Patent Publication Number: US-8538047-B2

Title: Digital sound projector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201010146847.2, filed on Apr. 14, 2010, in the China Intellectual Property Office, the contents of which are hereby incorporated by reference. This application is related to application entitled, “DIGITAL SOUND PROJECTOR”, filed Nov. 26, 2010 Ser. No 12/954,752. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a digital sound projector. 
     2. Description of Related Art 
     Nowadays, digital sound projectors attract a great attention because the digital sound projector can produce surround sound without complex wires. The digital sound projector includes a panel and a plurality of speakers arranged on a surface of the panel in an array. The digital sound projector delays the time and changes the direction of the sound of the speakers. In the WO0123104A1, a method how to direct sound has been described detailed, and the teachings of which are incorporated by reference. Thus, the sound of the speakers will be focused in at least two directions to form at least two sound beams. Each of the at least two sound beams are spread along a predetermined direction and may be reflected by a wall of a room. The at least two sound beams form a sound source that surrounds a listener. 
     However, the digital sound projector needs a signal processing device. The signal processing device delays the sound from the speakers to form at least two sound beams from different directions. The structure of the digital sound projector is complex due to the signal processing device. 
     What is needed, therefore, is a digital sound projector with a simple structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic structural view of one embodiment of a digital sound projector. 
         FIG. 2  is a schematic structural view of one embodiment of a first flat speaker of the digital sound projector of  FIG. 1 . 
         FIG. 3  is a schematic view of one embodiment of a structure of an insulated panel. 
         FIG. 4  is a Scanning Electron Microscope (SEM) image of a drawn carbon nanotube film. 
         FIG. 5  is a schematic structural view of a carbon nanotube segment of the drawn carbon nanotube film. 
         FIG. 6  is a schematic view of one embodiment of a spreading route of sound beams produced by the digital sound projector of  FIG. 1 . 
         FIG. 7  is a schematic view of one embodiment of a spreading route of sound beams produced by a digital sound projector. 
         FIG. 8  is a schematic view of one embodiment of a spreading route of sound beams produced by a digital sound projector. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     Referring to  FIG. 1 , a digital sound projector  10  of one embodiment is illustrated. The digital sound projector  10  includes a first flat speaker  1 , a second flat speaker  2 , a connecting device  11 , and a signal input device  13 . The first speaker  1  and the second speaker  2  are pivotally connected to the connecting device  11  and capable of rotating around the connecting device  11 . In one embodiment, the connecting device  11  has a hinge configuration. An angle between the first speaker  1  and the second speaker  2  can be changed by rotating the first speaker  1  and the second speaker  2  around the connecting device  11 . Both of the first speaker  1  and the second speaker  2  are electrically connected to the signal input device  13 . The signal input device  13  inputs independent electrical signals to the first speaker  1  and the second speaker  2 . Thus, the first speaker  1  and the second speaker  2  can produce two independent sound beams to form a sound source surrounding the listener. 
     In one embodiment, a structure of the first speaker  1  is the same as a structure of the second speaker  2 . Referring to  FIG. 2 , the first speaker  1  includes a first electrode  142 , a second electrode  144 , an insulated panel  111  and an acoustic element  16 . The acoustic element  16  contacts and is electrically connected to both the first electrode  142  and the second electrode  144 . The first electrode  142  and the second electrode  144  are located on the two opposite flanks of the acoustic element  16 . The first electrode  142  and the second electrode  144  are spaced apart from each other and electrically connected to the signal input device  13  by a plurality of conductive wires  149 . The signal input device  13  can input electrical signals to the acoustic element  16  through the first electrode  142  and the second electrode  144 . The acoustic element  16  transforms the electrical signals into thermal energy via a thermal acoustic effect. The thermal energy heats up surrounding medium, and thus creates sounds. 
