JP5920418B2 - Acoustic structure - Google Patents

Description

  The present invention relates to a technique for absorbing sound and scattering sound.

  In order to remove acoustic obstacles such as flutter echo in an acoustic space such as a hall or a theater, an acoustic member for scattering sound is installed. For example, Patent Document 1 discloses an acoustic structure in which a cavity extending in one direction is formed, and a plurality of members having openings that communicate the cavity with an external space are arranged. Is incident, the sound is re-radiated from the opening and a scattering effect can be obtained.

JP 2002-30744 A

In a relatively small space such as a residential room, a conference room, or a music room, it is required to obtain a sound absorbing effect as well as an appropriate scattering effect. Therefore, if the acoustic member for obtaining the scattering effect and the acoustic member for obtaining the sound absorbing effect are separately provided in the space, the space is taken up, and a low-frequency using a porous sound absorbing material such as felt is used. If an attempt is made to increase the sound absorption effect on the band, the size in the thickness direction increases and the space is further narrowed.
The present invention has been made in view of the above-described problems, and its purpose is to effectively absorb and scatter sound while suppressing the increase in size of the acoustic member, and to absorb and scatter sound in a wide frequency band. Is to get.

In order to solve the above-described problem, the acoustic structure of the first configuration according to the present invention includes a plurality of sound wave transmission regions that transmit sound waves, and reflected waves that are adjacent to the sound wave transmission regions and correspond to incident sound waves. possess a reflection region that emits the reflection in response to sound waves the acoustic transmissive region and the reflective region is incident and reflector facing the space of the object to scatter the sound, to the reflector from the space When the region radiates a reflected wave to the space, the phase in the sound wave transmission region is different from the phase in the reflection region of the reflected wave, and the specific acoustic impedance in the sound wave transmission region is determined by the medium of the sound wave transmission region. the sound waves substantially zero real part of a value obtained by dividing the characteristic impedance, and a sound wave radiating unit that radiates into the space via the wave transmittable region, the center point of the acoustic wave transmission region adjacent to each other Spacing, characterized in that it is a distance of approximately four times the length of the sound wave transmission region in 該隣 Ri fit direction.

Acoustic structure of the second configuration according to the present invention, in the acoustic structure according to the first configuration, the sound wave of a predetermined frequency band is incident from the space via the wave transmittable region, corresponding to the acoustic resonance the reflected waves caused by, characterized in that it comprises a resonator for radiating through the wave transmittable region between those space.

Acoustic structure of the third configuration according to the present invention, in the acoustic structure of the first configuration, the sound pickup means, a sound emitting means for radiating sound waves into said space via the wave transmittable region, the analyzes the audio signal collected by the sound collecting means identifies sound waves phase incident on the reflector from between the previous picked up Kisora that by the sound collection unit, based on the specified phase, the The phase in the sound wave transmission region is different from the phase in the reflection region of the reflected wave, and the real part of the value obtained by dividing the specific acoustic impedance in the sound wave transmission region by the characteristic impedance of the medium in the sound wave transmission region is substantially zero. And control means for controlling the sound emitting means so as to emit sound waves.

  ADVANTAGE OF THE INVENTION According to this invention, while suppressing the enlargement of the size of an acoustic member, a sound can be absorbed and scattered effectively and the sound absorption and scattering effect can be obtained in a wide frequency band.

It is a perspective view which shows the external appearance of an acoustic structure. It is the figure which looked at the acoustic structure from the arrow II direction (upper surface) of FIG. It is the figure showing the cross section when an acoustic structure is cut | disconnected by yz plane. 3 is a graph showing a relationship between a specific acoustic impedance ratio ζ and a phase change amount φ. It is a graph which shows the relationship between specific acoustic impedance ratio (zeta) and amplitude | R | of a complex sound pressure reflection coefficient. It is a figure explaining the behavior of the sound wave near the opening surface. FIG. 7 is a diagram for explaining the behavior of a sound wave in the vicinity of an opening surface at the time of FIG. 6. It is a figure showing the mode of propagation of the reflected wave in each direction seen from the opening surface. It is the figure which looked at the acoustic structure from the perpendicular direction of the reflective surface. It is the figure showing the cross section when an acoustic structure is cut | disconnected by the cutting line VIII-VIII of FIG. It is the figure showing the cross section when an acoustic structure is cut | disconnected by yz plane shown in FIG. It is a figure explaining the structure of a resonance body.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
First, a first embodiment of the present invention will be described.
FIG. 1 is a perspective view showing the appearance of the acoustic structure 1. FIG. 2 is a view of the acoustic structure 1 as viewed from the direction of arrow II (upper surface) in FIG.
The acoustic structure 1 is made of a reflective material having a high rigidity such as acrylic resin, and is a rectangular parallelepiped member having a relatively small length in the thickness direction. On the smooth upper surface of the acoustic structure 1, opening surfaces 20-1 to 20 to 4 are provided. These opening surfaces 20-1 to 20-4 are sound wave transmission regions that transmit sound waves incident from one surface side to the opposite side. On the upper surface of the acoustic structure 1, the reflection surface 2 is configured to be adjacent to the opening surfaces 20-1 to 20-4, and radiates reflected waves to the external space according to sound waves incident from the external space. It is a reflection area. The upper surface of the acoustic structure 1 including the opening surfaces 20-1 to 20-4 and the reflection surface 2 functions as a reflector.
In the following, for convenience of explanation, as shown in FIG. 1, one direction parallel to one side of the reflection surface 2 of the acoustic structure 1 is referred to as an “x direction”, and a direction orthogonal thereto is a “y direction”. And Moreover, it is the normal line direction of the reflective surface 2, and let the thickness direction of the acoustic structure 1 be a “z direction”.

