Helmholtz resonator

Abstract

To reduce a change amount of a resonance frequency due to adjustment of neck length in a Helmholtz resonator.SOLUTION: A Helmholtz resonator 1A includes: a cavity part 10; and a neck part 20A which communicates an inner space 11 of the cavity part 10 to an outer space 31 and whose opening area of an opening end on an outer space 31-side is wider compared to an opening area of an opening end of an inner space 11-side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a Helmholtz resonator suitable for an acoustic device or the like. [Background technology]

[0002] Helmholtz resonators are used in various acoustic devices such as bass reflex speakers. The Helmholtz resonator is a resonator consisting of a cavity and a neck that connects the internal space of the cavity to the external space. To perform acoustic tuning using the Helmholtz resonator, it is necessary to adjust the resonant frequency of the Helmholtz resonator to match the frequency to be tuned.

[0003] Thus, the Helmholtz resonator of Patent Document 1 (called a Helmholtz damper in Patent Document 1) has an enclosure with a neck extending therefrom. A pipe is inserted into and fits into the neck. In this Helmholtz resonator, the pipe can be rotated to move within the neck, thereby adjusting the neck length. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-2501 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the resonance frequency of the Helmholtz resonator changes significantly when the neck length is adjusted. In order to adjust the resonance frequency with sufficient precision using the technique disclosed in Patent Document 1, it is necessary to improve the mechanical precision of each part of the Helmholtz resonator, which results in a problem that the Helmholtz resonator becomes expensive.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide a technical means for reducing the amount of change in resonance frequency caused by adjustment of the neck length in a Helmholtz resonator. [Means for solving the problem]

[0007] The present invention provides a Helmholtz resonator comprising a cavity portion and a neck portion that connects the internal space of the cavity portion with an external space, the opening area of ​​the opening end of the neck portion facing the external space being larger than the opening area of ​​the opening end facing the internal space. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing the configuration of a Helmholtz resonator according to a first embodiment of the present invention. [Diagram 2] FIG. 4 is a cross-sectional view showing the configuration of a Helmholtz resonator according to a first modified example of the embodiment. [Diagram 3] FIG. 11 is a cross-sectional view showing the configuration of a Helmholtz resonator according to a second modified example of the embodiment. [Figure 4] 4 is a cross-sectional view showing the configuration of a Helmholtz resonator according to a second embodiment of the present invention. FIG. [Diagram 5] FIG. 2 is an enlarged cross-sectional view of the Helmholtz resonator. [Figure 6] FIG. 4 is a cross-sectional view showing the configuration of a Helmholtz resonator according to a third embodiment of the present invention. [Figure 7] FIG. 11 is a cross-sectional view showing the configuration of a Helmholtz resonator according to a fourth embodiment of the present invention. [Figure 8] FIG. 1 is a diagram showing an example of use of a Helmholtz resonator. [Figure 9] FIG. 1 is a diagram showing an example of use of a Helmholtz resonator. [Figure 10] FIG. 1 is a diagram showing an example of use of a Helmholtz resonator. [Figure 11] FIG. 1 is a diagram showing an example of use of a Helmholtz resonator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] First Embodiment 1 is a cross-sectional view showing the configuration of a Helmholtz resonator 1A according to a first embodiment of the present invention. This Helmholtz resonator 1A includes a cavity portion 10 and a neck portion 20A that connects an internal space 11 of the cavity portion 10 to an external space 31. The neck portion 20A has an opening area S2 of an opening end on the external space 31 side that is larger than an opening area S1 of an opening end on the internal space 11 side. The shape of the cavity portion 10 is arbitrary, and can be, for example, a three-dimensional shape such as a sphere or a rectangular parallelepiped.

