JP2011244030A - Acoustic reproducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acoustic producer which produces good sound even though the acoustic producer is used in a small place such as a mobile communications device where an acoustic device cannot have sufficiently large space to resonate an acoustic field inside a housing, making it difficult to obtain enough output power of low-frequency components, and sometimes causing significant changes in input and output characteristics especially in high frequencies, and due to these, sound quality may greatly change by slight difference in placement or shapes of members.SOLUTION: An acoustic producer comprises an acoustic tube whose radius from the center gradually changes according to a revolving angle, and a sound source in the center of the acoustic tube, and a sound hole at the other end of the acoustic tube. An inner radius of the acoustic tube is made shorter than a half wavelength corresponding to an upper limit frequency, and a path length is made longer than a half wavelength corresponding to a lower limit frequency. The acoustic tube is made to expand on a flat plane parallel to a revolution plane of the acoustic tube.

Description

  The present invention relates to an acoustic reproduction apparatus that generates sound waves in response to input of acoustic signals. For example, the present invention relates to a device used as a receiving means for portable audio equipment such as a mobile phone.

  A small-sized sound reproduction device cannot provide sufficient internal space for resonating sound waves, and therefore has low input / output characteristics in a low frequency range. In addition, there is a problem that the frequency characteristics of the input / output characteristics fluctuate significantly due to resonance caused by the reflection of sound waves in an internal space of a certain size.

  Thus, attempts have been made to solve this problem. For example, Patent Document 1 discloses a compact handset in which a cavity is added to a surface that emits sound waves from a sound source, and the frequency characteristics of sound pressure are flattened by resonating sound in the cavity. ing.

  Patent Document 2 discloses a sound reproducing device that guides sound waves generated by a sound source to a spiral-shaped sound wave guiding means and emits sound waves from the other end. In this method, the output characteristics are improved by resonating the low frequency components inside the sound wave guiding means having a sufficient length.

JP 2004-129192 A JP 2006-506003 A

  In the conventional method of adding a cavity, there is a problem that the frequency characteristics of the input / output characteristics accompanying the resonance vary greatly depending on the shape of the cavity. Considering the cavity of the rectangular parallelepiped illustrated in FIG. 1, the characteristics variation of the power ratio between the input from the sound source and the output from the cavity when the shape is changed were studied.

  FIG. 1 (a) shows that the cavity 1 has a vertical and horizontal dimension of 50 mm and a height of 19 mm, and radiates sound waves from a sound source 2 placed in the center of the bottom, and a sound hole 3 having a diameter of 3 mm is formed on the opposite surface. This is an example. FIG. 1 (b) shows the height of FIG. 1 (a) being 11 mm. FIG. 1C shows the position of the sound hole 3 in FIG. 1A shifted by 12 mm toward one side. In FIG. 1 (d), the shape of the cavity 1 is the same as FIG. 1 (a), and a total of four sound holes are provided, two at a distance of 30 mm in the direction orthogonal to the sound hole 3. Is.

  The thickness of the rectangular parallelepiped housing is 2 mm, and the reflectivity of air and the housing is 1.0. FIG. 2 shows the result of measuring the frequency characteristics of the input / output power ratio at a location 1 cm away from the outside front of the sound hole 3 under these conditions. The horizontal axis in FIG. 2 is the frequency (kHz), and the vertical axis is the power ratio (dB) between the input from the sound source and the output from the cavity. The frequency characteristics measured under the conditions of FIG. 1B is indicated by a broken line, FIG. 1C is indicated by a one-dot chain line, and FIG. 1D is indicated by a two-dot chain line. The origin of each characteristic is shifted.

  The maximum and minimum values fluctuate greatly at frequencies above 10 kHz, and sufficient output cannot be obtained at low frequencies below 1 kHz. Thus, the input / output frequency characteristics vary greatly depending on the shape of the cavity 1 and the number of sound holes 3. In view of the fact that the dimensions of the cavity portion 1 in this example are substantially the same as the receiving mechanisms of mobile phones that have become widespread recently, this phenomenon appears more prominently in those devices.

  In addition, the method of providing the spiral-shaped sound wave guiding means increases the bulk of the sound reproducing device because the outer shape of the sound wave guiding means extends in the direction of the helical rotation axis. Therefore, it is not suitable for small portable devices.

  The invention of the present application has been made in view of such problems, and an acoustic reproduction device suitable for use in portable audio equipment while ensuring sufficient output in a low range while flattening input / output characteristics from a sound source. The purpose is to provide.

