Abstract:
The present invention includes: a front L-channel speaker unit for outputting a front L-minus-R signal; a front R-channel speaker unit for outputting a front R-minus-L signal; a front center speaker unit for outputting a front center signal consisting of front R-plus-front L; a rear L-channel speaker unit for outputting a rear L-minus-R signal; a rear R-channel speaker unit for outputting a rear R-minus-L signal; and a rear center speaker unit for outputting a rear L-plus-R signal. The subtracted signals contain only frequency components below a predetermined frequency.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a speaker system for playing back multi-channel signals, e.g., Dolby digital signals.  
           [0002]    Playback of multi-channel signals, such as Dolby digital signals, generally requires a speaker for each channel In the case of a Dolby digital system, for example, a total of six channels are played back: an L channel, an R channel, a center channel for the front, a surround L channel and a surround R channel for the rear, and a subwoofer channel for low frequencies. Thus, six speakers must be used.  
           [0003]    A speaker cable must be laid from the amp to each of these speakers. For hi-fi playback, these speaker cables must be as short as possible. Laying of six cables laid across the floor can damage the appearance of the room and can prevent the speakers from being placed in appropriate places.  
         OBJECT AND SUMMARY OF THE INVENTION  
         [0004]    An object of the present invention is to overcome the problem described above.  
           [0005]    The present invention includes: a front L-channel speaker unit outputting a signal in which the front R-channel signal is subtracted from the front L-channel signal; a front R-channel speaker unit outputting a signal in which the front L-channel signal is subtracted from the front R-channel signal; a front center speaker unit outputting the front center signal; a front enclosure equipped with the front L-channel speaker unit, the front R-channel speaker unit, and the front center speaker unit; a rear L-channel speaker unit outputting a signal in which the rear R-channel signal is subtracted from the rear L-channel signal; a rear R-channel speaker unit outputting a signal in which the rear L-channel signal is subtracted from the rear R-channel signal; a rear center speaker unit outputting a signal in which the rear L-channel signal is added to the rear R-channel signal; and a rear enclosure equipped with the rear L-channel speaker unit, the rear R-channel speaker unit, and the rear center speaker unit.  
           [0006]    The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a plan drawing of a front enclosure.  
         [0008]    [0008]FIG. 2 is a right-side drawing of a front enclosure.  
         [0009]    [0009]FIG. 3 is a plan drawing of a rear enclosure.  
         [0010]    [0010]FIG. 4 is a front-view drawing of a rear enclosure.  
         [0011]    [0011]FIG. 5 is a plan drawing showing the front and rear enclosures installed in a room.  
         [0012]    [0012]FIG. 6 is a block diagram of a signal processing device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    In a Dolby digital system, which is one type of multi-channel surround-sound system, speakers must be provided for a total of six channels: three channels in the front (a L channel, a R channel and a center channel), two channels in the rear (a rear L channel and a rear R channel), and one subwoofer channel.  
         [0014]    Referring to FIG. 1 and FIG. 2, an enclosure  200  is positioned in front of the listener. A center speaker unit  201  is disposed in the front center of enclosure, facing the listener. The center speaker unit  201  receives what is essentially a mono signal The mono signal may be the L+R component of the recorded sound or some other mono source. On the left side of enclosure  200 , an L-channel speaker unit  202  faces diagonally in the left rear direction from the center speaker unit  201 . The L-channel speaker unit  202  receives the L-minus-R component (L−R). On the right side, an R-channel speaker unit  203  similarly faces diagonally in the right rear direction. The R-channel speaker unit  203  receives the R-minus-L component (R−L). This design assumes the presence of a wall  10  behind the enclosure  200 . The sound from the L- and R-speaker units  202 ,  203  radiate diagonally at approximately 45 degrees toward the wall  10 . Thus, the vibration axes of the speaker units  202 ,  203  form an angle of approximately 90 degrees.  
         [0015]    When the L−R and R−L signals are subtracted, the in-phase portions of these signals are cancelled, while the out-of-phase components are preserved. Such out-of-phase components, when reproduced in the manner disclosed herein, expands the stereo image. Low-pass filtering removes frequency components above about 2 kHz from the L and R signals before the subtraction. Removal is required because the removed high-frequency signals would otherwise produce noise, without contributing to the stereo image.  
         [0016]    Expanding the stereo image in this way is disclosed in U.S. Pat. Nos. 4,819,269 and 5,610,986, the disclosures of which are hereby incorporated by reference.  
         [0017]    As a result, the speaker unit  202  has a virtual position at a reflection point  11  where the sound from the speaker unit  202  reflects off the wall  10 . The speaker unit  203  has a virtual position at a reflection position  12  where the sound from the speaker unit  203  reflects off of the wall  10 . Thus, even though the speaker units  203 ,  203  are placed compactly within the single enclosure  200 , the speaker units  202 ,  203  are perceived as being spaced far apart, thus providing a wider stereo image.  
