Loudspeaker system

Abstract

The present invention addresses the problem of providing a speaker system capable of switching the output range of sound. A solution is provided. A vehicle approach notification device (100) is provided with: a travel sound generation unit (110) that generates sound to be output; an ultrasonic speaker (120); an SP drive unit (130) that drives the ultrasonic speaker (120) and outputs the sound generated by the travel sound generation unit (110) from the ultrasonic speaker (120); and a drive unit (130) that drives the ultrasonic speaker (120) and outputs the sound generated by the travel sound generation unit (110) from the ultrasonic speaker (120). And a switching control unit (140) in which the distance from which the outputted sound wave propagates in the air until the sound wave becomes a shock wave is variable.

Description

Technical Field

[0001] The present invention relates to a speaker system formed by combining a plurality of speakers. Background Art

[0002] Conventionally, a vehicle presence notification device has been known which uses a speaker array formed by combining a plurality of ultrasonic speakers and adjusts the phases of sound waves output from the respective ultrasonic speakers to change the directivity of a notification sound (see, for example, Patent Document 1).

[0003] Prior Art Documents:

[0004] Patent Documents:

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-31695 Summary of the Invention

[0006] Problems to be Solved by the Invention:

[0007] In addition, the vehicle presence notification device disclosed in the above Patent Document 1 can change the directivity of the entire speaker array by adjusting the phases of sound waves output from the respective speakers constituting the speaker array, but cannot change the output range of the notification sound. For example, it is impossible to switch between the case of outputting sound over a long distance and the case of outputting sound over a wide range around the vehicle according to the state of the vehicle during travel.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a speaker system capable of switching the output range of sound.

[0009] Means for Solving the Problems:

[0010] To solve the above problems, the speaker system of the present invention includes: an output sound generation mechanism that generates sound to be output; an ultrasonic speaker; a speaker drive mechanism that drives the ultrasonic speaker to output the generated sound of the output sound generation mechanism from the ultrasonic speaker; and a shock wave distance variable mechanism that makes variable the distance from when the sound wave output from the ultrasonic speaker propagates in the air until it becomes a shock wave.

[0011] When the distance until it becomes a shock wave is long, two types of difference tones of carriers are repeatedly generated and synthesized during the period before becoming the shock wave, and thus these difference tones become virtual sound sources and are synthesized along the direction of travel of the sound wave and the directivity becomes narrow. On the other hand, when the distance until it becomes a shock wave is short, the length of the virtual sound source extension is short, and the sound wave diffuses spherically from the position where the sound wave disappears from the virtual sound source, and thus the directivity becomes wide. In this way, by making variable the distance until it becomes a shock wave, it is possible to change the directivity and switch the output range of the radiated sound of the speaker.

[0012] Preferably, the shock wave distance variable mechanism sends an instruction to the speaker drive mechanism to change the initial sound pressure of the sound wave when output from the ultrasonic speaker, thereby varying the distance. Alternatively preferably, the shock wave distance variable mechanism sends an instruction to the speaker drive mechanism to change the carrier frequency of the sound wave output from the ultrasonic speaker, thereby varying the distance. Preferably, the shock wave distance variable mechanism sends an instruction to the speaker drive mechanism to change the initial sound pressure of the sound wave when output from the ultrasonic speaker and the carrier frequency of the sound wave output from the ultrasonic speaker, thereby varying the distance.

[0013] The distortion of the sound wave waveform accumulatively increases as the waveform of one cycle is repeatedly propagated, thereby generating a shock wave. The louder the volume (the greater the initial sound pressure) with a greater distortion of the waveform, the easier it is to generate a shock wave at a short distance. In addition, the higher the carrier frequency and the more the number of propagations of the waveform of one cycle, the easier it is to generate a shock wave at a short distance. For these reasons, by changing at least one of the initial sound pressure and the carrier frequency, the directivity characteristics, that is, the output range of the sound emitted from the speaker, can be switched.

[0014] Preferably, a surrounding condition judging mechanism for judging the surrounding conditions is further provided, and the shock wave distance variable mechanism varies the distance based on the surrounding conditions judged by the surrounding condition judging mechanism. Thereby, the width of the directivity characteristics can be automatically switched according to the surrounding conditions.