  The sound reproduction device of the present invention is a sound reproduction device that has a sound source and a sound guide part and emits sound waves from a part of the sound guide part, and the path length of the sound guide part corresponds to the lower limit frequency of the reproduction frequency band The sound guide part is larger than the first half wavelength, the inner diameter of the sound guide part is smaller than the second half wavelength corresponding to the upper limit frequency, and the linear path of the sound guide part is smaller than the second half wavelength. The part turns.

  According to the sound reproducing device of the present invention, since the inner diameter of the sound guide section is smaller than the second half wavelength corresponding to the upper limit frequency, resonance does not occur in the inner diameter direction of the sound guide section at frequencies below the upper limit frequency. No noticeable change in input / output characteristics. The path length of the sound guide section is larger than the first half wavelength corresponding to the lower limit frequency, and the linear path inside thereof is larger than the second half wavelength corresponding to the upper limit frequency and corresponds to the lower limit frequency. Since it does not have anything smaller than one half wavelength, there is no significant change in input / output characteristics from the lower limit frequency to the upper limit frequency.

  Note that by setting the lower limit frequency to the low-frequency representative frequency, resonance within the sound guide section occurs near the frequency, but the input / output characteristics are gradually enhanced by the emission of sound waves and the attenuation in the path until they are emitted.

  Therefore, the low frequency component that tends to be insufficient in a small portable audio device is enhanced while the input / output characteristics are flattened in the reproduction frequency band. Therefore, by setting the reproduction frequency band region as a call band or a frequency band for music reproduction, favorable input / output characteristics are brought about in a call or music reproduction.

  Furthermore, since the sound guide portion is swiveled in a direction perpendicular to the swivel axis, the unevenness does not occur in the direction parallel to the swivel axis, and the sound guide portion is configured in one plane. Therefore, the sound reproducing unit is not bulky more than necessary, and a sound reproducing apparatus suitable for use in a small portable audio device can be provided.

The figure which shows the example of the cavity part 1 for examining the influence which the shape of the cavity part 1 has on input-output characteristics. The figure which shows the example of the frequency characteristic of the power ratio of the input from a sound source, and the output from a cavity part. It is a figure which shows the sound reproduction apparatus 100 of this invention, (a) is a top view, (b) is AA sectional drawing. The figure explaining the maximum value g of a straight path by enlarging a part of the acoustic tube 30. It is a figure which shows the one aspect | mode of the sound reproduction apparatus 200 which concerns on 3rd invention which is 1 type of 2nd invention of this application, (a) is a top view, (b) is AA sectional drawing. It is a figure which shows one aspect | mode of the sound reproduction apparatus 300 which concerns on this invention 4th invention which is 1 type of this invention 2nd invention, (a) is a top view, (b) is AA sectional drawing, (c) is FIG. It is BB sectional drawing. The figure which shows the example of the input-output characteristic obtained by dividing the power of the output signal of the sound reproduction apparatus 100 for every frequency by the power of an input signal. The figure which shows the example of the input-output characteristic obtained by dividing the power of the output signal of the sound reproduction apparatus 200 for every frequency by the power of an input signal. The figure which shows the example of the frequency characteristic of the electroacoustic transducer with inferior low-frequency input / output characteristics.

    Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are given to the same components in a plurality of drawings, and the description will not be repeated.

  FIG. 3 shows an aspect of the sound reproducing device 100 according to the first invention of the present application. FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line AA. The sound reproducing device 100 includes a sound guide unit 25 and a sound source 20. These are housed in an outer case 80 made of a material that is substantially disk-shaped and insulates acoustic vibrations. The sound guide portion 25 is composed of the acoustic tube 30 and constitutes a space continuous with the cavity portion 10, and includes a sound hole 40 at the end opposite to the sound source 20.

  The sound source 20 is provided in the cavity 10 located in the center. The acoustic tube 30 smoothly turns outward from one end of the cavity 10, and the other end is rounded and has a sound hole 40 in a direction parallel to the turning axis near the end. . An external sound hole 90 is provided at the position of the sound hole 40 of the external case 80. By storing the sound guide section 25 and the sound source 20 in the outer case 80, the mechanical strength of the sound reproducing device 100 can be increased, and the handling thereof can be facilitated. Note that the outer case 80 may be omitted.

  As the sound source 20, for example, an electroacoustic transducer such as a dynamic receiver or a piezoelectric element may be used. The shape of the sound source 20 is, for example, a disk shape, and is provided such that the surface thereof is in contact with the bottom surface of one end of the cylindrical cavity portion 10. The inner diameter of the cavity 10 and the diameter of the sound source 20 are approximately equal. As apparent from the cross-sectional view of FIG. 3B, the cavity 10 and the acoustic tube 30 are integrated at one end of the cavity 10 to form a continuous space.

