Abstract:
A speaker system utilizes dipole speaker drivers in conjunction with monopole speaker drivers in a listening area to disperse a surround sound effect to a listener. The dipole speaker drivers are physically mounted on top of the front left and right speakers and are angled in a way that the surround information is delivered to the listener via wall/room reflections. By reflecting the sound off the walls, the system provides a delayed diffuse audio signal from the dipole speakers, enhancing the surround effect.

Description:
This application includes material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office files or records, but otherwise reserves all copyright rights whatsoever. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of audio speakers used to provide sound from multiple directions to the listener. 
     BACKGROUND OF THE INVENTION 
     Audio systems often include at least two speakers positioned to the front left and right of a listener. In a conventional home theater setting, the two speakers are positioned to the left and right of a television screen. In a conventional desktop setting having a computer, the two speakers are positioned to the left and right of a computer screen. Optionally, bass units or subwoofers are added, which can deliver the lower frequency range and permit smaller speakers. The subwoofer can be placed at almost any location. An optional center speaker may be positioned directly in front of the listener, between the left and right speakers. A conventional audio system having left and right speakers and a subwoofer (known as a “2.1” configuration) and the optional center speaker (known as a “3.1” configuration) is compact, but does not provide surround sound to the listener. 
     One conventional approach to providing surround sound to the listener is to add rear speakers to the listening area, located behind or to the sides of the listener. The speakers form a circular, square or rectangular array with the listener at or near the center. A surround sound processor may incorporate positional encoding by means of specific phase differences and amplitude ratios to enhance the effect of spatially surrounding the listener. A five speaker arrangement with a subwoofer (known as a “5.1” configuration) provides a desired surround sound effect. It is desirable, however, to achieve a surround sound effect with a more compact configuration. 
     U.S. Pat. No. 5,109,416 to Croft discloses a dipole speaker for producing ambient sound in a multichannel sound reproduction system. Used in conjunction with direct path speakers connected to the audio system, the additional surround dipole speakers are placed in front of and behind the listener on the centerline of the listening setup. The radiation from the dipole speaker is such that one lobe of the sound pressure output is 180 degrees out of phase with the other so that they cancel each other out to produce a null zone aligned towards the listener. The sound pressure lobes are directed toward the walls so the acoustical signal of the dipole is reflected therefrom and arrives at the listener by an indirect path. The delayed indirect path of the signal from the dipole enhances the ambience of the effect of the dipole speaker. However, Croft does not achieve a compact design because a rear dipole speaker is required directly behind a listener. If the listener is using the Croft system with a computer on a desktop, the use of a rear dipole speaker may not be feasible. 
     One conventional system attempts to provide a system with a surround sound effect for use with a computer. U.S. Pat. No. 5,809,150 to Eberbach discloses a surround speaker system that utilizes skewed hypercardioid sound energy fields from right front and left front “surround” speakers with the principle nulls directed at the expected listener location. This produces the effect of side wall and rear wall speakers in a home theater setting without actual side wall or rear wall speakers. The effect is enhanced by secondary nulls that are directed so as to reflect off the front wall of the room toward the expected listener location. Each surround speaker contains an antiphase driver and circuitry that powers the drivers to create the skewed hypercardioid sound energy field. However, Eberbach&#39;s hypercardioid sound energy fields do not produce a sufficient dispersion of sound. With a very tight pattern, hypercardioid speakers do not provide a wide distribution across the horizontal plane. As a result, the surround sound effect is minimized. 
     Conventional surround sound systems generally require rear speakers for proper production of a surround sound effect. It would be desirable, therefore, to have a system which is capable of producing such surround sound effect without speakers positioned in the rear of the listening area. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a speaker system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. In particular, the present invention provides a surround sound effect without positioning speakers in the rear of the listening area. The conventional surround sound configuration having rear speakers is less desirable in a smaller listening area or where rear speakers cannot be properly positioned. It is desired to use a speaker configuration, e.g., a 2.1 or 3.1 configuration, that provides a 5.1 configuration surround sound effect without the use of rear speakers. 
