JP2017011409A - Acoustic structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make generation of a standing wave controllable, in an acoustic structure including a cavity through which a sound wave propagates.SOLUTION: An acoustic device 1A is a three-way speaker, and a squawker 102 has a driver 10 and an acoustic structure 20A. The acoustic structure 20A is provided with a refine section 220 where the inner diameter near the center is smaller than that at other part, and an end 210. Frequency of a standing wave is shifted to the low frequency side by the shape of the refine section 220, i.e., the position of the node of primary standing wave generated in the internal cavity.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an acoustic structure including a cavity through which sound waves propagate.

  An example of this type of acoustic structure is a speaker back chamber. In this type of acoustic structure, when a sound wave of a specific frequency propagates in the cavity, a standing wave is generated due to the superposition of the sound wave and the reflected wave from the wall surface defining the cavity, and the frequency characteristics are disturbed. May occur. For example, when the frequency of the standing wave is included in the reproduction charge band of the speaker (that is, the frequency band determined by the lower limit and the upper limit of the frequency of the sound represented by the audio signal input to the speaker), For example, a peak or a dip corresponding to the frequency of the standing wave appears in the frequency characteristics of the speaker that should be essentially flat. Therefore, various techniques for preventing the disturbance of the frequency characteristics due to such standing waves have been proposed, and examples thereof include Non-Patent Document 1 and Non-Patent Document 2, or Patent Document 1 and Patent Document 2. Disclosed technology.

  In Non-Patent Document 1 and Non-Patent Document 2, the acoustic structure (in these documents, the back chamber of the speaker) is a conical tapering tube to suppress the reflection of sound waves and to generate a standing wave. Techniques for suppressing are disclosed. The reason why the acoustic structure is a tapered tube is to avoid the occurrence of a location where the acoustic impedance changes suddenly in the internal cavity. This is because the reflection of the sound wave occurs at a location where the acoustic impedance changes rapidly. Patent Documents 1 and 2 disclose a technique for suppressing the occurrence of standing waves by providing a sound absorbing member in a cavity inside an acoustic structure.

Bowers-Wilkins, April 21, 2015 search [online], <URL: http://www.bowers-wilkins.jp/Discover/Discover/Technologies/nautilus-tapering-tubes.html> Norh, May 26, 2015 search, [online], <URL: http://www.norh.com/Norh_Loudspeakers/Technlogy.html>

U.S. Pat. No. 4,127,751 Japanese Patent Application Laid-Open No. 56-140779 JP 2014-175807 A

  Non-patent document 1, Non-patent document 2, Patent document 1 and Patent document 2 disclose the technologies disclosed in the prior art documents in a wide frequency band with respect to the frequency characteristics of an acoustic structure or an acoustic device including the acoustic structure. There is a common problem that there is a risk that it may have an impact on the environment. With the techniques disclosed in Non-Patent Document 1, Non-Patent Document 2, Patent Document 1 and Patent Document 2, it is not possible to control only the propagation of sound waves of a specific frequency, but propagate through a cavity inside the acoustic structure. This is because sound waves of all frequencies are affected. In addition, the techniques disclosed in these documents have the following problems. That is, the techniques disclosed in Non-Patent Literature 1 and Non-Patent Literature 2 cannot suppress a standing wave caused by a reflected wave from a wall surface, and there is a problem that a question remains whether a sufficient effect can be obtained. The techniques disclosed in Patent Literature 1 and Patent Literature 2 have a problem that the manufacturing cost of the acoustic structure (or the acoustic device including the acoustic structure) increases by the amount of the sound absorbing member.

  This invention is made | formed in view of the above situations, and it aims at providing the technique which enables control of generation | occurrence | production of a standing wave in the acoustic structure containing the cavity which a sound wave propagates.

  In order to solve the above problems, the present invention provides an acoustic structure including a cavity through which a sound wave propagates, wherein a cross-sectional area of the cavity by a plane orthogonal to the sound wave propagation direction is a standing wave generated in the cavity. It is an open tube that communicates with the cavity through an open end, and is an integer multiple of substantially half the wavelength of the standing wave, which is different between the position of the approximate node or the position of the antinode of the standing wave and another position. An acoustic structure having a tube length, wherein the open end has an open tube disposed at at least one of a position of a substantially antinode of the standing wave and a position of a node of the standing wave; provide. When the acoustic structure body excluding the open tube from the acoustic structure is formed in a tubular shape, the surface orthogonal to the sound wave propagation direction is orthogonal to the tube axis direction, that is, the longitudinal direction of the acoustic structure body The surface to be used should be adopted. This is because in such an acoustic structure, a standing wave generated in the tube axis direction has a great influence on the frequency characteristics. Note that the position of the abbreviated node refers to a position separated by 1/8 of the wavelength of the standing wave before the reference with respect to the position of the sound pressure node of the standing wave. Later, it refers to a position separated by 1/8 of the wavelength of the standing wave. That is, the position of the approximate node refers to a position within a range of ¼ length of the wavelength of the standing wave centered on the position of the node of the standing wave. The applicant has confirmed through experiments that the same effects as those obtained at the position of the standing wave node can be obtained within this range. The same applies to the position of the approximately antinode, and the same applies to the tube length of the open tube that is an integral multiple of approximately half the wavelength of the standing wave. In the following, the position of the node or the position of the antinode corresponds to the position of the approximate node or the position of the antinode, respectively.

