Technical field
[0001]
This technology relates to an acoustic tube and an audio reproducing device, in particular, it relates to an acoustic tube and the sound reproducing apparatus that can generate an evanescent wave at a lower cost.
BACKGROUND
[0002]
In situ as many people sharing the public facilities, techniques for transmitting information only for a specific person can be said to be very useful.
[0003]
　For example, the people who are waiting for the down train on the train home, for the people who are waiting for the up-train, station staff should often want to convey different information, respectively. In addition, although the bank is a lot of people use, interact with, such as the reception is often related to personal information, it is desirable to not hear as far as possible.
[0004]
　Therefore, only the person in a particular area is developed technology called spot play to be able to hear the sound reproduced, it is actually applied.
[0005]
　For example, such and flat type speaker at a train platform, such as parametric loudspeaker for generating sound of an audible band by modulating the ultrasonic wave is utilized. These speakers, utilizing the directionality of the strength, it is possible to propagate the sound only in one direction, it is possible to deliver sound only a listener who is in a particular direction. However, in this method, the less attenuation with respect to a specific direction, thereby reaching the sound far.
[0006]
　In contrast, in the spot reproduction technology, there are methods to realize the spot reproduction with respect to the distance direction from the speaker. This is a method of generating a wavefront that very fast evanescent wave attenuation as compared to a spherical wave.
[0007]
　Evanescent wave is a wave that occurs under conditions such becomes a wavelength shorter than the wavelength of ordinary propagating waves for some reason. As a method for generating such evanescent wave, the method according to the combination of the speaker array and the signal processing has been proposed (e.g., refer to Patent Documents 1 to 3).
[0008]
　More specifically, for example when it is desired to generate an evanescent wave for the sound of 1 kHz (wavelengths 34cm) using a linear loudspeaker array, stepwise phase differences among all of the speaker units constituting a linear loudspeaker array with a spacing of the phase makes one rotation (2 [pi) may be such that less than 34cm.
CITATION
Patent Document
[0009]
Patent Document 1: JP 2013-236216 Patent Publication
Patent Document 2: JP 2013-26715 JP
Patent Document 3: JP 2012-44572 JP
Summary of the Invention
Problems that the Invention is to Solve
[0010]
　However, when generating the evanescent wave in the wave field synthesis by the speaker array, because the speaker and amplifier, DA (Digital to Analog) converter is required only channels of the array, also the load of the signal processing operation also becomes enormous, the cost of the surface practical use is said to be difficult from.
[0011]
　Therefore, a smaller number of speakers and the operation load, i.e. a technique for generating an evanescent wave at a low cost is required.
[0012]
　This technology has been made in view of such circumstances, it is to be able to generate an evanescent wave at a lower cost.
Means for Solving the Problems
[0013]
　Sound tube of the first embodiment of the present technology has a long acoustic path than the outer dimension of its own, having a plurality of openings or slit-like openings.
[0014]
　Wherein the plurality of the openings may be so provided are arranged in a predetermined direction.
[0015]
　Together it can be made to the distance between the openings adjacent ones of the plurality of the opening is provided to a predetermined distance.
[0016]
　The acoustic path, the speed of sound waves in a predetermined direction, may be shaped to the said wave is less than the rate at which advances the acoustic path.
[0017]
　Wherein the sound tube, wherein the plurality of whether to output a sound wave from each of the openings, or to output a sound wave from a plurality of positions of the slit-like of the opening, it is possible to generate an evanescent wave.
[0018]
　The acoustic tube, the cylindrical tube may be those obtained by spirally winding.
[0019]
　The acoustic tube can be those obtained by a cylindrical tube which is deformed into waveforms annularly.
[0020]
　The acoustic tube can be those obtained by providing a partition therein.
[0021]
　In the first aspect of the present technique, a long acoustic path is provided than its external dimensions to the sound tube, the openings of the plurality of openings or slit-shaped is provided.
[0022]
　Sound reproducing apparatus of the second embodiment of the present technology has a long acoustic path than the outer dimension of its own, and outputs an acoustic tube having a plurality of openings or slit-like opening, the sound wave to the acoustic tube and a speaker.
[0023]
　The acoustic path, the speed in a predetermined direction of the sound waves, can be shaped to its the sound wave is less than the rate at which advances the acoustic path.
[0024]
　Wherein the acoustic tube, said one of each of the plurality of openings to output the sound wave, or by outputting the sound waves from a plurality of positions of the slit-like of the opening, it is possible to generate an evanescent wave .
[0025]
　The sound reproducing apparatus, it is possible to provide a plurality of speakers for outputting sound waves in the acoustic pipe.
[0026]
　The sound reproducing apparatus may further include a sound correction unit for performing acoustic correction to the acoustic signal supplied to the loudspeaker.
[0027]
　The sound reproducing apparatus, it is possible to the acoustic tube and providing a plurality of the speakers.
[0028]
　The sound reproducing apparatus, it is possible to perform band splitting for the acoustic signals, further provided with a band division unit for generating a plurality of acoustic signal output to each of the plurality of speakers.
[0029]
　The plurality of the acoustic tube, a first distance in a predetermined direction, the sound wave traveling through the acoustic path, while the advances by the first distance in the predetermined direction, a second distance traveled said acoustic path ratio between can be so contained different the sound tube to each other.
[0030]
　In the second aspect of the present technology, the speaker has a longer acoustic path than the outer dimension of the own sound waves in the acoustic pipe having a plurality of openings or slit-like opening is output.
Effect of the invention
[0031]
　According to the first aspect and the second aspect of the present technology, it is possible to generate an evanescent wave at a lower cost.
[0032]
　Here, the advantages described in the present invention is not necessarily limited, it may be any of the effects described in the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033]
FIG. 1 is a diagram illustrating an end fire array.
It is a diagram illustrating a configuration example of the acoustic tube according to the [2] The present technology.
Is a diagram illustrating a configuration example of FIG. 3 sound reproducing apparatus according to the present technology.
4 is a diagram showing another configuration example of the acoustic tube.
5 is a diagram showing another configuration example of the acoustic tube.
6 is a diagram showing another configuration example of the acoustic tube.
7 is a diagram showing another configuration example of the acoustic tube.
8 is a diagram illustrating another configuration example of the acoustic tube.
9 is a diagram illustrating partitioning of the acoustic tube.
10 is a diagram showing another configuration example of the acoustic tube.
11 is a diagram showing another configuration example of the acoustic tube.
12 is a diagram showing another configuration example of the sound reproducing apparatus.
13 is a diagram showing another configuration example of the sound reproducing apparatus.
14 is a diagram showing another configuration example of the sound reproducing apparatus.
FIG. 15 is a diagram illustrating another configuration example of the sound reproducing apparatus.
16 is a diagram showing another configuration example of the sound reproducing apparatus.
FIG. 17 is a diagram illustrating another configuration example of the sound reproducing apparatus.
18 is a diagram showing another configuration example of the sound reproducing apparatus.
19 is a diagram illustrating another configuration example of the sound reproducing apparatus.
FIG. 20 is a diagram illustrating another configuration example of the sound reproducing apparatus.
DESCRIPTION OF THE INVENTION
[0034]
　Hereinafter, with reference to the accompanying drawings, a description will be given of an embodiment according to the present technology.
[0035]

　This technique, by determining the shape of the acoustic tube in consideration of the attenuation rate of the evanescent wave, as can be realized spot reproduced using a single speaker it is intended to. The present technology is not limited to spot play, it is applicable to other various applications.
[0036]
(Plane wave and the derivation of the evanescent wave by wave equation)
　is the propagation of sound is described by the wave equation, description will be made of the evanescent wave by using this. Wave equation first free space is represented by the following formula (1).
[0037]
[Number 1]

[0038]
　In the equation (1), t represents time, x v the coordinates of the two-dimensional space, that is, the position on the two-dimensional space. In particular, where the position x v is assumed to be represented by the x and y coordinates. Further, p (x v , t) is the position x at time t v represents the sound pressure, c is shows the speed of sound. Furthermore, ∇ in Equation (1) 2 represents the partial derivative of the secondary as shown in the following equation (2).
[0039]
[Number 2]