     Referring to  FIG. 3 , in one embodiment, the insulated panel  111  can define a first hole  114 . A surface of the insulated panel  111  which is configured to face the listener in use is defined as a front surface. A surface of the insulated panel  111  which is opposite to the front surface is defined as a back surface. When the acoustic element  16  is located on the front surface of the insulated panel  111 , the first hole  114  can be a through hole or a blind hole on the front surface of the insulated panel  111 . When the acoustic element  16  is located on the back surface of the insulated panel  111 , the first hole  114  should be a through hole so that the sound beam produced by the first speaker  1  will not be blocked by the insulated panel  111 . In one embodiment, the acoustic element  16  is located on the front surface of the insulated panel  111  and the first hole  114  is a through hole. The shape of the first hole  114  is not limited. The shape of each of the first holes  32  can be the same as the shape of the acoustic element  14 . In one embodiment, the shape of the first hole  114  is substantially rectangle as is the acoustic element  14 . The position of the first hole  114  corresponds to the position of the acoustic element  16 . The first electrode  142  and the second electrode  144  are also located on two opposite flanks of the first hole  114 . The acoustic element  16  is fastened on the insulated panel  111  by the first electrode  142  and the second electrode  144  in one embodiment. In one embodiment, the acoustic element  16  is located on the front surface of insulated panel  111  and covers the first hole  114 . Referring to FIG.  2 ., a portion of the acoustic element  16  covers the first hole  114 . Another portion of acoustic element  16  covers the first electrode  142  and the second electrode  144 . At least a portion of the acoustic element  16  is suspended over the first hole  114  in one embodiment. The weight of the insulated panel  111  is lighter because of the first hole  114 . 
     Two second holes  36  may be further defined in the insulated panel  111 . Therefore, the conductive wires  149  can connect the first electrode  142  or the second electrode  144  to the signal input device  13  through the second holes  36 . Each of the two second holes  36  corresponds to one of the first electrode  142  and the second electrode  144 . Because the second holes  36 , the length of the conductive wires  149  can be reduced, and the energy conversion efficiency of the first speaker  1  can be improved. The conductive wires  149  can get through the second holes  36  and transfer the electrical signals from the signal input device  13  to the first speaker  1 . 
     In another embodiment, the first electrode  142  and the second electrode  144  are located on the front surface of the insulated panel  111 . The acoustic element  16  is located on surfaces of the first electrode  142  and the second electrode  144  away from the insulated panel  111 . The acoustic element  16  is suspended by the first electrode  142  and the second electrode  144 . No first hole should be defined. 
     In one embodiment, the acoustic element  16  is a carbon nanotube film structure. The carbon nanotube film structure can be a freestanding structure. The term “freestanding”, includes, but is not limited to a structure that does not have to be formed on a surface of a substrate and/or can support its own weight. The carbon nanotube film structure includes at least one carbon nanotube film. If the carbon nanotube film structure includes a plurality of carbon nanotube films, the carbon nanotube films can be stacked. Two adjacent carbon nanotube films are combined by Van der Waals attractive force. An angle between aligned directions of the carbon nanotubes in two adjacent carbon nanotube films can range from about 0 degrees to about 90 degrees (0°≦α≦90°). 
     In one embodiment, the carbon nanotube film structure can be a drawn film. The drawn film can be drawn from a carbon nanotube array. Examples of the drawn carbon nanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang et al. The drawn carbon nanotube film includes a plurality of carbon nanotubes arranged substantially parallel to a surface of the drawn carbon nanotube film. A large number of the carbon nanotubes in the drawn carbon nanotube film can be oriented along a preferred orientation, meaning that a large number of the carbon nanotubes in the drawn carbon nanotube film are arranged substantially along the same direction. An end of one carbon nanotube is joined to another end of an adjacent carbon nanotube arranged substantially along the same direction by Van der Waals attractive force. The drawn carbon nanotube film is capable of forming a freestanding structure. The successive carbon nanotubes joined end to end by Van der Waals attractive force realizes the freestanding structure of the drawn carbon nanotube film. 
     Some variations can occur in the orientation of the carbon nanotubes in the drawn carbon nanotube film. Microscopically, the carbon nanotubes oriented substantially along the same direction may not be perfectly aligned in a straight line, and some curve portions may exist. It can be understood that a contact between some carbon nanotubes located substantially side by side and oriented along the same direction cannot be totally excluded. 
     Referring to  FIG. 4  and  FIG. 5 , the drawn carbon nanotube film can include a plurality of successively oriented carbon nanotube segments  143   a  joined end-to-end by Van der Waals attractive force therebetween. Each carbon nanotube segment  143   a  includes a plurality of carbon nanotubes  145  substantially parallel to each other, and joined by Van der Waals attractive force therebetween. The carbon nanotube segments  143   a  can vary in width, thickness, uniformity, and shape. A thickness of the drawn carbon nanotube film can range from about 0.5 nm to about 100 μm. Therefore, a thickness of the acoustic element  16  can range from about 0.5 nm to about 1 millimeter. A width of the drawn carbon nanotube film relates to the carbon nanotube array from which the drawn carbon nanotube film is drawn. When the carbon nanotube film structure  104  consist of the drawn carbon nanotube film, and a thickness of the carbon nanotube film structure  104  can be relatively small (e.g., smaller than 10 μm), the carbon nanotube film structure  104  can have a good transparency, and the transmittance of the light can reach about 90%. 