  When an electric signal is input to the sound source 20, sound waves are radiated to the cavity 10, and the sound waves are reflected and resonated on the inner wall. At the same time, the sound wave is transmitted through the acoustic tube 30 and a part of the sound wave is radiated from the sound hole 40 to the outside.

Here, it is assumed that the sound reproducing device 100 performs sound reproduction from the lower limit frequency f ₁ to the upper limit frequency f ₂ as a reproduction frequency band. The reproduction frequency band is typically 0.3 to 3.4 kHz for telephones and 0.2 to 7.0 kHz for radio broadcasting and high-quality communication conferences. Therefore, when used in these applications, it is desirable that the input / output frequency characteristics in the frequency band be flat.

Therefore, the width of the diameter and the acoustic pipe 30 of the cavity 10, i.e. the inner diameter d of the cross section perpendicular to the extension direction, smaller than half the wavelength lambda _2/2 corresponding to the upper limit frequency f _2. In general the frequency f and wavelength λ λ = c / f (c is speed of sound, about 340m / s in air of one atmosphere at room temperature) for uniquely associated with, the _{λ 2/2 = c / 2f} 2. The inner diameter d is a representative value of the size across the cross section, such as vertical and horizontal lengths when the cross section is rectangular, and diameter when the cross section is circular. Here, as shown in the cross-sectional view of FIG. 3B, the larger one (horizontal width) of the vertical and horizontal dimensions is indicated. Thus, it does not occur resonance sectional direction in the lower regeneration zone than the upper limit frequency f _2.

Both ends of the acoustic tube 30, that is, the path length L in the extending direction are set larger than the half wavelength λ _1/2 corresponding to the lower limit frequency f ₁ . Here, the path length L is a total extension indicated by a broken line until the sound source 20 turns outward from one end portion in contact with the cavity 10 and reaches the other end as shown in FIG. As a result, no resonance occurs in the cross-sectional direction in the reproduction frequency band higher than the lower limit frequency f ₁ . Furthermore the inner wall of the acoustic tube 30 is smooth, that is because the vehicle is turning so as not to have a larger linear path than small and the half wavelength lambda _2/2 than at least half the wavelength lambda _1/2, the resonance in the reproduction frequency band Is avoided, and the input / output frequency characteristics are flat. In other words, to avoid resonance by half wavelength lambda _1/2 less than and half wavelength lambda _2/2 larger linear path than output frequency characteristics can be avoided that vary significantly.

  The straight path refers to a distance that can be signaled without a sound wave colliding with the inner wall inside the acoustic tube 30. When the turning radius increases at a constant rate with respect to the turning angle, the maximum value of the straight path can be easily estimated.

FIG. 4 shows an enlarged view of a part of the acoustic tube 30. In FIG. 4, when r ₁ is the maximum value of the turning radius and the turning radius of the portion facing this is r ₂ , the maximum value g of the straight path is g = 2r ₁ cos θ ₁₂ (where θ ₁₂ = cos ⁻¹ ( r ₂ / r ₁ ), r ₁ = r ₂ + d, where d is the inner diameter of the acoustic tube 30 in the turning radius direction). In FIG. 4, for the sake of explanation, the maximum turning radius on the outer periphery of the acoustic tube 30 is constant, so g is slightly smaller than this value in practice, but is only a guide. It is sufficient to be smaller than a half wavelength lambda _2/2 the maximum value g of the straight line path corresponds to the upper limit frequency f _2. In order to smoothly turn the acoustic tube 30, the turning radius is increased at a constant rate with respect to the turning angle, and the design is easy if it is a spiral type.

  In addition, the acoustic tube 30 swivels in a direction perpendicular to the swivel axis and spreads in a certain plane, so that it does not have to be bulky more than necessary. That is, the thickness of the sound reproducing device 100 is nothing but the thickness of the outer case 80, and the thickness of the inner portion of the sound reproducing device 100 is only at least one of the height of the outer shape of the acoustic tube 30 and the thickness of the sound source 20. Convenient for mounting as a device. The acoustic tube 30 insulates the sound source 10 from the surrounding sound field. However, the inner diameter d is reduced and the turning interval is increased to arrange wiring and other minute members in the space between the acoustic tubes 30. It becomes possible. This space between the acoustic tubes 30 is convenient for mounting.