[0015] Preferably, the speaker system is mounted on a vehicle to output a sound notifying of the approach of the vehicle to people around. The surrounding condition judging mechanism is a speed acquisition mechanism for acquiring the traveling speed of the vehicle, and the shock wave distance variable mechanism gives a switching instruction, which is to set the distance longer to narrow the directivity characteristics of the sound output from the speaker when the traveling speed acquired by the speed acquisition mechanism is high, and to set the distance shorter to widen the directivity characteristics of the sound output from the speaker when the traveling speed acquired by the speed acquisition mechanism is low. Thereby, when traveling at a low speed, pedestrians and the like around the vehicle can widely hear the sound notifying of the approach, and when traveling at a medium speed or higher, pedestrians and the like in a place slightly farther away can hear the sound notifying that the vehicle is approaching.

[0016] Preferably, the speaker system is mounted on a vehicle and outputs a sound notifying of the approach of the vehicle to people around. The surrounding condition judging mechanism is a driving environment judging mechanism that judges whether the driving position of the vehicle is an urban built-up area or the suburbs. The shock wave distance variable mechanism gives a switching instruction, which is to set a longer distance to narrow the directivity characteristic of the sound output from the set speaker array when the driving environment judging mechanism judges that the driving position of the vehicle is in the suburbs, and to set a shorter distance to widen the directivity characteristic of the sound output from the speaker when the driving environment judging mechanism judges that the driving position of the vehicle is in an urban built-up area. Thus, in an urban built-up area where there is a high possibility of many pedestrians and the like around the vehicle, people around the vehicle such as pedestrians can widely hear the approaching notification sound, and in the suburbs where there are fewer people, pedestrians in a slightly distant place can hear the sound notifying of the approaching vehicle.

[0017] Preferably, the shock wave distance variable mechanism gives a switching instruction to alternately set the length of the distance. Thus, for the spaces both near and far around, the radiated sound of the speaker can be heard.

[0018] Preferably, the surrounding condition judging mechanism includes a camera mechanism that captures images of the surroundings and an image analysis mechanism that analyzes the surrounding conditions based on the images obtained by the camera mechanism. The shock wave distance variable mechanism gives a switching instruction to switch the length of the distance based on the surrounding conditions analyzed by the image analysis mechanism. Thus, the width of the directivity characteristic of the radiated sound of the speaker can be switched on the basis of accurately grasping the surrounding conditions.

[0019] Preferably, the surrounding condition judging mechanism is a congestion state judging mechanism that judges the congestion state of the surroundings. The shock wave distance variable mechanism gives a switching instruction to switch the length of the distance based on the congestion state of the surroundings judged by the congestion state judging mechanism. Thus, the width of the directivity characteristic of the radiated sound of the speaker array can be switched according to the congestion state of the surroundings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a diagram showing the configuration of a vehicle approach notification device according to an embodiment.

[0021] Figure 2 is a diagram for explaining waveform distortion.

[0022] Figure 3 is the distance x until it becomes an N-wave S explanatory diagram of the sound field in the case of variable.

[0023] Figure 4 is a diagram showing a specific example in the case of switching the directivity characteristic of the speaker according to the driving speed of the vehicle.

[0024] Figure 5 This is a diagram showing a specific example in the case where the directivity characteristic of the speaker is switched according to whether the driving position of the vehicle is in an urban built-up area or the outskirts.

[0025] Figure 6 This is a diagram showing a specific example in the case where the surrounding conditions are judged based on an image obtained by photographing the surroundings.

[0026] Figure 7 This is a diagram showing a modified example in which the directivity characteristic of the speaker is made variable according to the crowded state indoors.

