JP7092635B2 - Sound source housing - Google Patents

Description

The present invention relates to a sound source accommodating body including a sound source and a cylindrical housing for accommodating the sound source inside, and more particularly to a sound source accommodating body capable of reducing the sound emitted by the sound source.

A housing with at least two openings has multiple resonance modes for sound waves. Further, in the configuration in which the sound source is housed inside the housing, when a sound having a frequency close to the resonance frequency of the housing is generated in the sound source, the sound is amplified by the influence of the shape of the housing. Therefore, in the above case, a louder sound is generated (that is, the sound from the sound source is amplified) as compared with the case where the housing is not provided. The amplified sound comes out of the housing and becomes noise, which is a problem.

As a countermeasure against the above noise, it is possible to change the design contents related to the housing such as the shape of the housing and change the resonance frequency with respect to the sound of the housing. Although such a method is an effective soundproofing method, various restrictions may be imposed on the housing, such as the need to ensure ventilation and rigidity. Due to such circumstances, it is often difficult to change the design of the housing.

Further, as another measure, a method of reducing noise by arranging a sound absorbing material in the housing can be considered. For example, in Patent Document 1, in a configuration in which a blower as a sound source is arranged in a housing (specifically, a tubular body constituting a ventilation path), a first having a high density at a position on the upstream side of the blower. The sound absorbing material of No. 1 and the second sound absorbing material having a low density are arranged in the housing. The first sound absorbing material mainly causes friction loss, and the second sound absorbing material mainly causes vibration loss. This makes it possible to obtain a muffling device capable of muffling in a wide frequency band.

Japanese Unexamined Patent Publication No. 10-103728

However, if the sound absorbing material is arranged in the housing as shown in Patent Document 1, the cost increases by the amount of using the sound absorbing material. Further, by arranging the sound absorbing material inside the housing, the space inside the housing is occupied by the sound absorbing material, and the air permeability (ventilation) is impaired by that amount. In order to ensure ventilation while using a soundproofing device such as a sound absorbing material, for example, it is conceivable to install the soundproofing device on the side surface of the housing. In that case, the soundproofing device is installed near the side surface of the housing. Since space is provided, the size of the equipment will be increased. Therefore, in a situation where miniaturization of the device is required, it becomes difficult to install the soundproof device on the side surface of the housing.

The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the following object.
Specifically, the present invention solves the above-mentioned problems of the prior art and reduces the sound generated by the sound source arranged in the housing without changing the configuration of the housing and without impairing the air permeability. It is an object of the present invention to provide a sound source accommodating body capable of capable.

As a result of diligent studies to solve the above problems, the present inventors must take some measures when the resonance frequency in the nth-order mode of the housing is close to the maximum frequency at which the sound generated by the sound source is maximum. It was found that the sound was amplified and became louder and emitted from the housing. Further, in the above case, if the sound source is arranged near the position of the standing wave node of the sound pressure generated in the housing at the frequency corresponding to the nth-order mode, the sound is reduced. And completed the present invention.
That is, the present inventors have found that the above problem can be solved by the following configuration.

[1] A sound source accommodating body including a sound source and a housing for accommodating the sound source inside, and the housing is a cylindrical body extending linearly, and has a first opening and a second opening. The housing has a plurality of resonance modes for sound waves, and the sound source is arranged between the first opening and the second opening inside the housing, and n or more natural numbers. Let fn be the resonance frequency of the housing in the nth-order mode, and Δf be the difference between the resonance frequencies of the housing in each of the mode of the order continuous with n and the nth-order mode. There are fn and fx such that the following relational expression holds when the maximum frequency fx that maximizes the intensity in the audible range is used.
fn−Δf / 4 ≦ fx ≦ fn + Δf / 4
When the wavelength of the sound in the nth-th order mode is λ, the position of the sound source is λ / 8 from the node position of the standing wave of the sound pressure generated in the housing at the frequency corresponding to the nth-order mode. A sound source housing characterized in that it is arranged within the following range.