         [0018]    The attachment height of the center speaker unit  201  is higher the attachment height of the L-channel speaker unit  202  and the R-channel speaker unit  203 . Thus, the output source for the positive-phase component from the speaker unit  201  and the negative-phase component from the speaker unit  202  are perceived as being positioned at distinctly different heights, resulting in improved localization of sound. Elevating the center speaker unit  201  provides superior sound quality. Referring to FIGS. 3 and 4, a rear enclosure  100  includes center speaker unit  101  is disposed on the front of the enclosure  100  to play back the sum of the rear L-channel and the rear R-channel An L-channel speaker unit  102  plays back the L−R component in which the rear R-channel is subtracted from the rear L-channel. A rear R-channel speaker unit  103  plays back the R−L component in which the rear L-channel is subtracted from the rear R-channel.  
         [0019]    The L-channel and R-channel speaker units  102 ,  103  are oriented outward to form an angle of approximately 50 degree angles relative to the center speaker unit  101 . As with the front enclosure  200 , the L-channel and R-channel speaker units  102 ,  103  are placed at a different height from the speaker unit  101  to provide improved spatial definition in the sound.  
         [0020]    Referring to FIG. 5, the enclosure  200  is placed in front of a listener  13  and an enclosure  100  is placed behind the listener. A DVD player  20  and an A/V amp  21  are connected by an optical cable. When a DVD is loaded in the DVD player  20 , the video signal and the undecoded 5.1-channel audio signal are sent to the A/V amp  21 . The AN amp  21  decodes the audio signal from the DVD player  20  and converts the signal to a 5.1-channel audio signal This is then output to a signal processing device  30 . Audio from a CD in the DVD player  20 , is sent as a two-channel audio signal to the AN amp  21 .  
         [0021]    The signal processing device  30  is connected by cables  22 ,  23  to the front enclosure  200  and the subwoofer  204  respectively. The signal processing device  30  is connected to the rear enclosure via an infrared signal. Thus, by connecting the signal processing device  30  to the enclosure  200  with a six-line cable, a single cable is sufficient to connect the signal processing device  30  and the front speaker device  200 . Since the rear enclosure  100  is connected via an infrared signal, no cable is required. As a result, the amount of speaker cable used is much less than if the speakers were mounted in the corner of the room, and the look of the room is not affected negatively. Also, since a 5.1-channel system can be set up with the front enclosure  200 , the rear enclosure  100 , and the subwoofer  204 , fewer speaker units need to be installed.  
         [0022]    Referring to FIG. 6, there is shown a block diagram of the signal processing device  30 . L-channel signals from stereo output signals such as CD players and tuners are sent to an L-in terminal  31 , and R-channel signals are sent to an R-in terminal  32 . The two signals are added using an adder  40  to form an L+R signal, which then goes through an adder  41  and a low-pass filter  42  (hereinafter referred to as LPF). The LPF  42  removes high frequencies above approximately 2 kHz. The signal then goes through a variable resister  43  for gain adjustment and then to an amplifier  62  and is output through the center speaker  201 .  
         [0023]    The signal also goes through a low-pass filter (LPF)  44  which removes frequencies above approximately 150 Hz from the L+R signal The resulting low-frequency signal passes through an adder  45  and is amplified by an amplifier  64 . This signal is output from the subwoofer  204 .  
         [0024]    The R-channel signal is level-adjusted with a variable resister  46  and subtracted from the L-channel signal received from the L-in terminal  31  by a subtracter  47 , resulting in an L−R signal. This is then amplified by an amplifier  61  and is output from the L-channel speaker  202 . Similarly, the L-channel signal is level-adjusted with a variable resister  48  and subtracted from the R-channel signal from the R-in terminal  32  by a subtracter  49 , resulting in an R−L signal This is then amplified by an amplifier  63  and is output through the R-channel speaker  203 .  
         [0025]    Thus, the L−R signal is output from the speaker  202 , the low- and mid-range components of the L+R signal are output from the speaker  201 , the R−L signal is output from the speaker  203 , and the low-range component of the L+R signal is output from the subwoofer  204 . As a result of the signal processing described above, a negative R-channel signal is added to the L-channel signal, and a negative L-channel signal is added to the R-channel signal. This provides a broad sound field space even though the speakers may be close together.  
         [0026]    Also, since high-frequency components have a significant effect on sound image localization, the LPF  42  is used to prevent the high-frequency components of the L+R signal from being output from the center speaker  201 .  
         [0027]    By placing the enclosure  200  close to the wall  10 , the L−R signal and the R−L signal travel toward the listener after being reflected by the wall  10  as indicated by the arrows in FIG. 1. Thus, the sound image is dispersed over a wider range, and a broader stereo image results.  