FIG. 3 is a view showing a cross section when the acoustic structure 1 is cut along the yz plane, and FIG. 3A is a view showing a cross section when cut along the cutting line III-III shown in FIG. FIG. 5B is a diagram showing a cross section taken along the cutting line IV-IV shown in FIG.
As shown in FIG. 3, four isolated hollow regions 30-1, 30-2, 30-3, and 30-4 are formed inside the acoustic structure 1, as shown in FIG. 2. A partition is provided at the position of the dotted line, and each is separated. The hollow regions 30-1 to 30-4 communicate with the external space through holes passing through the opening surfaces 20-1 to 20-4, respectively. The hole 21-1 passes through the opening surface 20-1, and communicates the hollow region 30-1 of the acoustic structure 1 and the external space. The hole 21-2 passes through the opening surface 20-1, The hollow region 30-2 communicates with the external space. The hole 21-3 communicates the hollow region 30-3 and the external space through the opening surface 20-3, and the hole 21-4 passes through the opening surface 20-4. And external space. Moreover, the area of the opening surfaces 20-1 to 20-4 is S, and the cross-sectional area when the positions of the hole portions 21-1 to 21-4 are cut along the xy plane is also S.

In the acoustic structure 1, portions corresponding to the hole portions 21-1 to 21-4 and the hollow regions 30-1 to 30-4 function as Helmholtz resonators as sound wave emission means. These function as Helmholtz resonators with the gas in the holes 21-1 to 21-4 as mass components and the gas layers of the hollow regions 30-1 to 30-4 as closed spaces as spring components. A spring mass system is formed. The volumes of the gas layers in the hollow regions 30-1 to 30-4 are V ₁ , V _2, V ₃ , and V ₄ , respectively, and the resonance frequencies f ₀₁ , f ₀₂ , f ₀₃ , and f ₀₄ of the acoustic structure 1 are The relationship of the formula (1) is satisfied. However, in the formula (1), c represents a sound velocity, L _e denotes the effective length of the hole 21 - 1 to 21 -. As shown in FIG. 3, the effective length _Le is a value obtained by correcting the distance from the boundary surface between each hole and the hollow region to the opening surface that is the boundary surface with the external space by opening edge correction. Then, the effective length is the same for each resonator.
f _0i = c / 2π · (S / L _e · V _i ) ^1/2 (i = 1, 2, 3, 4) (1)

Here, V ₁ ≠ V ₂ ≠ V ₃ ≠ V ₄ , and the acoustic structure 1 has four different resonance frequencies from the relationship shown in Expression (1). The configuration of the acoustic structure 1 is as described above.
The acoustic structure 1 having such a configuration exhibits a high sound absorption effect and a scattering effect that scatters sound in a frequency band including the resonance frequencies f _{01 to} f ₀₄ .

  Next, the sound absorption effect and the scattering effect obtained by the acoustic structure 1 will be described. Each Helmholtz resonator has the same structural characteristics except that the resonance frequency is different. Therefore, below, each structure which comprises a resonator is demonstrated generically as "opening surface 20", "hole 21", and "hollow area | region 30".

The acoustic structure 1 exhibits a sound absorption effect and a scattering effect when it can be considered that a resonance phenomenon occurs in the Helmholtz resonator. Then, the effect | action which concerns on the sound absorption and scattering of the acoustic structure 1 is demonstrated.
Here, the specific acoustic impedance ratio ζ when the incident wave is incident from the external space in the direction perpendicular to the opening surface 20 (z direction) satisfies the relationship of Expression (2). However, ρ represents the density of the medium (air) of the opening surface 20, and p ₀ is the sound pressure in the opening surface 20, and the sound pressure of the incident wave and the Helmholtz resonator depending on the sound pressure. This is the sound pressure obtained by synthesizing the sound pressure of the reflected wave radiated by resonance by the functioning hollow region 30. u ₀ is the particle velocity of gas molecules acting in the normal direction of the opening surface 20, and the velocity acting in the direction of the external space from the opening surface 20 is expressed as a positive value, and the direction from the opening surface 20 to the hollow region 30 The speed acting on is expressed as a negative value. t is a variable representing time.

As shown in Expression (2), the specific acoustic impedance ratio ζ is a value obtained by dividing the specific acoustic impedance p ₀ / u ₀ of the opening surface 20 by the characteristic impedance ρc of the medium (air) of the opening surface 20. In short, the specific acoustic impedance ratio ζ is a value representing the ratio between the specific acoustic impedance at a certain point in the sound field and the characteristic impedance of the medium at that point. However, the characteristic impedance (specific acoustic resistance) of the external space in contact with the opening surface 20 is synonymous with the characteristic impedance of the opening surface 20 here. When an incident wave belonging to the resonance frequency is incident in a direction perpendicular to the opening surface 20, a reflected wave generated by the resonance is generated from the hollow region 30 according to the magnitude of the specific acoustic impedance ratio ζ that satisfies the relationship of Expression (2). It is radiated to the external space through the opening surface 20.

  Here, the specific acoustic impedance ratio ζ = r + jx is determined. r is a real part (that is, Re (ζ)) of the specific acoustic impedance ratio ζ, and is a value sometimes referred to as a specific acoustic resistance ratio. x is an imaginary part (that is, Im (ζ)) of the specific acoustic impedance ratio ζ, and is a value sometimes called a specific acoustic reactance ratio. Next, the relationship between the specific acoustic impedance ratio ζ and the reflected wave will be described.

(I) When ζ = 0, that is, r = 0 and x = 0 When an incident wave is incident on a region satisfying ζ = 0 (r = 0 and x = 0), the incident wave is generated as a reflected wave caused by resonance. The reflected wave having the same amplitude and the phase shifted by 180 ° is emitted from the region. Accordingly, the incident wave and the reflected wave act so as to completely cancel each other's amplitude due to interference. Such resonance is called “complete resonance”.
(II) When ζ = 1, that is, when r = 1 and x = 0 When an incident wave enters a region satisfying ζ = 1 (r = 1 and x = 0), no reflected wave is emitted from the region. . This phenomenon is called “complete sound absorption”.
(III) When ζ = ∞, that is, r = ∞ and x = 0 When an incident wave enters a region (that is, a rigid body) that satisfies ζ = ∞ (r = ∞ and x = 0), A reflected wave having the same amplitude as that of the incident wave and having no phase shift (the phase shift is 0 °) is emitted. In this case, the incident wave and the reflected wave interfere to generate a standing wave. This phenomenon is called “complete reflection”.