  For example, if the acoustic structure is formed so that the cross-sectional area of the cavity becomes small at the position of the node of the standing wave generated in the cavity when the cross-sectional area of the cavity is uniform, the constant is obtained. The resonance frequency corresponding to the standing wave shifts to the low frequency side. On the contrary, if the acoustic structure is formed so that the cross-sectional area of the cavity becomes small at the position of the antinode of the standing wave generated in the cavity when the cross-sectional area of the cavity is uniform, The resonance frequency corresponding to the standing wave slightly shifts to the high frequency side. Further, if the acoustic structure is formed so that the cross-sectional area of the cavity becomes large at the antinode position, the resonance frequency corresponding to the standing wave is slightly shifted to the low frequency side. That is, according to the present invention, when the cross-sectional area of the cavity is uniform, the cross-sectional area of the cavity at the approximate node position or the antinode position of the standing wave generated in the cavity is changed to another value. By making it different from the cross-sectional area at the position, the frequency of the standing wave generated in the cavity can be controlled. Further, when an open tube is provided as in the present invention, the effect of controlling the frequency of the standing wave as described above overlaps with the effect of providing the open tube, and thus a higher effect. Is played. For details of the effect obtained by providing the above open tube, refer to Patent Document 3.

  In another preferable aspect of the present invention, a plurality of the above-described open tubes are provided, and the plurality of open tubes have different tube lengths. According to this aspect, it is possible to give the effect of providing the above open tube for various resonance frequencies. Moreover, in another preferable aspect, the aspect which has two or more said open pipes, and the pipe length of the at least 2 open pipe in several open pipes corresponds can be considered. According to this aspect, the shift of the resonance frequency to the low frequency side or the high frequency side becomes more remarkable. In order to enhance the effect of providing the open tube, a sound absorbing material that fills at least a part of at least one of the space in the open tube and the space in the cavity may be packed. Moreover, in order to make the said acoustic structure compact, the said open tube should just be bent at least once.

It is a figure which shows the structural example of 20 A of acoustic structures of 1st Embodiment of this invention, and the acoustic apparatus 1A containing the acoustic structure 20A. It is a figure of the model for considering the resonance phenomenon which generate | occur | produces in the internal cavity of the acoustic structure 20A. It is a figure which shows the simulation result about the model shown in FIG. FIG. 6 is a diagram for explaining a relationship between a shift amount and peak value of a resonance frequency and an inner diameter of a narrowing portion. FIG. 6 is a diagram for explaining a relationship between a shift amount and peak value of a resonance frequency and an inner diameter of a narrowing portion. It is a figure which shows the simulation result about the frequency characteristic of the acoustic structure 20A. It is a figure for demonstrating the other Example of the acoustic structure 20A. It is a figure which shows the simulation result about the frequency characteristic of the acoustic structure of 2nd Embodiment of this invention. It is a figure for demonstrating the other Example of the same acoustic structure. It is a figure which shows the structural example of 20 C of acoustic structures of 3rd Embodiment of this invention. It is a figure which shows the simulation result about the frequency characteristic of the acoustic structure 20C. It is a figure which shows the structural example of the acoustic apparatus 1 containing the acoustic structure 20D of 4th Embodiment of this invention, and the acoustic structure 20D. It is a figure for demonstrating a modification (1). It is a figure for demonstrating a modification (2). It is a figure for demonstrating a modification (3). It is a figure for demonstrating a modification (4). It is a figure for demonstrating a modification (5). It is a figure for demonstrating a modification (6). It is a figure for demonstrating a modification (6).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(A: 1st Embodiment)
FIG. 1A is a perspective view showing a configuration of an acoustic device 1A including the acoustic structure 20A according to the first embodiment of the present invention. The acoustic device 1A is a three-way speaker, and has a woofer 101, a squawker 102, and a tweeter 103 attached to the front surface of a cabinet 100. Audio signals in a specific frequency range are input to the three speakers (that is, the woofer 101, the squawker 102, and the tweeter 103) included in the audio device 1A. For example, when focusing on the center frequency of the frequency range of the audio signal input to each of these three speakers, the center frequency for the woofer 101 is the lowest and the center frequency for the tweeter 103 is the highest. Note that the playback charge band of the woofer 101 and the playback charge band of the squawker 102 may partially overlap or may not overlap. Similarly, the reproduction responsible band of the tweeter 103 and the reproduction responsible band of the squawker 102 may or may not partially overlap. In the present embodiment, the squawker 102 includes an acoustic structure 20A. Hereinafter, the squawker 102 will be described in detail.