[0011] More specifically, in this embodiment, the neck portion 20A has a first neck portion 21A on the inner space 11 side, which has a uniform opening area S1 along the axial direction, and a second neck portion 22A on the outer space 31 side, which has a uniform opening area S2 along the axial direction. In the illustrated example, the first neck portion 21A has a neck length l1, and the second neck portion 22A has a neck length l2. Here, the axial direction is the direction in which the first neck portion 21A and the second neck portion 22A extend. When the first neck portion 21A and the second neck portion 22A have an axially symmetrical shape, the direction of the symmetry axis is the axial direction. The cross-sectional shape of the first neck portion 21A and the second neck portion 22A is arbitrary, and can be, for example, a polygon (e.g., a rectangle), a circle, an ellipse, or the like.

[0012] The resonant frequency of the Helmholtz resonator 1A will be described below. In the Helmholtz resonator 1A shown in FIG. 1, the following continuity equation holds for the position x1 of an air particle in the first neck 21A and the position x2 of an air particle in the second neck 22A:

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[0013] The kinetic energy K of the air particles in the first neck portion 21A and the second neck portion 22A is given by the following equation:

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[0014] In this embodiment, since the above formula (1) is satisfied and S2>S1, the second term on the right side of formula (2) becomes smaller, and the kinetic energy of the air particles in the second neck portion 22A per unit neck length becomes smaller, which reduces the dependency of the resonant frequency on the neck length.

[0015] Moreover, the potential U of the air particles in the Helmholtz resonator 1A is expressed by the following equation.

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[0016] Next, the Lagrangian equation is applied to the kinetic energy K in equation (2) and the potential U in equation (3). Here, the Lagrangian equation is the partial differential equation of the following equation (5) that holds when the Lagrangian L shown in the following equation (4) is given.

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[0017] When the kinetic energy K and potential U are given by the above equations (2) and (3), the following equation of motion can be obtained from the Lagrange equation. The resonant frequency of the Helmholtz resonator 1A can be obtained from the solution of this equation of motion.

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[0018] As a comparative example, a conventional Helmholtz resonator is used, in which the volume of the internal space of the cavity is V and the opening area S is uniform over the entire length of the neck length l. The resonant frequency ωN is given by the following equation:

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[0019] This resonance frequency ω N The dependence of on the neck length l is given by

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[0020] In contrast, the resonant frequency ω of the Helmholtz resonator 1A obtained by solving the above equation (6) is N12 is expressed by the following formula:

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[0021] This resonance frequency ω N12 The dependence of on the neck length l2 is given by the following equation.

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[0022] Comparing equation (8) and equation (10), the resonant frequency ω N12 The dependence of on the neck length l2 is the resonant frequency ω N It can be seen that the dependence of the saturation temperature on the neck length l is smaller than that of the saturation temperature.

[0023] Incidentally, even in conventional Helmholtz resonators, the amount of change in resonant frequency with respect to a change in neck length becomes smaller if the neck length is long (see formula (8) above), but it is not realistic to make the neck length too long. According to this embodiment, it is possible to reduce the amount of change in resonant frequency with respect to a change in neck length without making the neck length long as in the conventional technology. This point will be explained below. First, as shown in the following formulas (11) and (12), assume a condition in which the resonant frequencies of a conventional Helmholtz resonator and the Helmholtz resonator 1A of this embodiment are equal, and the dependencies of both resonant frequencies on neck length are also equal.

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[0024] In this case, if the opening areas S, S1, and S2 and the neck lengths l, l1, and l2 satisfy the following equations (13) and (14), the conditions of the above equations (11) and (12) are met.

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[0025] Here, consider the case where the conditions of the following expressions (15) and (16) are satisfied.

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[0026] In this case, the following equations (17) and (18) are obtained as examples that satisfy the conditions of the above equations (13) and (14).

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[0027] In this embodiment, in order to make the amount of change in the Helmholtz resonance frequency with respect to the change in neck length the same as that of the conventional Helmholtz resonator, the neck length l1+l2 may be set to 1 / 5 of the neck length l of the conventional Helmholtz resonator. A specific example is as follows. For example, if the neck length of the conventional Helmholtz resonator is 2 cm and the resonance frequency is 200 Hz, the resonance frequency changes by 1 Hz with a change in neck length of 0.2 mm. In order to maintain this amount of change in the resonance frequency and change the resonance frequency by 1 Hz with a change in neck length of 1 mm, the neck length must be set to 10 cm. However, in this embodiment, when realizing a Helmholtz resonator in which the resonance frequency changes by 1 Hz with a change in neck length of 1 mm, the neck length may be set to 2 cm, which is 1 / 5 of 10 cm, if S1:S2=1:9 and l1:l2=1:1. In the above description, the opening area S2 is set to 9 times the opening area S1, but if the opening area S2 is at least twice the opening area S1, the same effect as that described above can be obtained.