     The present invention provides a surround sound effect to a home theater or other setting having speakers positioned only in front of the listener. The speaker arrangement can provide a 5.1 configuration surround sound effect with a 2.1 or 3.1 configuration in a reflective or reverberant space such as an office or living room. When the speaker system is used in conjunction with a center speaker and a subwoofer, the resultant 5.1 soundstage offers a more homogenous and cohesive effect when sounds are panned across the speakers as compared to a conventional 5.1 configuration where the sounds seem to appear in each speaker. The invention in its preferred embodiment provides a dipole/monopole combination in a speaker system which allows a more compact and user-friendly set up with fewer speaker units, less wiring, and less space required, while still providing a full 5.1 soundstage. This is useful in combination with a desktop or laptop computer as well as in a home theater that is placed in a normal listening space that has reflective surfaces. 
     The speaker system utilizes dipole speakers in conjunction with monopole speakers in a listening area to disperse a surround sound effect to a listener. In one embodiment, the dipole speakers are physically mounted on top of the front left and right speakers and are angled in a way that the surround information is delivered to the listener via wall/room reflections. The left and right information from the sealed enclosures are on a direct path to the listener&#39;s ears while the signals from the angled dipole speakers, which contain the surround information, are reflected off of the room boundary walls and eventually arrive at the listening position. This reflected signal path provides the time delay and diffusion that enhances the surround effect even though the sealed and dipole speakers are in a coincident position. 
     In one embodiment, a speaker system has one speaker unit to front left and one speaker unit to the front right of a listener. The speaker unit comprises a monopole driver directed at the listener&#39;s location and a dipole driver having an area of consistently lower output directed in the general vicinity of the listener. The speaker system may also comprise a center speaker or subwoofer. The dipole driver is located above the monopole driver in each speaker unit. The direction of the dipole driver is rotated from the direction of the monopole driver, wherein the degree of rotation is related to the location of the area of consistently lower output of the dipole driver. The left dipole driver is preferably rotated 45 to 75 degrees left from the direction of the left monopole driver direction, and the right dipole driver is preferably rotated 45 to 75 degrees right from the direction of the right monopole driver direction. In an alternative embodiment, the dipole driver is rotated 60 to 70 degrees from the direction of the monopole driver. In another alternative embodiment, the dipole driver is rotated 68 degrees from the direction of the monopole driver. The dipole driver has a straight baffle. Alternatively, the dipole driver has a wrapped baffle. The depth of the baffle is substantially equal to depth of the dipole driver. 
     In another embodiment, a method for providing a surround sound effect comprises the steps of providing a room for listening to the surround sound effect; positioning a left monopole speaker to the front left of a listener in the room, wherein the left monopole speaker provides a signal directed at the listener; positioning a right monopole speaker to the front right of a listener in the room, wherein the right monopole speaker provides a signal directed at the listener; positioning a left dipole speaker to the front left of a listener in the room, wherein the left dipole speaker provides a signal having an area of consistently lower output directed at the listener and the signal reflecting off a wall in the room; and positioning a right dipole speaker to the front right of a listener in the room, wherein the right dipole speaker provides a signal having an area of consistently lower output directed at the listener and the signal reflecting off a wall in the room. The left dipole speaker is directed at an angle of 45 degrees to 75 degrees to the left of the left monopole speaker. The right dipole speaker is directed at an angle of 45 degrees to 75 degrees to the right of the right monopole speaker. A center speaker is positioned between the right monopole speaker and the left monopole speaker, wherein the center speaker is directed at the listener. The left and right dipole speakers have a straight baffle. 
     In yet another embodiment, a system for providing a surround sound effect to a listening area comprises a front left speaker having a left monopole driver and a left dipole driver, the left monopole driver being directed at a listening area and the left dipole driver rotated to the left of the left monopole driver such that the area of consistently lower output of the left dipole driver is directed towards the listening area; and a front right speaker having a right monopole driver and a right dipole driver, the right monopole driver being directed at a listening area and the right dipole driver rotated to the right of the right monopole driver such that the area of consistently lower output of the right dipole driver is directed towards the listening area. The left and right dipole drivers have a wrapped baffle that extends substantially the length of the dipole driver. In one embodiment, the left and right dipole drivers have a straight baffle. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of at least one embodiment of the invention. 
