Display device and sound emitting method thereof

Abstract

An embodiment of the present invention discloses a display device and a sound-generating method thereof. In a specific embodiment of the invention, the display device includes: a display screen, a controller, and at least one phased speaker array, the phased speaker array including a plurality of speakers, and the controller is configured to control the focusing deflection or sound beam deflection of the phased speaker array to emit sound waves toward the top surface of the listening environment so as to be reflected to the listening area within the listening environment. This embodiment provides a phased speaker array in the display device and controls the focusing deflection or sound beam deflection of the phased speaker array so that the listening area can receive a sound wave signal containing height information reflected from the top surface of the listening environment, thereby enhancing the listener's spatial height perception and having broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of audio signal processing, and more particularly to a display device and a sound generating method thereof. Background Art

[0002] Ultra-thin, narrow-frame, and even full-screen designs of display devices leave less and less space for sound-generating devices. Currently, there are display devices that use the entire screen as a diaphragm to achieve sound generation. In this design, the display device directly generates sound to achieve synchronization between sound and picture, which can effectively utilize space and save resources. When combined with a large-size screen, it can further increase the sound power and achieve different sound field effects. Existing screen sound-generating units can attach an exciter, such as a piezoelectric film, to the back of the screen. The exciter drives the screen to vibrate, which in turn drives the entire screen to vibrate, thereby promoting the screen to produce sound.

[0003] A good sound effect can provide viewers with immersion and high-precision audio positioning, which involves arranging multiple speaker arrays in the room. In a home entertainment environment, when watching TV, viewers also strive to reproduce the audio information coming from above the viewers in three-dimensional space. To achieve this, the conventional practice is to install additional height speakers on the ceiling, but for many consumers, such height speakers may be difficult to install. If you simply add a speaker unit to the TV to play the sound source of height information, such as Figure 1 As shown, most of the sound wave information will be radiated directly to the sofa, thus losing the height information of the sound source, reducing the sense of direction of the sound waves, and failing to provide customers with the experience of radiating sound waves from a high altitude.

[0004] Therefore, a speaker design is needed that is easy to install or does not require installation, can emit sound equivalent to a sound source from the ceiling, and can effectively play audio of audio objects representing height information. Summary of the Invention

[0005] The purpose of the present application is to provide a display device and a sound generating method thereof to solve at least one of the problems existing in the prior art.

[0006] To achieve the above objectives, this application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a display device comprising a display screen, a controller, and at least one phased speaker array, wherein the phased speaker array comprises a plurality of speakers, and the controller is configured to control the focusing deflection or the sound beam deflection of the phased speaker array to emit sound waves toward a top surface of a listening environment so as to be reflected to a listening area within the listening environment.

[0008] In some optional embodiments, the speaker is a piezoelectric speaker.

[0009] In some optional embodiments, the display device is a screen sound display device.

[0010] In some optional embodiments, the display device includes two phase-controlled speaker arrays arranged in the upper areas of the left and right sides.

[0011] In some optional embodiments, the phased-control loudspeaker array is a one-dimensional phased-control loudspeaker array or a two-dimensional phased-control loudspeaker array.

[0012] In some optional embodiments, the multiple speakers in the one-dimensional phased speaker array are arranged vertically.

[0013] In some optional embodiments, the multiple speakers in the two-dimensional phased speaker array are arranged in a rectangular arrangement or a circular arrangement.

[0014] In some optional embodiments, the controller is configured to control the focus deflection or the sound beam deflection of the phased speaker array by controlling the sound emission delay of the speakers in the phased speaker array.

[0015] In some optional embodiments, the controller is configured to calculate the deflection angle based on the sound waves reflected by the top surface of the listening environment and the sound waves reflected by objects in the listening area received by the piezoelectric speaker, and control the focusing deflection or the sound beam deflection of the phased speaker array according to the deflection angle.

[0016] A second aspect of the present invention provides a sound emitting method for a display device, comprising:

[0017] At least one phased speaker array provided in the display device is controlled to focus and deflect or to deflect a sound beam so as to emit sound waves toward a top surface of a listening environment so as to be reflected to a listening area in the listening environment.