[0028] <First Modification of First Embodiment> FIG. 2 is a cross-sectional view showing the configuration of a Helmholtz resonator 1A1 which is a first modified example of the first embodiment. In this Helmholtz resonator 1A1, the neck portion 20A of the first embodiment is replaced with a neck portion 20A1. This neck portion 20A1 is composed of a first neck portion 21A1 on the inner space 11 side of the cavity portion 10 and a second neck portion 22A1 on the outer space 31 side. The second neck portion 22A1 has a uniform opening area S2 along the axial direction, similar to the second neck portion 22A of the first embodiment. The first neck portion 21A1 is a tapered neck portion having an opening area S1 on the inner space 11 side and an opening area S2 (>S1) on the second neck portion 22A1 side. In this modified example, the kinetic energy per neck length of the air particles in the second neck portion 22A1 on the outer space 31 side is reduced, so that the neck length dependency of the resonance frequency can be reduced.

[0029] <Second Modification of First Embodiment> 3 is a cross-sectional view showing the configuration of a Helmholtz resonator 1A2 which is a first modified example of the first embodiment. In this Helmholtz resonator 1A2, the neck portion 20A of the first embodiment is replaced with a neck portion 20A2. This neck portion 20A2 is a tapered neck portion with an opening area S1 on the internal space 11 side and an opening area S2 (>S1) on the external space 31 side. In this modified example, the kinetic energy per neck length of air particles in the region of the neck portion 20A2 near the external space 31 is also reduced, so that the neck length dependency of the resonance frequency can be reduced.

[0030] <Second embodiment> FIG. 4 is a cross-sectional view showing the configuration of a Helmholtz resonator 1B according to a second embodiment of the present invention. FIG. 5 is a cross-sectional view showing an enlarged view of a second neck portion 22B of the Helmholtz resonator 1B. In this Helmholtz resonator 1B, the neck portion 20A in the first embodiment is replaced with a neck portion 20B. This neck portion 20B is composed of a first neck portion 21B on the side of the internal space 11 and a second neck portion 22B on the side of the external space 31. The first neck portion 21B has a neck length l1 and a uniform opening area S along the axial direction. 12 The second neck portion 22B has a neck length l2 and, like the first neck portion 21B, has a uniform opening area S 12 However, a plurality of through holes 25 are formed in the side wall of the second neck portion 22B. In the second neck portion 22B, air leakage occurs through the through holes 25, whereby air particles leak out into the external space 31.

[0031] In this embodiment, since a plurality of through holes 25 are formed in the side wall of the second neck portion 22B on the external space 31 side, the kinetic energy per neck length of air particles in the area of ​​the second neck portion 22B near the external space 31 is reduced. Therefore, similar to the first embodiment, the dependency of the resonance frequency on the neck length can be reduced.

[0032] The resonant frequency of the Helmholtz resonator 1B will be described below. In Fig. 5, assuming a y-axis parallel to the axial direction of second neck portion 22B, the position of the open end of second neck portion 22B on the side of external space 31 is set to y=0, and the position of the open end on the side of first neck portion 21B (see Fig. 4) is set to y=-l2. In Fig. 5, in any infinitesimal region y to y+Δy within second neck portion 22B, the continuity equation shown below holds.

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[0033] In this formula (19), x w is the displacement of the air leaking from the second neck portion 22B to the external space 31, and l w is the path length of the air leakage in the second neck portion 22B. From this equation (19), the following equation is obtained:

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[0034] Here, the displacement of the leak x w depends on the air pressure p2 at the position y as shown in the following equation (21). However, for simplicity, it is assumed here that the following equation (22) holds.