[2] The sound source accommodating body according to [1], wherein the sound source is a rotating body.
[3] The sound source accommodating body according to [2], wherein the sound source is a fan.
[4] The sound source accommodating body according to [3], wherein the fan has a rotation axis along the extending direction of the housing.
[5] The fan has X blades and rotates R times per minute in a steady state, and the maximum frequency fx is an integral multiple of XR / 60. [3] or [4]. Sound source housing.
[6] The sound source is the sound source accommodating body according to [1], which generates a wind noise due to a gas flowing in the housing.
[7] The sound source is the sound source accommodating body according to [6], which is a resistor against the flow of gas.
[8] The housing is provided through a wall separating the two spaces, and gas flows from one of the two spaces toward the other in the housing [6] or [7]. Sound source housing.
[9] Any of [1] to [8], wherein the first opening is located at one end of the housing and the second opening is located at the other end of the housing in the extending direction of the housing. The sound source housing described in item 1.
[10] The sound source accommodating body according to any one of [1] to [9], wherein the sound source is arranged at the same position as the node position of the standing wave.

The sound source accommodating body of the present invention can reduce the sound generated by the sound source arranged in the housing without changing the configuration of the housing and without impairing the air permeability.

It is sectional drawing which shows the structure of the sound source accommodating body. It is a figure which shows the structure of the sound source accommodating body which concerns on the 1st modification. It is a figure which shows the structure of the sound source accommodating body which concerns on the 2nd modification. It is explanatory drawing of the sound pressure measurement performed by arranging a sound source outside the housing. It is a figure which shows the measurement result of the sound pressure in the mode of each order. It is a figure which shows the simulation model for calculating the mode of a housing. It is a figure which shows the simulation result about the spectrum of a sound pressure level. It is a figure which shows the standing wave of the sound pressure generated in the housing at the mode corresponding to each order mode. It is explanatory drawing of the sound pressure measurement performed by arranging a sound source inside a housing. It is a figure which shows the spectrum of the sound pressure level for ideal white noise. It is a figure which shows the arrangement position of the sound source in a housing. FIG. 10 is a diagram showing a spectrum of a sound pressure level when the arrangement position of the sound source that generates the white noise shown in FIG. 10 is changed inside the housing. It is a figure which shows the spectrum of the sound generated by the sound source which concerns on this invention. FIG. 13 is a diagram showing a spectrum of sound pressure levels when the arrangement position of the sound source having the spectrum shown in FIG. 13 is changed inside the housing. It is a figure which shows the spectrum of the sound pressure level of the sound generated by the sound source used in Example 1. FIG. It is explanatory drawing about the arrangement position of a sound source and a measurement microphone. It is a figure which shows the result of the sound pressure measurement about Example 1. FIG. It is a figure which shows the result of the sound pressure measurement about the comparative example 1. FIG. It is a figure which shows the result of the sound pressure measurement about the comparative example 2. It is a figure which shows the model for simulating the sound pressure under the conditions of Example 1, Comparative Example 1 and Comparative Example 2. It is a figure which shows the simulation result of a sound pressure. It is a figure which shows the simulation result of the sound pressure obtained by changing the arrangement position of a sound source.

The sound source accommodating body according to the embodiment of the present invention will be described in detail below with reference to the preferred embodiments shown in the accompanying drawings. However, the description of the constituent elements described below may be made based on a typical embodiment of the present invention, but the present invention is not limited to such an embodiment.

In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

As used herein, "same," "similar," and "same" include the error ranges generally tolerated in the art to which the invention belongs. Further, in the present specification, the terms "all", "all", "whole surface", etc. include not only the case of 100% but also the error range generally accepted in the technical field to which the present invention belongs, for example. It shall include cases where it is 99% or more, 95% or more, or 90% or more.

[Sound source housing]
The sound source accommodating body 10 of the present invention is, for example, a sound source accommodating body composed of a housing accommodating a motor, and a housing accommodating a rotating body such as a fan (specifically, a housing of a server fan for a computer). It is a sound source accommodating body composed of a body, a housing of a dryer, a housing of a vacuum cleaner, etc.). Examples of other sound source accommodating bodies 10 include a sound source accommodating body forming a ventilation facility (ventilation duct) of a building, a sound source accommodating body forming a transport path for transporting gas or liquid (fluid), a device accommodating space, and the like. Examples thereof include a sound source accommodating body used for the purpose of providing the sound source.

As shown in FIG. 1, the sound source accommodating body 10 of the present invention has a housing 12 and a sound source. FIG. 1 is a schematic cross-sectional view showing the configuration of the sound source accommodating body 10 according to the embodiment of the present invention.