  In FIG. 3, the sound hole 40 is provided at the other end of the acoustic tube 30, but a sound hole may be provided in front of the sound source 20 in the cavity 10. When the frequency characteristic of the sound source 20 is relatively flat, the characteristic can be effectively utilized by providing a sound hole in front of the sound source 20. Even in this case, the effect of the acoustic tube 30 reinforces low-frequency components that are difficult to leak to the outside and difficult to be detected in the surroundings, so that it is possible to reduce the influence of sound leakage to the surroundings, which is a problem in portable audio equipment. .

  FIG. 5 shows an aspect of the sound reproducing device 200 according to the third invention which is a kind of the second invention of the present application. FIG. 5A is a plan view of the sound reproducing device 200, and FIG. 5B is a cross-sectional view taken along line AA. The sound reproducing device 200 is different from the sound reproducing device 100 in that a first sound guiding unit 25 ′ and a second sound guiding unit 55 are provided. The first sound guide portion 25 ′ is composed of the surface side acoustic tube 30 ′ and forms a space continuous with the surface side cavity portion 10 ′, and includes a sound hole 40 ′ at the end opposite to the sound source 20. The surface side cavity 10 ′ corresponds to the cavity 10, and the surface side acoustic tube 30 ′ corresponds to the acoustic tube 30. The sound source 20 also corresponds to the sound source of the sound reproducing device 100.

  The second sound guide portion 55 is a space that is composed of the back surface side acoustic tube 60 and is continuous with the back surface side cavity portion 50. As shown in FIG. 5 (a), the first sound guide portion 25 'and the second sound guide portion 55 are overlapped with each other in the swivel plane, and are formed in the cavity portions 10' and 50 that are continuous with one end of each portion. The sound source 20 is arranged so as to be sandwiched. That is, the turning surface of the first sound guide portion 25 'and the turning surface of the second sound guide portion 55 face each other in parallel, and one surface of the sound source 20 is stored or in contact with one end of the first sound guide portion 25'. The other surface of the sound source 20 is stored or in contact with one end of the second sound guide portion 55 so that the sound source 20 is sandwiched between the first sound guide portion 25 ′ and the second sound guide portion 55. Is done. FIG. 5 shows an example in which the above-described configuration is housed in the outer case 80 ′. An external sound hole 90 'is provided at the position of the sound hole 40'.

  The sound source 20 is provided so that the surface of the sound source 20 is in contact with one end of the bottom surface of the front surface side cavity portion 10 ′, and one end of the bottom surface of the back surface side cavity portion 50 is in contact with the back surface of the sound source 20. The sound source 20 divides the front side cavity 10 ′ and the back side cavity 50 into two halves in the vertical direction. The inner diameter of the front surface side cavity 10 'and the rear surface side cavity 50 and the diameter of the sound source 20 are approximately equal. The front side cavity 10 'sound source 20 and the back side cavity 50 constitute a central part.

  Similarly to the sound reproducing device 100 (FIG. 3), the surface-side acoustic tube 30 ′ smoothly turns outward from one end of the surface-side cavity 10 ′, and the other end is rounded and terminated. Near the terminal end, a sound hole 40 'is provided in a direction parallel to the pivot axis. The back surface side acoustic tube 60 smoothly turns outward from one end of the back surface side cavity 50 in the same direction as the front surface side acoustic tube 30, and the other end is rounded and ends. No sound hole is provided on the other end side of the back-side acoustic tube 60.

  As is clear from the plan view of FIG. 5A, the front surface side acoustic tube 30 'and the back surface side acoustic tube 60 in this example have the same shape. The front side cavity 10 ′ and the back side cavity 50, and the front side acoustic tube 30 ′ and the back side acoustic tube 60 are insulated from the sound field except at the center, that is, the surface in contact with the sound source 20.

  When an acoustic signal is input to the sound source 20, sound waves having the same phase are radiated from the front and back to the front surface side cavity portion 10 'and the back surface side cavity portion 50, and the sound waves are reflected and resonated on the respective inner walls. If the path lengths of the front surface side acoustic tube 30 'and the back surface side acoustic tube 60 are equal, the sound source 20 is positioned in the middle of the entire acoustic tube. Then, a part of the sound wave reaching the sound hole 40 ′ provided at the other end of the surface side acoustic tube 30 ′ is radiated to the outside in the direction parallel to the turning axis, and the remaining part is reflected to be acoustically reflected. It will resonate inside the tube.