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[0035] Then, the following equation (23) is obtained from the above equation (20).

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[0036] Moreover, the following equation (24) can be obtained from the above equation (22).

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[0037] And, the following equations (25) and (26) can be obtained from the above equations (22) to (24).

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[0038] Here, the boundary conditions shown in the following equations (27) and (28) are assumed.

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[0039] Then, the following equation (29) is obtained as a solution to the above equation (26).

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[0040] In this equation (29), λ is as shown in the following equation.

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[0041] Then, by solving the above equation (29), the following equations (31) and (32) are obtained.

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[0042] Here, the boundary condition of the following equation (33) is assumed.

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[0043] Then, the kinetic energy K shown in the following equation (34) and the potential U shown in the following equation (35) are obtained.

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[0044] Next, the Lagrange equation is applied to the kinetic energy K in the above equation (34) and the potential U in the above equation (35). When the kinetic energy K and the potential U are given by the above equations (34) and (35), the Lagrange equation gives the equation of motion shown in the following equation (36). The resonant frequency of the Helmholtz resonator 1A can be obtained from the solution of this equation of motion.

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[0045] In this equation (36), l 2e is as shown in the following equation.

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[0046] As a comparative example, a conventional Helmholtz resonator is used, in which the volume of the internal space of the cavity is V and the opening area S is uniform over the entire length of the neck length l. The resonant frequency ω N is given by the above equation (7), and the resonant frequency ω N The neck length dependence of is given by the above equation (8).

[0047] In contrast, the resonant frequency ω of the Helmholtz resonator 1B obtained by solving the above equation (36) is N12 is expressed by the following formula:

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[0048] This resonance frequency ω N12 The dependence of on the neck length l2 is given by

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[0049] Comparing equation (8) and equation (39), the resonant frequency ω N12 The dependence of on the neck length l2 is the resonant frequency ω N It can be seen that the dependence of the saturation temperature on the neck length l is smaller than that of the saturation temperature.

[0050] Incidentally, even in a conventional Helmholtz resonator, the amount of change in resonant frequency with respect to a change in neck length becomes smaller if the neck length is long (see formula (8) above), but it is not realistic to make the neck length too long. According to this embodiment, it is possible to reduce the amount of change in resonant frequency with respect to a change in neck length without making the neck length long as in the conventional technology. This point will be explained below. First, as shown in formulas (11) and (12) above, assume that the resonant frequencies of the conventional Helmholtz resonator and the Helmholtz resonator of this embodiment are equal, and that the dependencies of both resonant frequencies on neck length are also equal. In this case, the opening areas S and S 12 If the neck lengths l, l1, and l2 satisfy the following equations (40) and (41), then the conditions of the above equations (11) and (12) are met.

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[0051] Here, consider the case where the conditions of the following expressions (42) and (43) are satisfied.

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[0052] In this case, the following equations (44) and (45) are obtained as examples that satisfy the conditions of the above equations (40) and (41).

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[0053] In this embodiment, in order to make the amount of change in Helmholtz resonance frequency with respect to the change in neck length the same as that of a conventional Helmholtz resonator, the neck length l1+l2 should be set to about half the neck length l of a conventional Helmholtz resonator.

[0054] <Third embodiment> FIG. 6 is a cross-sectional view showing the configuration of a Helmholtz resonator 1C according to a third embodiment of the present invention. The Helmholtz resonator 1C is composed of a straight pipe 40 and a sound-absorbing material 50. The straight pipe 40 has a closed end 41 and an open end 42 at each end, and is cylindrical in shape with a uniform opening area along the axial direction. The open end 42 faces the external space 31 of the Helmholtz resonator 1C. The sound-absorbing material 50 has an opening 51 in the center and is annular in shape to fit just inside the opening of the straight pipe 40. The sound-absorbing material 50 is disposed in a position in the straight pipe 40 near the external space 31.