[0027] Explanation of reference numerals:

[0028] 100, 100A, 100B, 100C Vehicle approach notification device

[0029] 100D Broadcasting device

[0030] 110 Driving sound generation unit

[0031] 110D Broadcasting sound generation unit

[0032] 120 Speaker

[0033] 130 SP (Speaker) drive unit

[0034] 140, 140A, 140B, 140C, 140D Switching control unit

[0035] 150 Surrounding condition judgment unit

[0036] 150A Speed acquisition unit

[0037] 150B Driving environment judgment unit

[0038] 150C Image analysis unit

[0039] 150D Crowded state judgment unit

[0040] 152 Camera Detailed implementation mode

[0041] Hereinafter, a vehicle approach notification device according to an embodiment of the speaker system to which the present invention is applied will be described with reference to the accompanying drawings.

[0042] Figure 1 This is a diagram showing the configuration of a vehicle approach notification device according to an embodiment. Figure 1The vehicle approach notification device 100 shown is mounted on a vehicle with a quiet driving sound (such as an electric vehicle) and is used to output a virtual driving sound to the periphery of the vehicle to notify pedestrians and the like around of the approach of the vehicle. Therefore, the vehicle approach notification device 100 includes a driving sound generation unit 110, an ultrasonic speaker (parametric speaker) 120, an SP (speaker) drive unit 130, a switching control unit 140, and a surrounding condition determination unit 150.

[0043] The driving sound generation unit 110 generates a specified sound for notifying pedestrians and the like around the vehicle of the approach of the vehicle. This generated sound is conceived as a virtual driving sound of the vehicle, but since its purpose is to notify the approach of the vehicle using sound, it does not necessarily have to be similar to the driving sound and can also be a notification sound other than that.

[0044] The ultrasonic speaker 120 reproduces an audible sound with a narrow directivity characteristic by using the waveform distortion generated by radiating two types of ultrasonic waves with a large sound pressure. If the frequency of one ultrasonic wave (carrier wave) is set to f1, distortion components of 2f1, 3f1, 4f1,... which are integer multiples of it are generated. Additionally, if the frequency of the other ultrasonic wave (carrier wave) is set to f2, distortion components of 2f2, 3f2, 4f2,... which are integer multiples of it are generated. When both frequencies f1 and f2 are ultrasonic waves (sounds with a frequency higher than the human audible range), the frequencies of these integer multiple distortions are also higher than the audible range, so they cannot be heard by the human ear. However, when radiating such two types of carrier wave ultrasonic waves simultaneously, components of their difference tone (frequency f2 - f1) and sum tone (frequency f1 + f2) are generated. Among them, by setting the frequency of the difference tone (f2 - f1) to be within the audible range, the generated sound as an audible sound can be radiated from the ultrasonic speaker 120. For example, if f1 is set to 41 kHz and f2 is set to 40 kHz, a difference tone of f2 - f1 = 1 kHz can be radiated. In addition, the ultrasonic speaker 120 can also be configured as a speaker array formed by combining multiple elements.

[0045] The instantaneous sound speed c of a plane sound wave can be expressed by the following formula.

[0046] [Mathematical formula 1]

[0047]

[0048] Here, β is the nonlinear parameter (constant) of the medium, ρ 0 is the initial density of air (constant), C 0 is the initial speed of the sound wave (constant), and p is the instantaneous sound pressure (p = 0 at static pressure).

[0049] According to the above formula, since the pressure p changes, the instantaneous sound speed c also changes, and the waveform distorts as the sound wave travels. This distortion is manifested as the above-mentioned integer multiple distortion.

[0050] Therefore, in the case of a large volume where the change amount Δp of the pressure is large, waveform distortion is more likely to occur. In addition, this waveform distortion accumulatively increases as the number of propagation times of the waveform in one cycle increases. When the propagation distance is the same, the higher the frequency, the more the number of propagation times of the one-cycle waveform increases, and the easier the waveform is to be distorted.

[0051] Figure 2 It is a diagram for explaining waveform distortion. For example, it shows the case of ultrasonic waves representing a radiated sine wave waveform. According to Figure 2 (A) of Figure 2 and Figure 2 (C) of Figure 2 , the distance from the speaker 120 becomes farther in this order. The waveform distortion is small at the position close to the speaker 120 ( Figure 2 (A) of

[0052] ), and as the distance becomes farther, the waveform distortion gradually becomes larger ( S (B) of

[0053] ). Then, if the distance becomes even farther, the waveform becomes a shock wave close to the N shape (this shock wave is referred to as the "N wave" in this specification). At the timing of becoming this N wave, the distortion becomes the maximum, and no further distortion occurs even if it propagates. No distortion means that no audible sound as a difference tone is generated even in the case of radiating ultrasonic waves of two types of frequencies.