  FIG. 1B is a diagram showing a configuration of the squawker 102. As shown in FIG. 1B, the squawker 102 includes a driver 10 and an acoustic structure 20A. The driver 10 is a vibration unit that generates acoustic vibration by an audio signal supplied from an amplifier (not shown). The acoustic structure 20A is a so-called back chamber. The acoustic structure 20A is a hollow member formed in a substantially tubular shape. One end of the acoustic structure 20A is an open end that opens toward the back of the driver 10, and the other end 210 is a closed end. That is, the acoustic structure 20A is a one-side closed tube. However, in this embodiment, since the acoustic structure 20A is arranged so that the open end thereof is continuous with the back surface of the driver 10, a closed tube on both sides is formed by the back surface of the driver 10 and the acoustic structure 20A.

  As shown in FIG. 1B, the acoustic structure 20A has an inner diameter in the vicinity of the center in the tube axis direction (that is, the propagation direction of the sound wave generated by the driver 10) smaller than the inner diameter in other portions. The shape is narrowed down near the center. That is, paying attention to the internal cavity of the acoustic structure 20A of the present embodiment, the cross-sectional area of the cross section by the plane perpendicular to the tube axis in the vicinity of the center in the tube axis direction is smaller than the cross-sectional areas at other positions. In the present embodiment, a portion near the center of the acoustic structure 20A, that is, a portion where the inner diameter is smaller than the inner diameter in other portions is referred to as a “squeezed portion 220”. The feature of this embodiment lies in the provision of such a narrowing portion 220.

  If there is no narrowing portion 220, the acoustic structure 20A is a one-side closed tube having a substantially uniform inner diameter, and a double-sided closed tube having a substantially uniform inner diameter is formed by the back surface of the driver 10 and the acoustic structure 20A. In this case, the sound wave generated by the vibration of the driver 10 propagates in the cavity of the acoustic structure 20A in the tube axis direction, and resonance occurs at a frequency corresponding to the tube length of the acoustic structure 20A (that is, a standing wave is generated). To do. Hereinafter, among such standing waves, a wave having the longest wavelength (n is an arbitrary natural number greater than or equal to 1) is referred to as an “n-order standing wave”. The primary standing wave refers to a standing wave whose wavelength is approximately twice the tube length of the acoustic structure 20A. In the primary standing wave, the sound pressure near the center of the acoustic structure 20A hardly fluctuates and becomes a node. In FIG. 1B, a primary standing wave generated in the internal cavity of the acoustic structure 20A when the narrowing portion 220 is not present is represented by a dotted line. Hereinafter, the frequency of the n-th standing wave is referred to as “n-th resonance frequency”.

  The inventor of the present application provides a narrowed portion in a double-sided closed acoustic structure having a uniform inner diameter so that the resonance phenomenon occurring in the cavity inside the acoustic structure exhibits a behavior close to so-called Helmholtz resonance from so-called tube resonance. (Hereinafter referred to as Helmholtz), it was thought that the resonance frequency could be controlled, and it was confirmed by simulation that it could actually be controlled. The acoustic structure 20A of the present embodiment is based on this knowledge. Hereinafter, the simulation performed by the inventor will be described in detail.

FIG. 2A is a diagram showing an outline of a model (hereinafter referred to as model A) corresponding to a closed tubular acoustic structure, and FIG. 2B is a model corresponding to an acoustic structure provided with a narrowing portion. It is a figure which shows the outline of (following, model B). As shown in FIG. 2 (A), model A is a two-sided closed tube with a tube length of 2L ₀ , and the cross section of the cavity by a plane perpendicular to the tube axis is a circle with an area of S ₀ at any position in the tube axis direction. It has become. Model B contrast, narrowed down over the vicinity of the center of the model A to the width 2L _H has a shape, the narrowed portion corresponds to the narrowing section 220. That is, in Model B, the narrowing portion is provided at the position of the node of the primary standing wave that occurs when there is no narrowing portion (that is, when the inner diameter of the tube is uniform). In the model B, the cross section of the cavity in the narrowed portion is a circle having an area of S _H (S ₀ > S _H ).

一方、モデルＢについては、図２（Ｂ）において点線で示す面Pを境にネックの長さがＬ_Ｈかつ体積Ｖ＝Ｓ_０×（Ｌ_０−Ｌ_Ｈ）のヘルムホルツ共鳴器が向かい合っていると考えると、モデルＢにおける共鳴周波数ｆ_Ｈはヘルムホルツ共鳴の理論式より以下の数２のように表される。なお、数２においてπは円周率を意味し、Ｌ_Ｈ´は開口端補正を含むＬ_Ｈの値を意味する（他の数式においても同様）。

The first-order resonance frequency f _t for the model A is expressed as the following _{equation (} 1). In Equation 1, c means the speed of sound (the same applies to other mathematical expressions).

On the other hand, for model B, Helmholtz resonators having a neck length of L _H and volume V = S ₀ × (L ₀ −L _H ) face each other with a plane P indicated by a dotted line in FIG. Therefore, the resonance frequency f _H in the model B is expressed by the following formula 2 from the theoretical formula of Helmholtz resonance. In Equation 2, π means a circular ratio, and L _H ′ means a value of L _H including opening end correction (the same applies to other mathematical expressions).