[0040]
　Moreover, the sound pressure p (x v , t) position x v about functions X (x v and), the variable is separated function T (t) and about time t, and the sound pressure p (x v , t) is the following formula it can be represented by (3).
[0041]
[Number 3]

[0042]
　Here, the angular frequency and omega, the Fourier transform of the function T (t) imaginary as i T F When (omega), T F (omega) is shown in the following equation (4).
[0043]
[Formula 4]

[0044]
　Further, T F when the inverse Fourier transform of (omega) and T (t), T (t) is as shown in the following equation (5).
[0045]
[Formula 5]

[0046]
　Further, since the second-order partial derivatives of the inverse Fourier transform T (t) = is represented by the following equation (6), the Fourier transform of the second order partial derivative is shown in the following equation (7) .
[0047]
[Number 6]

[0048]
[Number 7]

[0049]
　Now, the sound pressure p (x v , t) the Fourier transform P (x of v , omega) and when the formula (3) from P (x v , omega), so as shown in the following equation (8) , as a general solution of the wave equation in the equation (1) described above, solutions directed to the following equation (9).
[0050]
[Number 8]

[0051]
[Number 9]

[0052]
　Incidentally, an arbitrary function A (omega) is the angular frequency omega as a variable in the equation (9), i denotes the imaginary number. Further, in the equation (9), x v and k v , respectively on the two-dimensional space, i.e. shows a vector of the vector, and the wave number indicates the position in the xy coordinate system, these x v and k v , respectively represented by the following equation (10) and (11).
[0053]
[Formula 10]

[0054]
[Number 11]

[0055]
　In the equation (10) and Equation (11), v i and v j represent unit vectors in the unit vector and the y direction of the x-direction at each xy coordinate system. Further, x and y in equation (10) shows the x and y coordinates on the xy coordinate system, k in equation (11) x and k y are each an wavenumber of wavenumber and y direction of the x-direction ing.
[0056]
　The following position vector x v simply the position x of v referred to as, the wave vector k v simply wave number k to v and also referred to. In particular, the wave number k v is the spatial frequency represented by 2 [pi / lambda When the wavelength of sound lambda.
[0057]
　The position x v and the wave number k v inner product of is as shown in the following equation (12), the wave number k v absolute value of, and wavenumber k v square value of the absolute value of each following equation (13 ) and is shown in equation (14).
[0058]
[Number 12]

[0059]
[Formula 13]

[0060]
[Number 14]

[0061]
　Here, the wave number k v absolute value of the x direction of the wave k x when at least the absolute value of, i.e. when the following equation (15) is satisfied, the wave number k of the y-direction from equation (14) y the following formula as shown in (16). Therefore, in this case, the sound pressure P obtained by equation (9) (x v waves represented by, omega) is a plane wave.
[0062]
[Number 15]

[0063]
[Number 16]

[0064]
　In contrast, the wave number k v absolute value of the x direction of the wave k x time is less than the absolute value of, i.e. when the following equation (17) is satisfied, the wave number k of the y-direction y the following formula (18) as it is shown in.
[0065]
[Formula 17]

[0066]
[Equation 18]

[0067]
　Incidentally, i is shows the imaginary in Equation (18). Thus if the condition of Equation (17) is satisfied, the wave number k of the y-direction y becomes the imaginary.
[0068]
　Wave number k shown in the equation (18) y the sound pressure P (x of formula (9) v Substituting, omega) to, the following equation (19).
[0069]
[Number 19]

[0070]
　The sound pressure P (x represented by the formula (19) v , omega) See in the x direction when the wave number k x appears wavefront is also the sound pressure P (x v , omega) a when viewed in the y-direction , it can be seen that the sound pressure is obtained sound field to decay exponentially. Such waves are evanescent waves.
[0071]
　Incidentally, y> sound pressure P at 0 (x v , omega) is the wave number k y for making the physical meaning only when the become formula (20) below, in the calculation for obtaining the equation (19), wherein wave number k shown in (20) y is the calculation is substituted is performed.
[0072]
[Number 20]

[0073]
(For end fire array)
　However, consider the elongated cylindrical tube 11 as shown in FIG. 1, for example. In Figure 1, the left end of the cylindrical tube 11 is installed a speaker 12, a plurality of openings is provided in the upper portion of the cylindrical tube 11.
[0074]
　In FIG. 1, a transverse direction is x-direction, a direction perpendicular to the x-direction and y-direction. These x and y directions, the position vector x shown in Equation (10) v corresponding to the x and y directions. In the example shown in FIG. 1, on the upper surface of the cylindrical tube 11, a plurality of openings are arranged in the x direction.
[0075]
　For example the sound of the angular frequency ω from the speaker 12 is issued, the cylindrical tube 11, the sound waves in the x direction is propagated at the speed of sound c.
[0076]
　At this time, the wave number k in the x direction within the cylindrical tube 11 x is as shown in the following equation (21).
[0077]
[Number 21]

[0078]
　The sound emitted from the loudspeaker 12 reaches the opening provided in the cylindrical tube 11, the sound that has been propagated through the cylindrical tube 11 is output to the outer cylindrical tube 11 through the opening. Wave number k in the x direction of the sound that is output to the outer cylindrical tube 11 x , as shown in the following equation (22), the case shown in equation (21), that the wave number k in the cylindrical tube 11 x remains the same to become.
[0079]
[Equation 22]

[0080]
　Thus, since the equation (15) holds in this case, the plane wave appears on the outside of the cylindrical tube 11. Also, the wave number k of the y-direction in this case y is becomes zero as shown in the following equation (23), the direction of the plane waves appearing in the outer cylindrical tube 11 is seen to be equal to x direction.
[0081]
[Number 23]

[0082]
　Such an array of openings is referred to as the end fire array, are actually applications such as gun microphone.
[0083]
(For this technique)
　In contrast, a sound tube to propagate sound in the art, to ensure that slower than the actual sound velocity c of the sound velocity c 'of the apparent sound as seen from outside of the sound tube in, and as evanescent wave from the acoustic pipe is output. More particularly, the evanescent wave in the acoustic pipe outside was made to occur.
[0084]
　Here, the sound velocity c 'from the input end of the acoustic tube which sound is input, in the direction towards the end of the acoustic tube, the speed of sound traveling acoustic tube. That is, the sound velocity c 'is the velocity of sound in the direction advances when viewed into perspective. Further, where the input end of the acoustic tube, the direction towards the end of the acoustic tube and x-direction, the x-direction and the direction perpendicular to the y-direction. These x and y directions, the position vector x shown in Equation (10) v corresponding to the x and y directions.
[0085]
　To generate an evanescent wave decays by controlling the speed of sound c 'in the y direction, x direction of the wave number k x for, the necessary and sufficient conditions are the conditions shown in the following equation (24). That is, it is necessary to equation (24) is established.
[0086]
[Number 24]