The housing 12 is a cylindrical body that houses a sound source inside the housing 12, and extends linearly. The housing 12 is arranged and used in a free space or a closed space. Further, the housing 12 has a first opening 12a and a second opening 12b. The first opening 12a is located at one end of the housing 12 in the extending direction of the housing 12, and the second opening 12b is located at the other end of the housing 12. The sound source is arranged between the first opening 12a and the second opening 12b inside the housing 12.

In the following, a cylindrical housing 12 will be described as an example, but the shape of the housing 12 is not particularly limited, and the cross-sectional shape (opening shape) may be other than circular, for example. It may be a polygonal shape such as a quadrangle, a triangle, a pentagon, an ellipse, or an indefinite shape. Further, with respect to the housing 12 described below, the size of the inner diameter is constant, but the inner diameter is not limited to this, and the inner diameter may change at an intermediate position in the extending direction of the housing 12. That is, the opening size of the first opening 12a and the opening size of the second opening 12b may be different from each other.
Further, the housing 12 may be arranged so as to penetrate the wall B as shown in FIG. FIG. 2 is a diagram showing a sound source accommodating body 10X according to the first modification. In the case shown in FIG. 2, the housing 12 is provided so as to penetrate the wall B separating the two spaces, and the housing 12 serves as a fluid from one of the two spaces toward the other. A gas, for example, air W flows. The housing 12 may be arranged so as to be completely buried in the wall B.

Examples of the sound source housed inside the housing 12 include devices that generate sound by the sound source itself, and examples thereof include devices that generate operating sound or driving sound (specifically, rotating bodies such as fans, motors, and pumps). Etc.), electrical control equipment that generates noise during operation (specifically, power control units (PCUs) including inverters, power supplies, boosters, step-up converters and inverters, large-capacity capacitors, ceramic capacitors, inductors) , Coil, switching power supply, transformer, etc.), and mechanical parts that generate frictional noise (specifically, a moving mechanism by a gear or an actuator, etc.).

Sound (noise) is generated from the sound sources listed above, and the noise propagates in the air. When the sound source is a rotating body, a sound having a frequency corresponding to the rotation speed is generated. Explaining the configuration shown in FIG. 1 as an example, in the configuration shown in FIG. 1, the fan 14 as a rotating body is housed inside the housing 12. The fan 14 is an axial flow fan and has X blades 16 and a rotating shaft 18 along the extending direction of the housing 12. Further, the fan 14 rotates R times per minute in a steady state. In such a configuration, the rotation of the fan 14 generates a sound corresponding to the rotation speed, and the maximum frequency fx of the sound is an integral multiple of XR / 60. Here, the maximum frequency fx is a frequency at which the intensity of the sound generated by the sound source in the audible range (specifically, sound pressure: Sound Pressure Level [unit: dB]) is maximized. Also called peak frequency.

Further, the sound source includes a device that generates a wind noise due to a gas (fluid) flowing in the housing 12, in addition to a device that the sound source itself generates a sound. Examples of the sound source that generates the wind noise include the fan 14 and the resistor 20 shown in FIG. 3 arranged in the housing 12. The resistor 20 is a resistor against the flow of the air flow, and is an object that hits the air flow on the downstream side of the fan 14, for example, a sound absorbing material such as urethane, glass wool, and felt; a resonance made of a metal or acrylic resin made of a rigid body. Mold soundproof structure; a board for controlling the drive of the fan 14 and attached wiring; a fixture such as a screw used for assembling the housing 12 and the like.
Note that FIG. 3 is a schematic cross-sectional view of the sound source accommodating body 10Y according to the second modification, and in the configuration shown in the figure, the fan 14 and the resistor 20 are housed inside the housing 12. However, the present invention is not limited to this, and the configuration may be such that there is no fan 14 and only the resistor 20 is housed inside the housing 12.

By the way, it is known that there are resonance frequencies of the housing 12 in a plurality of resonance modes, more specifically, a primary mode and a mode having an order of n (n is a natural number of 2 or more) or higher. That is, the housing 12 has a plurality of resonance modes with respect to sound waves. Further, the resonance frequency of the housing 12 is determined according to the shape of the housing 12. Further, according to the study by the present inventors, it has been found that the sound near the resonance frequency tends to pass through the housing 12 and be resonantly amplified and output from the housing 12. This can be clarified by the experimental system shown in FIG. Specifically, a white noise sound is generated from a sound source MS arranged on the outside of the housing 12 (specifically, a position facing the opening on one end side of the housing 12), and the sound pressure of the sound is generated. The level (SPL) is measured by a measurement microphone MP arranged at a position facing the opening on the other end side of the housing 12. By this measurement, as shown in FIG. 5, at the resonance frequencies fn, fn + 1, fn + 2 ... Of the housing 12 in each mode of n (n is a natural number of 2 or more) or higher, the sound from the sound source MS is the housing. It was found that it was easy to go out to the measurement microphone MP side after passing through 12.
Note that FIG. 4 is an explanatory diagram of sound pressure measurement performed by arranging the sound source MS on the outside of the housing. FIG. 5 is a diagram showing the measurement results of sound pressure in each mode of order, in which the horizontal axis represents frequency and the vertical axis represents sound pressure (SPL). Further, in FIG. 5, the part indicated by the arrow indicates the sound pressure at the resonance frequency in each resonance mode of order n or higher.