[0018] The beneficial effects of the present invention are as follows:

[0019] In response to the current problems, the present invention develops a display device and a sound-generating method thereof. By arranging a phased speaker array and a controller in the display device, and controlling the focusing deflection or sound beam deflection of the phased speaker array by the controller, the phased speaker array emits sound waves toward the top of the listening environment, which are reflected to the listening area within the listening environment. This allows the listener to experience overhead radiated sound without having to install additional ceiling speakers, thereby enhancing the listener's spatial height perception and meeting the listener's need for surround sound from overhead sound sources. The present invention has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] Figure 1A schematic side view of a display device in the prior art is shown in which the emitted sound waves are not deflected but directly emit sound.

[0022] Figure 2 A schematic side view showing a display device according to an embodiment of the present invention emitting sound waves toward a ceiling.

[0023] Figure 3 A schematic front view showing a display device according to an embodiment of the present invention emitting sound waves toward a ceiling.

[0024] Figure 4 A schematic structural diagram of a speaker in a display device according to an embodiment of the present invention is shown.

[0025] Figure 5a A schematic diagram showing the focusing deflection principle of a two-dimensional phased loudspeaker array in a display device according to an embodiment of the present invention is shown.

[0026] Figure 5b A schematic diagram showing the principle of sound beam deflection of a one-dimensional phased loudspeaker array in a display device according to an embodiment of the present invention is shown.

[0027] Figure 6 A schematic diagram illustrating physical parameters of a listening environment of a display device according to an embodiment of the present invention.

[0028] Figure 7 A schematic perspective top view shows a display device according to an embodiment of the present invention.

[0029] Figure 8 A schematic perspective top view shows a display device according to another embodiment of the present invention.

[0030] Figure 9 A schematic perspective top view shows a display device according to another embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same or similar reference numerals. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0032] It should be noted that the terms “having”, “including”, “comprising”, etc. described in the present invention all have open meanings, that is, when describing a module as “having”, “including” or “comprising” a first element, a second element and / or a third element, it means that the module includes other elements in addition to the first element, the second element and / or the third element.

[0033] In order to solve one of the above problems, an embodiment of the present invention provides a display device, including a display screen, a controller and at least one phase-controlled speaker array, the phase-controlled speaker array including a plurality of speakers, and the controller is configured to control the focus deflection or sound beam deflection of the phase-controlled speaker array to emit sound waves toward the top surface of the listening environment so as to be reflected to the listening area within the listening environment.

[0034] In this embodiment, a phased speaker array and a controller are provided in the display device, and the controller controls the focus deflection or sound beam deflection of the phased speaker array, so that the phased speaker array emits sound waves toward the top of the listening environment, which are reflected to the listening area within the listening environment. This allows the listener to experience overhead radiated sound without having to install additional ceiling speakers, thereby enhancing the listener's spatial height perception and meeting the listener's demand for surround sound from overhead sound sources. The embodiment has broad application prospects.

[0035] In a specific example, referring to Figure 2 and Figure 3 As shown, in a listening environment, for example, a living room, a television 200 serving as a display device is installed or set up. The television includes a display screen 201, a controller (not shown), and two phased speaker arrays 202-1 and 202-2. A sofa is placed in front of the display screen of the television 200. The area where the sofa is located is the listening area of ​​the listening environment.

[0036] Of course, the display device may also be a computer, electronic whiteboard, or other display device including a display screen. The listening environment may be an office or conference room, and the listening area may correspondingly be a seat in the office or conference room. For ease of description, the following description uses the living room television as a substitute for the display device. Persons skilled in the art should not interpret this as a limitation of the present invention.

[0037] Optionally, the speakers in the phased speaker arrays 202-1 and 202-2 may be piezoelectric speakers. Figure 4 As shown, the specific composition of the piezoelectric speaker is a piezoelectric multi-layer stack structure, including upper and lower electrodes and a piezoelectric layer in the middle. The upper and lower electrodes cover the upper and lower parts of the piezoelectric material respectively. After the electrodes are energized, an electric field is applied to the piezoelectric material, causing the piezoelectric material to deform and produce sound under the action of the electric field. The electrode material may contain silver as its main component, and the piezoelectric layer material may be a film-type piezoelectric ceramic PZT, or a PVDF film, etc. The length and width dimensions of the piezoelectric speaker are greater than or equal to 0.5 cm and less than or equal to 5 cm. When the piezoelectric speakers are arranged in a two-dimensional array, the horizontal or vertical dimensions of the array may be greater than or equal to 5 cm and less than or equal to 50 cm. The television 200 in the embodiment of the present invention is a screen sound display device.