[0087]
　For equation (24) is satisfied, the path of the sound traveling acoustic tube, i.e. to deform the acoustic path of the sound tube may be slow acoustic velocity c 'apparent when viewed from the acoustic pipe outside.
[0088]
　More specifically, as shown in FIG. 2, by deforming the was cylindrical tube spirally, sound is prevented proceed linearly.
[0089]
　Figure 2 is a diagram showing a configuration example of an embodiment of the acoustic tube according to the present technology. In this example, the acoustic tube 41 has a shape wound cylindrical tube interior is hollow spirally. Accordingly, external dimensions of the acoustic tube 41 is shorter than the acoustic path of the sound tube 41.
[0090]
　Specifically, in view of the acoustic tube 41, the left end is an input end of the sound, in the figures of the drawing of the acoustic tube 41, although the right end is reached to the end of the sound, from these input end to end, horizontal the distance direction and external dimensions of the acoustic pipe 41. Also, when you enter the sound waves from the input end of the acoustic tube 41, when the sound waves with acoustic paths the path followed to reach to the termination from the input end inside the acoustic pipe 41, external dimensions of the acoustic tube 41 is acoustically less than the length of the path. In other words, the acoustic tube 41 has a long acoustic path than the outer dimension of its own.
[0091]
　Here, a direction toward the end from the input end of the acoustic tube 41, i.e. in the figure, the horizontal direction is the x-direction, x direction perpendicular to the direction is the y direction.
[0092]
　In this example, in the drawing of the tube constituting the acoustic tube 41, the opening 42-1 to opening 42-6 at the front side is a plurality of openings for outputting sound (release) is arranged in the x-direction It is provided. In the following description, when it is necessary to distinguish the opening 42-1 to opening 42-6, simply and also referred to as aperture 42.
[0093]
　Aperture 42 is a through hole that connects the interior of the acoustic tube 41, i.e. the acoustic path, and an external acoustic tube 41. Accordingly, these apertures 42 is provided on the acoustic path, which functions as an opening for sound waves traveling acoustic path emits sound waves to the outside at a timing to pass through the opening 42.
[0094]
　The shape and position of the opening 42 provided in the acoustic pipe 41, the number of apertures 42, the spacing between the openings 42 is not particularly limited. In other words, the opening 42 is a slit shape is not limited to a circle, may be any shape, it is possible to position the opening 42 provided in the acoustic pipe 41 is also an arbitrary position. Further, there may in several number of openings 42 can be the distance between the opening 42 adjacent to each other and any distance. For example, in Figure 2, each aperture 42 are arranged in equal intervals in the x-direction, the openings 42 may be arranged at irregular intervals.
[0095]
　However, if the distance of the opening 42 to each other too wide, because it becomes impossible to reproduce the sound of a higher frequency by evanescent waves, it is preferable that the opening 42 is provided at reasonably closely spaced.
[0096]
　Further, where the plurality of openings 42 in the acoustic tube 41 is provided, for example, it may be a slit is provided along the tube constituting the input end of the acoustic tube 41 to terminate the acoustic pipe 41. That is, the sound of a plurality of portions other than the end in the tube constituting the acoustic tube 41 may be to be released.
[0097]
　In the drawing of the acoustic tube 41, the left end, in other words the input end, the speaker 43 is disposed. Therefore, the speaker 43 outputs a sound, the sound reaching the end of the acoustic tube 41 to follow within the acoustic pipe 41, that is, the acoustic path of the acoustic pipe 41.
[0098]
　At this time, it sound emitted from the speaker 43, at the timing when reaching the respective openings 42 located on the acoustic path of the acoustic tube 41, so that the sound from the openings 42 to the outside is released.
[0099]
　That is, sound emitted from the speaker 43, inside the acoustic pipe 41, that is going forward on acoustic path of the acoustic tube 41 is first to reach the opening 42-1. Then, with a sound toward the opening 42-1 to the outside is released, the sound emitted from the speaker 43 is further advances through the sound tube 41.
[0100]
　Until the sound emitted from the speaker 43 reaches the end, the sound whenever it reaches the opening 42 located on the acoustic path, sound from the opening 42 is released. In this way, the sound from the speaker 43 is output, in order from the opening 42-1 to the opening 42-6, the sound is emitted from the opening 42, the outer sound tube 41 is released from the openings 42 sound, i.e. so that the waves are synthesized.
[0101]
　By deformed differently than straight tubes were cylindrical as acoustic tube 41, ultrasonic from the input end from reaching the end in the shortest distance, i.e. a linear acoustic path of the acoustic tube 41 different as the route of shape, that the waves traveling in the acoustic tube 41 is prevented from straight in the x direction to the end, it can be the x-direction of the sound velocity c 'is made to be less than the sound velocity c.
[0102]
　At this time, the speed of sound waves traveling in the acoustic tube 41 is c, the wave number k in the traveling direction of the acoustic waves in the sound tube 41 c is sound velocity the angular frequency ω of the sound as shown in the following equation (25) obtained by dividing c. in
[0103]
[Number 25]

[0104]
　Here, the path of the sound wave traveling in the acoustic pipe 41 to the end, that the acoustic path of the sound tube 41, the distance a sound wave travels in the x direction, i.e. the distance in the x direction from the input end of the acoustic tube 41 to the end (the distance m times (where the), and the length of m> 1). In other words, the length of the acoustic path of the sound tube 41, and is m times the external dimensions of the acoustic pipe 41.
[0105]
　Hereinafter, the length of such actual acoustic path, and that the m is the ratio of the distance in the x direction from the input end to end is also referred to as compression ratio m of the acoustic path.
[0106]
　The compression ratio m is the distance that sound waves in the sound tube 41 advances in the x direction is a first distance, while the wave advances a first distance in the x direction, the wave acoustic path of the acoustic tube 41 When the distance traveled and the second distance may be referred to as a first distance and a ratio of the second distance.
[0107]
　If the compression ratio of the acoustic path of the acoustic tube 41 is m times, the wave number k of the sound wave in the acoustic pipe 41 c and, wavenumber k in the x direction of the sound wave outside the sound tube 41 x relationship is expressed by the following equation (26) as it is shown in.
[0108]
[Number 26]

[0109]
　In equation (26), the wave number k x the absolute value of the wave number k c so larger than the absolute value of, i.e. so indicated condition is satisfied the above-mentioned formula (24), released from the opening 42 a composite of waves it is understood that the evanescent wave. In other words, it can be seen that the evanescent wave by the acoustic pipe 41 is generated.
[0110]
　At this time, the wave number k of the y-direction of the sound wave outside the sound tube 41 y is as shown in the following equation (27).
[0111]
[Number 27]

[0112]
　By way different viewpoint, the wavefront of the sound propagating through the acoustic path in the sound tube 41, when viewed from the outer sound tube 41, the sound velocity c 'is the velocity of the apparent in the x direction of the sound, the following becomes as shown in equation (28), it is understood that less than the sound velocity c.
[0113]
[Number 28]

[0114]
　Therefore, the wave number k x following equation (29) is satisfied for, are sound waves emitted are synthesized from the acoustic pipe 41 it can be seen that the evanescent wave.
[0115]
[Number 29]

[0116]
　x direction is a traveling direction of the acoustic waves in the sound tube 41 as seen into perspective. As described with reference to equation (28) and (29), the speed c 'in the x-direction of the sound wave in the acoustic pipe 41, and less than the sound velocity c of the sound wave travels acoustic path in the sound tube 41 if, evanescent waves are generated sound wave output to the outside the sound tube 41 is synthesized. Thus, the shape of the acoustic path of the acoustic tube 41 if it is a shape that satisfies the condition of Formula (28) may be any shape. In other words, the acoustic pipe 41 as long as it has a long acoustic path than outer dimensions, may be of any type.
[0117]