The above phenomenon is also clear from the simulation using the model shown in FIG. For the simulation, the acoustic module of the finite element method calculation software COMSOL MultiPhysics ver5.3a (COMSOL) is used, and for the model, the hemisphere of one of the two spaces connected by the tubular housing 12 is used. A sound wave was incident from the surface (incident surface Si) to reach the hemispherical surface (emission surface So) of the other space. The outside of the exit surface So was a perfect matched layer (PML), and a cylindrical axis symmetry model with respect to the Z axis (axis corresponding to the vertical direction in FIG. 6) was used. The inner diameter of the housing 12 was 75 mm, and the total length (length d in FIG. 6) was 195 mm. Then, the sound pressure spectrum of the sound wave in each part of the exit surface So was obtained, the average value of the squared values was calculated, and the spectrum of the sound pressure level was acquired using the value. Incidentally, FIG. 6 is a diagram showing a simulation model for calculating the mode of the housing 12.

According to the above simulation result, as shown in FIG. 7, at the resonance frequency in each of the 1st to 4th order modes, the sound pressure of the sound that has passed through the housing 12 and reached the exit surface So becomes maximum. That is, when the maximum frequency (peak frequency) of the sound generated by the sound source matches the resonance frequency of the housing 12, the above sound is amplified in the housing 12 and comes out of the housing 12. The amplified sound becomes noise and becomes a problem. By the way, at the frequency corresponding to the resonance mode of the nth order (n is a natural number of 2 or more), a standing wave of sound pressure with a node is generated inside the housing as shown in FIG. .. This standing wave represents the sound pressure distribution in the housing 12. By the way, when n is 1, there is no node inside the housing.
Note that FIG. 7 is a diagram showing the results of a simulation relating to the sound pressure spectrum. FIG. 8 is a diagram showing a standing wave of sound pressure generated in the housing 12 at a frequency corresponding to the nth-order mode, and more specifically, a standing wave when n is 2, 3 and 4. Shows.

Further, according to the study by the present inventors, in a configuration in which a sound source is housed inside the housing 12, when a sound having a frequency close to the resonance frequency of the housing 12 is generated by the sound source, the sound is generated by the housing 12. It was found that it could be amplified by resonance. In this case, the sound coming out of the housing 12 may be louder than the sound when the housing 12 is not provided.

On the other hand, in the configuration in which the sound source is housed inside the housing 12, the present inventors adjust the arrangement position of the sound source inside the housing 12 to suppress the resonance of the housing 12 and suppress the resonance of the housing 12. It was clarified that the intensity (sound pressure) of the sound coming out of 12 becomes smaller. This can be clarified by the experimental system shown in FIG. FIG. 9 is an explanatory diagram of sound pressure measurement performed by arranging a sound source inside the housing.

Specifically, the sound source MS generates a white noise sound having a spectrum as shown in FIG. Further, in the experimental system of FIG. 9, the arrangement position of the sound source MS is adjusted inside the housing 12, and specifically, the sound source Ms is arranged at the position P1 or the position P2 shown in FIG. Here, the position P1 is a standing wave of the secondary resonance mode generated in the housing 12 in the extending direction of the housing 12 (strictly speaking, the housing 12 at a frequency corresponding to the secondary resonance mode). It is a position that coincides with the node position of the standing wave of sound pressure generated inside. The position P2 is a position separated from the above-mentioned node position in the extending direction of the housing 12, specifically, the distance from the node position when the wavelength of the standing wave is λ (unit is m). It is a position that is larger than λ / 8.
Note that FIG. 10 is a diagram showing a spectrum of sound pressure levels for ideal white noise. FIG. 11 is a diagram showing the arrangement position of the sound source MS in the housing 12.