Here, the condition where f _t > f _H , that is, the condition where the primary resonance frequency shifts to the low frequency side by changing from tube resonance to Helmholtz resonance will be considered. Substituting equation 1 into the left side of f _t > f _H and substituting equation 2 into the right side to remove the root sign, the following equation 3 is obtained. It should be noted that a _{H in the} left side of Equation 3 below is the radius at the narrowed portion 220 (ie, πa _H ² = S _H ), and a ₀ in the left side of Equation 3 is the radius in the portion other than the narrowed portion 220 (ie, πa ₀ ² = S ₀ ).

When Helmholtz resonators face each other as shown in FIG. 2 (B), it is not clear what value L _H ′ will be. Therefore, in the following, the most severe condition, that is, L _H ′ = L _H Consider the case of. If a _H / a ₀ and L _H / L ₀ are equal, Expression 3 is always satisfied if the following Expression 4 is satisfied when a _H / a ₀ = L _H / L ₀ = t. Note that d in Equation 4 is a value shown in Equation 5. Regardless of whether or not a _H / a ₀ and L _H / L ₀ are equal, if 0 <a _H / a ₀ <f (see Equation 6), L _H / L ₀ = 1/2 If so, Equation 3 holds. If 0 <a _H / a ₀ <d (see Equation 5), then Equation 3 holds if e (see Equation 7) <L _H / L ₀ <d.

A more general study of the conditions shown in Equation 3 is as follows. First, the value L _H L _H The including an open end correction _'can be generally expressed by the following equation 8. X on the right side of Expression 8 is a parameter representing the opening end correction, and x = 1.7 when there is a baffle surface. Substituting Equation 8 into the right side of Equation 3 and further substituting Equation 3 with a _H / a ₀ = t, L _H / L ₀ = r, and u = x (a _H / L ₀ ) 9 is obtained.

Here, when t≈1 and r≈0, that is, when a _H ≈a ₀ and L _H ≈0 (in other words, the vicinity of the center of the straight tubular body is slightly narrowed to narrow the narrowing portion 220. (If formed). Substituting t = 1 and r = 0 into Equation 9 and rearranging Equation 9 in consideration of u = x (a _H / L ₀ ), the following Equation 10 is obtained. The above-mentioned number 3 holds. The left side of Equation 10 represents the ratio of the tube diameter a _{0 to} the tube length L ₀ . As is clear from Equation 10, if the ratio of the tube diameter a ₀ to the tube length L ₀ is larger than a certain value (the value on the right side of Equation 10), the center of the tube is slightly narrowed to form the narrowed portion 220. Thus, it can be seen that the condition shown in Equation 3 is satisfied, that is, the resonance frequency can be shifted to the low frequency side by Helmholtz.

FIG. 3 is a graph showing the simulation results of the frequency characteristics for model A and model B in which L ₀ and a ₀ are determined so that f _t = 760 Hz and Equation 10 is satisfied. Note that the tube lengths (that is, 2 × L ₀ ) of model A and model B in this simulation are 224 mm, and the width in the tube axis direction of the narrowed portion 220 (that is, 2 × L _H ) in model B is 10 mm. A graph curve GA in FIG. 3 represents the frequency characteristic of the model A, and a graph curve GB represents the frequency characteristic of the model B. As is apparent from FIG. 3, the graph curve GA has a vicinity of 760 Hz corresponding to the first-order resonance frequency of model A, a vicinity of 1520 Hz corresponding to the second-order resonance frequency, and 2280 Hz corresponding to the third-order resonance frequency. Peaks PA1, PA2 and PA3 appear in the vicinity. On the other hand, in the graph curve GB, the peak PB1 corresponding to the peak PA1 and the peak PB3 corresponding to the peak PA3 are shifted to the low frequency side, and the peak value is also reduced and corresponds to the peak PA2. The peak PB2 is slightly shifted to the high frequency side and the peak value is slightly increased.

  Of the resonance phenomena that occur in an acoustic device, the primary resonance phenomenon often has the most influence on the frequency characteristics of the acoustic device. As is apparent from the simulation results, the acoustic structure having both sides closed tubular is formed so as to satisfy the condition shown in Equation 10, and further, a narrowing portion is provided at the position of the primary standing wave node. And the peak value can be reduced. By utilizing this, it is expected that the disturbance of the frequency characteristics caused by the first-order resonance phenomenon can be alleviated. In the simulation results, the third-order resonance frequency shows the same change as the first-order resonance frequency because the position of the node of the first-order standing wave is the position of the node of the third-order standing wave. It is also a position, and is considered to be a change due to Helmholtz formation as in the first-order resonance phenomenon.

  The reason why the secondary resonance phenomenon is different from the primary resonance phenomenon is that the position of the node of the primary standing wave is the position of the antinode of the secondary standing wave. It is done. Since the resonance frequency is shifted to the high frequency side, it is considered that providing the narrowing portion 220 at the antinode position of the standing wave is equivalent to shortening the tube length. Compared to this, the shift amount is considered to be small. As apparent from comparing the magnitude of the shift amount between the primary resonance frequency and the secondary resonance frequency, the secondary caused by providing the narrowing portion 220 at the position of the node of the primary standing wave. The influence on the resonance frequency can be almost ignored.