[0038] Phased speaker arrays 202-1 and 202-2 can be Figure 2 The arrangement shown is on the back of the display screen 201, but it can also be arranged on the front side of the display screen opposite the back side. When arranged on the back side of the display screen 201, compared to the case where the phased speaker array is arranged on the front side, it does not occupy the display area of ​​the display screen, thus not affecting the full-screen display, and the display screen can be realized as a narrow-frame display screen.

[0039] In addition, although the television set 200 is shown in this example to include two phased speaker arrays 202-1 and 202-2, the present application is not intended to be limited thereto. The television set 200 may also include one or more phased speaker arrays, and the specific location of each phased speaker array on the television set 200 is not limited. For example, Figure 3 As shown, when two phased speaker arrays 202-1 and 202-2 are provided, the two phased speaker arrays 202-1 and 202-2 are disposed in the upper left and right areas of the television 200. When one phased speaker array is provided, the phased speaker array may be disposed in the upper middle area of ​​the television or in other locations deemed appropriate by the designer.

[0040] Each of the phased-control speaker arrays 202 - 1 and 202 - 2 includes a plurality of speakers, which may form a one-dimensional phased-control speaker array or a two-dimensional phased-control speaker array.

[0041] In particular, through the setting of this example, two phased speaker arrays 202-1 and 202-2 are set in the TV 200, which can perform focus deflection or sound beam deflection under the control of the controller. Through the focus deflection or sound beam deflection, the two phased speaker arrays 202-1 and 202-2 enable the TV 200 to emit sound waves toward the ceiling of the living room. The sound waves are reflected at the ceiling and reflected to the listening area where the sofa is located, so that listeners sitting at any position on the sofa can receive the sound wave signal radiated from the direction of the ceiling above their heads, so that there is no need to install additional speaker equipment on the ceiling, and the listeners on the sofa as the listening area can perceive the sound effect with spatial height, thereby realizing a surround sound effect with high information.

[0042] Specifically, the controller is configured to control the focus deflection or the sound beam deflection of the phased-controlled loudspeaker array by controlling the sound emission delay of the loudspeakers in the phased-controlled loudspeaker array.

[0043] Because sound waves can be superimposed, for multiple sound wave signals, the intensity of sound wave signals with the same phase increases at the location where the signals overlap, while the intensity of sound wave signals with opposite phases decreases. In an embodiment of the present invention, the corresponding relationship between the delay and phase of transmitted sound waves is utilized to control the delay relationship of the sound wave signals emitted by different speakers in a phased array speaker, thereby controlling the phase, so that the sound wave signals overlap and focus or beam deflection is achieved.

[0044] In order to further understand the focus deflection and beam deflection of the phased speaker array. Figure 5a-5b Describe the control principles of focus deflection and beam deflection.

[0045] Figure 5a A schematic diagram showing the principle of focusing and deflection of a two-dimensional phased loudspeaker array.

[0046] First, for focus deflection, each speaker in each phased speaker array deflects the emitted sound wave signal at an angle θi relative to the vertical center axis of the speaker array to calculate the transmitted sound wave delay, where i represents the i-th speaker in the two-dimensional phased speaker array. Figure 5a , so that the wavefront of the sound waves generated by each speaker is concentrated on a point on the ceiling, thus achieving the focusing and deflection of the sound beam. Because the wavefront of the sound waves is concentrated on a point on the ceiling, and after the sound waves are focused and deflected, they will be Figure 3 The illustrated approach reflects radiation from the ceiling and covers the listening area where the sofa is located. The speakers have different deviation angles θi relative to the vertical center axis of the speaker array. In an implementation method that uses the delay of the sound wave signal to control the phase of the outgoing sound wave to produce focus deflection, the delay expression for calculating focus deflection uses the deviation angle between the outgoing direction of the speaker at the center of the array and the center axis as the deflection angle θ of the two-dimensional phased speaker array.