When the sound source MS is at the position P2, as shown in FIG. 12, the sound is amplified at the frequency f2 corresponding to the secondary mode and the frequency in the vicinity thereof as compared with the case without the housing, and the housing is amplified. Comes out of twelve.

On the other hand, when the sound source MS is at the position P1, as shown in FIG. 12, the sound having a frequency extremely close to the frequency f2 corresponding to the secondary mode is weakened.
Note that FIG. 12 is a diagram showing a spectrum of the sound pressure level when the arrangement position of the sound source MS that generates the white noise shown in FIG. 10 is changed inside the housing.

As described above, if the sound source MS is arranged near the node position of the standing wave of the sound pressure at the frequency corresponding to the n-th order mode inside the housing 12, the housing 12 in the n-th order mode It is possible to weaken the resonance of the housing 12 and reduce the sound emitted from the housing 12.
In the above example, the white noise is generated from the sound source MS, but when the spectrum of the sound emitted from the sound source MS has a maximum value near the frequency f2 in the audible range, the frequency f2 in the noise of the entire audible range. The ratio (contribution) of the noise of the noise increases. In such a case, if the sound source MS is arranged near the node position of the standing wave of the sound pressure at the frequency f2, the resonance at the frequency f2 having a large contribution can be weakened. As a result, the noise itself is greatly reduced.

Focusing on the above points, in the present invention, when the wavelength of the sound at the frequency corresponding to the nth-order mode is λ, the position of the sound source in the housing 12 is the distance from the node position of the standing wave. It is set within the range of λ / 8 or less. Further, between the resonance frequency fn of the housing in the nth-order mode in the audible range and the maximum frequency fx (that is, the peak frequency) at which the sound pressure of the sound generated by the sound source in the audible range is maximized, the following There are fn and fx such that the relational expression (1) of is satisfied.
fn−Δf / 4 ≦ fx ≦ fn + Δf / 4 (1)
Here, Δf is the difference between the resonance frequencies of the housing 12 in each of the mode of the order continuous with n (that is, n + 1 or n-1) and the mode of the nth order, as described above.

That is, in the present invention, the spectrum of the sound emitted by the sound source arranged in the housing 12 has a distribution as shown in FIG. 13, and the maximum frequency fx (peak frequency) is in the vicinity of the resonance frequency fn, and strictly speaking. Is a value that satisfies the above relational expression (1). FIG. 13 shows a spectrum of a sound generated by a sound source according to the present invention, and more specifically, is a diagram showing a spectrum of a sound having a maximum sound pressure at a frequency fx near the resonance frequency.

In the case where the spectrum of the sound generated by the sound source according to the present invention is the spectrum shown in FIG. 13, if the sound source is arranged at the position P2, the sound is amplified at the resonance frequency and the sound is amplified as shown in FIG. The pressure increases. In FIG. 14, the resonance frequency of the housing 12 in the secondary mode is f2.
On the other hand, when the sound source is arranged at the position P1 (the node position of the standing wave in the second-order resonance mode), as shown in FIG. 14, the sound source resonates as compared with the case where the sound source is arranged at the position P2. The sound pressure at the frequency drops significantly. The sound source accommodating body of the present invention utilizes such a phenomenon, and aims to reduce the sound emitted from the housing 12 by adjusting the arrangement position of the sound source.
Note that FIG. 14 is a diagram showing the sound pressure when the arrangement position of the sound source, which is the spectrum of the sound shown in FIG. 13, is changed inside the housing 12. Specifically, FIG. 14 shows a graph when the sound source is arranged at the position P1 and a graph when the sound source is arranged at the position P2.

As described above, in the sound source accommodating body of the present invention, it is possible to effectively reduce the sound generated by the sound source only by adjusting the arrangement position of the sound source in the housing 12. That is, according to the sound source accommodating body of the present invention, it is not necessary to change the shape of the housing 12 or the like, and it is not necessary to arrange the sound absorbing material or the like in the housing 12, so that the sound absorbing material or the like is used for ventilation. Does not impair sex. In this respect, the sound source accommodating body of the present invention is more advantageous than the muffling device described in Patent Document 1.