  In (I) above, r = 0, and the acoustic structure 1 does not have a resistance component, but the acoustic structure 1 may have a resistance component. In this case, when a sound wave having a resonance frequency of the Helmholtz resonator is incident on the hollow region 30, the real part r of the specific acoustic impedance ratio ζ at the opening surface 20 is 0, as in the cases (II) and (III), for example. May take a non-value. At this time, when an incident wave is incident perpendicular to the opening surface 20, the amplitude of the reflected wave generated by resonance radiated from the opening surface 20 is attenuated according to the resistance component of the acoustic structure 1. To do. In this way, in addition to the case of complete resonance where the specific acoustic impedance ratio ζ of the opening surface 20 is 0, it can be considered that a “resonance phenomenon” in which the resonance body emits a reflected wave due to resonance has occurred. There is.

  By the way, the specific acoustic impedance ratio ζ = r + jx and the complex sound pressure reflection coefficient R = | R | exp (jφ) at a point in a region on a certain member have a relationship of R = (ζ−1) / (ζ + 1). Meet. The complex sound pressure reflection coefficient is a physical quantity that represents a complex number ratio between a reflected wave and an incident wave at a certain point in space. | R | is a value representing the relative amplitude of the reflected wave with respect to the incident wave, and means that the larger the value, the larger the amplitude of the reflected wave. φ is a value (hereinafter referred to as “phase change amount”) indicating the magnitude of the phase change of the reflected wave with respect to the incident wave. As is clear from the above relational expression, if one of the specific acoustic impedance ratio ζ and the complex sound pressure reflection coefficient R is determined, the other is also uniquely determined. For example, when ζ = 0 (that is, complete resonance), R = −1, and the reflected wave at this time has an opposite phase to the incident wave, and the amplitude is the same. When ζ = 1 (that is, complete sound absorption), R = 0. At this time, the reflected wave is not radiated and its amplitude is zero. When ζ = ∞ (that is, complete reflection), R = 1, and the reflected wave at this time has the same phase as the incident wave, and the amplitude is the same.

Next, the sound absorption / scattering effect produced by the resonance phenomenon will be described separately from the viewpoint of phase and the viewpoint of amplitude. The sound absorbing effect is an effect produced by the reflected wave radiated from the opening surface 20 by the acoustic structure 1, and the scattering effect is reflected from the reflected wave radiated from the opening surface 20 by the acoustic structure 1 and the reflecting surface 2. This is an effect produced by the interaction with the radiated reflected wave. The operation for achieving these effects will be described in detail later.
First, it demonstrates from a viewpoint of a phase.
FIG. 4 is a graph showing the relationship between the specific acoustic impedance ratio ζ and the phase change amount φ. In this graph, the horizontal axis represents r = Re (ζ) which is the real part of the specific acoustic impedance ratio ζ, and the vertical axis represents x = Im (ζ) which is the imaginary part of the specific acoustic impedance ratio ζ. In the figure, at the point where ζ = ∞, the distance from the origin is ∞. At this time, the complete reflection occurs, and the phase change amount φ becomes 0 °.

  When | ζ | <1, it is represented by a hatched area in FIG. 4, and the phase change amount φ in this case is larger than 90 °. When this condition is satisfied, the phase change amount φ approaches ± 180 ° as the value of | ζ | decreases. More specifically, when x = Im (ζ)> 0, the phase change amount φ approaches 180 °, and when x = Im (ζ) <0, the phase change amount φ approaches −180 °. To go. Further, when the point is located on the horizontal axis and 0 ≦ Re (ζ) <1 and Im (ζ) = 0, the above-described complete resonance occurs and the phase change amount φ becomes ± 180 °. In this way, the area shown by hatching in the graph shown in FIG. 4 is represented by an area (not including the area on the line) expressed inside the circle whose radius is “1” with the origin at the center. In the case of the value of ζ, the sound absorption effect due to the phase interference between the incident wave and the reflected wave can be exhibited particularly effectively. On the other hand, when the value of | ζ | is 1 or more, for example, as indicated by the broken line in FIG. 4, the phase change amount φ is smaller than 90 °. In this region, a sound absorbing effect can be obtained, but the sound absorbing effect due to phase interference is lower than when the value of | ζ | is less than 1. As for the scattering effect, there is a phase difference that is not in phase between the reflected wave radiated from the aperture surface 20 and the reflected wave radiated from the reflective surface 2, and the effect becomes more prominent as the phase relationship is particularly close. Play. Therefore, the effect of the scattering effect is exhibited even when the value of | ζ | is 1 or more, but it is preferable that | ζ | <1, more preferably | ζ | It is preferable that the condition where the phase change amount φ is close to ± 180 ° is realized.

  That is, in the resonance phenomenon for producing the sound absorption / scattering effect, it is ideal that Im (ζ) = 0 so that φ = ± 180 °, but 90 ° ≦ φ ≦ 180 ° or − If the relationship of 180 ° ≦ φ ≦ −90 ° is satisfied, that is, if the value of | ζ | is less than 1, the sound absorption / scattering effect by resonance is effectively exhibited. Further, under the condition that the value of | ζ | is less than 1, more preferably, 135 ° ≦ φ ≦ 180 ° or −180 ° ≦ φ ≦ −135 ° is satisfied, and further preferably 160 ° ≦ φ ≦. It is preferable that the condition of 180 ° or −180 ° ≦ φ ≦ −160 ° is satisfied.