[0047] As shown in the figure, for a two-dimensional phased speaker array, if the plane of the two-dimensional phased speaker array serves as the plane of the y-axis and x-axis in the figure, an xyz coordinate system is established with the center of the array as the origin. The central axis is the z-axis, and θ is the angle at which the direction of the sound waves emitted by the speaker at the center of the array deviates from the z-axis. Those skilled in the art will understand that the same principle applies to a one-dimensional phased speaker array, with θ being the angle at which the direction of the emitted sound waves deviates from the arrangement direction of the phased speaker array.

[0048] Reference Figure 6 As shown, in the embodiment of the present invention, the output deflection angle θ is an angle determined according to the distance D between the TV set 200 and the object (sofa) in the listening area and the distance H between the TV set 200 and the ceiling:

[0049] θ=atan((H / 2) / D) (1).

[0050] If the acoustic wave is focused and deflected, the required exit delay is determined by the deflection angle, and the specific exit delay tm in each column satisfies:

[0051]

[0052] Where F is the focal depth, c is the speed of sound, Xm is the axial length from the mth speaker in a row to the focal point, d is the distance between the speakers, and θ is the deflection angle.

[0053] Therefore, the above control method indicates that the radiation directions of each column of focused sound waves are arranged parallel to each other, and the delay times of speaker units in different columns but the same row are the same. Accordingly, it can be understood that the multiple speakers in the one-dimensional phased speaker array are arranged vertically, that is, perpendicular to the lower frame of the display screen of television 200, to ensure that the sound waves emitted by each speaker have a delay, thereby ensuring focused deflection.

[0054] Figure 5b The figure shows the principle diagram of the sound beam deflection of a one-dimensional phased speaker array. For the sound beam deflection, by controlling each speaker in the array to deflect the sound in parallel at the same deflection angle θ, it does not need to be focused on the ceiling. After being reflected by the ceiling, the sound can also radiate to cover the listening area where the sofa is located. In addition, although Figure 5b Only a schematic diagram of the principle of sound beam deflection of a one-dimensional phased loudspeaker array is shown. Sound beam deflection can also be used for a two-dimensional phased loudspeaker array.

[0055] When using the beam deflection method, the phased speaker array emits sound waves obliquely upward at an angle θ based on the sound path difference. The delay time of each sound wave satisfies:

[0056] Tm=m*l0*sin(θ) / c (3),

[0057] Where Tm is the delay time of the mth speaker unit in a speaker array, l0 is the length of the speaker, θ is the deflection angle, and c is the speed of sound. The deflection angle θ is also determined by expression (1).

[0058] It should be noted that, regardless of whether the phased speaker array is one-dimensional or two-dimensional, and regardless of whether the focus deflection or beam deflection method is used, the method for obtaining the deflection angle θ can be specifically implemented as a controller executing control to cause the speakers of the television to radiate sound wave signals to the listening environment, and receive sound waves reflected from the top surface of the listening environment and sound waves reflected from objects in the listening area, for example, receiving sound waves reflected from the ceiling and sound waves reflected from the sofa. Based on the received reflected sound waves, the controller obtains the distance D from the television 200 to the sofa and the distance H from the television 200 to the ceiling, and calculates the deflection angle θ according to expression (1). Furthermore, the controller can control the phased speaker array to achieve focus deflection or beam deflection according to the deflection angle θ.

[0059] For example, Figure 4 As shown in the figure, if the room is 2.8 meters high, the TV is 1.5 meters from the ceiling, and the sofa is 3 meters from the TV, the sound wave deflection angle is 45 degrees. To prevent excessive sound beam spread, the distance between the sofa and the TV can be adjusted to achieve a deflection angle θ between 15° and 45°.