　Next, explained in the above, it will be described sound reproducing apparatus using an acoustic tube according to the present technology. Such sound reproducing apparatus is configured as shown in FIG. 3, for example. In FIG. 3, portions corresponding to the case in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.
[0118]
　Sound reproducing apparatus 61 shown in FIG. 3 includes a sound tube 41 of the helical type, serves as an evanescent wave generator. Sound reproducing device 61, DA (Digital Analog) conversion unit 71, an amplifier 72, a speaker 43 and the acoustic pipe 41.
[0119]
　In the sound reproducing device 61, a speaker 43 for outputting sound, an input end of the acoustic tube 41 shown in FIG. 2 are connected. Further, in the sound reproducing apparatus 61, the acoustic signal of the sound to be reproduced from now is supplied to the DA conversion unit 71.
[0120]
　DA conversion unit 71 converts into an analog signal a sound signal which is supplied externally from the digital signal, and supplies to the amplifier 72. Amplifier 72 is supplied to the speaker 43 by amplifying the audio signal of analog supplied from the DA conversion unit 71.
[0121]
　Speaker 43 reproduces sound based on the sound signal supplied from the amplifier 72. That is, the speaker 43 outputs toward the sound waves based on the acoustic signal in the acoustic tube 41.
[0122]
　Sound wave output from the speaker 43 in this manner is input from the input end of the acoustic tube 41 attached to the speaker 43 in the acoustic tube 41 is propagated to the end through the acoustic path of the sound tube 41. At this time, when the sound wave traveling in the acoustic pipe 41 reaches the opening 42, the sound wave is a spherical wave from the opening 42 is released, the sound waves emitted from the respective openings 42 are being synthesized evanescent wave.
[0123]
　Since the sound based on the sound signal is reproduced by the evanescent wave, persons in the vicinity of the acoustic tube 41 can listen to the sound. In contrast, the people in a position away from the acoustic pipe 41, sound reproduced by the sound reproduction device 61 is not that most sounds.
[0124]
　By thus reproducing the sound by sound reproducing device 61 having the acoustic tube 41, it is possible to realize a spot playback. Moreover, the acoustic reproducing apparatus 61, since the acoustic path may only use acoustic tube 41 which is physically deformed so as to be compressed to m times, it is possible to generate an evanescent wave in a simple and low cost. That is, it is possible to speakers and amplifier, even without providing a plurality of DA conversion section generates the evanescent wave.
[0125]
　In the acoustic pipe 41, by deforming the cylindrical tube spirally, have been made as the x direction of the path of the sound wave becomes m times before deformation, the rate at which the path of the sound wave extends is represented by the compression ratio m that.
[0126]
　Incidentally, the termination of the acoustic tube 41 has an open state, i.e. may have an open end, sealed state, that may be are closed end. In particular, when the end of the acoustic tube 41 is sealed in order to prevent the reflection of sound at the end, it may be adapted to seal the end by sound absorbing material.
[0127]
　Further, in the example shown in FIG. 3, but a speaker 43 is connected to the input end of the acoustic tube 41, without the speaker 43 provided to the input end of the acoustic tube 41, pronouncing subject that already exists in the acoustic pipe 41 it may be such as attached to the input end. In other words, the sound input through the input end of the acoustic tube 41 is not limited to output from the speaker 43, or may be emitted from any other kind of sound.
[0128]

　The acoustic tube according to the present technology is not limited to the example shown in FIG. 2, outer dimensions is less than the length of the acoustic path There, sound waves from two or more of the plurality of locations to the outside as long as it has an aperture, such as is emitted, may be of any type. In the following, with reference to FIGS. 4 to 11, a description of another configuration example of such an acoustic tube. In FIG. 4 to FIG. 11, portions corresponding to the case in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.
[0129]
　In the example shown in FIG. 4, the sound tube 101, which internally is obtained by deforming the cylindrical tube has a hollow corrugated, in view of the acoustic tube 101, figure on the front side , circular opening 102-1 through opening 102-7 arranged linearly in the lateral direction is formed.
[0130]
　In the drawing of the acoustic tube 101, the left end are an input terminal, a speaker 43 is connected to the input end. In the drawing of the acoustic tube 101, right end are terminating, in this example end is open.
[0131]
　In the figure from the input end of the acoustic tube 101 to the end, in the lateral direction length, that external dimensions of the acoustic tube 101, since a less than the length of the acoustic path having the acoustic tube 101, the generation of the evanescent wave possible it is.
[0132]
　When sound waves are output from the acoustic tube 101 in the speaker 43, the waves are sound waves sequentially from each discharge opening 102-1 through opening 102-7 before reaching the end of the acoustic tube 101, of which wave obtained by combining the sound wave is evanescent wave.
[0133]

　In the example shown in FIG. 5, the sound tube 121, to deform the cylindrical tube interior is a hollow mound are those was collected using, in view of the acoustic tube 121, in the figure on the front side, circular opening 122-1 to the opening 122-7 arranged linearly in the lateral direction is formed.
[0134]
　In the drawing of the acoustic tube 121, the left end are an input terminal, a speaker 43 is connected to the input end. In the drawing of the acoustic tube 121, and the right end is the end, in this example has a state in which termination is closed, that is, the state of being sealed.
[0135]
　During this drawing from the input terminal even in the acoustic tube 121 to the end, in the lateral direction length, that external dimensions of the acoustic tube 121 is made less than the length of the acoustic path having the acoustic tube 121. Therefore, when the sound waves from the speaker 43 is output, the waves are sound waves sequentially from each discharge opening 122-1 to the opening 122-7 before reaching the end of the acoustic tube 121, those sound waves It is synthesized by the evanescent wave.
[0136]

　In the example shown in FIG. 6, the appearance of the sound tube 151 has a tubular cylindrical shape and a partition is provided in its interior cage, acoustic path has not been a straight line shape. In FIG. 6, the cross section of the acoustic tube 151 is shown.
[0137]
　In this example, the vertical partition with respect to the inner wall of the acoustic tube 151, are formed inside the acoustic pipe 151. In the drawing of the acoustic tube 151, the lower left end are an input terminal, a speaker 43 is connected to the input end. In contrast, in the figure in the acoustic tube 151, the end of the upper right are terminating, in this example is in a state in which termination is closed. Furthermore, the acoustic tube 151, in the figure, circular opening 152-1 through opening 152-16 aligned linearly in the lateral direction is formed.
[0138]
　Since the inside of the acoustic tube 151 is a partition is formed, the acoustic path of the sound tube 151 is longer by the partition. In the acoustic tube 151, sound wave output from the speaker 43, proceed to the end of the acoustic tube 151 while wraparound partition inside the acoustic pipe 151. In other words, the interior of the acoustic path the acoustic tube 151 is not a straight line, wave input from the input terminal is not straight.
[0139]
　Even in the acoustic tube 151, in the figure from the input end to end, in the lateral direction length, that external dimensions of the acoustic tube 151 is made less than the length of the acoustic path having the acoustic tube 151. Therefore, when the sound waves from the speaker 43 is output, the waves are sound waves sequentially from each discharge opening 152-1 through opening 152-16 before reaching the end of the acoustic tube 151, those sound waves It is synthesized by the evanescent wave.
[0140]

　In the example shown in FIG. 7, the examples as well as the appearance of the acoustic tube 181 of FIG. 6 has a cylindrical shape, in its interior partition is provided. Note that the cross-section of the acoustic tube 181 in FIG. 7 is shown.
[0141]
　In this example, a partition projecting in an oblique direction with respect to the inner wall of the acoustic tube 181 is formed. In the drawing of the acoustic tube 181, the upper left end are an input terminal, a speaker 43 is connected to the input end. In contrast, in the figure in the acoustic tube 181, the end of the lower right side are terminating, in this example is in a state in which termination is closed. Furthermore, the acoustic tube 181, in the figure, circular opening 182-1 openings 182-13 aligned linearly in the lateral direction is formed.
[0142]
　Since the inside of the acoustic tube 181 is a partition is formed, the acoustic path of the sound tube 181 is longer by the partition. That is, in the acoustic tube 181, sound wave output from the speaker 43, proceed to the end of the acoustic tube 181 while wraparound partition inside the acoustic pipe 181.
[0143]
　Even in the acoustic tube 181, in the figure from the input end to end, in the lateral direction length, that external dimensions of the acoustic tube 181 is made less than the length of the acoustic path having the acoustic tube 181. Therefore, when the sound waves from the speaker 43 is output, the waves are sound waves sequentially from each discharge opening 182-1 openings 182-13 before reaching the end of the acoustic tube 181, those sound waves It is synthesized by the evanescent wave.
[0144]