  Further, in order to confirm the influence of the size of the narrowing in the narrowing-down unit 220 on the shift amount of the primary resonance frequency and the fluctuation amount of the peak value, the inventor of the present application confirms the influence of a plurality of models (models R10, R7 having different cross-sectional areas). , R5, R3, and R1 in the order of the smaller cross-sectional area, and FIG. 4 shows models R10, R7, R5, and R1). The relationship between the shift amount of the resonance frequency to the low frequency side and the peak value was investigated. In this simulation, a model modeled including the space behind the diaphragm in the driver 10 (semicircular space in FIG. 4) was used. However, the space is smaller than the back chamber, and the simulation results can be obtained with or without the space. There is almost no change. FIG. 5 is a diagram illustrating the frequency characteristics obtained by the simulation. As shown in FIG. 5, it can be seen that the smaller the cross-sectional area of the narrowed portion 220, the larger the shift amount and the smaller the peak value.

  The acoustic structure 20A of the present embodiment is configured based on the simulation result. FIG. 6 is a diagram illustrating a simulation result of frequency characteristics of the acoustic structure 20A designed so that the primary resonance frequency is 1 kHz when the narrowing-down portion 220 is not provided. The graph curve GA ′ in FIG. 6 is a graph curve showing the frequency characteristics when there is no narrowing portion 220, and the graph curve GB ′ is a graph curve showing the frequency characteristics of the acoustic structure 20A. As is apparent from FIG. 6, it is understood that the resonance frequency of each order is shifted and the peak value is changed as in the case of the model B by providing the narrowing-down portion 220. Therefore, when the frequency characteristic of the squawker 102 is disturbed by the primary standing wave, the primary resonance frequency is narrowed down so as to move to a lower frequency side than the lower limit of the assigned frequency band of the squawker 102. By adjusting the cross-sectional area of the cavity in the portion 220, it is possible to avoid the disturbance of the frequency characteristics caused by the first-order standing wave from the viewpoint of hearing.

  In the present embodiment, the primary resonance frequency generated in the internal cavity of the acoustic structure 20A (that is, the one-side closed tubular acoustic structure that forms a closed tube on both sides together with the back surface of the driver 10) when the narrowing portion 220 is not provided. In the case of shifting the secondary resonance frequency together with the primary resonance frequency, the position of the node of the secondary standing wave as shown in FIG. Further, a narrowing portion 220 ′ may be further provided. In FIG. 7A, the secondary standing wave in the absence of the narrowing-down portions 220 and 220 ′ is drawn with a dotted line. By providing the narrowing portion 220 ′ in addition to the narrowing portion 220, the secondary resonance frequency can be shifted to the low frequency side as shown in FIG. 7B.

  As described above, according to the present embodiment, the acoustic device 1 having the acoustic structure 20A is caused by a standing wave having a specific frequency while avoiding an influence on the frequency characteristics over the entire frequency band. It becomes possible to alleviate the disturbance of the frequency characteristics. In addition, according to the present embodiment, since a sound absorbing member or the like is not required separately, the acoustic structure 20A or the acoustic device including the acoustic structure 20A (the squawker 102 or the acoustic device 1 including the squawker 102). ) Manufacturing cost does not increase. In this embodiment, the application example of the present invention to the back chamber of the squawker 102 has been described. However, the present invention may of course be applied to the back chamber of the woofer 101 or the tweeter 103, and the following second and third embodiments will be described. The same applies to the form.

(B: Second embodiment)
The acoustic structure according to the second embodiment of the present invention is a back chamber in a squawker or the like, similar to the acoustic structure 20A, but the end 210 on the side opposite to the side facing the driver 10 is an open end. Different from the acoustic structure 20A. Since the end 210 opposite to the side facing the driver 10 is an open end, when the acoustic structure 20A in the squawker 102 of the first embodiment is replaced with the acoustic structure of the present embodiment, A one-side closed tube is formed by the acoustic structure.

  The position of the node of the primary standing wave generated in the internal cavity of the one-side closed tubular acoustic structure without the narrowing portion 220 is near the open end of the acoustic structure, and the secondary standing wave The position of the node is a position away from the open end by a half wavelength from the closed end side. The inventor of the present application also confirms by simulation that the resonance frequency corresponding to the standing wave shifts to the low frequency side by providing a narrowing portion at the position of the node of the standing wave for the acoustic structure of one side closed tubular did. FIG. 8 shows a simulation result of the frequency characteristic of the one-side closed tubular acoustic structure, that is, the frequency characteristic when the narrowing portion 220 is provided at the position of the primary standing wave node of the one-side closed tubular acoustic structure. It is a figure which shows the simulation result. As apparent from FIG. 8, by providing the narrowing portion 220 at the position of the primary standing wave node of the one-side closed tubular acoustic structure, the primary resonance frequency is shifted to the low frequency side. . Similarly, when the secondary resonance frequency is shifted to the low frequency side, as shown in FIG. 9A, the narrowing-down portion 220 is placed at a position that is 1/2 wavelength away from the end portion 210 toward the back side of the driver 10. It only has to be provided. By doing so, the secondary resonance frequency can be shifted to the low frequency side as shown in FIG. 9B.

