JP2018159733A - Sound resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound resonator in which resonance at a resonance frequency to be suppressed in an acoustic space easily occurs and resonance at other resonance frequencies than the resonance frequency to be suppressed is hard to occur.SOLUTION: A sound resonator 100 comprises: a tubular member 1 which resonates at a plurality of resonance frequencies including a first resonance frequency, a second resonance frequency and other frequencies than the first resonance frequency and the second resonance frequency and in which a hollow region 13 is configured; a sound absorber 3 which is installed in a region becoming an antinode of sound pressure distribution in a standing wave of the second resonance frequency and resonates at the second resonance frequency; and a sound absorbing material 2 arranged in a region becoming an antinode of particle speed distribution in the standing wave of the other resonance frequency in the hollow region.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an acoustic resonator.

  When a standing wave is generated in the acoustic space, a sound having a specific frequency is emphasized or attenuated and heard, and thus the frequency characteristics of the acoustic space are biased. Conventionally, resonator sound absorption using a resonance tube is known as a technique for suppressing a standing wave generated in an acoustic space.

  Sound generated in the acoustic space enters the resonance tube. The sound incident on the resonance tube resonates according to the resonance frequency of the resonance tube and generates a standing wave in the resonance tube. Near the opening end of the resonance tube, the incident wave and the reflected wave interfere and cancel each other, and the sound pressure near the opening end of the resonance tube is reduced around the resonance frequency. As a result, the resonance tube can suppress a standing wave having the resonance frequency in the acoustic space.

  That is, if the resonance frequency of the standing wave to be suppressed in the acoustic space is the resonance frequency of the resonance tube, the resonance tube can suppress the standing wave of the resonance frequency in the acoustic space. By changing the resonance frequency of the resonance tube, the resonance frequency to be suppressed in the acoustic space can be changed.

  Patent Document 1 describes an acoustic resonator (resonance tube) that can change the resonance frequency to a low range without increasing the size of the housing. A sound absorbing material is provided inside the acoustic resonator, and the resonance frequency of the acoustic resonator is changed to a low range.

JP 2011-133855 A

  However, a general resonance tube has a plurality of other resonance frequencies in addition to the resonance frequency to be suppressed. Therefore, the resonance tube resonates even at a resonance frequency that is not the suppression target, and suppresses the standing wave of the resonance frequency that is not the suppression target in the acoustic space. If standing waves with resonance frequencies that are not to be suppressed are suppressed, the sound generated in the acoustic space may be affected unintentionally. For example, the sound generated in the acoustic space sometimes becomes a sound lacking in force.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an acoustic resonator that easily generates resonance at a resonance frequency to be suppressed in an acoustic space and hardly generates resonance at other resonance frequencies. To do.

In order to solve the above problems, the present invention proposes the following means.
The acoustic resonator according to the present invention resonates at a plurality of resonance frequencies including a first resonance frequency, a second resonance frequency, and other resonance frequencies other than the first resonance frequency and the second resonance frequency. A tubular member in which a hollow region is configured, a sound absorber that is provided in an antinode region of a sound pressure distribution in the standing wave of the second resonance frequency, and that resonates at the second resonance frequency; And a sound absorbing material provided in a region that becomes an antinode of the particle velocity distribution in the standing wave of the other resonance frequency.

  According to the present invention, it is possible to provide an acoustic resonator that easily generates resonance at a resonance frequency to be suppressed in an acoustic space and hardly generates resonance at other resonance frequencies.

1 is a diagram illustrating an overall configuration of an acoustic resonator according to an embodiment of the present invention. It is sectional drawing of the tubular member of the acoustic resonator based on one Embodiment of this invention. It is a figure which shows the particle velocity distribution of the standing wave in the tubular member of the acoustic resonator based on one Embodiment of this invention. It is the figure which showed the particle velocity of the standing wave in the tubular member of the acoustic resonator which concerns on one Embodiment of this invention for every standing wave. It is a figure which shows the particle velocity distribution of the standing wave in the tubular member of the acoustic resonator based on one Embodiment of this invention. It is a figure which shows the whole structure of the sound absorber of the acoustic resonator which concerns on one Embodiment of this invention. It is a figure which shows the sound pressure distribution of the standing wave in the tubular member of the acoustic resonator based on one Embodiment of this invention. It is the figure which showed the sound pressure of the standing wave in the tubular member of the acoustic resonator which concerns on one Embodiment of this invention for every standing wave. It is a figure which shows the whole structure of the modification of the sound absorber of the acoustic resonator based on one Embodiment of this invention. It is a figure which shows the whole structure of the modification of the sound absorber of the acoustic resonator based on one Embodiment of this invention. It is a figure which shows the whole structure of the modification of the sound absorber of the acoustic resonator based on one Embodiment of this invention. It is sectional drawing of the modification of the tubular member of the acoustic resonator which concerns on one Embodiment of this invention. It is a figure which shows the whole structure of the modification of the acoustic resonator based on one Embodiment of this invention.