Specifically, in the sound deadening device described in Patent Document 1, a sound absorbing material is arranged in the housing for sound deadening, but the cost increases due to the use of the sound absorbing material, and the inside of the housing is increased. Breathability (ventilation) is impaired because the space is occupied by the sound absorbing material. On the other hand, in order to ensure ventilation while using a soundproofing device such as a sound absorbing material, for example, it is conceivable to install the soundproofing device on the side surface of the housing or increase the size of the housing. In that case, it leads to enlargement (larger size) of the housing and the periphery of the housing.

On the other hand, in the sound source accommodating body of the present invention, the sound pressure of the sound generated by the sound source can be lowered only by adjusting the arrangement position of the sound source without arranging the sound absorbing material in the housing 12 (Fig.). 14). Therefore, it is not necessary to change the configuration of the housing 12 and the periphery of the housing 12, and the air permeability of the housing 12 is not impaired. Therefore, with the sound source accommodating body of the present invention, it is possible to effectively reduce the sound generated by the sound source while avoiding the enlargement of the housing and the loss of air permeability.

In order to more effectively reduce the sound generated by the sound source, the distance between the arrangement position of the sound source and the node position of the standing wave is such that the arrangement position of the sound source is the same as the node position. preferable.
Further, when the housing 12 is a linear housing, the frequency corresponding to the mode and the positions of the antinodes and nodes at the frequency are uniquely determined according to the length of the housing, but the housing 12 Even if is a housing having a complicated shape other than a straight line, the sound pressure at an arbitrary frequency can be measured by measuring the sound pressure while shifting the position of the microphone little by little (for example, by 5 mm) inside the housing 12. The position of the abdomen and nodes can be identified.

Hereinafter, the present invention will be described in more detail based on the following examples. The materials, amounts, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the invention should not be construed as limiting by the examples below.

[Example 1]
-About the sound source-
In Example 1 and Comparative Examples 1 and 2 described later, a sound source that generates sound so as to have a spectrum of the sound pressure level shown in FIG. 15 was used as a sound source. FIG. 15 is a diagram showing a spectrum of a sound pressure level of a sound generated by the sound source used in the first embodiment. The spectrum of the sound pressure level shown in FIG. 15 was measured with a measurement microphone arranged at a position 300 mm away from the sound source, using only the sound source without installing the housing.
As shown in FIG. 15, the sound generated by the above sound source is a combination of white noise having a substantially constant sound pressure (specifically, constant near 0 dB) and a peak sound having a sound pressure of 30 dB at a frequency of 1400 Hz. It was done. That is, the spectrum of the sound pressure level of the sound generated by the above sound source reaches the maximum (peak) at 1400 Hz.

-About the housing-
In Example 1 and Comparative Examples 1 and 2, a cylindrical housing 12 was prepared. Explaining the shape of the housing 12 with reference to FIG. 16, the diameter r is 75 mm, and the total length L (length in the extension direction) is 195 mm. Further, when the end correction value La is calculated as 0.6 L (= 22.5 mm), the total length L + 2La of the housing 12 after the end correction is 240 mm. The housing having the above-mentioned shape was placed on a sound-absorbing urethane (not shown) having a side of 50 cm and a thickness of 5 cm. Incidentally, FIG. 16 is an explanatory diagram regarding the arrangement position of the sound source and the measurement microphone MP.
Further, the above-mentioned sound source is arranged in the housing 12. Further, in order to measure the sound pressure of the sound generated by the sound source and output from the housing 12, the measurement microphone MP is arranged outside the housing 12. Here, as shown in FIG. 16, the measurement microphone MP is arranged at a position separated from the central portion of the housing 12 in the extending direction of the housing 12 by a distance I (specifically, 30 cm). The height of the measurement microphone MP from the floor was set to 15 cm.
In the following, each of the arrangement position of the sound source and the node position of the standing wave in the extension direction of the housing 12 will be represented by the distance from the corrected open end (the open end on the left side in FIG. 16). do.

Table 1 shows the corresponding frequencies (resonance frequencies) of each resonance mode and the node positions of the standing waves generated in each resonance mode with respect to the housing 12 having the above-mentioned shape.

Here, the maximum frequency fx (peak frequency) of the sound generated by the above sound source is 1400 Hz as described above. Further, as is clear from Table 1, the difference Δf of the corresponding frequencies (resonance frequencies) in each of the two consecutive modes is 714.6 Hz. Therefore, the maximum frequency fx satisfies the following relational expression with the resonance frequency fn when the mode order n of the resonance is 2. In other words, in Example 1, Comparative Example 1 and Comparative Example 2, there is a resonance frequency fn (n = 2) that satisfies the following relational expression between the maximum frequencies fx.
fn−Δf / 4 ≦ fx ≦ fn + Δf / 4 (n = 2)

The corresponding frequency (resonance frequency) of each resonance mode shown in Table 1 can also be obtained from the simulation using the model of FIG. 6 described above, and the sound pressure simulation result shown in FIG. 7 (specifically, It is substantially the same as the peak frequency shown in FIG. 7.