  Also according to the present embodiment, the frequency characteristics are disturbed due to the standing wave of a specific frequency while avoiding the influence on the frequency characteristics over the entire frequency band of the acoustic device having an acoustic structure such as the back chamber. It can be mitigated. In addition, according to the present embodiment, since a sound absorbing member or the like is not required separately, the manufacturing cost of the acoustic structure or the acoustic device including the acoustic structure is not increased.

(C: Third embodiment)
FIG. 10 is a diagram illustrating a configuration example of an acoustic structure 20C according to the third embodiment of the present invention. The acoustic structure 20C of this embodiment is also a back chamber in a squawker or the like. In FIG. 10, the same components as those in FIG. 1B are denoted by the same reference numerals. As is clear from FIG. 10, the acoustic structure 20C has a first-order resonance frequency generated in the internal cavity of the acoustic structure 20C when the narrowed portion 220 is not provided, as in the acoustic structure 20A. A narrowing portion 220 is provided at the node position. As is clear from the comparison between FIG. 10 and FIG. 1B, the acoustic structure 20C includes an open tube 21 that communicates with the internal cavity of the acoustic structure 20C via the first and second opening ends, and The point which has 22 and the point which has sound-absorbing material 23a-23f differ from 20 A of acoustic structures.

  The tube lengths of the open tube 21 and the open tube 22 are equal, and the tube length is an integral multiple of approximately half the wavelength of the primary standing wave. The first open end 21a of the open tube 21 is disposed at a substantially antinode position of the standing wave, and the second open end 21b is disposed at an approximate node position of the standing wave. The open tube 21 is packed with a sound absorbing material 23 a that fills at least a part of the space in the open tube 21. Similarly, the first opening end 22a of the open tube 22 is disposed at a position substantially corresponding to the standing wave, and the second opening end 22b is disposed at a position corresponding to the node of the standing wave. The open tube 22 is also filled with a sound absorbing material 23 b that fills at least a part of the space in the open tube 22. The reason for providing such open tubes 21 and 22 is as follows.

  In Patent Document 3, a tubular acoustic structure including a cavity through which a sound wave propagates is an open tube that communicates with the cavity via first and second open ends, and is a standing tube that is generated in the cavity. The tube has a tube length that is an integral multiple of approximately half the wavelength of the wave, the first open end is disposed at the position of the antinode of the standing wave, and the second open end is disposed at the position of the approximate node of the standing wave. It is described that by providing such an open tube, a peak or a dip appearing in the frequency characteristics of the acoustic structure due to the standing wave can be alleviated. The reason why the open tubes 21 and 22 are provided in the acoustic structure 20C is that the effects of the narrowing portion 220 and the effects (effects described in Patent Document 3) provided by the open tubes 21 and 22 are superimposed, This is to further enhance the dip relaxation effect. The reason why the sound absorbing materials 23a and 23b are packed in the open tubes 21 and 22, respectively, is to further enhance the effect of providing the open tubes 21 and 22.

  FIG. 11 shows the case where the narrowed portion 220 is not provided (that is, the case where the open tubes 21 and 22 are provided in the straight tubular acoustic structure and the sound absorbing materials 23a to 23f are provided) (the case where the narrowed portion 220 is provided). It is a figure which shows the simulation result of the frequency characteristic of 20 C of acoustic structures about each of the case where the open tubes 21 and 22 are provided in an acoustic structure, and the sound-absorbing materials 23a-23f are provided. As can be seen from FIG. 11, by providing the narrowing portion 220, it can be seen that the first-order resonance frequency is shifted to the low frequency side as compared with the case where the narrowing portion 220 is not provided. In the present embodiment, the sound absorbing materials 23a and 23b are packed in the open tubes 21 and 22 in order to further enhance the peak and dip mitigating effects of the open tubes 21 and 22, respectively. In addition, a sound absorbing material that fills at least a part of the internal space may be filled, or the sound absorbing material may be omitted. Similarly, any or all of the sound absorbing materials 23c to 23f may be omitted.

(D: 4th Embodiment)
FIG. 12 is a diagram illustrating a configuration example of an acoustic device 1D having the acoustic structure 20D according to the fourth embodiment of the present invention. More specifically, FIG. 12A is a perspective view of the acoustic device 1D, and FIG. 12B is a cross-section (XX ′ line) along the line XX ′ of FIG. 12A of the acoustic device 1D. 12C is a cross-sectional view taken along a plane perpendicular to the z-axis, and FIG. 12C is a cross-section taken along a line YY ′ in FIG. FIG. The acoustic device 1D of the present embodiment includes a plurality of (in this embodiment) a plurality of hollow prismatic acoustic structures 20D each having an opening 205 on a side surface with the openings 205 facing in the same direction (z-axis direction in the present embodiment). 2) Arranged acoustic panels.

  In FIG. 12B, the position of the opening 205 is drawn with a dotted line. The acoustic structure 20D functions as a one-side closed tube with the opening 205 as an open end. As is clear from FIGS. 12B and 12C, the inner wall of the acoustic structure 20D is in the vicinity of the closed end corresponding to the open end (that is, the cavity inside the acoustic structure 20D). (The position of the antinode of the first-order standing wave generated in FIG. 1), and this projecting portion plays the role of the narrowing portion 220. For this reason, the primary resonance frequency for the acoustic structure 20D is shifted to the high frequency side as compared with the case where the protruding portion (that is, the narrowing portion 220) is not provided.