Then, it demonstrates from a viewpoint of an amplitude.
FIG. 5 is a graph showing the relationship between the specific acoustic impedance ratio ζ and the amplitude | R | of the complex sound pressure reflection coefficient. In the figure, Re (ζ when taking values of | R | = 0.0, 0.1, 0.3, 0.5, 0.7, 0.8, 0.9, 1.0. ) And Im (ζ). As shown in the figure, when Re (ζ) = 1 and Im (ζ) = 0, | R | = 0, and the amplitude is 0 and the minimum. That is, the complete sound absorption occurs and no reflected wave is generated.
A region indicated by a broken line in FIG. 4 is a region where | ζ | = 1 described with reference to FIG. 4. In this inner region (however, the region on the line is not included), the resonance phenomenon causes There is a phase difference of 90 ° to 180 ° between the incident wave and the reflected wave. In this region, since | R |> 0, the amplitude of the reflected wave exceeds zero.

  Subsequently, when the position is on the vertical axis and Re (ζ) = 0, | R | is 1.0 regardless of the value of Im (ζ). At this time, since a reflected wave having the same amplitude as the incident wave is radiated, from the viewpoint of amplitude, it is most preferable when the sound absorption / scattering effect is achieved under the condition that the phase of the incident wave and the reflected wave is different. As can be seen from the figure, under the condition of Re (ζ) <1, when Im (ζ) is assumed to be constant, the value of | R | increases as the value of Re (ζ) decreases. I understand. That is, when the value of the real part Re (ζ) of the specific acoustic impedance ratio ζ is small, especially when the value is almost 0, the amplitude of the reflected wave is large regardless of the value of Im (ζ). This is suitable for the sound absorption / scattering effect produced by phase interference when the phase of the reflected wave differs from that of the reflected wave.

  In the acoustic structure 1 of this embodiment, the opening surface 20 is directly connected to the Helmholtz resonator. Therefore, the condition of | Im (ζ) | <1 is satisfied in the aperture plane 20 at a frequency near each resonance frequency of the Helmholtz resonator. Therefore, in this case, the phase of the reflected wave from the opening surface 20 is displaced by 90 ° or more with respect to the incident wave. For example, when Re (ζ) = 0.30, since the amplitude of the reflected wave is | R | = 0.54, a reflected wave having an amplitude of 1/2 or more with respect to the amplitude of the incident wave is radiated. . As described above, when both Re (ζ) and Im (ζ) of the opening surface 20 are sufficiently small, the amplitude from the opening surface 20 is sufficient for the reflected wave from the reflecting surface adjacent to the opening surface 20. And a reflected wave having a large phase change can be obtained. Ideally, when Re (ζ) = 0 and Im (ζ) = 0, | R | = 1.0, and the above-described complete resonance in which the amplitudes of the incident wave and the reflected wave are the same is realized. The case where | R | is less than 1.0 will be described in detail as follows.

For example, in the case of | R | = 0.5, approximately 1/4 energy is radiated from the opening surface 20, and also in this case, the sound absorption / scattering effect can be effectively obtained. When Im (ζ) = 0, Re (ζ) ≈0.335, and the value of the real part of the specific acoustic impedance is approximately 139.025 Kg / m ² · sec or less. More preferably, the condition of | R | = 0.7 is satisfied. In this case, approximately ½ energy is radiated from the opening surface 20, and the above-described effect is more strongly exerted. In this case, if Im (ζ) = 0, Re (ζ) ≈0.175, and the value of the real part of the specific acoustic impedance is approximately 72.625 Kg / m ² · sec or less. More preferably, the condition of | R | = 0.9 is satisfied. In this case, approximately 4/5 of the energy is radiated from the opening surface 20, and the sound absorption / scattering effect can be obtained remarkably. In this case, if Im (ζ) = 0, Re (ζ) ≈0.055, and the value of the real part of the specific acoustic impedance is approximately 22.825 Kg / m ² · sec or less.
For example, as shown in FIG. 5, when | R | ≧ 0.7 which is a preferred embodiment, Re (ζ) is about 0.175 or less, and | R | ≧ which is a more preferred embodiment. When 0.9, Re (ζ) is approximately 0.055 or less. Therefore, in view of these results, the acoustic structure 1 is configured so that the value of Re (ζ) is substantially zero. It can be seen that this is suitable for achieving a good sound absorption / scattering effect.

  By the way, in the acoustic structure 1, a member such as a resistance material that inhibits the movement of gas molecules is not provided in the hole 21 or the hollow region 30 constituting the Helmholtz resonator. Thereby, a large particle velocity generated by the resonance of the Helmholtz resonator can be generated on the opening surface 20. Further, because the resonance of the Helmholtz resonator adjacent to the opening surface 20 satisfies the condition | ζ | <1 at the opening surface 20, the sound pressure at that place becomes considerably low due to the occurrence of the resonance phenomenon (ideal 0). In the acoustic structure 1, the real number of the specific acoustic impedance ratio ζ at the opening surface 20 is obtained by causing the phenomenon that the particle velocity of gas molecules is high and the sound pressure is low on the opening surface 20 by the resonance of the Helmholtz resonator. The condition that the part r = Re (ζ) is almost zero is realized. As described above, the value of Re (ζ) is preferably closer to 0. However, according to the configuration of the acoustic structure 1, the condition can be realized by resonance of the Helmholtz resonator.

Then, the effect | action for having a sound absorption effect and a scattering effect is demonstrated.
FIG. 6 is a diagram for explaining the behavior of the reflected wave during resonance when the external space around the opening surface 20 of the acoustic structure 1 is viewed from the x direction orthogonal to the yz plane. The figure shows a state where a “mountain” where the sound pressure of the incident wave is maximized perpendicular to the reflecting surface 2 and the opening surface 20 reaches the reflecting surface 2 and a corresponding reflected wave is generated. . However, here, it is assumed that the above-mentioned “complete resonance” occurs when the specific acoustic impedance ratio ζ = 0 of the opening surface 20. In addition, in the same figure, the reflected wave is indicated by a solid line and a broken line, but the solid line indicates the position of the “mountain” where the sound pressure of the reflected wave is maximum, and the broken line indicates the minimum sound pressure ( It represents the position of the “valley” that is the opposite phase.