　In the example shown in FIG. 8, although the appearance of the sound tube 211 has a cylindrical shape, a partition is provided in its interior.
[0145]
　In the figure of the acoustic tube 211, the left end are an input terminal, a speaker 43 is connected to the input end. In contrast, in the figure in the acoustic tube 211, right end are terminating, in this example is in a state in which end is open. Furthermore, the acoustic tube 211, in the figure, circular opening 212-1 openings 212-6 arranged linearly in the lateral direction is formed.
[0146]
　Further, a partition provided inside the sound tube 211 has a partition that divides the circle is a cross-section of the acoustic tube 211 into two spaces, drawing the cross-sectional position, it is moved in the horizontal direction, seems to partition is rotated.
[0147]
　That is, the position of the cross section shown by the respective arrows A11 to arrow A15 for example in the acoustic pipe 211 is as shown in FIG. Note that portions corresponding to the case in FIG. 8 9 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.
[0148]
　For example the cross section of the acoustic tube 211 as indicated by the arrow Q11 in FIG. 9 shows a cross section of the position indicated by the arrow A11 in FIG. 8. In this section, in FIG. 9 circular acoustic pipe 211, the right half portions are partitioned by a partition 213, in FIG. 9, a portion of the left half wave passes.
[0149]
　Also, the cross section of the acoustic tube 211 as indicated by the arrow Q12 in FIG. 9 shows a cross-section at the position indicated by the arrow A12 in FIG. 8, in FIG. 9 circular acoustic pipe 211, the portion of the upper half partition 213 are partitioned by, the sound waves of the remaining lower half passes.
[0150]
　Moreover, the cross section of the acoustic tube 211 as indicated by the arrow Q13 in FIG. 9 shows a cross-section at the position indicated by the arrow A13 in FIG. 8, in FIG. 9 circular acoustic pipe 211, a partition is part of the left half 213 are partitioned by, the sound waves of the remaining right half passes.
[0151]
　Section of the acoustic tube 211 as indicated by the arrow Q14 in FIG. 9 shows a cross-section at the position indicated by the arrow A14 in FIG. 8, in FIG. 9 circular acoustic pipe 211, half of underlying by a partition 213 partitioned and, sound wave portions of the upper half of the remaining passes.
[0152]
　Moreover, the cross section of the position indicated by the arrow A15 in FIG. 8 is a cross section shown by an arrow Q11 in FIG. In this way will move the cross-sectional position of the acoustic tube 211 to the end direction, a region partitioned by the partition 213 is gradually rotated in the counterclockwise direction. Although sound waves only space partition one of a pair has been described an example in passing, it may be allowed to pass at the same time the other identical sonic or another acoustic space.
[0153]
　Inside sound tube 211 By providing such a partition 213, the acoustic path of the sound tube 211 is long. That is, in the acoustic tube 211, sound wave output from the speaker 43, proceed to the end of the acoustic tube 211 while wraparound partition inside the acoustic pipe 211.
[0154]
　Even in the acoustic tube 211, in the figure from the input end to end, in the lateral direction length, that external dimensions of the acoustic tube 211 is made less than the length of the acoustic path with acoustic pipe 211. Therefore, when the sound waves from the speaker 43 is output, the waves are sound waves sequentially from each discharge opening 212-1 openings 212-6 before reaching the end of the acoustic tube 211, those sound waves It is synthesized by the evanescent wave. Feature of this variation, by adjusting the twisting degree of the partition 213, from 1 compression ratio m while maintaining the external dimensions of the acoustic tube 211 is that it can be relatively easily adjusted to a greater value.
[0155]

　For example, as shown in FIG. 10, an opening provided in the sound tube 211 shown in FIG. 8 is such that a slit it may be. Note that portions corresponding to the case in FIG. 8 in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.
[0156]
　In the example shown in FIG. 10, the inside of the acoustic tube 211, a partition 213 shown in FIG 9 is formed. Further, in FIG. 10 of the acoustic tube 211 in this example, with rectangular slit 221 in the front upper portion thereof provided as an opening, the end of the acoustic tube 211 is in a state of being sealed.
[0157]
　In this example, the slits 221, and ends the input and the output of the acoustic tube 211, in the drawing, transversely long rectangular shape, that is, an opening of the slit.
[0158]
　Although the sound tube 211 provided only one slit 221, sound waves output from the speaker 43, the before reaching the end of the acoustic tube 211, a plurality of the position of the slit 221, of which at a timing position sound waves to pass through, acoustic waves are emitted to the outside. Then, the evanescent wave waves emitted from the respective position of the slit 221 is synthesized.
[0159]
　In FIG 10, although one slit 221 is provided in the acoustic tube 211, it may be a slit is provided in other locations of the acoustic tube 211.
[0160]
　Also, other than the example described with reference to FIGS. 4 to 10, by a path whose shape is different from that of the straight path the acoustic path of the acoustic tube, which can be longer than the outer dimensions of the acoustic path if good, it may be combined and other examples described with reference to FIGS 10.
[0161]
　The compression ratio m described above, may not be constant between the input end of the acoustic tube to the end. That is, the ratio of the distance in the x direction in the acoustic tube, the distance of the actual acoustic path through while the distance waves in the x-direction proceeds is not constant between the input end of the acoustic tube to the end, that is it may be different depending on the position. Further, to the end of the sound tube may be open-ended, may be a closed end may be preventing reflection of sound at the end position by providing a sound absorbing material to the end position.
[0162]

　also does not need big picture seen shape of the acoustic tube has is linear, for example, as shown in FIG. 11, global manner the shape of the acoustic tube 251 may be a circular shape, an annular and more particularly seen.
[0163]
　Those in this example, the acoustic tube 251, a tube of corrugated same shape as the acoustic tube 101 shown in FIG. 4, that is that a cylindrical tube which is deformed into waveforms annularly, was connected to its input end and the terminal It has become.
[0164]
　Further, the interior of the annular sound tube 251 has a hollow, in Figure 11 of the acoustic tube 251, the front side, a circular-shaped opening 252-1 through opening 252-36 that are arranged in a circular ring shape is formed It is. Furthermore, and has a speaker 43 to an arbitrary position is connected, the input end of the acoustic tube 251 portions annular This speaker 43 is connected and the end of the acoustic tube 251. In particular, the input terminal and the terminal in this example have the same position. In other words, the input terminal and the terminal is connected.
[0165]
　In such a sound tube 251, the diameter of the circular acoustic pipe 251 when viewed acoustic tube 251 into perspective, i.e. outer dimension of the acoustic tube 251, and less than the length of the acoustic path having the acoustic tube 251 since going on, it is possible to generate the evanescent wave. Further, in the acoustic tube 251, the length of the circumference of the circular acoustic pipe 251 when viewed acoustic tube 251 into perspective is also a less than the length of the acoustic path of the sound tube 251.
[0166]
　When outputting the sound wave from the speaker 43, the sound wave goes around the sound tube 251 follows the acoustic path corrugated, come back to the position of the speaker 43. In this case, sound waves are emitted from the opening 252-1 through opening 252-36, the evanescent wave when synthesizing their emitted sound waves.
[0167]
　In FIG. 11, one of the speaker 43 to the acoustic tube 251 has been described the example to be connected, may be connected to speakers to each of the plurality of different positions of the acoustic tube 251. In such a case, to the same sound from each of a plurality of speakers (sound waves) may also be output, may be output different audio (sound waves) with each other.
[0168]
　Moreover, where in each opening 11 has been formed is directed to the front side, inside or outside the annular acoustic tube 251, i.e. such that the opening is provided directed to the inside or outside of the ring it may be.
[0169]
　Further, an example has been described in which a material obtained by the tube wave in an annular acoustic tube 251 may be an acoustic tube the tube other shapes such as a chevron as annular. Further, an example has been described in which the acoustic tube 251 is an annular shape, the shape of the acoustic pipe shape or arc shape plus an additional twist to the annular shape may be a any shape.
[0170]