  Hereinafter, an embodiment of an acoustic resonator according to the present invention will be described with reference to FIGS. 1 to 13. In addition, in order to make the drawings easy to see, the thicknesses and dimensional ratios of the respective constituent elements are appropriately adjusted.

FIG. 1 is a diagram illustrating an overall configuration of an acoustic resonator 100 according to the present embodiment.
As shown in FIG. 1, the acoustic resonator 100 according to the present embodiment includes a tubular member 1, a sound absorbing material 2, and a sound absorber 3.

The tubular member 1 is a one-end opening resonance tube having a first end portion 11 opened at one end and a second end portion 12 at the other end, and is formed in a tubular shape. The first end portion 11 and the second end portion 12 are circular, and a cylindrical hollow region 13 is formed between the first end portion 11 and the second end portion 12. The tubular member 1 is made of a material such as paper, metal, or plastic.
The hollow region 13 of the tubular member 1 is not limited to a cylindrical shape. For example, the cross section may be a triangle or a rectangle such as a polygonal column. The hollow region 13 of the tubular member 1 may have any shape as long as it functions as a resonance tube.

In the following description, the central axis of the hollow region 13 that passes through the center of the first end portion 11 and the center of the second end portion 12 of the tubular member 1 is referred to as an X axis. An axis orthogonal to the X axis is taken as a Y axis.
Let the distance in the X-axis direction between the first end 11 and the second end 12 be L. Further, the intersection of the X axis and the first end portion 11 is the origin of the XY coordinates, and the XY coordinate of the intersection of the X axis and the second end portion 12 is expressed as (X, Y) = (L, 0).

  FIG. 2 is a diagram illustrating a cross section when the tubular member 1 is cut along a plane including the X axis. The two-dot chain line shown in FIG. 2 indicates gas particles (here, air) with respect to the lowest frequency among standing waves that can be generated in the hollow region 13 of the tubular member 1, that is, the standing wave SW1 having the primary resonance frequency. ) Particle velocity distribution (amplitude distribution).

  As shown in FIG. 2, a standing wave is generated in the hollow region 13 of the tubular member 1 so as to satisfy the boundary condition that the particle velocity at the second end 12 is zero. That is, in the standing wave SW1, there is a “node” of the particle velocity distribution at the position of the second end portion 12, and the particle velocity is minimized. On the other hand, there is an “antinode” of the particle velocity distribution at the position of the first end portion 11, and the particle velocity becomes maximum.

  The standing wave SW1 is expressed by resonance occurring in the tubular member 1 in response to a sound wave having a wavelength λc (L = λc / 4) corresponding to four times the length L of the hollow region 13. At this time, the tubular member 1 radiates a reflected wave generated by resonance and having a phase different from the phase of the incident wave to the external space via the first end portion 11. In accordance with the phase difference between the reflected wave and the incident wave at this time, the sound wave having the resonance frequency corresponding to the wavelength λc interferes and cancels, and the sound near the first end 11 centering on the resonance frequency of the tubular member 1. There is an effect of reducing the pressure. As a result, the tubular member 1 can suppress the standing wave having the resonance frequency in the acoustic space.

  That is, if the resonance frequency of the standing wave that is desired to be suppressed in the acoustic space is a resonance frequency that is likely to resonate in the tubular member 1 (hereinafter referred to as “first resonance frequency”), the tubular member 1 has the resonance frequency in the acoustic space. Can be suppressed. The tubular member 1 is adjusted to facilitate resonance at the first resonance frequency.

  The acoustic resonator 100 of this embodiment is designed for installation in the acoustic space of an upright piano, and the resonance frequency of the standing wave to be suppressed is about 150 Hz, which is the lowest frequency of the acoustic mode of the upright piano. . That is, the acoustic resonator 100 is adjusted so as to suppress the generation of a standing wave having a resonance frequency of about 150 Hz in the acoustic space of the upright piano, and the first resonance frequency of the single tubular member 1 is adjusted to 150 Hz. Yes. In the present embodiment, the first resonance frequency is adjusted to be the primary resonance frequency of the tubular member 1 alone.