  Also according to the present embodiment, the disturbance of the frequency characteristic due to the standing wave of the specific frequency is reduced while avoiding the influence on the frequency characteristic over the entire frequency band of the acoustic device 1D having the acoustic structure 20D. It becomes possible. In addition, since a sound absorbing member or the like is not separately required in the present embodiment, the manufacturing cost of the acoustic structure 20D or the acoustic device 1D including the acoustic structure 20D does not increase. In the present embodiment, the acoustic device 1D is configured by arranging the plurality of acoustic structures 20D with the openings 205 facing the same direction. However, the openings 205 of the plurality of acoustic structures 20D constituting the acoustic device 1 are provided. They don't have to be in the same direction.

(E: Other embodiments)
Although each embodiment of the present invention has been described above, it goes without saying that the following modifications may be added to these embodiments.
(1) In the first embodiment, the shapes of the spaces communicated via the narrowing portion 220 are all the same, and the volumes of the spaces are also the same, but the acoustic structure 20E1 shown in FIG. Like the acoustic structure 20E2 shown in FIG. 13B, the shape and volume of each space communicating via the narrowing-down portion 220 may be different. As shown in FIGS. 13A and 13B, even if the shapes and volumes of the spaces communicating with each other through the narrowing-down portion 220 are different, a resonance frequency shift occurs due to Helmholtz formation. Because there is no change. Note that the resonance frequency due to Helmholtz is calculated by regarding each space communicating through the narrowing portion 220 as a spring, and considering the air in the narrowing portion 220 as a spring / mass system corresponding to the mass point. can do. In addition, the shape of each space communicating through the narrowing portion 220 is not limited to a cylindrical shape, and may be an ellipsoidal shape like an acoustic structure 20E3 illustrated in FIG.

(2) The narrowing-down portion 220 in each of the first to third embodiments may have a bent columnar shape like that in the acoustic structure 20F1 shown in FIG. 14 (A), as shown in FIG. 14 (B). It is good also as a shape which put in order a plurality of cylinders with a small cross-sectional area like the thing in acoustic structure 20F2 shown. Further, as in the acoustic structure 20F3 shown in FIG. 14C, the acoustic structure is formed so that the cross-sectional area of the tube gradually decreases from the end of the tube toward the position of the primary standing wave node. May be. The narrowing portion 220 in the fourth embodiment may also have the shape shown in each of FIGS. 14 (D) to (F). In FIGS. 14D to 14F, the position of the opening 205 is drawn with a dotted line. FIGS. 14D to 14F show the vicinity of the opening 205 of the acoustic structure constituting the acoustic panel (that is, The case where the narrowing portion 220 is provided at the position of the node of the primary standing wave) is illustrated. In the acoustic structures in each of the first to third embodiments, the narrowing portion 220 may be formed by providing the overhang shown in FIGS. 14D to 14F in the pipe. As a method of forming such an acoustic structure, for example, each member obtained by dividing the acoustic structure into two parts by a plane including the tube axis is formed by injection molding of a material such as resin, and the members are bonded together. A method is conceivable. When the resonance frequency is shifted by providing the narrowing portion, the shape of the narrowing portion 220 is any shape as long as the cross-sectional area of the cavity in the narrowing portion 220 is smaller than the cross-sectional area of the cavity in other portions. Any method may be used for forming the narrowed portion 220.

(3) In each of the above embodiments, a narrowing portion is provided at the position of the node of the standing wave generated in the internal cavity of the tubular acoustic structure (that is, the cross-sectional area of the cavity at the position of the node is set at another position). The resonance frequency corresponding to the standing wave is shifted to the low frequency side. However, when the resonance frequency shifted to the low frequency side is an even-order resonance frequency, the cross-sectional area at the antinode position of the standing wave corresponding to the resonance frequency is larger than the cross-sectional area at other positions. The same effect can be obtained by forming an acoustic structure.

  In FIG. 15A, an inflating portion 230 having a larger cross-sectional area than that at other positions is provided at the antinode position of the secondary standing wave (in other words, the position of the node of the primary standing wave). An acoustic structure 20G that is closed on both sides is illustrated, and FIG. 15B is a diagram illustrating a simulation result of the frequency characteristics of the acoustic structure 20G. As is clear from FIG. 15B, by providing the expansion portion 230 at the above position, the secondary resonance frequency is slightly shifted to the low frequency side, while the primary resonance frequency is almost shifted. You can see that they are not. The simulation results of the above embodiments and this modification are summarized as follows. That is, in a tubular acoustic structure including a cavity through which a sound wave propagates, the cross-sectional area of the cavity due to a surface intersecting with the propagation path of the sound wave at the position of the approximate node of the standing wave generated in the cavity is larger than that at other positions. By reducing the resonance frequency, the resonance frequency corresponding to the standing wave can be largely shifted to the low frequency side. Further, in the acoustic structure, the standing wave is made smaller by reducing the cross-sectional area of the cavity at a substantially antinode position of the standing wave generated in the cavity than the other position. The resonance frequency corresponding to the above can be shifted to the lower side, and conversely, if the former cross-sectional area is made larger than the latter, the resonance frequency can be shifted to the lower side.