  When an incident wave belonging to the resonance frequency is incident on the hollow surface 30 of the acoustic structure 1 in a direction perpendicular to the opening surface 20, the hollow region 30 functioning as a Helmholtz resonator is reflected in the incident wave as a reflected wave generated by resonance. On the other hand, a reflected wave having an opposite phase whose phase is displaced by 180 ° is radiated from the opening surface 20 to the external space. Due to this resonance phenomenon, as shown in the figure, the reflected wave at the opening 20 becomes a “valley”, and the sound pressure there is minimal. On the other hand, since the acoustic structure 1 is made of a material having a high rigidity such as acrylic resin as described above, the specific acoustic impedance ratio is considerably large. Therefore, the phase of the reflected wave radiated from the reflecting surface 2 is hardly displaced with respect to the phase of the incident wave. When the reflecting surface 2 is regarded as a rigid body, the above-mentioned “complete reflection” occurs, and the phase of the reflected wave radiated from the reflecting surface 2 is zero displacement with respect to the phase of the incident wave, and the reflected wave having the same phase as the incident wave. Radiate. Therefore, when the specific acoustic impedance ratio ζ of the aperture surface 20 is completely zero and the specific acoustic impedance ratio of the reflective surface 2 is completely reflected at ∞, the phase of the reflected wave on the aperture surface 20 and the reflective surface 2 The phase of the reflected wave is always opposite to that of the reflected wave, and the amplitudes thereof are the same.

FIG. 7 is a diagram showing “mountains” and “valleys” of reflected waves (spherical waves) radiated from the reflecting surface 2 and the opening surface 20 at the time shown in FIG.
Regions C1 and C2 shown in FIG. 6 correspond to the “sound absorption region” shown in FIG. In this sound absorbing region, as in the positions P1 and P2, the “mountain” of the reflected wave from the opening surface 20 and the “valley” of the reflected wave from the reflecting surface 2 overlap or are reflected from the opening surface 20. The “valley” of the wave and the “mountain” of the reflected wave from the reflecting surface 2 overlap. That is, in the “sound absorption region” in the z direction when viewed from the opening surface 20, they overlap with a phase difference that cancels the amplitude of each sound wave due to interference, so that a sound absorption effect by resonance is obtained in this sound absorption region. In particular, when the absolute value | ζ | of the specific acoustic impedance ratio satisfies 0 ≦ | ζ | <1, the reflected waves act so as to cancel each other in accordance with the phase angle, so that sound absorption is particularly effective. An effect is obtained.

  Further, in the regions C1 and C2 in which the reflected wave from the reflecting surface 2 and the reflected wave from the opening surface 20 are adjacent to each other, which are indicated by ellipses in FIG. 6, the phases of the reflected waves of both are discontinuous. Will occur. With the above operation, the sound absorption effect is manifested by the resonance phenomenon in the region near the opening surface 20. The scattering effect is caused by the interaction between the phase interference between the incident wave and the reflected wave incident on the reflecting surface 2 and the phase interference between the incident wave incident on the vicinity of the aperture surface 20 and the reflected wave caused by resonance. Due to this, a flow of gas molecules is generated in the vicinity of the opening surface 20 and appears. As described above, the reflected wave from the opening surface 20 and the reflected wave from the reflecting surface 2 have different phase angles, and different phenomena appear in close proximity according to the phase difference. Therefore, the acoustic structure 1 According to this, sound scattering and sound absorption can be expressed simultaneously.

FIG. 8 is a diagram schematically illustrating how acoustic energy propagates in each direction viewed from the opening surface 20. Here, the state of propagation of acoustic energy on the yz plane will be described, and an acute angle (angle θ) forming each direction on the yz plane viewed from the center point O of the opening surface 20 with the y direction will be used. Represent.
As shown in the figure, the sound absorption region shown in FIG. 7 is formed in a region near θ = 90 ° when viewed from the opening surface 20, and is formed as a region having a small acoustic energy to propagate. As a result, a high sound absorption effect is obtained in that region, and also contributes to suppression of acoustic disturbance such as coloration (flutter) between parallel reflecting surfaces. On the other hand, the smaller the angle θ shown in FIG. 8 is, the larger the acoustic energy is propagated, and the energy is particularly large in the region in the direction of 45 ° ≦ θ ≦ 90 °. This is because the flow of gas molecules is caused by the phase difference between the reflected wave from the opening surface 20 and the reflected wave from the reflection surface 2, and this gas molecule flow causes the particle velocity to be x. This is because it has a relatively large velocity component in the direction and the y direction. Therefore, a good scattering effect can be obtained in the direction where θ is small as in the “scattering region” shown in FIG.

According to the acoustic structure 1 of the embodiment described above, the phase interference between the incident wave and the reflected wave incident on the reflecting surface 2 and the phase interference between the incident wave incident on the vicinity of the opening surface 20 and the reflected wave caused by resonance. As a result, the flow of kinetic energy of gas molecules is generated in an oblique direction that is not orthogonal to the reflecting surface 2 and the opening surface 20, and a scattering effect is obtained. Further, in the external space near the opening surface 20 due to the resonance phenomenon, a sound absorption effect is also obtained by the reflected wave from the opening surface 20 canceling the amplitude of the incident wave to the opening surface 20 due to the phase difference.
The configuration for radiating sound waves from the aperture 20 may be a simple resonator such as a Helmholtz resonator, and the resonance frequency of the Helmholtz resonator is different from f _{01 to} f _04. Therefore, a high sound absorption effect is achieved in a wide frequency band including them. Further, if the absolute value | ζ | of the specific acoustic impedance ratio of the opening surface 20 is reduced, a sound absorption effect and a scattering effect are exhibited in a wider frequency band, and the progress of the incident wave with respect to the acoustic structure. A scattering effect can be produced also in the direction of the direction and the angle θ (for example, near 0 degrees), and the scattering effect can be expressed in a wide angle region.
Therefore, according to such an acoustic structure 1, sound can be scattered and a sound absorption effect can be obtained in a wide frequency band by the acoustic member that suppresses the increase in size.