　Further, in the example shown in FIG. 3, the sound reproducing apparatus 61 has been described a case where one of the acoustic tube 41 is provided but a plurality of the acoustic tube the acoustic reproducing apparatus as shown in FIG. 12 may also be provided, for example.
[0171]
　In the example shown in FIG. 12, the sound reproducing apparatus 281, six have acoustic tube 282-1 through sound tube 282-6 of the same shape are provided, their acoustic tube 282-1 through sound tube 282-6 the respective inputs of the connected speakers 283-1 to speaker 283-6 is.
[0172]
　In the following description, when it is necessary to distinguish the sound tube 282-1 through acoustic pipe 282-6, simply referred to as a sound tube 282, when it is not necessary to distinguish the speakers 283-1 to speaker 283-6, simply also referred to as speaker 283. Further, in the example shown in FIG. 12, such as an amplifier and the DA conversion unit which is connected to the speaker 283, shown in other components of the sound reproducing apparatus 281 is omitted.
[0173]
　Each acoustic tube 282 provided in the sound reproducing apparatus 281 has the same acoustic tube the acoustic tube 101 shown in FIG. That is, in the figure in the acoustic tube 282, the left end are an input terminal, a speaker 283 is connected to its input. Further, in the figure in the respective acoustic tubes 282, right end are terminating, in this example end is an open end.
[0174]
　More each acoustic tube 282 of the waveform, in the figure, are circular openings arranged in the horizontal direction is provided in plurality, during audio playback, sound waves emitted into the acoustic pipe 282 outside from the openings is synthesized evanescent It is a wave.
[0175]
　In the sound reproducing apparatus 281, may also be simultaneously the same wave to a plurality of the acoustic tube 282 is outputted, it may be different waves are outputted simultaneously.
[0176]
　Further, for example, depending on the audio language, sound waves sound tube 282 may be output. Waves More specifically, for example, when Japanese is selected as audio, sound waves corresponding to the Japanese audio is outputted in the acoustic pipe 282-1, if English is selected, corresponding to the English audio There may be a like is outputted to the acoustic pipe 282-2.
[0177]

　If multiple acoustic tube further sound reproducing device is provided, those of the acoustic tube shape and length, thickness, number of openings , the shape of the openings may be different to.
[0178]
　In such a case, an audio reproducing device is arranged as shown for example in FIG. 13. Sound reproducing apparatus 311 shown in FIG. 13, the speaker of the three acoustic tubes 312-1 to acoustic tube 312-3, which are connected to their respective inputs of the acoustic tube 312-1 through sound tube 312-3 313- 1 and a speaker 313-3.
[0179]
　In the sound reproducing apparatus 311, the sound tube 312-1 through sound tube 312-3 is configured from a tube of a waveform, in an acoustic pipe 312-1, a sound tube 312-2 and acoustic pipe 312-3 is thickness and length of the tube constituting the acoustic tube is different. There is also a same shape as the acoustic tube 312-2 and the acoustic pipe 312-3.
[0180]
　In this example, in the figure of the acoustic tube 312-1 through acoustic pipe 312-3, the left end are an input end, in the drawing of the acoustic tube 312-1 through acoustic pipe 312-3, the right end termination there is a. Also, the end of each acoustic tube is an open end.
[0181]
　Furthermore, the acoustic tube 312-1 through acoustic pipe 312-3, in the figure, circular opening arranged in the horizontal direction is provided, and the acoustic pipe 312-1, the acoustic pipe 312-2 and acoustic tube 312- 3 and in, are different from the size of the opening, the number of provided opening.
[0182]
　In the example shown in FIG. 13, such as an amplifier and the DA conversion unit which is connected to the speaker, illustration of other components of the sound reproducing apparatus 311 is omitted.
[0183]

　Further, for example, as shown in FIG. 14, the sound reproducing apparatus 341, a plurality of annular acoustic tubes 342-1 to sound tube 342 -6 may also be provided. In FIG 14, a speaker and an amplifier, such as DA conversion unit, illustration of other components of the sound reproducing apparatus 341 are omitted.
[0184]
　Sound reproducing apparatus acoustic tube 342-1 through sound tube 342-6 provided in 341, for example, has the same acoustic tube the acoustic tube 251 shown in FIG. 11, those of the acoustic tube 342-1 through sound tube 342-6 are arranged and disposed so as in FIG. 14, in the longitudinal direction. In the following description, when it is necessary to distinguish the sound tube 342-1 through acoustic pipe 342-6, simply and also referred to as a sound tube 342.
[0185]
　In this example, each acoustic tube 342 are equally spaced, and has a well their diameter of the acoustic tube 342 same. Such a sound reproducing apparatus 341, for example, a cylinder to display the advertising is effective when reproducing the sound of the advertisement by sound reproducing apparatus 341.
[0186]
　In this case, for example, so as to surround the cylinder ad appears, the acoustic tube 342 is disposed along the cylinder, towards the outside of the cylinder so that voice advertisement is evanescent wave from the acoustic pipe 342 is output do it. At this time, in each of the acoustic tube 342, it can be made to opening is formed toward the outside thereof of the acoustic tube 342. Further, for example when the cylindrical different for each area ad is displayed, as appropriate, by connecting a plurality of speakers in the acoustic tube 342, may be as different audio for each area of ​​the acoustic tube 342 is output.
[0187]

　even when the sound tube of the plurality of annular More sound reproducing device is provided, of which the acoustic tube size and thickness, shape , number of openings, the shape of the aperture, space or the like between the openings may be different to.
[0188]
　In such a case, the sound reproducing apparatus is configured as shown in FIG. 15 for example.
[0189]
　Sound reproducing apparatus 371 shown in FIG. 15 includes an acoustic pipe 372-1 through sound tube 372-7 of the plurality of annular shape. In FIG 15, a speaker and an amplifier, such as DA conversion unit, illustration of other components of the sound reproducing apparatus 371 are omitted.
[0190]
　Acoustic tube 372-1 through sound tube 372-7 provided in the sound reproducing apparatus 371 is, for example, has the same acoustic tube the acoustic tube 251 shown in FIG. 11, those of the acoustic tube 372-1 through acoustic tube 372-7 are global diameter, i.e. only external dimensions are different.
[0191]
　In the following description, when it is necessary to distinguish the sound tube 372-1 through acoustic pipe 372-7, simply and also referred to as a sound tube 372.
[0192]
　In this example, in the drawing each sound tube 372 at equal intervals, are arranged in the vertical direction is different from that their diameter of the acoustic tube 372. Such sound reproducing apparatus 371, for example, to display the advertising pillar shape is not cylindrical, it is effective in the case of reproducing the audio of the advertisement by the sound reproducing apparatus 371.
[0193]

　Further, in the sound reproducing apparatus 61 shown in FIG. 3, although waves are emitted from the respective openings 42, each time the sound waves from the opening 42 is emitted sound waves traveling in the acoustic pipe 41 is attenuated.
[0194]
　Then, since the sound waves as sound pressure that is output from the opening 42 of the position near the end of the acoustic tube 41 is lowered, the sound pressure of the evanescent wave obtained by combining the sound waves from the opening 42, a sound field that is being reproduced strictly no longer symmetrical in the x-direction viewed from the center of the acoustic pipe 41. In other words, the sound field is no longer in the left-right symmetry.
[0195]
　Therefore, for example, the speaker is arranged at the end of both of the acoustic tube 41, as shown in FIG. 16, it may be able to reproduce the sound field symmetrical. Note that portions corresponding to the case in FIG. 3 in FIG. 16 are denoted by identical reference numerals, and description thereof will be omitted as appropriate.
[0196]
　Configuration of a sound reproducing device 61 shown in FIG. 16, to the sound reproducing apparatus 61 shown in FIG. 3, and is further a structure in which a speaker 401.
[0197]
　That is, in the sound reproducing apparatus 61 shown in FIG. 16, a speaker 43 is connected to one end of the acoustic tube 41, a speaker 401 is connected to the other end of the acoustic tube 41.
[0198]
　And their speaker 43 and the speaker 401, the same sound signal from the amplifier 72 is supplied, a speaker 43 and the speaker 401 based on the sound signal supplied from the amplifier 72, simultaneously outputs the same sound wave.
[0199]
　Thus, viewed from the center of the acoustic pipe 41, it is possible to reproduce a sound field symmetrical in the x-direction. Note that the wave number k in the x direction of the acoustic tube 41 outside of the acoustic waves at this time x is as shown in the following equation (30), the position x of the sound wave outside the sound tube 41 v sound in pressure P (x v , omega) is as shown in the following equation (31).
[0200]
[Number 30]

