Abstract:
A sound reproduction system provided for in-vehicle use includes: a music signal source; a first group of a first transducer, a second transducer, a third transducer and a fourth transducer connected to the music signal source; a signal processor shifting the phase of first sound signals output from the music signal source; and a second group of a first transducer, a second transducer, a third transducer and a fourth transducers connected to the signal processor.

Description:
This application is a U.S. national phase application of PCT International Application PCT/JP2006/307914, filed Apr. 14, 2006. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a sound reproduction system and a vehicle using the same. 
     2. Description of the Related Art 
     A conventional sound reproduction system has a configuration as shown in  FIG. 5 . In  FIG. 5 , a plurality of audio files stored in memory  1  are transmitted to distribution box  2 . Distribution box  2  is controlled to transmit requested audio files to respective transducers  3 . Where, each transducer  3  stands for a headphone or a speaker embedded in a headrest. 
     Additionally, there is a technology called active noise canceling, as illustrated in  FIG. 6 . In  FIG. 6 , microphone  5  detects noises propagating in duct  4  to create a sound wave with an anti-phase to the detected sound wave by signal processor  6 , allowing speaker  7  to produce the anti-phase sound wave to cancel the noises out. 
     Known Information Disclosure Statements (IDS) for the present patent application are for instance Unexamined Japanese Patent Publication No. 2004-80765 and No. H05-223334. 
     However, a problem has been that a vehicle with the conventional sound reproduction system lacks comfortable in-vehicle environment. 
     That is, in the conventional system, passengers in the backseat need to use a headphone to prevent a driver from hearing a loud sound, such as an explosion sound in a movie, which damages a comfortable in-vehicle environment. Even if a speaker is embedded in a headrest instead of using a headphone, the sound volume is restricted to prevent a loud sound in a movie from leaking, causing a lack in a comfortable in-vehicle environment. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention aims at solving aforementioned problems and providing a sound reproduction system to realize a comfortable in-vehicle environment. 
     The sound reproduction system includes: a first sound signal source; a first transducer connected to the first sound signal source; a signal processor connected to the first sound signal source for shifting a phase of a first sound signal output from the first sound signal source by 180 degrees; and a second transducer connected to the signal processor. 
     In a vehicle using the sound reproduction system, only the sound output from the first transducer can be canceled for a certain passenger&#39;s seat. Therefore, passengers sitting on the backseat can enjoy movies or music that they request in a loud sound from the first transducer without using any headphone. Only the sound is canceled at the driver&#39;s seat but sounds necessary to hear such as horns or the like are not canceled, which can realize a comfortable in-vehicle environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of a sound reproduction system and a vehicle using the same in exemplary embodiment 1 of the present invention. 
         FIG. 2  shows a top view showing a positional relation between transducers of the sound reproduction system and a listener in exemplary embodiment 1 of the present invention. 
         FIG. 3  shows another block diagram of a sound reproduction system and a vehicle using the same in exemplary embodiment 1 of the present invention. 
         FIG. 4  shows a block diagram of a sound reproduction system and a vehicle using the same in exemplary embodiment 2 of the present invention. 
         FIG. 5  shows a view of a conventional sound reproduction system. 
         FIG. 6  shows another view of a conventional sound reproduction system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary Embodiment 1 
     The sound reproduction system and a vehicle using the same used in exemplary embodiment 1 of the present invention are described with reference to the drawings. 
       FIG. 1  is a block diagram of a sound reproduction system and a vehicle using the same used in exemplary embodiment 1 of the present invention. In  FIG. 1 , the first music signal (first sound signal) transmitted from music signal source  8  (first sound signal source) such as a DVD or CD player is input into preamplifier  9 . Subsequently, the first music signals are output as a plurality of channel signals by music signal processor  10  composed of: a signal selector, a signal mixer, an electronic volume, a bass/treble control, a fader/balance, a high-pass/low-pass filter, a fixed equalizer, a loudness control or the like (not shown in the drawing) in preamplifier  9 . A case using a four-channel speaker is described in this exemplary embodiment 1, though other channel numbers could be acceptable. Music signal processor  10  is described as a digital signal processor in this exemplary embodiment 1, though an analog signal processor could be acceptable. 
     Channel signals output from music signal processor  10  are amplified by power amplifier  11  and are output from transducers (first transducer):  12 A,  12 B,  12 C and  12 D respectively. The transducer could be composed of a plurality of speakers or of for instance a set of speakers including a woofer and squawker in a door portion, and a tweeter in a pillar portion. 
     Meanwhile, second music signals output from music signal source  13  (second sound source) are input into preamplifier  14 . Subsequently, the second music signals are output as a plurality of channel signals by music signal processor  15  composed of a signal selector, a signal mixer, an electronic volume, a bass/treble control, a fader/balance, a high-pass/low-pass filter, a fixed equalizer, a loudness control or the like (not shown) in preamplifier  9 . Similar to the first music signal a case of using a four-channel speaker is described also in the second music signal, though the other number of channels could be acceptable for the configuration. Music signal processor  15  is described as a digital signal processor, though an analog signal processor could be acceptable. 