  The acoustic resonator 100 that does not include the sound absorbing material 2 and the sound absorber 3 described later, that is, the tubular member 1 alone, is a general resonance tube that generates a plurality of standing waves that can be generated in the hollow region 13 of the tubular member 1. is there. Since the tubular member 1 is a resonance tube having an opening at one end, and the primary resonance frequency is adjusted to 150 Hz, the secondary resonance frequency is 450 Hz, the third resonance frequency is 750 Hz, the fourth resonance frequency is 1050 Hz, and 5 The next resonance frequency is 1350 Hz, and the sixth resonance frequency is 1650 Hz.

  The tubular member 1 resonates even at a resonance frequency other than the first resonance frequency (150 Hz), and suppresses standing waves of resonance frequencies that are not to be suppressed in the acoustic space. If the standing wave of the resonance frequency that is not the suppression target is suppressed, the sound generated in the acoustic space is affected unintentionally. Therefore, in the acoustic resonator 100, the sound absorbing material 2 and the sound absorber 3 described later make it difficult for resonance to occur at resonance frequencies other than the first resonance frequency.

The sound absorbing material 2 is made of urethane foam and is a member that resists the movement of gas particles and inhibits the movement of gas particles. The sound-absorbing material 2 exhibits a high sound-absorbing effect by being disposed at a place where the particle velocity is high.
Here, materials other than urethane foam can be used as long as they prevent movement of gas particles and generate (increase) resistance to the movement. Urethane foam is an example of an open-cell porous material, but an open-cell porous material using other resin materials (for example, foamed resin) may be used. Moreover, you may use the material which has a porous material of a closed cell at least in part.

  Moreover, the member applicable to the sound-absorbing material 2 is not limited to a member having a so-called structure having many holes, but also includes a structure that can be regarded as porous with respect to sound waves. As an example, a member that forms a structure that can be regarded as a porous material when glass fibers are entangled, such as glass wool, is also included. This member includes not only those formed by weaving cloth materials, but also those formed without weaving cloth materials (for example, non-woven fabric, metal fiber plate). Also, metal (for example, aluminum foam metal, metal fiber board), wood (for example, wood pieces and fragments thereof), paper (wood fiber, pulp fiber), glass (for example, MPP (Microperforated Panel), microporous panel, etching Absorbing material 2 including various materials such as fine fibers formed by treatment) and animal and vegetable fibers (cow felt, anti-felt felt, wool, cotton, nonwoven fabric, cloth, synthetic fiber, wood powder molding material, paper molding material) It is applicable to.

  As shown in FIG. 1, the sound absorbing material 2 is formed in an annular shape, and is provided in a region of the hollow region 13 where the X coordinate extends from X1 to X2. The center axis of the annular shape of the sound absorbing material 2 coincides with the X axis, and the outer diameter of the sound absorbing material 2 coincides with the inner diameter of the tubular member 1. A cylindrical cavity 21 through which the X axis passes is formed inside the sound absorbing material 2.

The sound absorbing material 2 is provided in a region of the hollow region 13 whose X coordinate extends from X1 to X2. Therefore, in the region where the X coordinate ranges from X1 to X2, the standing wave having a high particle velocity is prevented from moving the gas particles by the sound absorbing material 2. As a result, the particle velocity of the standing wave is reduced.
On the contrary, in the region where the X coordinate ranges from X1 to X2, the standing wave having a low particle velocity hardly affects the gas particles by the sound absorbing material 2.

  The sound absorbing material 2 may have any shape as long as it exhibits a function of preventing the movement of gas particles in the hollow region 13 in the region where the X coordinate ranges from X1 to X2. For example, the sound-absorbing material 2 may have a cylindrical shape that does not have the cavity 21 and may have a shape that covers all of the hollow region 13 in which the X coordinate ranges from X1 to X2.

  In the following description, the particle velocity is normalized and treated so that the minimum particle velocity is “0” in the “node” of the particle velocity distribution and the maximum particle velocity is “1” in the “antinode” of the particle velocity distribution.

  When the particle velocity of the standing wave is larger than the first reference particle velocity, it is determined that the particle velocity is high. In the present embodiment, when the first reference particle velocity is 1 / √2 and the particle velocity is 1 / √2 (first reference particle velocity) or more, it is determined that the particle velocity is high. The kinetic energy of the gas particles when the particle velocity is 1 / √2 or more is 0.5 or more of the kinetic energy of the gas particles when the particle velocity is 1. Therefore, if the particle speed is 1 / √2 or more, it may be determined that the particle speed is sufficiently high.