     In one embodiment, the carbon nanotube film can be a flocculated carbon nanotube film. The flocculated carbon nanotube film can include a plurality of long, curved, disordered carbon nanotubes entangled with each other. A length of each of the carbon nanotubes can be larger than about 10 μm. Further, the flocculated carbon nanotube film can be isotropic. Adjacent carbon nanotubes are acted upon by Van der Waals attractive force to obtain an entangled structure with micropores defined therein. The flocculated carbon nanotube film is very porous. The sizes of the micropores can be less than 10 μm. In one embodiment, the sizes of the micropores are in a range from about 1 nm to about 10 μm. Further, because the carbon nanotubes in the carbon nanotube film structure  104  are entangled with each other, the carbon nanotube film structure  104  employing the flocculated carbon nanotube film has excellent durability, and can be fashioned into desired shapes with a low risk to the integrity of the carbon nanotube film structure  104 . The flocculated carbon nanotube film is freestanding because the carbon nanotubes are entangled and are adhered together by Van der Waals attractive force therebetween. The thickness of the flocculated carbon nanotube film can range from about 1 micrometer (μm) to about 1 millimeter (mm). In one embodiment, the thickness of the flocculated carbon nanotube film is about 100 μm. The flocculated carbon nanotube film can be folded into any shape and will not be damaged because the carbon nanotubes in the flocculated carbon nanotube film are entangled with each other. 
     In another embodiment, the carbon nanotube film includes a plurality of carbon nanotubes arranged along a preferred orientation. The carbon nanotubes are substantially parallel with each other, have substantially equal lengths, and are combined side by side by Van der Waals attractive force therebetween. A length of the carbon nanotubes can reach up to several millimeters. The length of the film can be equal to the length of the carbon nanotubes. Such that at least one carbon nanotube will span the entire length of the carbon nanotube film. The length of the carbon nanotube film is only limited by the length of the carbon nanotubes. In one embodiment, the length of the carbon nanotubes can range from about 1 millimeter to about 30 millimeters. The carbon nanotube films have a plurality of excellent properties, such as electricity conductive property and thermal conductive property. 
     The heat capacity per unit area of the acoustic element  16  can be less than 2×10 −4  J/cm 2 ·K. In one embodiment, the heat capacity per unit area of the acoustic element  16  is less than or equal to about 1.7×10 −6  J/cm 2 ·K. The length and width of the acoustic element  16  is not limited. In one embodiment, the length of the acoustic element  16  is about 3 centimeters, the width of the acoustic element  16  is about 3 centimeters, and the thickness of the acoustic element  16  is about 50 nanometers. 
     The first electrode  142  and the second electrode  144  are made of conductive material. A shape of the first electrode  142  or the second electrode  144  is not limited and can be lamellar, rod, wire, and block among other shapes. A material of the first electrode  142  or the second electrode  144  can be metals, conductive adhesives, carbon nanotubes, and indium tin oxides among other materials. In one embodiment, the first electrode  142  and the second electrode  144  are rod-shaped metal electrodes. The acoustic element  16  is electrically connected to the first electrode  142  and the second electrode  144 . The first electrode  142  and the second electrode  144  can provide structural support for the acoustic element  16 . If the acoustic element  16  is composed of a carbon nanotube film structure, the first electrode  142  and the second electrode  144  can be located on the two opposite flanks of the carbon nanotube film structure. The air surrounding the carbon nanotube film structure is heated by the portion of the carbon nanotube film structure suspended between the first electrode  142  and the second electrode  144  to produce sounds. In use, when electrical signals with variations are applied to the carbon nanotube film structure of the acoustic element  16 , heating is produced in the carbon nanotube film structure according to the variations of the electrical signal and/or signal strength. Temperature waves, which are propagated into air. The temperature waves produce pressure waves in the air, resulting in sound generation. Because, the carbon nanotube film structure has large specific surface area, the acoustic element  16  can be adhered directly to the first electrode  142  and the second electrode  144 . This will result in a good electrical contact between the acoustic element  16  and the first electrode  142  and the second electrode  144 . 
