparative Example.

[0108] The case where weighting was performed according to response time will now be described. Assuming that speakers that are difficult for test subjects to localize are the ones that are difficult to localize, weighting was performed according to response time. The results are shown in Figure 19.

[0109] Fig. 19 shows the results of weighting according to response time. As shown in Fig. 19, it was confirmed that there was a difference in the slope between the Example and the Comparative Example. It is thought that there is a difference in the difficulty of localizing between speakers between the Example and the Comparative Example. The greater the slope, the more difficult it is to determine the position and direction of the speaker (sound source) (feeling vague).

[0110] From the above results, it can be said that the bending wave speaker (Example) tends to make it difficult to determine the position and direction of the speaker (sound source) (a vague feeling) compared to the conventional loudspeaker (Comparative Example), and can improve diffusion.

[0111] Fig. 20 is a perspective view of the bending wave speaker of the embodiment as seen from the front side. Fig. 21 is a perspective view of the bending wave speaker of the embodiment as seen from the back side. Fig. 22 is a perspective view of the bending wave speaker of the embodiment as seen from the side. In Figs. 20 to 22, the bending wave speaker is shown together with an SD card so that the size can be seen.

[0112] REFERENCE SIGNS LIST 1 bending wave speaker 2 diaphragm 2a, 2b liner portion 2c buffer portion 3 actuator 4 frame

Claims

1. A bending wave speaker comprising: a diaphragm; and an actuator disposed on the diaphragm for vibrating the diaphragm; wherein the diaphragm is a parallelogram or an ellipse; and when the diaphragm is a parallelogram, the ratio of the length of a first side, which is the longest side of the parallelogram, to the length in a direction perpendicular to the first side is an irrational number; and when the diaphragm is an ellipse, the ratio of the major axis to the minor axis of the ellipse is an irrational number.

2. The bending wave speaker according to claim 1, wherein the diaphragm is a parallelogram, the parallelogram having two of the first sides and two second sides shorter than the first sides, and wherein, when the length of the first sides is X, the length in the perpendicular direction is Y, the distance from the first side to the actuator along the extension direction of the second sides is Y1, and the distance from the second side to the actuator along the extension direction of the first sides is X1, a ratio Y1 / Y of Y1 to Y is 60 / 139, and a ratio X1 / X of X1 to X is 1 / 3.

3. A bending wave speaker as claimed in claim 2, wherein said diaphragm is rectangular.

4. A bending wave speaker as claimed in claim 3, wherein X is 450 mm, Y is 278 mm, X1 is 150 mm and Y1 is 120 mm.

5. The bending wave speaker according to claim 1, wherein the diaphragm is elliptical, and when a parallelogram inscribed in the ellipse is drawn, the parallelogram has two long sides and two short sides, and when the length of the long sides is X, the length of the short sides is Y, the distance from the long sides to the actuator along the extension direction of the short sides is Y1, and the distance from the short sides to the actuator along the extension direction of the long sides is X1, a ratio Y1 / Y of Y1 to Y is 60 / 139, and a ratio X1 / X of X1 to X is 1 / 3.

6. A bending wave speaker according to claim 1 or 2, wherein the diaphragm is made of resin cardboard.

7. A bending wave speaker according to claim 6, wherein the resin corrugated cardboard comprises two liner sections arranged substantially parallel to each other and facing each other, and a buffer section arranged between the liner sections and connected to the liner sections, and the buffer section has a rib structure arranged parallel to one direction and at equal intervals.

8. The bending wave speaker according to claim 6, wherein the resin cardboard is made of polypropylene.

9. The bending wave speaker according to claim 1, further comprising a frame disposed on the diaphragm around the outer periphery of the diaphragm to support the diaphragm.

10. A bending wave speaker according to claim 9, wherein when the diaphragm is a parallelogram, the frame has a parallelogram frame shape that follows the outer periphery of the parallelogram.

11. The bending wave speaker according to claim 10, wherein the diaphragm is a parallelogram, the parallelogram having two of the first sides and two second sides shorter than the first sides, wherein a dimension of the length of the first sides within the frame is X, a dimension of the length in the perpendicular direction within the frame is Y, a dimension of the distance from the first side to the actuator along the extension direction of the second side is Y1 within the frame, and a dimension of the distance from the second side to the actuator along the extension direction of the first side is X1 within the frame, a ratio Y1 / Y of Y1 to Y is 48 / 115 and a ratio X1 / X of X1 to X is 63 / 201.

12. A bending wave speaker as claimed in claim 11, wherein X is 402 mm, Y is 230 mm, X1 is 126 mm and Y1 is 96 mm.

13. A bending wave speaker as claimed in claim 9, wherein the frame is a wooden frame.

Images