  When the particle velocity of the standing wave is smaller than the second reference particle velocity, it is determined that the particle velocity is slow. In the present embodiment, when the second reference particle velocity is 0.3 and the particle velocity is 0.3 (second reference particle velocity) or less, it is determined that the particle velocity is low. The kinetic energy of gas particles when the particle velocity is 0.3 or less is 0.09 times or less than the kinetic energy of gas particles when the particle velocity is 1. Therefore, if the particle velocity is 0.3 or less, it is considered that the gas particles are less affected by the sound absorbing material 2 and may be determined to be sufficiently slow.

FIG. 3 is a diagram illustrating a cross section when the tubular member 1 is cut along a plane including the X axis, and among the standing waves that can be generated in the hollow region 13 of the tubular member 1, the primary standing wave SW1. To 4th order standing wave SW4, the particle velocity distribution (amplitude distribution) of gas particles (air in this case) is shown. 3A shows the primary standing wave SW1, FIG. 3B shows the secondary standing wave SW2, FIG. 3B shows the tertiary standing wave SW3, and FIG. 3C. Represents the particle velocity distribution of the fourth-order standing wave SW4.
In FIG. 3, the shaded area indicates a region where the particle velocity of each standing wave is 1 / √2 or more. In FIG. 3A, the hatched region indicates a region where the particle velocity of the standing wave SW1 is 0.3 or less.

  The acoustic resonator 100 of this embodiment is designed for installation in the acoustic space of an upright piano. In the acoustic space of the upright piano, the upper frequency limit (Schrader frequency) in which the acoustic modes exist independently is about 1000 Hz. Therefore, the standing wave has little influence on the acoustic space in the frequency band of 1000 Hz or higher. Therefore, the frequency band to be subjected to standing wave suppression control by the acoustic resonator 100 is up to about 1000 Hz which is the Schrader frequency. Therefore, in the present embodiment, the frequency band to be subjected to standing wave suppression control is set to about 1000 Hz.

Among the frequency bands up to about 1000 Hz, the resonance frequencies other than the first resonance frequency (150 Hz) are the second-order resonance frequency (450 Hz), the third-order resonance frequency (750 Hz), and the fourth-order resonance frequency (1050 Hz). .
The acoustic resonator 100 absorbs standing waves of the second, third, and fourth resonance frequencies, and makes it difficult for resonance to occur at resonance frequencies other than the first resonance frequency.

  FIG. 4 shows the X-axis coordinate on the horizontal axis and the mode order on the vertical axis. The particle velocity of the standing wave at each mode order is greater than the first reference particle velocity, and the X is determined to be fast. It is the graph which plotted the coordinate by ○. Here, regarding the primary standing wave, the X coordinate at which the particle velocity is determined to be smaller than the second reference particle velocity and the particle velocity is slow is also plotted with ●.

When the particle velocity of the second, third, and fourth standing waves is effectively reduced, the sound absorbing material 2 is plotted with a circle in the row of the second, third, and fourth standing waves in FIG. It suffices if they are arranged in the X coordinate range.
Conversely, in order not to reduce the particle velocity of the primary standing wave, the sound absorbing material 2 should be arranged in the X coordinate range in which ● is plotted in the row of the primary standing wave. That's fine.
The region satisfying both conditions is a region R1 having an X coordinate from 0.82L to 0.83L as shown in FIG.

FIG. 5 is a diagram illustrating a cross section when the tubular member 1 is cut along a plane including the X axis, and among the standing waves that can be generated in the hollow region 13 of the tubular member 1, the primary standing wave SW <b> 1. To the fourth-order standing wave SW4, the particle velocity distribution (amplitude distribution) of gas particles (air in this case) is shown superimposed.
By arranging the sound absorbing material 2 in the region R1 extending from X1 = 0.82L to X2 = 0.83L in the hollow region 13, the particle velocity of the primary standing wave is not reduced, but the secondary, tertiary, The particle velocity of the fourth-order standing wave can be effectively reduced. As shown in FIG. 5, in the region R1, the secondary, tertiary and quartic particle velocities are large, and the primary particle velocity is small. As a result, the sound absorbing material 2 can absorb the second, third and fourth standing waves without absorbing the first standing wave as much as possible.