     In other embodiments, a conductive adhesive layer (not shown) can be further provided between the first electrode  142  or the second electrode  144  and the acoustic element  16 . The conductive adhesive layer can be applied to the surface of the acoustic element  16 . The conductive adhesive layer can be used to provide electrical contact and more adhesion between the first electrode  142  or the second electrode  144  and the acoustic element  16 . In one embodiment, the conductive adhesive layer is a layer of silver paste. 
     The structures of the first and second speakers  1 ,  2  are not limited to the above-described structure in which the acoustic element  16  is made of the carbon nanotube film structure. Any speaker, which can produce directional sound beams can be used as the first or second speaker  1  or  2 . 
     The connecting device  11  is used to connect the first and the second speakers  1 ,  2 . The first and second speakers  1 ,  2  are pivotally mounted on the connecting device  11  and capable of rotating around the connecting device  11 . The angle is formed between the first and second speakers  1 ,  2  can vary from about 0 degrees to about 180 degrees. In one embodiment, the angle between the first and second speakers  1 ,  2  is greater 180 degrees when the digital sound projector  10  is located behind the user. The first angle can not be limited as long as the sounds of the two speaker  1 ,  2  from a surrounding sounds. The opening of the angle formed between the first and second speakers  1 ,  2  may be faced to the listener. The structure of the connecting device  11  is not limited. The connecting device  11  is made of an insulated material. In one embodiment, the connecting device is a plastic hinge. The plastic hinge can connect a side of the insulated panel  111  of the first speaker  1  and a side of an insulated panel of the second speaker  2  so that the first and second speaker  1 ,  2  are insulated from each other. 
     The signal input device  13  is electrically connected to both the first and second speaker  1 ,  2 . The signal input device  13  is electrically connected to the first electrode  142  and the second electrode  144  through the conductive wires  149 . The signal input device  13  can input electrical signals to the acoustic element  16  through the first electrode  142  and the second electrode  144 . The way that signal input device  13  connects to the second speaker  1  the same as the way that the signal input device  13  connects to the first speaker. 
     Referring to  FIG. 6 , in use, the digital sound projector  10  is located in a room which has four walls. The four walls can be defined as a front wall A, a left wall B, a back wall C, a right wall D. The first speaker  1  and the second speaker  2  are used for the digital sound projector  10 . A first sound beam  1   a  that is produced by the first speaker  1  spreads along a direction substantially perpendicular to a surface of the carbon nanotube film structure of the first speaker  1 . The first sound beam  1   a  spreads and is reflected by the right wall D to form a first reflected sound beam  1   b . The first reflected sound beam  1   b  reaches the listener. A second sound beam  2   a  that is produced by the second speaker  2  spreads along a direction substantially perpendicular to the surface of the second speaker  2 . The second sound beam  2   a  spreads and is reflected by the left wall B to form a second reflected sound beam  2   b . The second reflected sound beam  2   b  also reaches the listener. The first reflected sound beam  1   b  and the second reflected sound beam  2   b  form a sound source that surrounds the listener. Therefore, the positions of the first and second speaker  1 ,  2  are not limited, as long as the sound beams that are produced by the first speaker  1  and the second speaker  2  can reach the listener after being reflected. 
     The acoustic element  16  is a carbon nanotube film structure. Therefore, the sound beam that is produced by the first speaker  1  or the second speaker  2  spreads along two opposite directions which are substantially perpendicular to the surface of the carbon nanotube film structure. If the insulated panel  111  has a first through hole  32 , a portion of sound beams produced by the carbon nanotube film structures will reach the front wall A, a portion of the sound beams produced by the carbon nanotube film structures will reach the listener. In one embodiment, a sound absorbing device (not shown in  FIG. 6 ) can be located between the front wall A and the two speakers  1 ,  2 . The sound absorbing device allows the sounds of the digital sound projector be clearly heard by the listener. If the insulated panel  111  is a plate without a first through hole, the carbon nanotube film structure of the first speaker  1  and the second speaker  2  is opposite to the listener. 