[0201]
[Number 31]

[0202]
　From this equation (31), it can be seen that in the x direction can standing wave outside the acoustic pipe 41.
[0203]

　Further, in the sound reproducing apparatus 61 shown in FIG. 3, the wave number k of the y-direction as described with reference to equation (27) y the following formula as shown in (32). Therefore, sound pressure changes in the y-direction is as shown in the following equation (33).
[0204]
[Formula 32]

[0205]
[Formula 33]

[0206]
　Incidentally, formula (33) in P (y, omega) shows a sound pressure at each position of the acoustic tube external y-direction. This equation As seen from (33), y direction of the sound pressure P (y, ω) is thus rapidly attenuated as the angular frequency omega is large.
[0207]
　Therefore, by performing the frequency characteristic correction as acoustic correction in advance to the acoustic signal supplied to the speaker, the sound pressure P (y, ω) may be able to reduce the dependence on the angular frequency omega of .
[0208]
　Table For example, the correction coefficient for each angular frequency omega for position in the y direction to realize correction as the frequency characteristic becomes flat at the point of y = 1 G (omega) is the equation shown in the following equation (34) It is.
[0209]
[Formula 34]

[0210]
　Incidentally, a in formula (34) is a constant. Solutions shown in the following equation (35) is obtained by solving the equations represented by such formula (34).
[0211]
[Formula 35]

[0212]
　Using the thus obtained correction coefficient G (omega), is obtained by correcting the components of each angular frequency omega of the acoustic signal, flat at the position of y = 1, i.e. the evanescent wave of the flat frequency characteristic be able to. In other words, it is possible to make the sound pressure components of the angular frequency ω is equal at the position of y = 1.
[0213]
　When performing such correction of frequency characteristics, sound reproducing apparatus is arranged as shown for example in FIG. 17. Note that portions corresponding to the case in FIG. 3 in FIG. 17 are denoted by identical reference numerals, and description thereof will be omitted as appropriate.
[0214]
　Sound reproducing apparatus 431 shown in FIG. 17, the acoustic correction unit 432, DA conversion section 71, an amplifier 72, a speaker 43 and the acoustic pipe 41.
[0215]
　Configuration of the sound reproducing apparatus 431, the configuration of the sound reproducing apparatus 61 shown in FIG. 3, has a configuration further provided an acoustic correcting unit 432.
[0216]
　In this example, a digital audio signal is supplied to the acoustic correction unit 432, the acoustic correction unit 432 subjects the supplied audio signal, performs an acoustic correction, a sound signal obtained as a result to the DA conversion unit 71 supplies.
[0217]
　More specifically, for example, as acoustic correction, the correction of the frequency characteristic using a correction coefficient G (omega) held in advance is performed. When correction of the frequency characteristic in the acoustic correction unit 432, the correction coefficient component of each angular frequency omega of the acoustic signal G (omega) is the correction are multiplied performed.
[0218]
　DA conversion section 71, a sound signal supplied from the acoustic correction unit 432 converts the digital signal into an analog signal, and supplies to the amplifier 72. Amplifier 72 is supplied to the speaker 43 by amplifying the audio signal of analog supplied from the DA conversion unit 71. The speaker 43 reproduces sound based on the sound signal supplied from the amplifier 72. That is, the speaker 43 outputs the sound waves based on the acoustic signal in the acoustic tube 41.
[0219]
　Thus, sound wave is output from the acoustic pipe 41, an evanescent wave frequency characteristic is flat in the their wave synthesis positions of y = 1 is generated.
[0220]
　Here, although the correction of the frequency characteristics of the acoustic signal has been described the example that is performed in the digital domain, such as before or after the amplifier 72, it may be the correction of the frequency characteristic in the analog domain is performed.
[0221]
　Further, where it is described the example in which the frequency characteristic correction, as the frequency characteristics become flat at the position of y = 1, may be performed to correct the other what frequency characteristics.
[0222]

　In the third embodiment, the angular frequency omega is larger the y direction of the sound pressure P (y, omega) will rapidly attenuate as a method of suppressing the, acoustic characteristic correction, i.e. been described for correcting the frequency characteristic. However, other, by performing band division of the audio signal, may be made to reduce the difference in attenuation of the sound pressure for each angular frequency omega.
[0223]
　Incidentally, the division number in performing band division of the audio signal can be any number, it will be described a case where the division number is 2 as an example here.
[0224]
　When dividing the sound signal into two bands, an audio reproducing device is arranged as shown for example in FIG. 18. Note that portions corresponding to the case in FIG. 3 in FIG. 18 are denoted by identical reference numerals, and description thereof will be omitted as appropriate.
[0225]
　Sound reproducing apparatus 461 shown in FIG. 18, band dividing section 471, DA conversion section 71, an amplifier 72, a speaker 43, sound tube 41, DA conversion unit 472, an amplifier 473, and a speaker 474 and acoustic pipe 475, .
[0226]
　Here, DA conversion unit 472, each of the amplifiers 473, a speaker 474 and acoustic pipe 475,, DA conversion section 71, an amplifier 72, which corresponds to each of the speaker 43 and the acoustic pipe 41.
[0227]
　The acoustic pipe 475 has an opening 481-1 through opening 481-6, the position in the x direction of the opening 481-1 through opening 481-6 is to open 42-1 of the acoustic tube 41 opening 42 It has the same position as each of the six. Further a same length the length of the x-direction of the acoustic pipe 41 and the acoustic pipe 475.
[0228]
　In the following description, when it is necessary to distinguish the opening 481-1 through opening 481-6, simply and also referred to as aperture 481.
[0229]
　Acoustic tube 475 is basically has the same shape as the acoustic tube 41, global manner seen acoustic pipe 475 in the y-direction width, i.e. in FIG. 18, the vertical width is different. In other words, the acoustic pipe 41 and the acoustic pipe 475 has a different compression rate m of the acoustic path.
[0230]
　Hereinafter, the compression ratio m in the acoustic pipe 41, compression ratio m = m 1 and be referred to as a compression ratio m in the acoustic tube 475, a compression ratio m = m 2 and be referred to.
[0231]
　Band division unit 471, the supplied sound signal, for example, performs band division by filter processing or the like using a band division filter, divides the sound signal into two bands of the signal. That is, the acoustic signals of the two different angular frequency bands is generated with each other.
[0232]
　Band dividing section 471 supplies the one-band acoustic signal of which is obtained by band division supplies the DA conversion unit 71, a sound signal of the other band to the DA conversion unit 472.
[0233]
　The band of the acoustic signal supplied to the DA conversion section 71 side, that is the angular frequency omega = omega the angular frequency omega of the regeneration zone to be reproduced by the acoustic pipe 41 below 1 and also referred to, is reproduced by the acoustic pipe 475 that the angular frequency ω of the reproduction band angular frequency ω = ω 2 also and be referred to as.
[0234]
　Sound signal which is supplied to the DA conversion unit 71 from the band division section 471 is converted into an analog signal by the DA converter 71, is amplified by the amplifier 72 is supplied to the speaker 43, an acoustic signal by the loudspeaker 43 waves based is output to the sound tube 41.
[0235]
　Furthermore, DA conversion unit 472, a sound signal supplied from the band dividing section 471 converts the digital signal into an analog signal, and supplies to the amplifier 473. Amplifier 473 is supplied to the speaker 474 amplifies the sound signal supplied from the DA conversion unit 472. The speaker 474 reproduces sound based on the sound signal supplied from the amplifier 473. That is, the speaker 474 outputs a sound wave based on the acoustic signal to the acoustic tube 475.
[0236]
　In the sound reproducing apparatus 461, at the time of reproduction of the audio signal angular frequency omega = omega by the acoustic pipe 41 1 with the evanescent wave of the band of the is generated, angular frequency omega = omega by the acoustic pipe 475 2 evanescent wave band is generated that.
[0237]
　In sound reproduction apparatus 461 in this manner, by using acoustic tubes having different compression ratios m from each other, by reproducing the band acoustic signal in different angular frequencies omega to each other, according to the angular frequency omega y direction of the sound pressure P (y, it is possible to reduce the difference in attenuation of omega).
[0238]
　Specifically, the range of the division number and bandwidth of the regeneration zone is arbitrary, here, for example, the angular frequency omega = omega reproduction band of the sound tube 41 1 and omega 0 /20