[0054]

[0055] Here, p 0 is the initial sound pressure, and ω is the angular frequency (=2πf).

[0056] In addition, if a longitudinal speaker array formed by arranging speakers in the sound wave radiation direction is considered, the sound waves are concentrated near the center of the arrangement of each speaker, so the directivity becomes narrow. On the other hand, at the end of the area where each speaker is arranged and closer to the front than its front end, the synthesized sound waves spread in a spherical shape, so the directivity becomes wide.

[0057] The difference tones generated by radiating ultrasonic waves of two frequencies are sequentially generated during the process of increasing the distortion of the ultrasonic waves. Therefore, these sequentially generated difference tones become virtual multiple sound sources, and their operating principle is the same as that of the longitudinal speaker array. The width and narrowness of the directivity are determined by the longitudinal array length. Therefore, the longer the distance x S until it becomes the N wave, the narrower the directivity. On the contrary, the shorter the distance x S until it becomes the N wave, the wider the directivity.

[0058] Figure 3 is the distance x until it becomes an N-wave S Explanatory diagram of the sound field when the distance x is variable. As described above, by making the distance x until it becomes an N-wave S shorter, a wider directivity characteristic can be obtained, and sound is radiated in a large range from the speaker 120 provided at the front of the vehicle ( Figure 3 (B) of). In this case, the diffusion of the sound becomes larger, and the sound is likely to attenuate along the radiation direction, and pedestrians etc. located at a short distance can hear this sound.

[0059] On the other hand, by making the distance x until it becomes an N-wave S longer, a narrower directivity characteristic can be obtained, and thus sound is radiated in a small range from the speaker 120 provided at the front of the vehicle ( Figure 3 (A) of). In this case, the diffusion of the sound is small, and the sound is difficult to attenuate along the radiation direction, and pedestrians etc. located at a long distance can hear this sound.

[0060] The SP drive unit 130 drives the ultrasonic speaker 120 using two types of carrier waves in such a way that the sound generated by the running sound generation unit 110 becomes a difference tone, and makes the distance x until it becomes an N-wave S variable.

[0061] The switching control unit 140 gives a switching instruction for the distance x until it becomes an N-wave to the SP drive unit 130 S corresponding to the width of the directivity characteristic of the sound output from the speaker 120.

[0062] As described above, in the denominator of the mathematical formula for calculating the distance x S contains the initial sound pressure p 0 and the angular frequency ω(=2πf), so by making them variable, the distance x until it becomes an N-wave can be changed S . The switching control unit 140 gives an instruction to the SP drive unit 130 to change the initial sound pressure p 0 and / or the carrier frequency f(=ω / (2π)) to change the distance x until it becomes an N-wave S , thereby switching the width of the directivity characteristic of the ultrasonic wave and the audible range sound wave radiated from the ultrasonic speaker 120.

[0063] The surrounding condition determination unit 150 determines the surrounding conditions. Based on the surrounding conditions determined by the surrounding condition determination unit 150, a switching instruction of the switching control unit 140 is performed.

[0064] The above-mentioned driving sound generation unit 110 corresponds to the output sound generation mechanism, the SP driving unit 130 corresponds to the speaker driving mechanism, the switching control unit 140 corresponds to the shock wave distance variable mechanism, and the surrounding condition determination unit 150 corresponds to the surrounding condition determination mechanism.

[0065] The vehicle approach notification device 100 of the present embodiment has such a configuration. Next, a specific example of the surrounding condition determination unit 150 that switches the width of the directivity characteristics will be described.