       In the drawings: 
         FIG. 1  is a speaker unit according to an embodiment of the present invention. 
         FIG. 2  is rear view of a dipole speaker according to an embodiment of the present invention. 
         FIG. 3  shows left and right speaker units according to an embodiment of the present invention. 
         FIGS. 4 to 20  are polar plots of various multiple one-third octave spans for a dipole speaker according to an embodiment of the present invention. 
         FIG. 21  illustrates the direction of sound energy toward a listener according to an embodiment of the present invention. 
         FIG. 22  is a schematic diagram of the speaker system according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     The present invention provides a speaker system that allows for surround sound without the use of rear speakers. Although the exemplary embodiments do not discuss the use of the system in a particular setting, the system may be configured for use in a home, office, theater, vehicle, or other arena where a surround sound effect is desired. The system may be used for a home theater with a television or other means of viewing video. Similarly, the system may be used with a computer to achieve a surround sound effect at a desktop. A desktop application for the system may be two speakers, along with an optional subwoofer and center speaker. Alternatively, the system may be used to listen to audio, such as music, without a video feed. 
     The speaker system has at least two speaker units, each speaker having a monopole speaker and a dipole speaker. Optionally, the system may also include a center speaker and/or a subwoofer. Referring to  FIG. 1 , an exemplary speaker unit  10  is shown. Speaker unit  10  is constructed of a monopole speaker  20  and a dipole speaker  30 . 
     Monopole speaker  20  has at least one driver  22  installed on a single face  24  of a speaker cabinet  26 . Cabinet  26  is directed towards a listener or listening area. Because cabinet  26  completely encloses driver  22 , the sound is emitted in only one direction. In a surround sound system, the front left, front right, and center speakers are typically monopole speakers due to their directional sound. In the present embodiment, the front left, front right, and optional center speaker all have at least one monopole speaker. 
     In order to complete a 5.1 configuration for surround sound, dipole speaker  30  is positioned atop monopole speaker  20 . In this exemplary embodiment, dipole speaker  30  is fixed to a top surface  28  of monopole speaker  20 . However, dipole speaker  30  may be alternatively positioned to the side or below monopole speaker  20 . 
     Dipole speaker  30  emits sound in opposite directions. With a wide dispersion of sound, dipole speaker  30  emits the sound in a controlled pattern, substantially covering the room with limited output in the direction of the listener. Dipole speaker  30  is able to create a more diffuse sound due to the structure of dipole speaker  30 . Unlike monopole speaker  20 , dipole speaker  30  is not completely enclosed in a cabinet. 
     Dipole speaker  30  has a driver  32  installed on a face  34 . In this exemplary embodiment, the driver  32  is substantially wrapped. However, the rear of the driver remains exposed. 
     In a first embodiment, the dipole speaker has a straight baffle. As compared to straight and wrapped baffle designs of varying sizes the straight baffle has the highest attenuation of low frequencies with little affect on higher frequencies. In an alternative embodiment using a wrapped baffle, the low frequency response improves with a small baffle but there is no appreciable low frequency extension with an increase in baffle size. However, frequencies related to the size of the frontal surface area of the baffle may be affected at various levels as the frontal surface area of the baffle changes. As the frontal surface area of the wrapped baffle grows larger, the attenuation is less and moves slightly lower in frequency. There is no attenuation in this range without the baffle. 
     In a preferred embodiment, the dipole speaker has a wrapped baffle. The wrapped baffle substantially covers the sides of the driver. As the frontal area of the baffle increases, the attenuation of frequencies between 1 kHz and 3 kHz becomes slightly higher. Additionally, the increase in the low frequency response as compared to the straight baffle is limited. Preferably, the wrapped baffle is as deep as the driver itself. This configuration yields the flattest response between 1 kHz and 20 kHz and matches the low frequency response of speakers incorporating larger baffles. 