　Further, in the sound reproducing apparatus 461 shown in FIG. 18, the case has been described where the digital domain performs band division of the audio signal, the acoustic band division signals may be performed in the analog domain. In such a case, an audio reproducing device, is configured as shown in FIG. 19 for example. Note that portions corresponding to the case in FIG. 18 in FIG. 19 are denoted by identical reference numerals, and description thereof will be omitted as appropriate.
[0250]
　Sound reproducing apparatus 511 shown in FIG. 19, DA conversion section 71, an amplifier 72, band dividing section 521, a speaker 43, sound tube 41, and a speaker 474 and acoustic pipe 475.
[0251]
　In this example, an acoustic signal supplied to the DA conversion unit 71, the DA converter 71 is supplied is converted into an analog signal to the amplifier 72, it is being further amplified by the audio signal amplifier 72 supplied to the band dividing section 521 that.
[0252]
　Band dividing section 521 is composed of, for example, RC circuits or LCR circuit, divides the sound signal supplied from the amplifier 72 into two bands of the signal. Band dividing section 521 supplies the one-band acoustic signal of which is obtained by band division supplies to the speaker 43, the sound signal of the other band to the speaker 474.
[0253]
　Thus in the case of performing the band division of the audio signal in the analog domain, it is not necessary to provide a plurality of DA conversion unit and an amplifier. Also, here it is described an example of performing band division at the subsequent stage of the amplifier 72, may be performed band division in the preceding stage of the amplifier 72. In such a case, although the band division section 521 will be performing band division with respect to the analog sound signal supplied from the DA conversion unit 71, and between the band dividing section 521 and the speaker 43, the band division section 521, and and between the speakers 474, it is necessary to provide an amplifier, respectively. That is, the two amplifiers are required in total.
[0254]

　Further, the example for correcting a frequency characteristic for an acoustic signal in the above has been described with an example of performing band division of the audio signal, they it may be performed by combining the correction and band division of the frequency characteristic of. Thus combining the correction and band division of the frequency characteristics is effective in reducing the difference in attenuation of the sound pressure in the y direction for each angular frequency omega.
[0255]
　When performing a combination of a correction and band division of the frequency characteristics, sound reproducing apparatus is arranged as shown for example in FIG. 20. In FIG. 20, portions corresponding to the case in FIG. 18 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.
[0256]
　Sound reproducing apparatus 551 shown in FIG. 20, band dividing section 471, the acoustic correction unit 561, DA conversion section 71, an amplifier 72, a speaker 43, sound tube 41, the acoustic correction unit 562, DA conversion unit 472, an amplifier 473, a speaker 474 , and it has an acoustic tube 475.
[0257]
　Configuration of the sound reproducing apparatus 551, to the sound reproducing apparatus 461 shown in FIG. 18, further a structure in which an acoustic correction unit 561 and the acoustic correction unit 562.
[0258]
　That is, the acoustic correction unit 561 is provided between the band division section 471 and the DA conversion unit 71, the acoustic correction unit 562 is provided between the band division section 471 and the DA conversion unit 472.
[0259]
　Acoustic correction unit 561, is supplied from the band dividing section 471 performs correction of the frequency characteristic by using the correction coefficient stored in advance to the acoustic signal after band division, a sound signal obtained as a result DA and supplies to the converter 71. Similarly, the acoustic acoustic correction unit 562 is supplied from the band dividing section 471 performs correction of the frequency characteristic by using the correction coefficient stored in advance to the acoustic signal after band division, the resulting and it supplies a signal to the DA conversion unit 472. These acoustic correction unit 561 and the acoustic correction unit 562 corresponds to the acoustic correction unit 432 shown in FIG. 17.
[0260]
　In the following, the correction coefficient for each angular frequency omega of acoustic correction unit 561 holds G 1 also marked (omega), the correction coefficient for each angular frequency omega of acoustic correction unit 562 holds G 2 ( and also referred to as ω).
[0261]
　Further, in the band of the acoustic signal supplied to the acoustic correction unit 561, i.e. the angular frequency omega = omega the angular frequency omega of the regeneration zone to be reproduced by the acoustic pipe 41 below 1 also and be referred to, it is reproduced by the acoustic pipe 475 that the angular frequency ω of the reproduction band angular frequency ω = ω 2 also and be referred to as. Here, omega 0 /20 1 sound as the angular frequency omega is large in the area pressure P (y, ω) is reduced. In other words, in regions other than y = 1, it is impossible to obtain a flat frequency characteristic.
[0266]
　Further, as described with reference to FIG. 18, the sound reproducing apparatus 461 performs band division, the sound pressure P 1 (y, omega 1 ) = P 2 (y, 20Omega 1 ) and the compression ratio m such that 1 compression rate M 2 was determined the relationship.
[0267]
　However, in this case, for example, y = sound in 1 pressure P 1 (y, omega 0 /20) and the sound pressure P 1 (y, omega 0 ) When determining the ratio between, is as shown in the following equation (40) , still the sound pressure of the angular frequency ω is larger the y direction will rapidly decay.
[0268]
[Number 40]

[0269]
　Therefore, in the sound reproducing apparatus 551 performs the correction and band division of the frequency characteristic, by controlling the sound field by setting the time, for example, the following conditions, the angular frequency ω with obtaining a more flat frequency characteristic and to be able to reduce the difference in the attenuation of each of the sound pressure.
[0270]
　That is, for example, a flat frequency characteristic at a point y = 1, and the sound pressure P 1 (y, omega 1 ) = P 2 (y, 20Omega 1 ) to become such a correction coefficient G 1 (omega), the correction coefficient G 2 (omega), the compression ratio m 1 , and the compression ratio m 2 seeking, these correction coefficients and the compression ratio is to be used in the audio reproduction device 551.
[0271]
　First, it defined as the acoustic extravascular the y direction of the sound pressure P (y, omega) the following equation (41).
[0272]
[Formula 41]

[0273]
　However, the formula P in (41) 1 (y, omega) and P 2 (y, omega) are each as following equation (42) and (43).
[0274]
[Formula 42]

[0275]
[Number 43]

[0276]
　Here, the sound pressure P (y, ω) in the case of y = 1 is the correction factor that is constant irrespective of the angular frequency omega G 1 (omega) and the correction coefficient G 2 when obtaining the (omega), 1 (y, omega), i.e. correction coefficients G 1 for (omega)
[0277]
[Formula 44]

[0278]
　Correction coefficients G 1 (omega) in the same manner as in the sound pressure P 2 (y, omega), i.e. the correction factor G 2 for (omega)
[0279]
[Number 45]

[0280]
　Then, by solving the equations as shown in equation (46) below using the equation (44) Equation (45), the sound pressure regardless of the y-position P 1 (y, omega 1 ) = P 2 (y, 20Omega 1 ) become such compression rate m 1 and compression ratios m 2 is obtained.
[0281]
[Formula 46]

[0282]
　In the sound reproducing apparatus 551, the sound tube 41 and the acoustic pipe 475, the compression ratio m of the acoustic pipe 41 1 compression ratio m of the acoustic pipe 475 2 are as such have the relationship shown in equation (46).
[0283]
　Further, in the sound reproducing apparatus 551, the acoustic correction unit 561 corrects factor G shown in Equation (44) 1 corrects the frequency characteristics of the acoustic signal using the (omega), acoustic correction unit 562 shown in equation (45) correction coefficient G 2 corrects the frequency characteristics of the acoustic signal using the (omega).
[0284]
　In the sound reproducing apparatus 551 in this way, the frequency characteristics become flat at the point of the acoustic pipe outside of y = 1, and all of the angular frequency omega 1 (where, omega 0 /20