Here, it is assumed that the sound reproducing device 200 performs sound reproduction in the band from the lower limit frequency f ₁ to the upper limit frequency f ₂ . The inner diameter of the front side cavity 10 'and the backside cavity 50 smaller than the second half-wave lambda _2/2 corresponding to the upper limit frequency f _2. Then, the surface-side sound tube 30 'and the width of the back side the acoustic tube 60, i.e. the inner diameter d of the cross section perpendicular to the extending direction is smaller than the second half-wave lambda _2/2 corresponding to the upper limit frequency f _2. Thus, there is no resonance in the low regeneration frequency band than the upper limit frequency f ₂ in the respective inner diameter direction.

Further, the path length L between the front surface side acoustic tube 30 ′ and the back surface side acoustic tube 60 is made larger than the first wavelength λ ₁ corresponding to the lower limit frequency f ₁ . Since one end of the front surface side acoustic tube 30 'and the back surface side acoustic tube 60 is in contact with the sound source 20 that emits sound waves in the same phase, the resonance pattern has the highest sound pressure at that portion, and the front surface side acoustic tube 30' And the back-side acoustic tube 60 have the same path length, so that the entire acoustic tube has a half-wavelength, that is, a sound wave having a frequency corresponding to the path length of each of the front-side acoustic tube 30 ′ and the back-side acoustic tube 60. Resonance is induced. On the other hand, although the surface side acoustic tube 30 'and the back surface side acoustic tube 60 sandwich the sound source 20 and the path through which the sound waves propagate is physically bent, the surface side acoustic tube 30' and the back surface side acoustic tube 60 have their respective paths. Resonance of a sound wave having a frequency (or a frequency that is an even multiple thereof) corresponding to a half wavelength corresponding to the length hardly occurs despite being higher than the lower limit frequency f ₁ .

Furthermore both the acoustic tube 30 ', none of 60 the inner wall of the smooth, i.e. because the vehicle is turning so as not to have at least half wavelength lambda _1/2 small and the half wavelength lambda _2/2 larger linear path than than this Resonance within the reproduction frequency band is avoided, and the input / output frequency characteristics are flat. In other words, the resonance due to small and the half wavelength lambda _2/2 larger linear path than than half the wavelength lambda _1/2 can be avoided, input-output frequency characteristic is avoided can vary significantly. The maximum value g of a linear path as described above for the may be smaller than a half wavelength lambda _2/2.

  In order to smoothly turn the front surface side acoustic tube 30 ′ and the back surface side acoustic tube 60, the turning radius is increased at a constant rate with respect to the turning angle, and the design is easy if a spiral type is used.

  In addition, the front surface side acoustic tube 30 'and the back surface side acoustic tube 60 are swung in a direction perpendicular to the swivel axis and spread in a certain plane. These insulate the sound field and the sound waves propagating inside each do not interfere. Even if these are superposed in parallel, the thickness of the sound reproducing device 200 is nothing but the thickness of the outer case 80 ′, and the inner thickness of each of the outer shapes of the front acoustic tube 30 ′ and the rear acoustic tube 60 is at least. The total height of the sound source 20 and the thickness of the sound source 20 is convenient for mounting as a small portable sound reproducing apparatus.

If the turning interval is provided as in the present embodiment by reducing the inner diameter of each of the front surface side acoustic tube 30 'and the back surface side acoustic tube 60, wiring and other minute members can be arranged therethrough. This is convenient for implementation. In addition, the reproduction frequency band can be widened by reducing the maximum value g of the straight path and increasing the upper limit frequency f ₂ .

  In FIG. 5, the sound hole 40 is provided at the other end of the surface side acoustic tube 30 ′. However, the sound hole may be provided at one end of the front side cavity 10 ′, that is, at a position facing the sound source 20. If it does so, it will be easy to radiate | emit the output from the sound source 20 directly. For this reason, the input / output characteristics of the sound source 20 are relatively flat and good depending on the frequency, which is desirable when utilizing the characteristics. Even at this time, low-frequency components that are difficult to leak outside the device are reinforced, and high-frequency output that causes discomfort is suppressed, so that it is possible to reduce the influence on the surroundings due to sound leakage to the surroundings, which is a problem in portable audio devices.

  Although the sound hole 40 'is provided on the other end side of the surface side acoustic tube 30', the sound hole 40 may be provided on the other end of any one of the acoustic tubes. Further, the sound hole 40 ′ may be provided on the other end side of the back surface side acoustic tube 60.

  Since the inner diameters of the front-side acoustic tube 30 'and the rear-side acoustic tube 60 are smaller than the second half wavelength corresponding to the upper limit frequency, the acoustic reproduction device according to the second invention of the present application also has both acoustic tubes at frequencies below the upper limit frequency. Resonance in the inner diameter direction of 30 'and 60 does not occur, and a significant change in input / output characteristics due to frequency does not occur.