     Referring to  FIG. 2 , the rear side of a dipole speaker  200  is shown. A driver  210  is installed in a face  220  of dipole speaker  200  and housed within walls  230 ,  240 ,  250 ,  260 . The rear of driver  210  remains exposed. In order to achieve desirable sound dispersion, walls  230 ,  240 ,  250 ,  260  extend a length  270  substantially equal to a length  280  representing the depth of driver  210 . Also, wall  260  may be incorporated into the upper surface of a monopole speaker. The length of walls  230 ,  240 ,  250 ,  260  may be varied. Length  270  may be greater or less than length  280 . In one embodiment of the present invention, driver  210  is in a wrapped baffle, having one wall in common with a monopole speaker. In yet another alternative embodiment, the rear of driver  210  is substantially covered by a screen, dust cover, or similar material known in the art that does not affect the sound emissions. Similarly, driver  210  may be substantially surrounded by side walls, exposing only the rear of driver  210  through the rear wall. 
     Dipole speaker  30  is positioned on top surface  28  of monopole speaker  20  at an angle α. Monopole speaker  20  is directed towards a listener or listening area and dipole speaker  30  is rotated at an angle α from a direction  36  of monopole speaker  20 . Angle α corresponds to an area of consistently lower output for dipole driver  32  and may vary depending on the driver and baffle configuration used in dipole speaker  30 . 
     The area of consistently lower output is generally the direction of radiation with decreased, but similar in level, audio output compared to the level on-axis over a range of frequencies.  FIGS. 4 through 20  depict a series of polar plots of sound pressure level that illustrate a range of angles of consistently lower output for a dipole speaker between 45 degrees and 75 degrees. The concentric rings illustrate 10 dB intervals of pressure differential. The reference numbers to frequency in Hz refer to center frequencies for lower and upper octave bands that bound the frequency range of the test result. The polar plots range in frequency from 160 Hz to 8000 Hz and the angle of consistently lower output remains between 45 and 75 degrees. 
     The dipole speaker position is fixed such that an area of consistently lower output is directed in the general vicinity of the listener. In this embodiment, an angle of consistently lower output is between 45 and 75 degrees so angle α is between 45 and 75 degrees. In an exemplary embodiment, this angle is at 68 degrees. As a result, angle α is a rotation of 68 degrees from the monopole speaker position. 
     Both the left and right speaker units have a monopole speaker and a dipole speaker. In order to optimize the diffused sound emanating from the dipole speakers, the dipole speakers are rotated in different directions on the left and right speaker units. Referring to  FIG. 3 , a right speaker unit  310  and a left speaker unit  320  are shown. Right speaker unit  310  has a monopole speaker  312  and a dipole speaker  314 . Left speaker unit  320  has a monopole speaker  322  and a dipole speaker  324 . 
     On right monopole speaker  312 , dipole speaker  314  is rotated left an angle β from a direction  316  of monopole speaker  312 . Conversely, on left monopole speaker  322 , dipole speaker  324  is rotated right an angle σ from a direction  326  of monopole speaker  322 . 
     Referring now to  FIG. 21 , a listener  120  in a room utilizing the system of an embodiment of the present invention is shown. The room is shown with three walls  105 ,  110 ,  115  in a rectangular shape. However, walls  105 ,  110 ,  115  may be configured in a non-rectangular shape. A listener  120  is positioned substantially centered between wall  105  and wall  115 . Although referred to in the singular, listener  120  represents at least one person that is subjected to the surround sound effect according to the embodiment. For example, listener  120  may represent a person listening in a room of a house, a person sitting at desk having a computer, many people listening in a movie theater, or at least one passenger in an automobile. Additionally, listener  120  does not need to be positioned in the center of the room. Listener  120  may be located at any position in the room facing the speaker system of the present invention. The surround sound experience may even be enhanced if listener  120  is not centered, the speaker system of the present invention is not centered, or the room is not substantially symmetrical. 
     Listener  120  faces the speaker system of the present invention. The speaker system has a left monopole speaker  125  and a right monopole speaker  130  positioned to face listener  120 . The front face of monopole speaker  125 ,  130  is directed substantially to listener  120  in a direction  135 ,  140 . Due to the highly directional nature of a monopole speaker, sound emanates from monopole speakers  125 ,  130  to listener  120  in direction  135 ,  140 . 