[0066] Figure 4 It is a diagram showing a specific example in the case of switching the directivity characteristics of the speaker 120 according to the traveling speed of the vehicle. Figure 4 The shown vehicle approach notification device 100A is different from Figure 1 the shown vehicle approach notification device 100 in that the surrounding condition determination unit 150 is implemented by the speed acquisition unit 150A, and the switching control unit 140 is replaced with the switching control unit 140A. The speed acquisition unit 150A corresponds to the speed acquisition mechanism.

[0067] The speed acquisition unit 150A acquires the traveling speed of the vehicle. For example, it is possible to consider the case of detecting the traveling speed based on vehicle speed pulses output per a certain traveling distance, or the case of acquiring the traveling speed from a vehicle control unit that performs display processing such as a speedometer. In addition, since the relative speed of pedestrians and the like around the vehicle changes corresponding to the traveling speed of the vehicle, in this specification and the like, it is assumed that the traveling speed of the vehicle is also included in the "surrounding conditions".

[0068] The switching control unit 140A gives a switching instruction to the SP driving unit 130, and this switching instruction is that when the traveling speed acquired by the vehicle speed acquisition unit 150A is high, the distance x to the N wave S is lengthened to narrow the directivity characteristics of the sound output from the speaker 120, and when the traveling speed acquired by the speed acquisition unit 150A is low, the distance x to the N wave S is shortened to widen the directivity characteristics of the sound output from the speaker 120. For example, the initial sound pressure p S corresponding to the longer distance x 0 and / or the carrier frequency f, and the initial sound pressure p S corresponding to the shorter distance x 0 and / or the carrier frequency f are prepared in advance, and the initial sound pressure p S corresponding to the length of the switched distance x 0 and / or the carrier frequency f are indicated to the SP driving unit 130.

[0069] Accordingly, when traveling at a low speed, it is possible to widely notify pedestrians and the like around the vehicle of the approaching sound, and when traveling at a medium speed or higher, it is possible to hear the sound notifying that the vehicle is approaching.

[0070] Figure 5 It is a diagram showing a specific example in the case where the directivity characteristic of the speaker 120 is switched according to whether the driving position of the vehicle is in an urban area or the suburbs. Figure 5 The vehicle approach notification device 100B shown with respect to Figure 1 The difference between the vehicle approach notification device 100 shown is that the surrounding condition determination unit 150 is implemented by the driving environment determination unit 150B, and the switching control unit 140 is replaced with the switching control unit 140B. The driving environment determination unit 150B corresponds to the driving environment determination mechanism.

[0071] The driving environment determination unit 150B determines whether the driving position of the own vehicle is in an urban area or the suburbs. For example, it is possible to consider using a vehicle navigation device that continuously or at regular intervals processes whether the position of the own vehicle is included in an urban area or the suburbs based on map data as the driving environment determination unit 150B, or the case of obtaining information indicating whether the vehicle is traveling in an urban area or the suburbs from the vehicle navigation device.

[0072] The switching control unit 140B gives a switching instruction to the SP driving unit 130. This switching instruction is that when the driving environment determination unit 150B determines that the driving position of the own vehicle is in the suburbs, the distance x to the N wave is S lengthened to narrow the directivity characteristic of the sound output from the speaker 120, and when the driving environment determination unit 150B determines that the driving position of the own vehicle is in an urban area, the distance x to the N wave is S shortened to widen the directivity characteristic of the sound output from the speaker 120.

[0073] Accordingly, in an urban area where there is a high possibility of a lot of pedestrians and the like around the vehicle, it is possible to widely notify pedestrians and the like around the vehicle of the approaching sound, and in the suburbs where there are fewer people, it is possible to notify pedestrians and the like in a slightly distant place that the vehicle is approaching.

[0074] Figure 6 It is a diagram showing a specific example in the case of determining the surrounding condition based on an image obtained by photographing the surrounding area. Figure 6 The vehicle approach notification device 100C shown with respect to Figure 1The difference of the vehicle approach notification device 100 shown is that the surrounding condition determination unit 150 is implemented by the camera 152 and the image analysis unit 150C, and the switching control unit 140 is replaced by the switching control unit 140C. The camera 152 corresponds to the imaging mechanism, and the image analysis unit 150C corresponds to the image analysis mechanism.