[Second Embodiment]
Subsequently, a second embodiment of the present invention will be described.
The acoustic structure 1a of the second embodiment is configured to radiate sound waves from the acoustic unit to the external space instead of the Helmholtz resonator as the sound wave radiating means in the acoustic structure 1 of the first embodiment. . That is, the sound wave behavior equivalent to that when the sound absorption effect and the scattering effect described in the first embodiment are expressed is realized by the control of the acoustic unit. In addition, in the following description, about the structure which is the same as that of the acoustic structure 1 of 1st Embodiment, or respond | corresponds, an equivalent function is implement | achieved and the detailed description is abbreviate | omitted. In addition, about the structure corresponding to the acoustic structure 1, "a" is attached | subjected and shown to the end of a code | symbol.

  FIG. 9 is a view of the acoustic structure 1a viewed from a direction perpendicular to the reflecting surface 2a (the same direction as the arrow II direction in FIG. 1). As shown in the figure, the acoustic structure 1a is provided with one opening surface 20a which is a sound pressure transmission surface near the center of the reflection surface 2a. Although not shown, the acoustic structure 1a is a rectangular parallelepiped member having a small length in the thickness direction, and an internal space (hollow region) is formed.

FIG. 10 is a diagram showing a cross section near the opening surface 20a and a configuration around it when the acoustic structure 1a is cut along the cutting line VIII-VIII (yz plane) shown in FIG. As shown in the figure, in the acoustic structure 1a, in the internal space of the acoustic structure 1a with which the opening surface 20a contacts, the space opposite to the external space with respect to the opening surface 20a includes a housing 40, A microphone 50, speakers 60 and 60, and a control device 70 are provided. In the acoustic structure 1a, the microphone 50, the speakers 60 and 60, and the control device 70 constitute an acoustic unit (sound radiating means). The reflection surface on the upper surface of the acoustic structure 1a is referred to as “reflection surface 2a”.

  The housing 40 is a box-shaped member whose upper surface is open, and the internal space communicates with the external space through the hole 21a passing through the opening surface 20a and the opening surface 20a. Speakers 60 and 60 are accommodated in the housing 40. The casing 40 is preferably formed of a material having a certain level of sound insulation so that sound waves from the speakers 60, 60 do not leak from other than the opening surface 20a. The microphone 50 is, for example, a small condenser microphone, and is sound collection means provided in an external space near the opening surface 20a. The microphone 50 generates an audio signal representing the collected audio and supplies it to the control device 70. The speaker 60 is sound emitting means, and radiates sound waves corresponding to the sound signal supplied from the control device 70 to the external space. The speakers 60, 60 have a speaker box and a speaker unit housed in the speaker box, and are provided so as to face each other. The control device 70 includes an audio processing circuit (equalizer or the like) that generates an audio signal by controlling the amplitude and phase of the audio signal supplied from the microphone 50, an amplifier circuit, and the like. The control device 70 performs control to emit sound waves by supplying the generated audio signal to the speakers 60 and 60.

Next, control of the control device 70 will be described.
The control device 70 performs control for generating the same phenomenon as the behavior of the sound wave shown in FIG. 6 based on the sound representing the reflected wave collected by the microphone 50. That is, when the reflection surface 2a radiates a reflected wave to the external space according to the sound wave incident on the upper surface of the acoustic structure 1a from the external space, the control device 70 has a phase on the reflection surface 2a that reflects the reflected wave. 2a, and a sound wave having a real part of a value obtained by dividing the specific acoustic impedance of the aperture surface 20a at that time by the characteristic impedance of the medium of the aperture surface 20a is substantially zero through the aperture surface 20a. The speakers 60 and 60 are controlled so as to be radiated to each other. A sound wave having a preferable phase as a sound wave to be radiated to the speaker 60 by the control device 70 is a sound wave having an absolute value | ζ | of the specific acoustic impedance ratio at the opening surface 20a of 0 ≦ | ζ | <1, and more preferably a reflected sound wave. It is a sound wave having an opposite phase on the aperture surface 2a with respect to the phase of the reflected wave on the surface 2a. Regarding the amplitude, it is preferable that the control device 70 causes the speaker 60 to emit a sound wave having an amplitude as close as possible to the sound wave incident on the upper surface of the acoustic structure 1a.

For example, in the case of realizing the same sound wave behavior as that in the case where “complete resonance”, which is a preferred embodiment, is realized, the control device 70 analyzes the sound signal supplied from the microphone 50 and enters the aperture surface 20a. Specify the phase of the incident wave. And the control apparatus 70 is the phase control which radiates | emits the sound wave which becomes an antiphase in the opening surface 20a from the opening surface 20a with respect to the phase of the reflected wave in the reflective surface 2a, and the amplitude control which makes the amplitude of both sound waves correspond. Voice processing including (
Control). In addition, since the rigidity of the reflecting surface 2a is high, assuming that the phase of the incident wave and the phase of the reflected wave are the same phase, the reflecting surface 2a as shown in FIG. When the sound pressure is a “mountain” at which the sound pressure is maximum, a sound wave behavior can be realized in which a sound wave that radiates a “valley” at which the sound pressure is minimized at the opening surface 20a is emitted.

  By controlling the acoustic unit of the acoustic structure 1a described above, a high sound absorption effect can be obtained and sound can be effectively scattered in the external space around the opening surface 20a. Further, since the control device 70 performs the above-described control based on the sound collected by the microphone 50, the control for realizing the behavior of the sound wave close to complete resonance as shown in FIG. 6 can be relatively easily performed. Further, since the control device 70 can also control the frequency band in which the above control is performed, the control device 70 can control the sound wave in the frequency band in which the sound absorption effect and the scattering effect are desired, and the resonance body. The size of the entire acoustic structure can be made smaller than when it is used.