[0055] In the straight tube 40 of this Helmholtz resonator 1C, the region from the closed end 41 to the sound-absorbing material 50 functions as the cavity portion 10 of the first embodiment. The region within the opening 51 of the sound-absorbing material 50 functions as the first neck portion 21A of the first embodiment. In the straight tube 40, the region from the sound-absorbing material 50 to the open end 42 functions as the second neck portion 22A of the first embodiment. Therefore, according to this embodiment, the same effects as those of the first embodiment can be obtained.

[0056] Furthermore, according to this embodiment, the kinetic energy per unit neck length of air particles in the area near the external space 31 in the straight pipe 40 is reduced due to the sound absorbing effect of the sound absorbing material 50. Therefore, similar to the first embodiment, it is possible to reduce the dependency of the resonance frequency on the neck length (the length of the straight pipe 40 in this example).

[0057] <Fourth embodiment> FIG. 7 is a side view showing the configuration of a Helmholtz resonator 1D according to a fourth embodiment of the present invention. This Helmholtz resonator 1D is formed by molding a low-hardness material such as resin, and has a cavity portion 10D, a first neck portion 21D, and a second neck portion 22D. The cavity portion 10D, the first neck portion 21D, and the second neck portion 22D correspond to the cavity portion 10, the first neck portion 21A, and the second neck portion 22A, respectively, of the first embodiment (FIG. 1). The second neck portion 22D is provided with a scale 23 indicating a position in the axial direction. The scale 23 is a line that serves as a cutting mark, and may be printed or engraved on the surface of the second neck portion 22A.

[0058] According to this embodiment, the Helmholtz resonator 1D is formed from a low-hardness material such as resin, and the second neck portion 22A is provided with the scale 23, which makes it easy to adjust the neck length by cutting the second neck portion 22A. In this embodiment, resin is given as an example of the material for the Helmholtz resonator, but the material is not limited to resin, and wood or the like can be used as long as the shape is stable and the processing is easy. In addition, the material of the neck portion may be easy to process, and the materials of the cabinet portion and the neck portion may be different.

[0059] <Example of using a Helmholtz resonator> 8 to 11 are diagrams showing examples of use of the above-described Helmholtz resonator. In the examples of use described below, the Helmholtz resonator 1 may be any of the Helmholtz resonators according to the above-described embodiments or their modified examples.

[0060] In the example of use shown in Fig. 8, a speaker 130 and a Helmholtz resonator 1 are installed in a living space 120 in which a person 110 lives. In a living space having parallel walls facing each other, such as the living space 120, when sound is emitted from the speaker 130, standing waves are likely to occur between the parallel walls. Such standing waves cause deterioration of the reproduction quality of the speaker 130. Therefore, the Helmholtz resonator 1 is installed in the living space 5 in order to suppress the standing waves.

[0061] In the usage example shown in Figure 8, in order to suppress standing waves that occur between the floor surface 121 and the ceiling surface 122 of the living space 120, the Helmholtz resonator 1 is installed with its open end 1w (e.g., corresponding to the open end on the external space 31 side of the second neck portion 22A in the first embodiment described above) facing the ceiling surface 122.

[0062] In this use example, in order to appropriately suppress the standing wave, it is necessary to accurately match the resonant frequency of the Helmholtz resonator 1 with the frequency of the standing wave, which depends on the distance between the floor surface 121 and the ceiling surface 122. Here, the Helmholtz resonator 1 has a resonant frequency that is less dependent on the neck length than a conventional Helmholtz resonator. Therefore, by using the Helmholtz resonator 1 and adjusting its neck length, the standing wave generated in the living space 5 can be appropriately suppressed.