[0075] One or more cameras 152 are provided at the front or side of the vehicle, and image the surroundings including at least the front of the vehicle itself. The image analysis unit 150C analyzes the position or number of pedestrians or the like existing in the surroundings of the vehicle itself, or the width of the driving road, the driving lane, and other conditions of the surroundings of the vehicle itself based on the image obtained by imaging with the camera 152.

[0076] Based on the conditions of the surroundings of the vehicle itself analyzed by the image analysis unit 150C, the switching control unit 140C gives a switching instruction to the SP drive unit 130. This switching instruction is to make the distance x to the N wave S longer to narrow the directivity characteristic of the sound output from the speaker 120, or to make the distance x to the N wave S shorter to widen the directivity characteristic of the sound output from the speaker 120.

[0077] For example, when the result of analyzing the image is that there are many pedestrians or the like in the surroundings of the vehicle itself, a switching instruction for widening the directivity characteristic is given, otherwise a switching instruction for narrowing the directivity characteristic is given. Thus, it is possible to switch the width of the directivity of the emitted sound of the speaker 120 on the basis of accurately grasping the surrounding conditions. In addition, the captured image may be analyzed to perform the same processing as the Figure 4 shown speed acquisition unit 150A, and the same processing as the Figure 5 shown driving environment determination unit 150B may also be performed.

[0078] Figure 7 is a diagram showing a modified example in which the directivity characteristic of the speaker 120 is variable according to the degree of congestion in the room. Figure 7 The broadcast device 100D shown is provided, for example, in a department store sales floor, and emits a prescribed broadcast voice toward a part of the customers. This broadcast device 100D has a configuration similar to that of the Figure 1 shown vehicle approach notification device 100. The difference from the vehicle approach notification device 100 is that the surrounding condition determination unit 150 is implemented by the congestion state determination unit 150D, the driving sound generation unit 110 is replaced by the broadcast sound generation unit 110D, and the switching control unit 140 is replaced by the switching control unit 140D. The broadcast sound generation unit 110D corresponds to the output sound generation mechanism, and the congestion state determination unit 150D corresponds to the congestion state determination mechanism.

[0079] The congestion state determination unit 150D determines the congestion state of customers in the surrounding area (a specific area within the department store). It is possible to consider cases where this determination is made by analyzing the captured image of the camera 152 in the same way as the image analysis unit 150C shown in Figure 6 or cases where sensors for detecting the entry and exit of customers are provided at the entrances and exits and this determination is made based on the detection results.

[0080] Based on the congestion state of the surrounding area determined by the congestion state determination unit 150D, the switching control unit 140D gives a switching instruction to the SP driving unit 130. This switching instruction is to make the distance x to the N wave S longer to narrow the directivity characteristic of the broadcast sound output from the speaker 120, or to make the distance x to the N wave S shorter to widen the directivity characteristic of the broadcast sound output from the speaker 120.

[0081] For example, when it is loose and the number of customers in a specific area is small, in order to attract customers, a switching instruction to widen the directivity characteristic of the radiated broadcast sound is given. When it is congested and the number of customers in a specific area is large, in order to make only a certain number of customers hear, a switching instruction to narrow the directivity characteristic of the radiated broadcast sound is given. Thus, the width of the directivity characteristic of the radiated sound of the speaker 120 can be switched according to the congestion state of the surrounding area.

[0082] In addition, Figure 7 the broadcast device 100D shown can also be used for situations other than the broadcast sound in the department store. For example, in an art museum, when there are many students and congestion occurs in the exhibition room during a student study tour, a switching instruction to widen the directivity characteristic of the radiated broadcast sound is given, and in normal situations other than this, a switching instruction to narrow the directivity characteristic of the radiated broadcast sound is given.

[0083] Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist of the present invention. In the above-described embodiments, one of the lengths of the distance x to the N wave S is selected, but it is also possible to alternately switch the lengths of the distance x to the N wave S at a specified time to repeatedly achieve the wide directivity characteristic and the narrow directivity characteristic of the radiated sound of the speaker 120. Thus, for the spaces both near and far in the surrounding area, it is possible to make the radiated sound of the speaker 120 heard.