     An optional center speaker, not shown, may be positioned between monopole speakers  125 ,  130 . This optional center speaker may also be a monopole speaker. An optional subwoofer, not shown, may be positioned at substantially any location in the listening area. 
     A pair of dipole speakers  145 ,  150  are positioned atop monopole speakers  125 ,  130 . Dipole speakers  145 ,  150  are rotated an angle φ, γ from direction  135 ,  140 . Angle φ, γ corresponds to the area of consistently lower output of dipole speakers  145 ,  150 . In order to direct the area of consistently lower output towards listener  120 , dipole speakers  145 ,  150  are rotated by angle φ, γ. Left dipole speaker  145  is rotated by angle φ to the left and right dipole speaker  150  is rotated by angle γ to the right. Alternatively, these angles need not be equivalent to accommodate for the properties of the room or the speakers. 
     Dipole speakers  145 ,  150  emit sounds that reflect off walls of the room before reaching listener  120 . Because the sound reflects off the walls as opposed to the highly directed monopole speaker sounds, the reflected dipole speaker sounds arrive at listener  120  shortly after the monopole speaker sounds. The delay caused by the reflections enhances the surround sound effect. Rather than utilizing conventional rear speakers having a signal delay, the present invention has speakers positioned in front of the listener and takes advantage of the delay caused by reflected soundwaves. 
     The rotation of dipole speakers  145 ,  150  allows the sounds to be emitted in two directions, such that each direction reflects off a different wall. Each dipole speakers  145 ,  150  has a driver installed on a front side  147 ,  152  and the back of the driver is exposed on a rear side  146 ,  151 . Both the straight baffle and wrapped baffle design of the speakers allows for sound to be emitted in both the front and rear directions. 
     The front sides  147 ,  152  of dipole speakers  145 ,  150  emit sound in a first direction. Dipole speaker  145  emits sound in a direction  170  to wall  105 , which reflects the sound in a direction  171  to the left side of listener  120 . Dipole speaker  150  emits sound in a direction  175  to wall  115 , which reflects the sound in a direction  176  to the right side of listener  120 . 
     Dipole speaker  145 , located to the front left of listener  120 , also emits sound in a reverse direction on side  146  in the direction  160  to location  155  on wall  110 . The sound reflects in a direction  161  to wall  115 . The sound reflects from wall  115  in a direction  162  to the right side of listener  120 . Similarly, dipole speaker  150 , located to the front right of listener  120 , emits sound from the driver on side  151  in the direction  165  to location  155  on wall  105 . The sound reflects in a direction  166  to wall  105 . The sound reflects from wall  105  in a direction  167  to the left side of listener  120 . 
     Sound from the drivers in direction  160 ,  165  does not need to be aimed directly at location  155 , but may be preferable in a symmetrical listening area where listener  120  is positioned at a center point between walls  105 ,  115 . In a non-symmetrical setup, the delay of the reflected sounds may reach listener  120  at different times. However, this delay usually less than one second may serve to enhance the surround sound effect. 
     In operation, a user positions the speakers around the listening area to obtain a surround sound effect. A left speaker unit is positioned to the front left of the listener. A right speaker unit is positioned to the front right of the listener. An optional center speaker is positioned substantially directly in front of the listener. An optional subwoofer is positioned anywhere in the room. 
     A 5.1 configuration sound source may be used to provide a surround sound effect. Referring to  FIG. 22 , a schematic diagram of the signal distribution is shown. A sound source  2210  supplies signals to the speakers. A separate signal is provided to each of a front left monopole speaker  2220 , front left dipole speaker  2230 , center speaker  2240 , front right monopole speaker  2250 , front right dipole speaker  2260 , and subwoofer  2270 . This signal distribution allows for a 5.1 configuration with only three speaker units and a subwoofer. Alternatively, a sound source that produces fewer signals may be utilized. For example, the sound source provides only left and right audio signals which are distributed to the appropriate speakers. 
     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.