  Both acoustic tubes 30 ′ and 60 whose path length is longer than the wavelength corresponding to the lower limit frequency are connected to the front side cavity 10 ′ and the back side cavity 50, respectively. The sound source 10 sandwiched between 50 radiates sound waves in the same phase in both the cavity portions 10 ′ and 50. Therefore, the wavelength of the radiated sound wave extends over the entire path of both acoustic tubes 30 ′ and 60.

  Here, since the linear path inside the acoustic tubes 30 ', 60 does not have anything smaller than the second half wavelength corresponding to the upper limit frequency and smaller than the first half wavelength corresponding to the lower limit frequency, the lower limit In the frequency region between the frequency and the upper limit, resonance in the path length direction of the acoustic tube does not occur and no significant change in input / output characteristics due to frequency occurs. It is the same as in the first invention that the acoustic tube is swiveled in a direction perpendicular to the swivel axis, which is convenient for mounting the small form acoustic device.

  In the third invention of the present application, since the sound waves between the front surface side cavity 10 'and the back surface side cavity 50 are insulated from each other in the second invention, resonance over the entire path of the acoustic tube is induced. The front-side cavity 10 'and the back-side cavity 50 are arranged perpendicular to the swiveling surfaces of both acoustic tubes 30', 60 and are physically bent, but the sound source 20 that generates sound waves in the same phase. This is because the resonance with the wavelength substantially equal to the path length on each side does not occur significantly. Therefore, since the path on which the sound wave resonates can be lengthened while multiplexing the front surface side acoustic tube 30 ′ and the back surface side acoustic tube 60 in the direction perpendicular to the swiveling surface, the space required for mounting can be saved.

  FIG. 6 shows an aspect of the sound reproducing device 300 according to the fourth invention of the present application which is a kind of the second invention of the present application. 6A is a plan view of the sound reproducing device 300, FIG. 6B is a cross-sectional view taken along line AA, and FIG. 6C is a cross-sectional view taken along line BB. In the sound reproducing device 300, the first sound guide portion 67 and the second sound guide portion 68 are arranged on the same surface. The first sound guide portion 67 is composed of a surface-side acoustic tube 64, and one end thereof constitutes a space continuous with the surface-side cavity portion 61. The second sound guide portion 68 is composed of a back surface side acoustic tube 65, and one end thereof is a space continuous with the back surface side cavity portion 62. The sound guide portions 67 and 68 have the same shape and are fitted to each other if the front and back sides are reversed. The sound source 63 is disposed so that the front surface is directed to the front surface side cavity portion 61 and the back surface is directed to the back surface side cavity portion 62. That is, the turning surface of the first sound guiding unit 67 and the turning surface of the second sound guiding unit 68 are fitted on the same plane, and the sound source 68 of the first sound guiding unit 67 and the second sound guiding unit 68. Is arranged so that one surface of the sound source 67 is sandwiched between one end of the first sound guide portion 67 and the other surface of the sound source 67 is sandwiched between one end of the second sound guide portion 68. FIG. 6 shows an example in which the above-described configuration is housed in the outer case 80 ″. An external sound hole 90 ″ is provided at the position of the sound hole 66.

  The sound reproducing device 300 constitutes a central portion by causing the sound source 63 to face each other with the plane sides of the front-side cavity 61 and the back-side cavity 62, which are two substantially semi-cylindrical cavities. The surface-side acoustic tube 64 smoothly turns outward from the one end on the plane side of the surface-side cavity 61 along the back-side cavity 62 with a predetermined width, and the other end is rounded. Terminate with The back surface side acoustic tube 65 is directed outward from the end of the back surface side cavity portion 62 opposite to the one end on the plane side of the surface side cavity portion 61 with the same width as the surface side acoustic tube 64 and along the outside thereof. The other end is terminated with a rounded shape, and a sound hole 66 is provided near the end in a direction parallel to the pivot axis. In parts other than the sound hole 66, the two acoustic tubes 64 and 65 insulate the sound field from the outside. The sound field is also insulated between the front surface side cavity portion 61 and the back surface side cavity portion 62 except for the surface in contact with the sound source 63.

  The sound source 63 in this example is a square-shaped piezoelectric element, for example, as is apparent from the AA cross section of FIG. When an acoustic signal is input to the sound source 63, sound waves having the same phase are radiated from the front surface and the back surface to the front surface side cavity portion 61 and the back surface side cavity portion 62, and are reflected by the inner wall to resonate. If the path lengths of the front surface side acoustic tube 64 and the back surface side acoustic tube 65 are equal to each other, the sound source 63 is arranged in the middle of the entire acoustic tube. Then, a part of the sound wave reaching the sound hole 66 provided at the other end of the back surface side acoustic tube 65 is radiated to the outside in the direction parallel to the turning axis, and the other part is reflected to reflect both acoustic tubes. It will resonate inside 64,65.