  As described above, by arranging the sound absorbing material 2 in the region R1, the sound absorbing material 2 can effectively reduce the particle velocity of the second-order, third-order, and fourth-order standing waves. However, as shown in FIG. 5, in the region R1, the particle velocity of the second-order standing wave is smaller than the particle velocity of the third-order and fourth-order standing waves. Therefore, it is difficult to sufficiently absorb the secondary standing wave as much as the 3rd and 4th standing waves only by arranging the sound absorbing material 2 in the region R1. Therefore, a secondary standing wave is absorbed using a sound absorber 3 described later.

  The sound absorber 3 is a Helmholtz resonator which is one of resonance type sound absorbers. The sound absorber 3 absorbs the second lowest frequency among the standing waves generated in the hollow region 13 of the tubular member 1, that is, the standing wave SW2 having a secondary resonance frequency.

FIG. 6 is a diagram illustrating the overall configuration of the sound absorber 3.
As shown in FIG. 6, the sound absorber 3 has an opening 30, and the resonance frequency is determined by the shape of the opening 30 and the internal volume of the sound absorber 3. The resonance frequency of the sound absorber 3 (hereinafter referred to as “second resonance frequency”) coincides with the resonance frequency of the secondary standing wave SW2 generated in the hollow region 13 of the tubular member 1, that is, the secondary resonance frequency. ing. The resonance frequency of the sound absorber 3 can be adjusted by a method used for a known Helmholtz resonator.

  In the sound absorber 3, resonance occurs due to a change in sound pressure generated in the opening 30. Therefore, it is desirable that the opening 30 of the sound absorber 3 be provided in a region where the “antinode” of the sound pressure distribution where the change in sound pressure is large occurs.

  In the following description, in the standing wave that can be generated in the hollow region 13 of the tubular member 1, the sound pressure that is the minimum at the “node” of the sound pressure distribution is 0, and the sound pressure that is the maximum at the “belly” of the sound pressure distribution. The sound pressure is normalized so that becomes 1.

  When the sound pressure speed of the standing wave is larger than the reference sound pressure, it is determined that the sound pressure is large. In this embodiment, when the reference sound pressure is 1 / √2 and the sound pressure is 1 / √2 (reference sound pressure) or more, it is determined that the sound pressure is high. The potential energy of the gas particles when the sound pressure is 1 / √2 or more is 0.5 or more of the potential energy of the gas particles when the sound pressure is 1. Therefore, if the sound pressure is 1 / √2 or more, it may be determined that the sound pressure is sufficiently high.

FIG. 7 is a diagram illustrating a cross section when the tubular member 1 is cut along a plane including the X axis, and among the standing waves that can be generated in the hollow region 13 of the tubular member 1, the primary standing wave SW1. To 4th order standing wave SW4 represents the sound pressure distribution (amplitude distribution) of gas particles (air in this case). 7A shows the primary standing wave SW1, FIG. 7B shows the secondary standing wave SW2, FIG. 7C shows the tertiary standing wave SW3, FIG. 7D. Represents the sound pressure distribution of the fourth-order standing wave SW4.
In FIG. 7, the shaded area indicates an area where the sound pressure of each standing wave is 1 / √2 or more.

  As shown in FIG. 7, a standing wave is generated in the hollow region 13 of the tubular member 1 so as to satisfy the boundary condition that the sound pressure at the first end portion 11 is zero. That is, in the standing wave SW1, there is a “node” of the sound pressure distribution at the position of the first end portion 11, and the sound pressure is minimized. On the other hand, there is an “antinode” of the sound pressure distribution at the position of the second end portion 12, and the sound pressure becomes maximum.

  In the present embodiment, the opening 30 of the sound absorber 3 communicates with the opening 10 formed at the second end 12 of the hollow region 13 of the tubular member 1 where the sound pressure of the standing wave is maximized. .

FIG. 8 shows the X-axis coordinate on the horizontal axis, and the mode order on the vertical axis. It is a graph plotted with ○. For example, when the sound pressure of the primary standing wave is effectively reduced, the opening 30 of the sound absorber 3 is in the X coordinate range in which ◯ is plotted in the row of the primary standing wave in FIG. It only has to be arranged.
As shown in FIG. 6, a sound absorbing member 31 that covers at least a part of the opening 30 is provided in the opening 30 of the sound absorber 3. The sound absorbing member 31 is formed of a porous material similar to the sound absorbing material 2.