     Referring to  FIG. 7 , one embodiment of a digital sound projector  20  is illustrated. The digital sound projector  20  includes a first flat speaker  21 , a second flat speaker  22 , a third flat speaker  23 , a first connecting device (not labeled), a second connecting device (not labeled) and a signal input device (not shown in  FIG. 7 ). The structure of the first connecting device and the second connecting device is the same as the connecting device  11  of  FIG. 1 . The first speaker  21 , the second speaker  22 , and the third speaker  23  are electrically connected to the signal input device. The signal input device inputs independent electrical signals to the first speaker  21 , the second speaker  22 , and the third speaker  23 . Therefore, the first speaker  21 , the second speaker  22 , and the third speaker  23  can produce sound beams independently. The sound beams produced by the first speaker  21 , the second speaker  22 , and the third speaker  23  form a sound source surrounding the listener. 
     The structure of the first speaker  21 , the second speaker  22 , and the third speaker  23  is the same as the first speaker  1  of  FIG. 1 . The first speaker  21  and the second speaker  22  are pivotally connected by the first connecting device. The second speaker  22  and the third speaker  23  are pivotally connected by the second connecting device. The first speaker  21  and the third speaker  23  are symmetrical about the second speaker  22 . The second speaker  22  faces the listener. A first angle α 1  is formed between the first speaker  21  and the second speaker  22  and can vary from about 90 degrees to about 180 degrees. A second angle α 2  is formed between the second speaker  22  and the third speaker  23  and can vary from about 90 degrees to about 180 degrees. The first angle α 1  and the second angle can not be limited as long as the sounds of the three speaker  21 ,  22 ,  23  from a surrounding sounds. The first speaker  21 , the second speaker  22 , and the third speaker  23  form a bowl type structure. The opening of the bowl type structure is face to the user. The first angle α 1  and the second angle α 2  can be changed by rotating the three speakers  21 ,  22 , and  23  to obtain maximum acoustical properties of the digital sound projector  20 . The distance between the second speaker  22  and the listener can be the shortest, compared with the first speaker  21  and the third speaker  23 . 
     In other embodiments, a motor or other means to rotate the speakers. In other embodiments a remote control may be used to control the rotation means. 
     In use, the digital sound projector  20  can be located in a room which has four walls. The four walls can be defined as a front wall A, a left wall B, a back wall C and a right wall D. In one embodiment, a carbon nanotube film structure of the first speaker  21  faces the left wall B, a carbon nanotube film structure of the second speaker  22  faces the listener, and a carbon nanotube film structure of the third speaker  23  faces the right wall D. A first sound beam  21   a , produced by the first speaker  21  spreads along a direction substantially perpendicular to a surface of the carbon nanotube film structure of the first speaker  21 . The left wall B, reflects the first sound beam  21   a  to form a first reflected sound beam  21   b . The first reflected sound beam  21   b  reaches the listener. The second speaker  22  faces the listener, a second sound beam  22   a  produced by the second speaker  22  spreads along the direction substantially perpendicular to a surface of the carbon nanotube film structure of the second speaker  22 . The second sound beam  22   a  reaches the listener directly. A third sound beam  23   a  produced by the third speaker  23  spreads along a direction substantially perpendicular to a surface of the third speaker  23 . The third sound beam  23   a  spreads and is reflected by the right wall D to form a second reflected sound beam  23   b . The second reflected sound beam  23   b  reaches the listener. The first reflected sound beam  21   b , the second sound beam  22   a  and the second reflected sound beam  23   b  form a sound source surrounding the listener. 
     Referring to  FIG. 8 , a digital sound projector  30  is illustrated in one embodiment. The digital sound projector  30  includes a first flat speaker  31 , a second flat speaker  32 , a third flat speaker  33 , a fourth flat speaker  34 , and a fifth flat speaker  35 . A first connecting device (not labeled), a second connecting device (not labeled), a third connecting device (not labeled), a fourth connecting device (not labeled) and a signal input device (not shown). The signal input device inputs independent electrical signals to the five speakers  31 ,  32 ,  33 ,  34 , and  35 . The sound beams produce by the five speakers  31 ,  32 ,  33 ,  34 , and  35  forms a sound source surrounding the listener. 