  The inner diameters of the front surface side cavity portion 61 and the rear surface side cavity portion 62, the inner diameter d of the front surface side acoustic tube 64 and the rear surface side acoustic tube 65, the path length L, and the shape conditions for the straight path are as described above. , 200. Since the two sound tubes are arranged on the same plane, the overall shape of the sound reproducing device 300 can be reduced.

  In the fourth invention of the present application, since the sound waves between the front surface side cavity portion 61 and the back surface side cavity portion 62 are insulated from each other in the second invention, resonance over the entire path of the acoustic tube is induced. The outer diameter on both sides is equal to the swivel interval width, and it is physically bent by fitting on the same swivel plane, but the sound source that generates sound waves in the same phase is sandwiched, so the wavelength is the path on each side Resonance approximately equal to the length does not occur significantly. Accordingly, since the acoustic tube can be multiplexed on the same swivel plane and the path through which the sound wave resonates can be lengthened, the space required for mounting can be saved.

  The fifth invention of the present application takes a spiral shape in which the turning radius of the acoustic tube increases at a constant rate with respect to the turning angle in the first to fourth inventions. As a result, the curvature and the straight line portion inside the acoustic tube are larger than the second half wavelength corresponding to the upper limit frequency and have a smooth shape without having the smaller one than the first half wavelength corresponding to the lower limit frequency. For this reason, in the frequency region between the lower limit frequency and the upper limit frequency, resonance in the path length direction of the acoustic tube does not occur, and a significant change in input / output characteristics due to frequency does not occur.

As can be said with any of the above embodiments, it does not necessarily mean that the reproduction of the component in the frequency band below the lower limit frequency f ₁ is excluded. Rather, the resonance that occurs in this frequency band can be used to promote low-frequency input / output characteristics that are difficult to achieve with a small-sized sound reproducing device. This is because the sound wave is attenuated in the process of propagating inside the acoustic tube, or the input / output characteristics are not remarkably maximized near the lower limit frequency f ₁ due to the sound wave emission from the sound hole, and are gradually enhanced. Therefore, by setting the low-frequency representative frequency that reinforces the input / output characteristics as the lower limit frequency f ₁ , the input / output characteristics in the low frequency range, that is, in the surrounding frequency band, can be improved.

  If the maximization is still remarkable, it is desirable to use a member that absorbs and attenuates sound waves in the cavity and the acoustic tube, or to increase the diameter of the sound holes in order to promote the radiation of sound waves from the sound holes. Conversely, if the input / output characteristics are not sufficiently enhanced, a member with a high acoustic impedance and a smooth inner surface is used to suppress absorption and attenuation of sound waves in the cavity and acoustic tube, and sound wave emission is suppressed. For this reason, it is conceivable to form a sound hole with a small diameter or a member that is less likely to transmit sound waves.

  Further, if vibration is directly transmitted from the sound source to the cavity, the acoustic tube, or the outer case, abnormal noise is caused. As a member that absorbs vibration without transmitting it, it is desirable to place a buffer portion in a portion that contacts these members. For example, the contact may be made with a synthetic rubber (polyisoprene, butadiene rubber, etc.) or gel-like long chain hydrocarbons that are easily plastically deformed.

As for the sound reproducing devices according to Examples 1 and 2, the cavity and the sound tube are made of ABS (Acrylonitrile, Butadiene, Styrene Copolymerized Synthetic Resin) resin having the property of insulating sound waves. With an electroacoustic transducer having a diameter of 13 mm and a thickness of 2 mm in the center, a path length of 220 mm (one for each of the front side and the back side for Example 2), and an inner diameter of the cross section of 4 mm (parallel to the turning surface) Direction), 5 mm (direction perpendicular to the turning surface), and the input / output characteristics were measured. The maximum turning radius r ₁ was 21 mm. As a result, the maximum linear path g is 34 mm, and the upper limit frequency f ₂ is selected to be 5.0 kHz so as to be shorter than the half wavelength. The sound hole has a diameter of 3 mm and is open without a member that transmits sound waves. As a result, the lower limit frequency f ₁ is 0.39 and 0.77 kHz for the first and second embodiments, respectively. FIG. 7 shows the input / output characteristics obtained by dividing the output signal power of the first embodiment in FIG. 7 and the output signal of the second embodiment in FIG. 8 by the frequency of the input signal for each frequency.