         [0028]    The above description presents circuit operations performed when playing two-channel audio signals. This device can also receive Dolby digital 5.1-channel signals as well. In this case, in addition to the L-in terminal  31  and the R-in terminal  32  described above, the output signal from an A/V amp  71  is also sent as follows: a front center-channel signal is sent to a C-in terminal  33 ; a rear L-channel signal is sent to a RL-In terminal  34 ; a rear R-channel signal is sent to an RR-In terminal  35 ; and a subwoofer signal is sent to a Sub-in terminal  36 .  
         [0029]    The C-in terminal  33  is connected to the adder  41  so that the center-channel signal from the Dolby digital signal is added to the L+R signal described above. The high-frequency components are then removed by the LPF  42 , and the resulting signal is output from the center speaker unit  201 . The C-in terminal  33 , the RL-in terminal  34 , the RR-in terminal  35 , and the Sub-in terminal  36  are connected to an adder  50  so that the rear L-channel signal, the rear R-channel signal, and the subwoofer signal are added. An LPF  51  extracts the low-frequency signals of approximately 150 Hz or lower from this added signal. The adder  45  then adds the low-frequency components of the front L-channel signal, the front R-channel signal. The resulting signal is passed through the variable resister  55  for gain adjustment and then sent to an amplifier  64 .  
         [0030]    Thus, in addition to the signal sent to the subwoofer input terminal  35 , the subwoofer  204  outputs the low-frequency components from all channels. This allows the subwoofer  204  to output the low-frequency components that cannot be played back by the small apertures of the speaker units in the speaker devices  100 ,  200 , thus preventing inferior output of low frequencies, which can affect realism This takes advantage of the fact that humans cannot identify the directionality of low frequency components. For example, if a low-frequency component is present only in the rear L-channel, the listener will not be able to recognize that low frequencies are being output from the rear left. Thus, there is no problem with using the subwoofer to output low frequencies that should be coming from the rear left side.  
         [0031]    The rear L-channel signal and the rear R-channel signal from the RL-in terminal  34  and the RR-in terminal  35  are converted to serial signals by a signal converter  52 . The result is then output via an infrared connection from a light-emitting device  53 . A light-receiving device  80  disposed in the rear speaker device  100  receives this infrared signal which is then demodulated into a two-channel signal by a signal converter  81 . The demodulated rear L-channel signal and the rear R-channel signal are added by an adder  82 . High-frequency components are removed with an LPF  83 . The resulting signal is passed through a variable resister  84  for gain adjustment and amplified by an amplifier  92 . This is then output from the center speaker unit  101 .  
         [0032]    Also, the rear R-channel signal is adjusted to a prescribed level by a variable resister  85  for gain adjustment. The result is subtracted from the rear L-channel signal by a subtracter  86  to form the rear-channel L−R signal. This L−R signal is amplified by an amplifier  91  and output through the speaker unit  102 . Similarly, the rear L-channel signal is set to a prescribed level by a variable resister  87  for gain adjustment. The result is subtracted from the rear R-channel signal by a subtracter  88  to form a rear-channel R−L signal. This R−L signal is amplified by an amplifier  93  and is output from the speaker unit  103 .  
         [0033]    As in the front speakers, the L-channel speaker  102  outputs a negative-phase component of the R-channel signal, and the R-channel speaker  103  outputs a negative-phase component of the L-channel signal. Thus, as in the speaker device  200 , the sound image is dispersed over a wider range even if the speaker units  102 ,  103  are close together, thus providing a broader stereo image.  
         [0034]    In the embodiment described above, an infrared connection is used to transfer the playback signal to the rear enclosure. The present invention is not restricted to this. A speaker cable, RF link, or other signal transmission technique can be used to transfer the signal, without departing from the spirit and scope of the invention.  
         [0035]    Also, in the embodiment described above, a gain-adjusted R signal is subtracted from the L-channel signal to generate the L−R signal However, depending on the speaker units and the environment of the room in which the units are used, it would also be possible to perform signal subtraction and addition that takes frequency characteristics into account. For example, the mid-range signal of the R channel can be subtracted from the L-channel signal to generate the L−R signal  
         [0036]    Also, in the embodiment described above, the L, R speaker units  202 ,  203  face away from the center speaker unit  201 . However, it would also be possible to face these speakers in the same direction as the center speaker unit  201  so that the output is projected directly to the listener.  
         [0037]    As described above, a speaker system that requires three speakers in the front and two speakers in the rear can be set up with a total of two units. Thus, a multi-channel playback system can be set up easily so that less space is required for installing speakers, and the appearance of the listening room is not affected negatively.  
         [0038]    Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.