     Among channel signals output from music signal processor  10 , two channel signals each directing to transducers (first transducer)  12 A and  12 B are input into preamplifier  14 . Signal correction circuit  16  (signal processor) in preamplifier  14  shifts the phase of the channel signals by 180 degrees. However, the gain characteristics are kept unchanged. The four phase-shifted channel signals are added to the channel signals output from music signal processor  15  by adding circuit  17  (signal adder). After being added by adding circuit  17 , the four channel signals are amplified in power amplifier  18  and then output from transducers (second transducer)  19 A,  19 B,  19 C and  19 D respectively. 
       FIG. 2  shows a top view showing a positional relation between transducers of the sound reproduction system and a listener in exemplary embodiment 1 of the present invention. In  FIG. 2 , transducers  19 A and  12 A have a large relational influence on a sound transmission for ear  20 A. That is, the channel signal output from transducer  19 A is added to a 180-degree phase-shifted channel signal of the channel signal directing to transducer  12 A by adding circuit  17  in preamplifier  14  as shown in  FIG. 1 . As aforementioned, since the gain characteristics of the 180-degree phase-shifted signal are kept unchanged from the original signal, these two signals will cancel each other out. The output from transducer  12 A will be reduced by the output from transducer  19 A for ear  20 A shown in  FIG. 2  consequently. 
     Similarly, as shown in  FIG. 1 , the channel signal output from transducer  19 B is added to a 180-degree phase-shifted channel signal of the channel signal directing to transducer  12 B by adding circuit  17  in preamplifier  14 . As aforementioned, since the gain characteristics of the 180-degree phase-shifted signal are kept unchanged from the original signal, these two signals will cancel each other out. The output from transducer  12 B will be reduced by the output from transducer  19 B for ear  20 B shown in  FIG. 2  consequently. 
     Moreover, the channel signal output from transducer  19 C is added to a 180-degree phase-shifted channel signal of the channel signal directing to transducer  12 A by adding circuit  17  in preamplifier  14  as shown in  FIG. 1 . As aforementioned, since the gain characteristics of the 180-degree phase-shifted signal are kept unchanged from the original signal, these two signals will cancel each other out. The output from transducer  12 A will be reduced by the output from transducer  19 C for ear  20 C shown in  FIG. 2  consequently. 
     Additionally, the channel signal output from transducer  19 D is added to a 180-degree phase-shifted channel signal of the channel signal directing to transducer  12 B by adding circuit  17  in preamplifier  14  as shown in  FIG. 1 . As aforementioned, since the gain characteristics of the 180-degree phase-shifted signal are kept unchanged from the original signal, these two signals will cancel each other out. The output from transducer  12 B will be reduced by the output from transducer  19 D for ear  20 D as shown in  FIG. 2  consequently. 
     Since the configuration reduces the first music signal, from the driver&#39;s seat  21 A and the assistant driver&#39;s seat  21 B (located in a front portion of the vehicle) it becomes harder to listen to sounds of the first music signal but easier to sounds of the second music signal. Therefore, passengers sitting on backseat  22 A (located in a back portion of the vehicle) shown in  FIG. 1  can see and listen to a movie in a loud sound from the first music signal source by using transducers  12 A,  12 B,  12 C and  12 D, while a comfortable in-vehicle environment is maintained without being heard the loud sound by the driver. 
     Moreover, with the second music signal stopped temporarily, driver  21 A and assistant driver  21 B may be provided with the first music signal in a reduced condition. In  FIG. 2 , by switching off the power supply for transducers  19 C and  19 D assistant driver  21 B can also enjoy the output from transducers  12 A,  12 B,  12 C and  12 D. 
     Transducers  19 A and  19 B should preferably be disposed as near as possible to the driver&#39;s seat (e.g., near right and left back side portions of the driver&#39;s seat). “Near the driver&#39;s seat” means an area within one meter from the driver&#39;s ear. Transducers  19 C and  19 D should preferably be disposed as near as possible to the assistant driver&#39;s seat (e.g., near right and left back side portions of the assistant driver&#39;s seat). “Near the assistant driver&#39;s seat” means an area within one meter from the assistant driver&#39;s ear. Transducers  19 C and  19 D can be disposed not only near the assistant driver&#39;s seat but near the other passenger seat. “Near the other passenger seat” means an area within one meter from an ear of a passenger sitting on the seat. 