[0060] In addition, there is no limitation on the speakers that radiate sound wave signals to the listening environment. They can be the above-mentioned phased speaker arrays 202-1 and 202-2, or speakers set in the television 200 for emitting conventional sound waves. As for receiving reflected sound waves, those skilled in the art will understand that if the speakers in the phased speaker arrays 202-1 and 202-2 are piezoelectric speakers, the functions of sound wave emission and reception can be directly realized based on the characteristics of the piezoelectric effect. If the phased speaker arrays 202-1 and 202-2 are other types of speakers, corresponding microphones need to be set to receive reflected sound waves. The present invention does not impose any special restrictions on the specific implementation method of transmitting and receiving sound waves, and designers can choose according to their needs.

[0061] In addition, despite Figure 5b The principle diagram of a two-dimensional phased loudspeaker array shows multiple loudspeakers arranged in a rectangular shape, such as Figure 7 In the embodiment shown, the two-dimensional phased loudspeaker arrays 702-1 and 702-2 are arranged in a rectangular or square shape, but the arrangement of the two-dimensional array is not limited thereto.

[0062] Optionally, refer to Figure 8 As shown, the two-dimensional phased loudspeaker arrays 802-1 and 802-2 are circular arrays, but they can also be annular, elliptical, etc.

[0063] Accordingly, the shape of each speaker does not have to be limited to a square piece, and can also be Figure 8 and Figure 9The present invention does not limit the specific shape of the loudspeaker, and the specific shape is based on the layout during design or the ease of realization under process conditions.

[0064] Of course, it should also be noted that the phased speaker array in the embodiment of the present invention refers only to a speaker array for emitting and reflecting sound waves toward the ceiling, and does not include speakers that normally radiate sound waves directly toward the front listening area during the display process. Those skilled in the art should understand that the display device also includes one or more speakers that radiate sound waves, and the specific setting method, structure and position are not limited in this application. Of course, it can also include external speakers placed in the listening environment, such as other locations in the living room, to form a surround sound effect that radiates directly from all sides of the listening area to the listener, and the present invention is not intended to limit the setting of these speakers.

[0065] Based on the same inventive concept, another embodiment of the present invention also provides a sound-emitting method for the display device described above, comprising: controlling the focusing deflection or sound beam deflection of at least one phased speaker array arranged in the display device to emit sound waves toward the top surface of the listening environment so as to be reflected to the listening area within the listening environment.

[0066] In this embodiment, a phased speaker array is provided in the display device, and the focus deflection or sound beam deflection of the phased speaker array is controlled, so that the phased speaker array emits sound waves toward the top of the listening environment, which are reflected to the listening area within the listening environment. This allows the listener to experience overhead radiated sound without having to install additional ceiling speakers, thereby enhancing the listener's spatial height perception and meeting the listener's demand for surround sound from overhead sound sources. The embodiment has broad application prospects.

[0067] Optionally, in one example, controlling the focus deflection or beam deflection of at least one phased speaker array provided in the display device to emit sound waves toward a top surface of the listening environment so as to be reflected to a listening area within the listening environment further includes:

[0068] Controlling a phase-controlled speaker array of a display device to emit a first sound wave signal;

[0069] The phased speaker array receives a first reflection signal of the first sound wave signal reflected by the ceiling and a second reflection signal reflected by the sofa;

[0070] Determine a first distance H between the display device and the ceiling and a second distance D between the display device and the sofa based on the first reflection signal and the second reflection signal, and calculate a deflection angle θ according to the first distance and the second distance;

[0071] Determine the transmission delay of the sound wave of the speaker in the phased speaker array based on the deflection angle θ based on expression (2) or (3);

[0072] Then, the controller controls the array speaker array to emit a sound wave signal toward the ceiling so that the sound wave signal is reflected by the ceiling and then emitted toward the listening area in front of the display device.

[0073] In response to the current problems, the present invention develops a display device and a sound-generating method thereof. By arranging a phased speaker array in the display device and controlling the focusing deflection or sound beam deflection of the phased speaker array by a controller, the phased speaker array emits sound waves toward the top of the listening environment, which are reflected to the listening area within the listening environment. This allows the listener to experience overhead radiated sound without having to install additional ceiling speakers, thereby enhancing the listener's spatial height perception and meeting the listener's need for surround sound from overhead sound sources. The present invention has broad application prospects.