     Structures of the five speakers  31 ,  32 ,  33 ,  34 , and  35  can be the same as the structures of the first flat speaker  1  in  FIG. 1 . Structures of the three connecting devices of the digital sound projector  30  can be the same as the structure of the connecting device  11  of  FIG. 1 . The five speakers  31 ,  32 ,  33 ,  34 , and  35  are substantially perpendicular to a horizon. The five speakers  31 ,  32 ,  33 ,  34 , and  35  are connected in turn by the four connecting devices. The first flat speaker and the second flat speaker are pivotally connected to a first connecting device, the second flat speaker and the third flat speaker are pivotally connected to a second connecting device, the third flat speaker and the fourth speaker are pivotally connected to a third connecting device, the fourth flat speaker and the fifth flat speaker are pivotally connected to a fourth connecting device. A first angle β 1  formed between the first speaker  31  and the second speaker  32  is less than 180 degrees. The first angle β 1  can be changed by rotating the first speaker  31  and the second speaker  32 . A second angle β 2  is formed between the second speaker  32  and the third speaker  33  and can vary from 90 degrees to 180 degrees A third angle β 3  is formed between the third speaker  33  and the fourth speaker  34  and can vary from 90 degrees to 180 degrees. A fourth angle β 4  is formed between the fourth speaker  34  and the fifth speaker  35  is less than 180 degrees. The sum of the third angle β 3  and the fourth angle β 4  is greater than 180 degrees. The first angle β 1 , second angle β 2 . third angle β 3  and the fourth angle β 4  can not be limited as long as the sounds produced by the five speaker  31 ,  32 ,  33 ,  34 ,  35  can form surrounding sounds. The first speaker  31  and the fifth speaker  35  can be symmetrical about the third speaker  33 . The second speaker  32  and the fourth speaker  34  can be symmetrical about the third speaker  33 . The distance between the third speaker  33  and listener can be the shortest when compared with the other four speakers  31 ,  32 ,  34 , and  35 . The distance between the second speaker  32  and listener and the distance between the fourth speaker  34  and listener can be less when compared with the first speaker  31  and the fifth speaker  35 . The distance between the first speaker  31  and listener and the distance between the fifth speaker  35  and listener can be the longest when compared with the second speaker  32 , the third speaker  33 , and the fourth speaker  34 . 
     In use, the digital sound projector  30  can be located in a room having four walls. The four walls can be defined as a front wall A, a left wall B, a back wall C, and a right wall D. A carbon nanotube film structure of the first speaker  31  faces the front wall A. A carbon nanotube film structure of the second speaker  32  faces the left wall B. A carbon nanotube film structure of the third speaker  33  faces the listener. A carbon nanotube film structure of the fourth speaker  34  faces the right wall D. A carbon nanotube film structure of the fifth speaker  35  faces the front wall A. 
     A first sound beam  31   a  that is produced by the first speaker  31  spreads and is reflected by the front wall A to form a first reflected sound beam  31   b . The first reflected sound beam  31   b  spreads and is reflected by the left wall B to form a second reflected sound beam  31   c . The second reflected sound beam  31   c  reaches the listener. A second sound beam  32   a  that is produced by the second speaker  32  spreads and is reflected by the left wall B to form a third reflected sound beam  32   b . The third reflected sound beam  32   b  reaches the listener. The third speaker  33  faces the listener. A third sound beam  33   a  that is produced by the third speaker  33  reaches the listener directly. A fourth sound beam  34   a  that is produced by the fourth speaker  34  spreads and is reflected by the right wall D to form a fourth reflected sound beam  34   b . The fourth reflected sound beam  34   b  reaches the listener. A fifth sound beam  35   a  that is produced by the fifth speaker  35  spreads and is reflected by the front wall A to form a fifth reflected sound beam  35   b , the fifth reflected sound beam  35   b  spreads and is reflected by the left wall B to form a sixth reflected sound beam  35   c . The sixth reflected sound beam  35   c  reaches the listener. The second reflected sound beam  31   c , the third reflected sound beam  32   b , the third sound beam  33   a , the fourth reflected sound beam  34   b  and the sixth reflected sound beam  35   c  form a sound source surrounding the listener. 
     In the digital sound projector provided by the present disclosure, the acoustic element is made of a carbon nanotube film structure, the sound beam that is produced by the carbon nanotube film structure spreads along the direction which is substantially perpendicular to the carbon nanotube film structure. Therefore, the directivity of the sound beam produced by the carbon nanotube film structure is good. The digital sound projector needs no other device to control the delay of the sound beams produced by speakers. Therefore, the structure of the digital sound projector of the present disclosure is simple and the cost is decreased. 
     Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. Elements associated with any of the above embodiments are envisioned to be associated with any other embodiments. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.