[Summary of Embodiment]
As described above, according to the acoustic structure according to the first and second embodiments of the present invention, the sound absorption effect and the sound emission effect due to the actions described in the first and second embodiments can be expressed. it can. Therefore, as long as the same phenomenon can be created, any configuration of the sound wave emitting means for emitting sound waves under the above conditions may be used. Therefore, the Helmholtz resonator and the acoustic unit of the first and second embodiments described above are merely examples of sound wave radiating means.
Further, without providing the acoustic structure 1, 1a with a member that prevents vibration of gas molecules such as a resistance material in the acoustic structure, the particle velocity of the gas molecules on the opening surfaces 20, 20a is intentionally increased, and the sound absorption effect is increased. By reducing the sound pressure at the place, a high sound absorption / scattering effect is developed in the vicinity of the area. In addition, when the resistance material is provided, the resonance frequency moves or the sharpness of the resonance changes, so that a problem occurs when it is desired to strictly control the resonance frequency and the sound absorption effect. For this reason, by not providing the resistance material, it is possible to strictly control the sound absorption / scattering effect, and it is possible to easily design the sound absorption structure. It is expected to be applied to the development of future acoustic members based on the knowledge obtained by the present invention.

[Modification]
The present invention can be implemented in a form different from the above-described embodiment. The present invention can also be implemented in the following forms, for example. Further, the following modifications may be combined as appropriate.
[Modification 1]
In the acoustic structure 1 according to the first embodiment described above, a Helmholtz resonator is configured as a resonator that emits sound waves to the external space via the opening surface 20, but the resonator provided in the acoustic structure is provided. The type of is not limited to this. For example, tube resonance may be used.
FIG. 11 is a view showing a cross section when an acoustic structure having a shape equivalent to that of the acoustic structure 1 of FIG. 1 is cut along a yz plane including the opening surface 20. FIG. 12 is a diagram illustrating a resonator according to this modification.
The three tubular members 80, 81, 82 are accommodated in the internal space of the acoustic structure, and as shown in FIG. 11, the opening surfaces 90, 91, 92 are parallel to the opening surface 20, and the extending direction is reflected. It is provided so as to be perpendicular to the surface 2. Moreover, as shown in FIG. 11, each of the tubular members 80, 81, 82 is a closed tube with one end opened and the other end closed, and cylindrical cavities 100, 101, 102 are formed respectively. The lengths in the extending direction are different for l ₁ , l ₂ , and l ₃ , respectively, and the resonance frequencies f of the tubular members 80, 81, and 82 satisfy the relational expression (2). In Equation (2), c is the propagation speed of the sound wave, and n is an integer of 1 or more, and the aperture end correction is ignored here.
f = (2n−1) · c / 4l _i (i = 1, 2, 3) (2)

Here, one end of each of the tubular members 80, 81, and 82 is closed. However, an open tube having both ends opened may be used, and the resonance frequency f in this case is expressed by the relational expression (3). Fulfill. Here, the open end correction is ignored.
f = n · c / 2l _i (i = 1, 2, 3) (3)

    Even in such a configuration using tube resonance, a phenomenon that can be regarded as resonance occurs. Thereby, the sound absorption effect and the scattering effect by the same effect | action as embodiment can be acquired. Of course, other resonators may be used.

[Modification 2]
In the first and second embodiments described above, one surface of the acoustic structure is used as a reflection surface. However, an opening surface is provided on the surface opposite to the surface, and both surfaces of the acoustic structure are described in the embodiment. The sound absorption effect and the scattering effect may be obtained. Further, the acoustic structure may not be a rectangular parallelepiped shape, and any shape or size may be used, and the shape of the opening surface may be a shape such as a circle or a polygon. In addition, the acoustic structure may have a plurality of surfaces facing different directions, such as a polyhedron, and an opening surface may be provided there to form a sound absorption region and a scattering region in a plurality of directions. Good.
In addition, the acoustic structure has a rectangular parallelepiped shape in which an internal space is formed, but the surface opposite to the reflecting surfaces 2 and 2a does not contribute to the sound absorption effect and the scattering effect. Therefore, for example, an acoustic structure in which a sound wave radiating means such as a resonator is provided behind a plate-like reflector having a sound pressure transmission region that is an opening surface and a reflection surface (reflection region) adjacent thereto. You can also
In addition, the opening surface has sound pressure permeability and air permeability (particle velocity permeability), and the resistance component is sufficiently small with respect to the specific acoustic resistance of the medium (air). The sound wave transmitting region that transmits sound waves may be a region that transmits sound waves incident from one side to the other side, and an open configuration is not essential.

[Modification 3]
In the first embodiment described above, the reflective surface 2 is provided with four opening surfaces 20-1 to 20-4, and a Helmholtz resonator that radiates reflected sound due to resonance is provided for each of them. The number of the hollow regions constituting the opening surface and the Helmholtz resonator may be any number, and the position may be anywhere. For example, if the number of resonators and apertures is increased, the sound absorption effect and the scattering effect can be obtained in a wider area, and the area where these effects are exerted varies depending on the position of the aperture, so the installation of the acoustic structure It can be freely changed according to the position, application and the like.
Further, the inventors have a distance from the center point (center of gravity) of the opening surface 20 (for example, a square having a side of 50 mm) to about 100 mm for a component on the xy plane, that is, about twice the size of the opening surface 20. It was confirmed that the sound absorption rate in the distance range was equal to or greater than the threshold value, and that a high sound absorption effect was exhibited. Therefore, if the opening surfaces are provided at intervals of a predetermined distance or less over which the sound absorption coefficient is greater than or equal to the threshold over the entire reflection surface 2, a high sound absorption effect can be obtained in the external space around the reflection surface 2 side of the acoustic structure. Can be obtained. Therefore, according to the confirmation of the inventors, the distance from the center point to the center point of the adjacent opening surfaces may be set at a distance approximately four times the size of the opening surfaces.