       FIG. 3  shows another block diagram of a sound reproduction system and a vehicle using the same in exemplary embodiment 1 of the present invention. In  FIG. 3 , backseat  22 A is further provided with transducers  19 E,  19 F,  19 G and  19 H. Among channel signals output from music signal processor  10 , two channel signals each directing to transducers  12 A and  12 B are input into preamplifier  14 . Signal correction circuit  16  in preamplifier  14  shifts the phase of the channel signals by 180 degrees. However, the gain characteristics are kept unchanged. The four phase-shifted channel signals directing to transducers  12 A and  12 B are added to the channel signals output from music signal processor  15  by adding circuit  17 . After being added by adding circuit  17 , the four channel signals are amplified in power amplifier  18  and then output from transducers  19 E,  19 F,  19 G and  19 H, respectively. 
     The aforementioned configuration enables passengers to choose either of the first music signal or the second music signal which he/she likes to listen in every seat. 
     Exemplary Embodiment 2 
     The sound reproduction system and a vehicle using the same used in exemplary embodiment 2 of the present invention are described with reference to the drawings. Elements similar to those in exemplary embodiment 1 have the same reference marks and the detailed descriptions are omitted. 
       FIG. 4  shows a block diagram of a sound reproduction system and a vehicle using the same used in exemplary embodiment 2 of the present invention. In  FIG. 4 , transducer  12 E is disposed in front of driver&#39;s seat  22 B and transducer  12 F designed to reproduce bass only is at the back of backseat  22 A. Additionally, bass-shakers  24  are disposed on driver&#39;s seat  22 B and on assistant driver&#39;s seat  22 C. 
     First music signals output from music signal source  8  are input into preamplifier  9 . Subsequently, the first music signals are output as a plurality of channel signals by music signal processor  10  composed of: a signal selector, a signal mixer, an electronic volume, a bass/treble control, a fader/balance, a high-pass/low-pass filter, a fixed equalizer, a loudness control or the like (not shown in the drawing) in preamplifier  9 . The channel signals output from music signal processor  10  are amplified by power amplifiers  11  and are output from transducers:  12 A,  12 B,  12 C,  12 D,  12 E and  12 F respectively. 
     Meanwhile, second music signals output from music signal source  13  are input into preamplifier  14 . Subsequently, the second music signals are output as a plurality of channel signals by music signal processor  15  composed of: a signal selector, a signal mixer, an electronic volume, a bass/treble control, a fader/balance, a high-pass/low-pass filter, a fixed equalizer, a loudness control or the like (not shown) in preamplifier  14 . 
     Among the channel signals output from music signal processor  10 , two channel signals each directing to transducers  12 A and  12 B are input into preamplifier  14 . Signal correction circuit  16  in preamplifier  14  shifts the phase of the channel signals by 180 degrees. However, the gain characteristics are kept unchanged. 
     Similarly, among the channel signals output from music signal processor  10 , four channel signals directing to transducer  12 E are input into preamplifier  14 . Signal correction circuit  16  in preamplifier  14  shifts the phase of the channel signals by 180 degrees. However, the gain characteristics are kept unchanged. 
     Four phase-shifted channel signals directing to transducers  12 A and  12 B, four phase-shifted channel signals directing to transducer  12 E, and channel signal output from music signal processor  15  are added together by adding circuits  17  and  23 . Four channel signals that have been created by adding circuits  17  and  23  are amplified in power amplifier  18  and then output from transducers  19 A,  19 B,  19 C and  19 D respectively. 
     Among the channel signals output from music signal processor  10 , channel signals directing to transducer  12 F are input into preamplifier  14 . Signal correction circuit  16  in preamplifier  14  shifts the phase of the channel signals by 180 degrees. However, the gain characteristics are kept unchanged. 
     Phase-shifted channel signals directing to transducer  12 F and channel signals output from music signal processor  15  are added together by adding circuit  23 . Channel signals that have been created by adding circuit  23  are amplified in power amplifier  18  and then output from bass-shaker  24 . 
     This can realize a configuration suitable for 5.1-ch known as the surround-sound system. At the same time, the first music signal can be reduced for driver  21 A and assistant driver  21 B. That is, the output from transducer  12 E can be reduced by using the output from transducers  19 A,  19 B,  19 C and  19 D, and the output from transducer  12 F designed to reproduce bass only can be reduced by bass-shakers  24  effectively. Therefore, passengers sitting on backseat  22 A shown in  FIG. 1  can see and listen to a movie in a loud sound by using transducers  12 A,  12 B,  12 C,  12 D,  12 E and  12 F, while a comfortable in-vehicle environment is maintained without being heard the loud sound by the driver. 
     Moreover, with the second music signal stopped temporarily, driver  21 A and assistant driver  21 B may be provided with the first music signal in a lower level condition. In  FIG. 4 , by switching off the power supply for transducers  19 C and  19 D assistant driver  21 B can also enjoy the output from transducers  12 A,  12 B,  12 C,  12 D,  12 E and  12 F. 
     INDUSTRIAL APPLICABILITY 
     The sound reproduction system disclosed in this invention performs such that only the sound of movie or the like being listened in backseats can be canceled at the driver&#39;s seat, and that the driver can listen to other audio programs at the driver&#39;s seat, which is useful as a sound reproduction system for use in a vehicle or the like.