-Sound source placement position-
In the first embodiment, the sound source arrangement position X (specifically, the distance from the corrected opening end) in the housing 12 is set to 120 mm. As can be seen from Table 1, this position coincides with the node position of the standing wave generated in the housing 12 at the frequency corresponding to the second-order resonance mode.
Further, in Comparative Example 1, the sound source arrangement position X in the housing 12 was set to 180 mm. This position is 2λ / 8 from the node position of the standing wave (strictly speaking, the node position closer to the open end of the housing 12) when the wavelength of the frequency corresponding to the second-order resonance mode is λ. Only apart.
Further, in Comparative Example 2, the sound source arrangement position X in the housing 12 was set to 205 mm. This position is 1.2λ from the node position of the standing wave (strictly speaking, the node position closer to the open end of the housing 12) when the wavelength of the frequency corresponding to the second-order resonance mode is λ. Only / 8 apart.

-evaluation-
In each of Example 1, Comparative Example 1 and Comparative Example 2, the sound pressure of the sound generated by the sound source and passing through the housing 12 is measured by the measurement microphone MP (TYPE4152N manufactured by Accor) shown in FIG. did.
The sound pressure measurement result in Example 1 is shown in FIG. 17, the sound pressure measurement result in Comparative Example 1 is shown in FIG. 18, and the sound pressure measurement result in Comparative Example 2 is shown in FIG. In addition, each of FIG. 17, FIG. 18 and FIG. 19 shows the respective measurement results, and further, the spectrum of the sound pressure level of the sound generated by the sound source when the housing 12 is not provided (that is,). , The spectrum shown in FIG. 15) is shown as a reference example.

In Example 1, as can be seen from FIGS. 17 to 19, the sound pressure at the peak frequency is significantly reduced as compared with Comparative Examples 1 and 2 and the reference example in which the housing 12 is not provided. In Comparative Examples 1 and 2, the sound pressure at the peak frequency is higher than that in the reference example in which the housing 12 is not provided, because the sound generated by the sound source is amplified by the resonance of the housing 12. Is considered to be.

[Simulation 1]
Under the same conditions as in Example 1, Comparative Example 1 and Comparative Example 2 described above, the sound pressure generated by the sound source and coming out of the housing 12 is obtained by simulation using the model shown in FIG. 20. rice field. FIG. 20 is a diagram showing a model for simulating sound pressure under the conditions of Example 1, Comparative Example 1 and Comparative Example 2.

For the simulation, the acoustic module of the finite element method calculation software COMSOL MultiPhysics ver5.3a (COMSOL) was used. For the model, a point sound source (monopole point source) as a sound source MS is placed in the housing 12, and the sound emitted from this point sound source is transmitted to each of the two spaces connected by the cylindrical housing 12. It reached the provided hemispherical exit surface So. The outside of the exit surface So was a perfect absorbing boundary region PML. The sound emitted from the point sound source is a combination of white noise having a substantially constant sound pressure (specifically, constant at around 0 dB) and a peak sound having a sound pressure of 20 dB at a frequency of 1400 Hz. That is, the spectrum of the sound generated by the above-mentioned point sound source has a maximum (peak) at 1400 Hz.

Further, in the above model, the arrangement position of the sound source MS is changed corresponding to each of Example 1, Comparative Example 1 and Comparative Example 2. In Simulation 1, the center position in the extension direction of the housing 12 is set as the origin position, and the arrangement position Z of the sound source MS is represented by the distance from the origin position in the extension direction of the housing 12.

Under the conditions corresponding to the first embodiment, the arrangement position Z of the sound source MS is 0 mm. This position coincides with the node position of the standing wave generated in the housing 12 at the frequency corresponding to the second-order resonance mode.
Further, under the condition corresponding to Comparative Example 1, the arrangement position Z of the sound source MS is 60 mm. This position is close to the node position of the standing wave (strictly speaking, close to the center of the housing 12), where λ is the wavelength of the standing wave generated in the housing 12 at the frequency corresponding to the second-order resonance mode. It is 2λ / 8 away from the node position).
Further, under the condition corresponding to Comparative Example 2, the arrangement position Z of the sound source MS is 85 mm. This position is close to the node position of the standing wave (strictly speaking, close to the center of the housing 12), where λ is the wavelength of the standing wave generated in the housing 12 at the frequency corresponding to the second-order resonance mode. It is 1.2λ / 8 away from the node position).