[0084] Industrial applicability:

[0085] As described above, according to the present invention, when the distance until the shock wave is long, the difference tones of two types of carriers are repeatedly generated and synthesized during the period before the shock wave, so these difference tones become virtual sound sources and are synthesized along the direction of the sound wave travel, resulting in a narrowed directivity characteristic. In contrast, when the distance until the shock wave is short, the length of the virtual sound source extension is short, and the sound wave diffuses spherically from the position where the virtual sound source disappears, so the directivity characteristic becomes wider. In this way, by making the distance until the shock wave variable, the directivity characteristic can be changed, and the output range of the radiated sound of the speaker can be switched.

Claims

1. A speaker system, characterized in that: have: An output sound generating mechanism generates a sound as an output object; Ultrasonic speakers; a speaker driving mechanism that drives the ultrasonic speaker to output the sound generated by the output sound generating mechanism from the ultrasonic speaker; and The shock wave distance variable mechanism makes variable the distance from when the sound wave outputted from the ultrasonic speaker propagates in the air until it becomes a shock wave.

2. The speaker system according to claim 1, characterized in that The shock wave distance variable mechanism sends an instruction to the speaker driving mechanism to change the initial sound pressure of the sound wave when it is output from the ultrasonic speaker so as to make the distance variable.

3. The speaker system according to claim 1, characterized in that The shock wave distance variable mechanism sends an instruction to the speaker driving mechanism to change the carrier frequency of the sound wave output from the ultrasonic speaker so as to make the distance variable.

4. The speaker system according to claim 1, wherein: The shock wave distance variable mechanism sends an instruction to the speaker driving mechanism to change the initial sound pressure of the sound wave when output from the ultrasonic speaker and the carrier frequency of the sound wave output from the ultrasonic speaker, thereby making the distance variable.

5. The speaker system according to claim 1, wherein: Also available: The surrounding situation judgment mechanism judges the surrounding situation. The shock wave distance variable mechanism makes the distance variable based on the surrounding conditions determined by the surrounding condition determination mechanism.

6. The speaker system according to claim 5, characterized in that The speaker system is mounted on a vehicle and outputs a sound to notify surrounding people of the approach of the vehicle. The surrounding condition determination means is a speed acquisition means for acquiring the running speed of the vehicle. The shock wave distance variable mechanism performs a switching instruction, wherein when the traveling speed obtained by the speed obtaining mechanism is fast, the distance is set longer so that the directional characteristics of the sound output from the speaker become narrower, and when the traveling speed obtained by the speed obtaining mechanism is slow, the distance is set shorter so that the directional characteristics of the sound output from the speaker become wider.

7. The speaker system according to claim 5, characterized in that The speaker system is mounted on a vehicle and outputs a sound to notify surrounding people of the approach of the vehicle. The surrounding condition judgment unit is a driving environment judgment unit for judging whether the driving position of the vehicle is a built-up area in a city or a suburb. The variable shock wave distance mechanism performs a switching instruction, wherein when the driving environment judgment mechanism determines that the driving position of the vehicle is in the suburbs, the distance is set longer so that the directional characteristics of the sound output from the speaker array become narrower, and when the driving environment judgment mechanism determines that the driving position of the vehicle is in an urban built-up area, the distance is set shorter so that the directional characteristics of the sound output from the speaker become wider.

8. The speaker system according to claim 1, wherein: The shock wave distance variable mechanism performs a switching instruction to alternately set the length of the distance.

9. The speaker system according to claim 5, characterized in that The surrounding situation determination means includes a camera for photographing the surroundings, and an image analysis means for analyzing the surrounding situation based on the image obtained by the camera. The shock wave distance variable means issues a switching instruction to switch the length of the distance based on the surrounding conditions analyzed by the image analyzing means.

10. The speaker system according to claim 5, characterized in that The surrounding condition judging means is a congestion state judging means for judging the surrounding congestion state. The shock wave distance variable means issues a switching instruction to switch the length of the distance based on the surrounding congestion state determined by the congestion state determination means.

Images