In FIG. 7, (i) is an example in which the sound hole is provided at the other end of the acoustic tube, and (ii) is an example in which the sound hole is provided on the surface of the cavity facing the sound source. In either case, as shown in FIG. 2, the input / output characteristics are inferior at low frequencies or do not show remarkable frequency characteristics. In particular, the frequency characteristic of (ii) is flat. Even in (i), the fluctuation is only about a dozen dB at the upper limit frequency f ₂ = 5.0 kHz or less. In addition, the input / output characteristics in a relatively low frequency range are reinforced, and have a gradual maximum near the lower limit frequency f ₁ = 0.77 kHz.

In FIG. 8, (iii) is the case where the sound hole is provided on the other end of the acoustic tube, and (iv) is the case where the sound hole is provided on the surface of the cavity facing the sound source. In either case, as shown in FIG. 2, the input / output characteristics are inferior at low frequencies, or do not show remarkable frequency characteristics. Although the frequency dependence of the input / output characteristics seems to fluctuate more significantly than in FIG. 7, the substantial path length of the acoustic tube is doubled and the lower limit frequency f ₂ is halved to 0.39 kHz. Accordingly, the resonance frequency of the first half is also halved and the fluctuation period is only shortened.

In either case, the fluctuation is only a few tens of dB at the upper limit frequency f ₂ = 5.0 kHz or less. In (iii), the fluctuation of the input / output characteristics in the high range is somewhat remarkable, but the reinforcing effect in the low range is also relatively significant. In consideration of the input / output characteristics of the sound source, it is possible to select which one is appropriate in consideration of the frequency characteristics of the entire system from the input signal to the output sound pressure. That is, the selection differs depending on whether the input / output characteristics within the reproduction frequency band are flat or not depending on the frequency, or whether the reinforcement degree in the low band is emphasized relatively.

  For example, when using a sound source (electroacoustic transducer) having inferior input / output characteristics in a low frequency region as shown in FIG. 9, when obtaining flatness of frequency characteristics between an input signal and an output sound wave, It is appropriate that the low-frequency component is relatively reinforced as in i) and (iii).

  As shown in these embodiments, flat input / output characteristics are obtained in the reproduction frequency band, and sound reproduction more faithful to the input signal becomes possible. Furthermore, low frequency components that are difficult to obtain with conventional small-sized sound reproducing devices are enhanced. In particular, low frequency components that are difficult to leak to the outside of the device are reinforced, and high frequency output that causes discomfort is suppressed, so that it is possible to reduce the influence on the surroundings due to sound leakage to the surroundings, which is a problem in portable audio devices. In Example 3, the same effect as in Example 2 can be obtained.

Claims (5)

A sound reproducing device having a sound source and a sound guide part, and emitting sound waves from a part of the sound guide part,
The path length of the sound guide portion is larger than the first half wavelength corresponding to the lower limit frequency of the reproduction frequency band, and the inner diameter of the sound guide portion is smaller than the second half wavelength corresponding to the upper limit frequency,
The sound reproducing device according to claim 1, wherein the sound guiding unit is rotated so that a linear path of the sound guiding unit is smaller than the second half wavelength. The sound guide portion is composed of a first sound guide portion and a second sound guide portion having the same shape,
One surface of the sound source is stored or in contact with one end of the first sound guide part,
The other surface of the sound source is stored or in contact with one end of the second sound guide part,
Radiates sound waves in phase from both sides of the sound source,
The sound reproducing apparatus according to claim 1, wherein a sound wave is radiated from the other end of the first sound guide section. The turning surface of the first sound guiding portion and the turning surface of the second sound guiding portion are opposed in parallel,
One surface of the sound source is stored or in contact with one end of the first sound guide part,
By storing or contacting the other surface of the sound source at one end of the second sound guide unit,
3. The sound reproducing device according to claim 2, wherein the sound source is arranged so as to be sandwiched between the first sound guiding unit and the second sound guiding unit. The swiveling surface of the first sound guiding portion and the swiveling surface of the second sound guiding portion are fitted on the same plane,
One surface of the sound source of the first sound guide portion and the second sound guide portion is between one end of the first sound guide portion and the other surface of the sound source is between one end of the second sound guide portion. The sound reproducing device according to claim 2, wherein the sound reproducing device is disposed so as to be sandwiched.   5. The sound reproducing device according to claim 1, wherein the turning radius of the sound guide section changes at a constant rate with respect to the turning angle.

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