  In each of the above embodiments, the application example of the present invention to the tubular acoustic structure has been described. However, the application target of the present invention is not limited to the tubular acoustic structure, and is a box-shaped speaker enclosure or the like. An acoustic structure may be used. In short, an acoustic structure including a cavity through which sound waves propagate, that is, an acoustic structure having a space defined by walls that form the acoustic structure, and the sound waves generated by vibration of the vibrating body are For an acoustic structure that propagates in space, the cross-sectional area of the space defined by the plane perpendicular to the propagation direction of the sound wave is formed in a shape that differs between the position of the standing wave at the approximate node position or the approximate antinode position and other positions. By doing so, the resonance frequency corresponding to the standing wave can be shifted. In each of the above embodiments, the case where the resonance frequency corresponding to the standing wave generated in the tube axis direction of the tubular acoustic structure is shifted has been described. However, in the other direction (for example, the direction orthogonal to the tube axis). The resonance frequency corresponding to the generated standing wave is also shifted by making the sectional area of the cavity inside the acoustic structure at the position of the approximate node or the position of the antinode of the standing wave different from other positions. be able to. The point is that the cross-sectional area of the cavity by the plane orthogonal to the direction of propagation of the sound wave that generates the standing wave to be controlled is different between the position of the node of the standing wave or the position of the antinode and the other position. It ’s fine.

(4) In the third embodiment, the acoustic structure 20C has the open tubes 21 and 22 that communicate with the internal cavity of the acoustic structure 20C via the first and second opening ends, respectively. There may be only one or three or more open tubes. Furthermore, in the said 3rd Embodiment, although the pipe length of the open tube 21 and the open tube 22 is equal, you may differ, for example like FIG. That is, when the acoustic structure 20C has a plurality of open tubes, the tube lengths of the open tubes may be different from each other, and at least two tubes having the same tube length are included in the plurality of open tubes. May be. When the open tube lengths of the acoustic structure 20C are all equal, the peak and dip mitigating effects appearing in the frequency characteristics of the acoustic structure 20C due to the standing wave of the frequency corresponding to the open tube length are further enhanced. Can do. Moreover, if the tube lengths of the open tubes included in the acoustic structure 20C are different from each other, peaks and dips caused by standing waves of various frequencies corresponding to the tube lengths of the open tubes can be alleviated.

(5) In the third embodiment, as shown in FIG. 10, the open tubes 21 and 22 are bent twice. However, at least one of the open tube 21 and the open tube 22 may be bent three or more times or only once. For example, in the acoustic structure 20C of FIG. 17, the open tubes 21 and 22 are bent five times. When the open tubes 21 and 22 are bent at least once, the acoustic structure becomes compact, and the acoustic structure can be efficiently stored in the acoustic device. Note that the number of bends of the open tube 21 and the open tube 22 may or may not match.

  Further, the open tubes 21 and 22 may not be bent. In this embodiment, the open tubes 21 and 22 communicate with the internal cavity only through one of the first open end and the second open end. Even in this aspect, the peak and dip appearing in the frequency characteristics of the acoustic structure 20C due to the standing wave generated in the internal cavity can be reduced. Note that either one of the open tube 21 and the open tube 22 may communicate with the internal cavity only through the first open end or the second open end.

(6) The third embodiment may be combined with the second embodiment or the fourth embodiment. For example, in the mode in which the third embodiment and the fourth embodiment are combined, the open tubes 21 and 22 may be embedded in the wall surface forming the acoustic structure 20D as shown in FIG. 18, or the open tube 21 as shown in FIG. And 22 may be provided.

DESCRIPTION OF SYMBOLS 1A, 1D ... Acoustic apparatus, 10 ... Driver, 20A, 20C, 20D, 20E, 20F, 20G ... Acoustic structure, 210 ... End part, 220 ... Narrowing part, 230 ... Expansion part, 21,22 ... Open tube, 23a , 23b, 23c, 23d, 23e, 23f ... sound absorbing material, 100 ... cabinet, 101 ... woofer, 102 ... squawker, 103 ... tweeter.

Claims (4)

In an acoustic structure including a cavity through which sound waves propagate,
The cross-sectional area of the cavity due to the plane orthogonal to the propagation direction of the sound wave is different between the position of the standing wave approximately nodal or the position of the standing wave approximately generated in the cavity and another position,
An open tube that communicates with the cavity through an open end, and has a tube length that is an integral multiple of approximately half the wavelength of the standing wave, and the open end is positioned substantially at the position of the antinode of the standing wave and the standing wave An acoustic structure comprising: an open tube disposed at least one of the positions of the rough nodes of the wave. A plurality of the open tubes;
The acoustic structure according to claim 1, wherein tube lengths of the plurality of open tubes are different from each other. The acoustic structure according to claim 1, further comprising: a sound absorbing material that fills at least a part of at least one of the space in the open tube and the space in the cavity. . The acoustic structure according to any one of claims 1 to 3, wherein the open tube is bent at least once.

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