[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in this field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A display device comprising a display screen, characterized in that: The system further includes a controller and at least one phased speaker array, the phased speaker array including a plurality of speakers, the controller being configured to control the phased speaker array to focus deflection or beam deflection so as to emit sound waves toward a top surface of the listening environment so as to be reflected to a listening area within the listening environment; The speaker is a piezoelectric speaker; The controller is configured to calculate a deflection angle based on the sound waves reflected by the top surface of the listening environment and the sound waves reflected by the objects in the listening area and received by the piezoelectric speaker, and control the focus deflection or the sound beam deflection of the phased speaker array according to the deflection angle; Calculating the deflection angle according to the sound waves reflected by the top surface of the listening environment and the sound waves reflected by the objects in the listening area received by the piezoelectric speaker includes: the controller obtaining a distance D from the speaker to the objects in the listening area and a distance H from the speaker to the top surface of the listening environment based on the received reflected sound waves, and calculating the deflection angle θ according to the formula: θ=atan((H / 2) / D); The phased loudspeaker array comprises a column of loudspeakers arranged vertically; The controller is configured to control the focus deflection or sound beam deflection of the phased-controlled speaker array by controlling the sound emission delay of the speakers in the phased-controlled speaker array; When the focus is deflected, the emission delay tm in a row of speakers satisfies: Where F is the focal depth, c is the speed of sound, Xm is the axial length from the mth speaker in a row of speakers to the focal point, d is the distance between the speakers, and θ is the deflection angle; When the sound beam is deflected, the delay time of the sound wave in a row of speakers satisfies: Tm=m*l0*sin(θ) / c Where Tm is the delay time of the mth speaker unit in a row of speakers, l0 is the length of the speaker, θ is the deflection angle, and c is the speed of sound.

2. The device according to claim 1, characterized in that The display device is a screen sound display device.

3. The device according to claim 1, characterized in that The display device includes two phase-controlled speaker arrays arranged in upper areas of the left and right sides.

4. The device according to claim 1, characterized in that The phase-controlled loudspeaker array is a one-dimensional phase-controlled loudspeaker array or a two-dimensional phase-controlled loudspeaker array.

5. The device according to claim 4, characterized in that The multiple loudspeakers in the two-dimensional phased loudspeaker array are arranged in a rectangular arrangement or a circular arrangement.

6. A sound generating method for a display device, characterized in that: include: controlling the focus deflection or beam deflection of at least one phased speaker array provided in the display device to emit sound waves toward a top surface of the listening environment so as to be reflected to a listening area within the listening environment; The loudspeakers in the phased loudspeaker array are piezoelectric loudspeakers; The step of controlling the focus deflection or sound beam deflection of at least one phased speaker array provided on the display device comprises: calculating a deflection angle based on sound waves reflected by a top surface of a listening environment and sound waves reflected by objects in the listening area and received by the piezoelectric speaker, and controlling the focus deflection or sound beam deflection of the phased speaker array based on the deflection angle; Calculating the deflection angle according to the sound waves reflected by the top surface of the listening environment and the sound waves reflected by the objects in the listening area received by the piezoelectric speaker includes: a controller obtaining a distance D from the speaker to the objects in the listening area and a distance H from the speaker to the top surface of the listening environment based on the received reflected sound waves, and calculating the deflection angle θ according to the formula: θ=atan((H / 2) / D); The phased loudspeaker array comprises a column of loudspeakers arranged vertically; The controller is configured to control the focus deflection or sound beam deflection of the phased-controlled speaker array by controlling the sound emission delay of the speakers in the phased-controlled speaker array; When the focus is deflected, the emission delay tm in a row of speakers satisfies: Where F is the focal depth, c is the speed of sound, Xm is the axial length from the mth speaker in a row of speakers to the focal point, d is the distance between the speakers, and θ is the deflection angle; When the sound beam is deflected, the delay time of the sound wave in a row of speakers satisfies: Tm=m*l0*sin(θ) / c Where Tm is the delay time of the mth speaker unit in a row of speakers, l0 is the length of the speaker, θ is the deflection angle, and c is the speed of sound.

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