In the second embodiment described above, the number and installation positions of the speakers 60 are not limited to those of the embodiment, and the number of speakers 60 may be larger or smaller. Alternatively, a plurality of opening surfaces 20a may be provided in the acoustic structure 1a, and acoustic units that emit sound waves from each opening surface may be provided separately. If it does in this way, a sound wave can be radiated | emitted on optimal conditions according to each position of an acoustic structure. Also in this case, if the number of acoustic units and opening surfaces is increased, the sound absorbing effect can be obtained in a wider space, and the region where the sound absorbing effect is exhibited can be freely changed depending on the position of the opening surface. .
In addition, a single acoustic structure may be provided with both a resonator (Helmholtz resonator) as described in the first embodiment and an acoustic unit as described in the second embodiment.

[Modification 4]
In the second embodiment described above, the reflecting surface may not be planar, for example, a convex portion or a concave portion may be formed, and the surface shape thereof may be any. In this case, the direction in which the reflected wave travels varies depending on the surface shape of the reflecting surface. Therefore, the propagation direction of the reflected wave on the reflection surface coincides with the propagation direction of the opening surface of the sound wave radiated from the speaker 60, and a region where the phase is discontinuous is formed like regions C1 and C2 shown in FIG. The installation conditions such as the installation position and installation direction of the speaker 60 may be determined according to the surface shape. However, also in this case, the control device 70 performs control such that sound waves having different phases on the opening surface 20 are radiated with respect to the phase of the reflected wave on the reflecting surface 2a.

[Modification 5]
It is good also as a structure which performs control which a control apparatus changes the radiation | emission direction of the sound wave radiated | emitted from the opening surface 20a.
In this configuration, the sound emitting means for radiating the sound wave to the external space is, for example, a structure in which the speaker is rotatably provided and the speaker is rotated by a driving means such as a motor. So that the radiation direction can be changed. Then, when the control device specifies the sound wave radiation direction, for example, by indicating the sound absorption region and the direction in which the scattering effect is desired to be expressed from the external device (for example, the angle θ), the driving unit is activated based on the specified radiation direction. The sound wave is emitted after controlling and changing the radiation direction of the sound wave by the speaker.
Also, in this configuration, depending on the installation purpose such as the shape of the space in which the acoustic structure is installed, the installation environment conditions such as dimensions, materials such as wall surfaces, and the sound absorption efficiency and scattering efficiency for which direction, It is good also as a structure in which a control apparatus changes the radiation | emission direction of a sound wave. For example, the control device stores in advance the angle at which sound waves are emitted in association with installation environment conditions and installation purposes. And a control device specifies the angle which emits a sound wave based on the correspondence, and makes a sound wave emit in the direction. For example, if the sound field has little sound scattering in the direction of θ = 70 to 90 ° when viewed from the center point O of the aperture plane, the control device controls the radiation direction of the sound wave so that a scattering region is formed there. To do. In this configuration, when the surface shape of the reflecting surface is uneven as in the configuration of the modification example 4, the control device acquires shape information representing the shape, and the shape information and the reflection on the reflecting surface are obtained. Calculation may be performed using phase information representing the phase of the wave, and the sound wave radiation direction by the speaker may be obtained by calculation.

[Modification 6]
In the first and second embodiments described above, the case has been described in which the opening surface of the acoustic structure is installed on the inner wall surface or ceiling surface of the acoustic chamber so as to face the acoustic space that is the external space. On the other hand, the acoustic structure may be installed by being embedded in the wall surface or the ceiling. Moreover, you may be comprised as a movable panel body by providing moving means, such as a caster, on the side surface of the acoustic structure.
[Modification 7]
The acoustic structure according to the embodiment or the modification described above can be disposed in various acoustic chambers that control acoustic characteristics. Here, the various acoustic rooms are a soundproof room, a hall, a theater, a listening room for audio equipment, a room such as a conference room, a space for various transport equipment, a housing for speakers, musical instruments, and the like.
The control performed by the acoustic structure control device according to the second embodiment or the modification may be performed by cooperation of a plurality of hardware.

DESCRIPTION OF SYMBOLS 1, 1a ... Acoustic structure, 2, 2a ... Reflection surface, 20, 20a ... Opening surface, 21 ... Hole, 30 ... Hollow area, 40 ... Housing, 50 ... Microphone, 60 ... Speaker, 70 ... Control device, 80, 81, 82 ... tubular member, 90, 91, 92 ... open face, 100, 101, 102 ... cavity

Claims (3)

A plurality of wave transmittable region transmitting sound waves, adjacent to the wave transmittable region, the reflected wave corresponding to the acoustic waves incident possess a reflection region for emitting, the sonic transmissive region and the reflective region to scatter sound A reflector facing the space of interest ;
When the reflection region emits a reflected wave to the space according to the sound wave incident on the reflector from the space, the phase of the sound wave transmission region is different from the phase of the reflection wave in the reflection region, and the sound wave A sound wave radiating unit that radiates a sound wave having a real part of a value obtained by dividing the specific acoustic impedance in the transmission region by the characteristic impedance of the medium in the sound wave transmission region to approximately 0 through the sound wave transmission region; ,
The distance between the center points of the adjacent sound transmission regions is a distance approximately four times the length of the sound transmission region in the adjacent direction. When sound waves having a predetermined frequency band is incident from the space via the wave transmittable region, be provided with a reflected wave generated by resonance corresponding to the sound waves, the resonator for radiating through the wave transmittable region between those spatial The acoustic structure according to claim 1 . Sound collection means;
A sound emitting means for emitting sound waves into said space via the wave transmittable region,
The analyzes the audio signal collected by the sound collecting unit, the identifying sound waves phase incident on the reflector from between the previous picked up Kisora that the sound pickup means, based on the specified phase, The phase in the sound wave transmission region is different from the phase in the reflection region of the reflected wave, and the real part of the value obtained by dividing the specific acoustic impedance in the sound wave transmission region by the characteristic impedance of the medium in the sound wave transmission region is substantially 0. The acoustic structure according to claim 1, further comprising: a control unit that controls the sound emitting unit so as to radiate sound waves to be emitted.

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