A part of the sound incident on the tubular member 1 is incident on the sound absorber 3 communicating with the tubular member 1. The sound incident on the sound absorber 3 resonates according to the resonance frequency (second resonance frequency) of the sound absorber 3 and generates a standing wave in the sound absorber 3.
Due to the coupling between the resonance generated in the hollow region 13 of the tubular member 1 and the resonance generated in the sound absorber 3, the particle velocity of the secondary standing wave SW2 generated in the hollow region 13 of the tubular member 1 is reduced. Furthermore, the energy absorbing of the secondary standing wave SW2 generated in the hollow region 13 of the tubular member 1 is generated by the sound absorbing member 31 provided in the opening 30.
As a result, the secondary standing wave SW2 generated in the hollow region 13 of the tubular member 1 is absorbed by the sound absorber 3.

  The length L1 of the sound absorber 3 in the X-axis direction is sufficiently smaller than the length L of the tubular member 1 in the X-axis direction. Therefore, although the tubular member 1 communicates with the sound absorber 3 through the opening 10 at the second end 12, it can be considered that the resonance tube is closed at the second end 12. Therefore, the resonance frequency of the acoustic resonator 100 including the sound absorber 3 can be regarded as the same as the resonance frequency of the tubular member 1.

(Effect of embodiment)
The acoustic resonator 100 of the present embodiment configured as described above uses the sound absorbing material 2 and does not reduce the particle velocity of the first-order standing wave, but the second-order, third-order, and fourth-order standing waves. Can effectively reduce the particle velocity. As a result, the sound absorbing material 2 can absorb the second, third and fourth standing waves without absorbing the first standing wave as much as possible. Further, by further including the sound absorber 3, it is possible to more effectively absorb the secondary standing wave. That is, the acoustic resonator 100 can absorb the second, third, and fourth standing waves without absorbing the primary standing waves generated in the hollow region 13 of the tubular member 1.

  By arranging the acoustic resonator 100 in the acoustic space of the upright piano, the acoustic resonator 100 can suppress the generation of a standing wave having a resonance frequency of about 150 Hz in the acoustic space of the upright piano. On the other hand, the acoustic resonator 100 is less likely to generate resonance at the second resonance frequency (450 Hz), the third resonance frequency (750 Hz), and the fourth resonance frequency (1050 Hz). Therefore, the effect of suppressing standing waves of these frequencies is not exhibited in the acoustic space of the upright piano. In the frequency band of 1500 Hz or less that is the target of standing wave suppression control, the acoustic resonator 100 can suppress only the standing wave of the primary resonance frequency (150 Hz).

  As mentioned above, although one Embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this Embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included. In addition, the constituent elements shown in the above-described embodiment and the modifications shown below can be appropriately combined.

(Modification 1)
For example, in the above-described embodiment, the sound absorbing material 2 is disposed so as to absorb a secondary standing wave generated in the hollow region 13 of the tubular member 1. The secondary standing wave may be absorbed by the sound absorber 3, and the sound absorbing material 2 may be arranged so as to mainly absorb the third and fourth order standing waves. In that case, as shown in FIG. 4, the sound-absorbing material 2 is arranged in a region 0 extending from X1 = 0.82L to X2 = 0.89L in the hollow region 13.

(Modification 2)
Moreover, in the said embodiment, the acoustic resonator 100 is designed in order to install in the acoustic space of an upright piano, and about 150Hz which is the minimum frequency of the acoustic mode of an upright piano is suppressed, The resonance frequency was used. The application place of the acoustic resonator according to the present invention is not limited to the acoustic space of the upright piano. For example, you may apply to the acoustic space of an acoustic acoustic guitar. In this case, the first resonance frequency of the acoustic resonator is about 470 Hz, which is the lowest frequency of the acoustic mode of the acoustic guitar. In the acoustic space of an acoustic guitar, since the upper frequency limit (Schrader frequency) where the acoustic mode exists independently is about 2800 Hz, the frequency band to be subjected to the standing wave suppression control by the acoustic resonator is Schrader. The frequency is up to about 2800 Hz. Accordingly, it is difficult to generate resonance at the second resonance frequency (1410 Hz), the third resonance frequency (2390 Hz), and the fourth resonance frequency (3290 Hz), which are resonance frequencies other than the first resonance frequency in the acoustic resonator. . The acoustic resonator can suppress only the standing wave of the resonance frequency (470 Hz) to be suppressed in the acoustic space of the acoustic guitar.