[0063] In the example of use shown in Fig. 9, a Helmholtz resonator 1 is installed to suppress standing waves generated in a speaker box 130b of a speaker 130. A speaker unit 131a and a bass reflex port 131b are provided on a front surface 131 of the speaker box 130b. The bass reflex port 131b plays a role of emphasizing the reproduced sound of the speaker 130 by inverting the phase of the sound emitted from the rear surface of the speaker unit 131a into the speaker box 130b and emitting the sound from the front surface of the speaker box 130b. In the example of use shown in Fig. 9, the Helmholtz resonator 1 is installed so as not to impede the function of the bass reflex port 131b. Specifically, in order to suppress standing waves occurring between the floor surface 133 and the ceiling surface 134 of the speaker box 130b, the Helmholtz resonator 1 is installed in the speaker box 130b with the open end 1w (for example, the open end on the external space 31 side of the second neck portion 22A in the first embodiment) facing the ceiling surface 134. In this usage example as well, the same effect as the usage example in FIG. 8 can be obtained.

[0064] In the use example shown in Fig. 10, the Helmholtz resonator 1 is installed in a vehicle cabin 140 of a vehicle driven by a person 110. When road noise or the like while the vehicle is traveling propagates into the vehicle cabin 140, standing waves are generated in the vehicle cabin 140 due to the road noise, which causes noise inside the vehicle cabin. In the use example shown in Fig. 10, in order to suppress standing waves generated between a floor surface 141 and a ceiling surface 142 of the vehicle cabin 140, the Helmholtz resonator 1 is installed in the vehicle cabin 140 with an open end 1w (for example, an open end on the external space 31 side of the second neck portion 22A in the first embodiment) facing the ceiling surface 142. In this use example, the same effect as in the use example in Fig. 8 can be obtained.

[0065] In the example of use shown in FIG. 11, a Helmholtz resonator 1 is installed in a tire 150. Tire cavity resonance is known as one type of vehicle noise. When a vehicle is traveling, the tire 150 vibrates due to unevenness in a road surface 160. An air chamber 151 is formed between the tire 150 and a rim provided on the outer circumferential edge of a wheel 170, and the air in the air chamber 151 vibrates due to the vibration of the tire 150. When the vibration frequency of this air matches a resonance frequency determined according to the circumferential length of the tire 150, a phenomenon called cavity resonance occurs in which the air in the tire 150 resonates. The vibration due to cavity resonance is propagated as noise inside the vehicle.

[0066] In order to suppress such cavity resonance, in FIG. W The Helmholtz resonator 1 is installed in the air chamber 151 with its direction coinciding with the circumferential direction of the tire 150. In this example as well, the same effects as in the example of FIG. 8 can be obtained. [Explanation of symbols]

[0067] 1, 1A, 1B, 1C, 1D...Helmholtz resonator, 10, 10D...cavity portion, 20A, 20A1, 20A2...neck portion, 21A, 21A1, 21B, 21D...first neck portion, 22A, 22A1, 22B, 22D...second neck portion, 11...inner space, 31...outer space, 25...through hole, 40...straight pipe, 41...closed end, 42...open end, 50...sound absorption material, 23...scale, 110...person, 120...living space, 130...speaker, 131, 141...floor surface, 132, 142...ceiling surface, 130b...speaker box, 131...front, 131a...speaker unit, 131b...bass reflex port, 140...vehicle interior, 150...tire, 151...air chamber, 160...road surface, 170...wheel, 1w...opening end.

Claims

1. A cavity portion; a neck portion that connects an internal space of the cavity portion to an external space, the neck portion having an opening area at an opening end on the external space side that is larger than an opening area at an opening end on the internal space side; A Helmholtz resonator comprising:

2. 2. The Helmholtz resonator according to claim 1, wherein the neck portion has a first neck portion on the internal space side, the opening area of ​​which is uniform along the axial direction, and a second neck portion on the external space side, the opening area of ​​which is uniform along the axial direction.

3. 2. The Helmholtz resonator according to claim 1, wherein an opening area of ​​the open end of the neck portion facing the external space is at least twice as large as an opening area of ​​the open end facing the internal space.

4. 2. The Helmholtz resonator according to claim 1, wherein the neck portion is made of a material that is easy to cut.

5. 5. The Helmholtz resonator according to claim 4, wherein a line is formed on the surface of the neck portion as a cutting guide.

6. 2. The Helmholtz resonator according to claim 1, wherein the opening area of ​​the neck portion changes continuously along the axial direction of the neck portion.

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