FIG. 21 shows spectra of sound pressure levels simulated under the conditions of Example 1, Comparative Example 1 and Comparative Example 2. As shown in FIG. 21, it was found that the spectrum of the sound pressure level simulated under each condition was in good agreement with the measured results (results shown in FIGS. 17 to 19) described above. In Simulation 1, the sound pressure is obtained by squared the sound pressure on the exit surface So, calculate the average value of the squared sound pressure, obtain the logarithm, and further convert it into dB (decibel). ..

[Simulation 2]
In the simulation 2, the peak sound (specifically, the sound of 1400 Hz) emitted from the housing 12 is changed while changing the arrangement position Z of the sound source MS by using the same method and simulation model as the simulation 1 described above. The pressure was simulated. FIG. 22 shows the simulation result of the sound pressure of the peak sound obtained by changing the arrangement position Z of the sound source MS. As shown in FIG. 22, when the arrangement position Z of the sound source MS is in the range of λ / 8 or less (the range indicated by the arrow with the symbol A in FIG. 22), the arrangement position Z of the sound source MS is λ / 8. It was found that the sound pressure of the peak sound became smaller than that in the case of exceeding. From this, when the maximum frequency fx of the sound is near the resonance frequency fn of the housing 12, the sound source MS is arranged within the range of λ / 8 or less from the node position of the standing wave to obtain the maximum frequency fx. It was clarified that the sound pressure of the sound pressure can be effectively reduced.

Since the conditions corresponding to Example 1 of the present invention and Example 1 of Simulations 1 and 2 described above are all within the scope of the present invention, the effect of the present invention is clear.

10 Sound source housing 10X Sound source housing according to the first modification 10Y Sound source accommodation according to the second modification 12 Housing 12a First opening 12b Second opening 14 Fan 16 Blades 18 Rotating shaft 20 Resistor MS Sound source MP Measurement microphone W Air flow

Claims (9)

A sound source accommodating body having a sound source and a housing for accommodating the sound source inside.
The housing is a cylindrical body extending in a straight line, has a first opening and a second opening, and has a first opening and a second opening.
The housing has a plurality of resonance modes with respect to sound waves.
The sound source is arranged inside the housing between the first opening and the second opening, and includes a resistor against the flow of gas flowing in the housing .
Let n be a natural number of 2 or more, let fn be the resonance frequency of the audible range of the housing in the nth-order mode, and be between the resonance frequency of the housing in each of the mode of the order continuous with n and the mode of the nth order. When the difference is Δf and the maximum frequency fx is the maximum intensity of the sound generated by the sound source in the audible range, fn and fx such that the following relational expression holds exist.
fn−Δf / 4 ≦ fx ≦ fn + Δf / 4
When the wavelength of the sound at the frequency of the nth order mode is λ, the arrangement position of the sound source is the distance from the node position of the standing wave of the sound pressure generated in the housing at the frequency corresponding to the nth order mode. A sound source accommodating body characterized in that is arranged within a range of λ / 8 or less. The sound source accommodating body according to claim 1, wherein the sound source includes a rotating body. The sound source accommodating body according to claim 2, wherein the sound source includes a fan. The sound source accommodating body according to claim 3, wherein the fan has a rotation axis along an extension direction of the housing. The fan has X blades and, in a steady state, rotates R times per minute.
The sound source accommodating body according to claim 3 or 4, wherein the maximum frequency fx is an integral multiple of XR / 60. The sound source housing according to claim 1, wherein the sound source generates a wind noise due to a gas flowing in the housing. The housing is provided so as to penetrate a wall separating the two spaces.
The sound source accommodating body according to any one of claims 1 to 6, wherein the gas flows from one of the two spaces toward the other in the housing. Any of claims 1 to 7 , wherein the first opening is located at one end of the housing and the second opening is located at the other end of the housing in the extending direction of the housing. The sound source accommodating body described in the first item. The sound source accommodating body according to any one of claims 1 to 8 , wherein the arrangement position of the sound source is the same position as the node position of the standing wave.

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