  Even in the acoustic space of other musical instruments, the tubular member is designed so that the resonance frequency to be suppressed becomes the first resonance frequency of the acoustic resonator. Furthermore, using a sound absorbing material and a sound absorber, it is difficult to generate resonance at other resonance frequencies in the frequency band that should be the target of standing wave suppression control. By doing so, the acoustic resonator can suppress only the standing wave of the resonance frequency to be suppressed in the acoustic space of the musical instrument.

(Modification 3)
Moreover, in the said embodiment, the sound absorber 3 was adjusted and arrange | positioned so that the secondary standing wave which generate | occur | produces in the hollow area | region 13 of the tubular member 1 may be absorbed. The usage mode of the sound absorber of the present invention is not limited to this. For example, the sound absorber 3 may be adjusted and arranged so as to absorb a third-order or fourth-order standing wave generated in the hollow region 13 of the tubular member 1.

FIG. 9 is a diagram illustrating an overall configuration of a sound absorber 3A and a sound absorber 3B, which are modifications of the sound absorber 3.
The resonance frequency of the sound absorber 3A matches the resonance frequency of the third-order standing wave SW3 generated in the hollow region 13 of the tubular member 1, that is, the third-order resonance frequency.
The opening 30A of the sound absorber 3A communicates with the opening 10A of the tubular member 1 provided in a region where the X coordinate at which the sound pressure of the standing wave SW3 becomes maximum is near (3/5) L.
The sound absorber 3 </ b> A can absorb the standing wave SW <b> 3 having a third-order resonance frequency among the standing waves generated in the hollow region 13 of the tubular member 1.

The resonance frequency of the sound absorber 3B matches the resonance frequency of the fourth-order standing wave SW4 generated in the hollow region 13 of the tubular member 1, that is, the fourth-order resonance frequency.
The opening 30B of the sound absorber 3B communicates with the opening 10B of the tubular member 1 provided in a region where the X coordinate where the sound pressure of the standing wave SW4 becomes maximum is near (3/7) L.
The sound absorber 3B can absorb the standing wave SW4 having the third resonance frequency (second resonance frequency) among the standing waves generated in the hollow region 13 of the tubular member 1.

(Modification 4)
Moreover, in the said embodiment, although the sound absorber 3 is a Helmholtz resonator which is one of the resonance type sound absorbers, the structure of a sound absorber is not limited to this.
FIG. 10 is a diagram illustrating an overall configuration of a sound absorber 3 </ b> C that is a modification of the sound absorber 3.
The sound absorber 3C is a tube resonator that is one of resonance type sound absorbers. Similarly to the sound absorber 3, the opening 30 of the sound absorber 3 </ b> C communicates with the opening 10 formed in the second end 12 of the hollow region 13 of the tubular member 1 where the sound pressure of the standing wave is maximized. Yes.
The resonance frequency of the sound absorber 3C coincides with the resonance frequency of the secondary standing wave SW2 generated in the hollow region 13 of the tubular member 1, that is, the secondary resonance frequency. The sound absorber 3 </ b> C configured as described above has the same functions and effects as the sound absorber 3, and can absorb the secondary standing wave SW <b> 2 generated in the hollow region 13 of the tubular member 1.

FIG. 11 is a diagram illustrating an overall configuration of a sound absorber 3D that is a modification of the sound absorber 3.
The sound absorber 3D is a plate vibration type sound absorber formed of an airtight plate, and is formed in a cylindrical shape. The bottom surface of the sound absorber 3D is in contact with the second end 12 of the hollow region 13 of the tubular member 1 where the sound pressure of the standing wave is maximized.
The natural frequency of the sound absorber 3D matches the resonance frequency of the secondary standing wave SW2 generated in the hollow region 13 of the tubular member 1, that is, the secondary resonance frequency. The sound absorber 3D configured in this manner has the same functions and effects as the sound absorber 3, and can absorb the secondary standing wave SW2 generated in the hollow region 13 of the tubular member 1.

(Modification 5)
In the said embodiment, although the tubular member 1 was the resonance pipe of one end opening, the structure of a tubular member is not limited to this. For example, the tubular member may be a resonance tube having openings at both ends.
FIG. 12 is a diagram illustrating a cross section when a tubular member 1A, which is a modification of the tubular member 1, is cut along a plane including the X axis. Of the standing waves that can be generated in the hollow region 13 of the tubular member 1A, the particle velocity distribution (amplitude distribution) of the primary-to-fourth-order standing-wave gas particles (in this case, air) is also shown. .
As shown in FIG. 12, the tubular member 1A is a resonance tube having openings at both ends. As shown in FIG. 12, a standing wave is generated in the tubular member 1A so as to satisfy a boundary condition in which the particle velocity at the opening end is maximized. In other words, there is an “antinode” of the particle velocity distribution at both end positions, and the particle velocity is maximized.

  Also in the tubular member 1A, which is a resonance tube having openings at both ends, by arranging the sound absorbing material 2 in a region where the particle velocity of the standing wave is high, the particle velocity of the standing wave is reduced and the standing wave is absorbed. be able to. The standing wave can also be absorbed by providing the sound absorber 3 in the “antinode” region of the sound pressure distribution of the standing wave generated in the tubular member 1A.

FIG. 13 is a diagram illustrating an overall configuration of an acoustic resonator 100D that is a modification of the acoustic resonator 100, including the tubular member 1A.
The sound absorbing material 2A is disposed in a region where the particle velocity of the second, third, and fourth standing waves is high, and reduces the particle velocity of the second, third, and fourth standing waves, and reduces the second, third, and fourth standing waves. Second and fourth order standing waves can be absorbed.
The resonance frequency of the sound absorber 3E matches the resonance frequency of the secondary standing wave generated in the hollow region 13 of the tubular member 1.
The opening 30E of the sound absorber 3E communicates with the opening 10E of the tubular member 1 provided in the region near the X coordinate where the sound pressure of the secondary standing wave is maximized.
The sound absorber 3E can absorb a secondary standing wave generated in the tubular member 1A.

(Modification 6)
In the embodiment, the resonance frequency (first resonance frequency) that does not absorb sound in the hollow region of the tubular member 1 is the primary resonance frequency. The resonance frequency (second resonance frequency) absorbed by the sound absorber 3 was a secondary resonance frequency. The first resonance frequency and the second resonance frequency are not limited to this. For example, the second resonance frequency may be a third-order resonance frequency as in a sound absorber 3A that is a modification of the sound absorber 3. Further, the resonance frequency (first resonance frequency) that does not absorb sound in the hollow region of the tubular member 1 may be a secondary or tertiary resonance frequency instead of the primary resonance frequency.

DESCRIPTION OF SYMBOLS 100 ... Acoustic resonance body, 1 ... Tubular member, 10 ... Opening part, 11 ... 1st end part, 12 ... 2nd end part, 13 ... Hollow region, 2 ... Sound-absorbing material, 21 ... Cavity, 3 ... Sound absorber, 30 ... Opening part, 31 ... Sound absorbing member

Claims (8)

A tubular member configured with a hollow region that resonates at a plurality of resonance frequencies including a first resonance frequency, a second resonance frequency, and a resonance frequency other than the first resonance frequency and the second resonance frequency; ,
A sound absorber that resonates at the second resonance frequency, provided in an antinode region of the sound pressure distribution in the standing wave of the second resonance frequency;
Of the hollow region, the sound absorbing material provided in the region that becomes the antinode of the particle velocity distribution in the standing wave of the other resonance frequency,
Comprising
Acoustic resonator. The sound absorbing material is provided in a region where the particle velocity in the standing wave of the first resonance frequency is 0.3 or less with respect to the normalized velocity.
The acoustic resonator according to claim 1. The sound absorbing material is at least partially composed of a porous material or a fiber material,
The acoustic resonator according to claim 1 or 2. The sound absorber is a resonance type sound absorber connected through an opening provided in the tubular member.
The acoustic resonator according to any one of claims 1 to 3. The sound absorber is a plate vibration type sound absorber,
The acoustic resonator according to any one of claims 1 to 3. The tubular member has an open end at one end and a closed end at the other end,
The sound absorber is provided at the closed end,
The acoustic resonator according to any one of claims 1 to 5. The first resonance frequency is a primary resonance frequency;
The second resonance frequency is a secondary resonance frequency;
The acoustic resonator according to any one of claims 1 to 6. The first resonance frequency is a primary resonance frequency;
The second resonance frequency is a secondary resonance frequency;
The other resonance frequencies are a third resonance frequency and a fourth resonance frequency,
When the center axis of the hollow region passing through the center of the opening end and the center of the closing end is a coordinate axis, the opening end is 0, and the closing end is 1, the sound absorbing material is 0.82 to 0.00. Arrange in 89 coordinate range,
The acoustic resonator according to claim 6.

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