JP2012181234A - Sound reduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound reduction method for preventing emission of sound, from an opening toward the same direction together with air fed by a blower means toward the outside, of a specific frequency generated by a driving mechanism such as a motor without being reduced.SOLUTION: In the method of reducing the sound generated from a sound source and emitted from the opening communicating the inside/outside of a housing, a plurality of channels whose openings communicate the inside/outside of the housing and whose center-to-center distances between adjacent channels are the same are formed, and the lengths of the adjacent channels are set so that phase differences are produced in sound waves emitted through the plurality of channels from the sound source.

Description

  The present invention relates to a sound reduction method, and more particularly to a sound reduction method that can be suitably employed in an apparatus that requires air permeability.

  Conventionally, in a product such as an air conditioner, a duct, or a personal computer, for example, a blower such as a fan is rotated by a driving mechanism such as a motor provided inside the casing, and the opening is provided in the casing. A device that exhibits a heating effect or a cooling effect by releasing air to the outside is known.

JP-A-6-35489

However, in the product having the above configuration, the sound generated from the driving mechanism such as a motor is sent out from the opening in the same direction together with the air sent to the outside by the blowing means, There is a drawback that even unpleasant noise is sent out to those who enjoy the air sent out to the outside and nearby dwellings.
Therefore, the present invention provides a sound reduction method for suppressing sound generated from a driving mechanism such as a motor together with the air sent to the outside by the blowing means without being reduced in the same direction from the opening. The purpose is to do.

In order to solve the above problems, the present invention provides a method for reducing sound emitted from a sound source that emits sound from a sound source through an opening communicating with the inside and outside of a housing. Are formed as a plurality of channels having the same center-to-center distance between adjacent channels, and the lengths of the channels adjacent to each other cause a phase difference in sound waves emitted from the sound source through the plurality of channels. It was set as the flow path length to be made.
According to this aspect, the length of the adjacent channels is set to a channel length that causes a phase difference in the sound waves emitted from the sound source through the plurality of channels, so that the sound waves emitted from the channels are mutually connected. Since they interfere with each other, the emitted sound can be reduced, or the direction of the emitted sound can be directed in a direction different from the extending direction of the flow path.
As another aspect, the lengths of the plurality of channels are set to the same channel length in which the phase differences of the sound waves emitted through the channels adjacent to each other are equal.
According to this aspect, the length of the adjacent channels is set to the channel length in which the phase difference is equal to the sound wave emitted from the sound source through the plurality of channels, so that the sound waves emitted from the channel are mutually Since they interfere with each other, the emitted sound can be easily reduced, or the direction of the emitted sound can be directed in a direction different from the extending direction of the flow path.
As another aspect, the lengths of the channels adjacent to each other are the channel lengths in which sound waves emitted from the sound source through the plurality of channels have the same amplitude and opposite phase.
According to this aspect, since the sound waves emitted from the sound source through the plurality of flow paths have the same length and the opposite phase, the sound waves emitted from the flow paths can be obtained. Since they interfere so as to cancel each other, the emitted sound can be reduced. In particular, the effect of canceling out sound waves due to interference can be maximized by adopting the same amplitude and opposite phase.
As another aspect, the angle of the virtual emission surface connecting the sound emission side end portions in the plurality of flow paths is 45 ° with respect to the virtual entry surface connecting the sound entry side end portions in the plurality of flow paths. It was set as a certain aspect.
According to this aspect, the angle of the virtual emission surface connecting the sound emission side end portions in the plurality of flow paths is set to 45 ° with respect to the virtual entry surface connecting the sound entry side end portions in the plurality of flow paths. Thus, the position where the sound wave emitted from the virtual emission surface interferes with the direction in which the sound travels, so that the direction of the sound wave can be separated from the extending direction of the flow path.
As another aspect, the angle of the virtual emission surface connecting the sound emission side end portions in the plurality of flow paths is 90 ° with respect to the virtual entry surface connecting the sound entry side end portions in the plurality of flow paths. It was set as a certain aspect.
According to this aspect, the angle of the virtual emission surface connecting the sound emission side end portions in the plurality of flow paths is set to 90 ° with respect to the virtual entry surface connecting the sound entry side end portions in the plurality of flow paths. As a result, the sound waves emitted from the adjacent flow paths cancel each other, so that the emitted sound can be reduced.

The schematic diagram which shows the housing | casing which has a sound reduction mechanism. The cross-sectional view which shows the shape of an opening part. The sound pressure distribution map of the opening part which does not have several flow paths. The sound pressure distribution map of the opening part which has a sound reduction mechanism. The model figure when a sound reduction mechanism is applied to a ventilation duct. The sound pressure distribution diagram when the 4000 Hz sound wave S is emitted into the ventilation duct. The sound pressure distribution diagram when the sound wave S of 5000 Hz is emitted into the ventilation duct. The cross-sectional view which shows the opening part which concerns on another form. The sound pressure distribution map in the case of having a sound reduction mechanism according to another embodiment.

  Hereinafter, the present invention will be described in detail through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are included in the invention. It is not necessarily essential to the solution, but includes a configuration that is selectively adopted.

FIG. 1 is a plan view schematically showing a sound reduction method and a sound reduction mechanism according to the present invention.
In the figure, a housing 1 is, for example, an acrylic box, and has a rectangular bottom surface 1A on which a sound source 2 is placed, a wall surface 1B that rises from four sides of the bottom surface 1A, and a lid that closes on the wall surface 1B. Consists of faces. The configuration of the housing 1 is not limited to the above configuration. For example, a box such as a speaker box having a diaphragm inside and a casing of an air conditioner having a driving motor inside is assumed. The housing 1 is not limited to acrylic, but may be formed by molding another resin or metal sheet metal.

  A sound source 2 is provided inside the housing 1. In the present embodiment, the sound source 2 is, for example, a speaker that can output a sine sound having a frequency in a predetermined band. The sine sound output from the sound source 2 is output toward the wall surface 1B facing the sound source 2, and is emitted from the opening 3 provided in the wall surface 1B.

FIG. 2 is a cross-sectional view of the opening 3.
As shown in the figure, the opening 3 is an opening provided in one of the four wall surfaces 1 </ b> B and communicates with the inside and outside of the housing 1. Further, as shown in FIG. 2, the opening 3 in the present embodiment is configured by a plurality of flow paths 3A to 3D, and the sound wave S output from the sound source passes through each flow path 3A to 3D and is externally transmitted. To be released. Hereinafter, details of the opening 3 will be described.

As shown in FIG. 2, the plurality of flow paths 3A to 3D constituting the opening 3 are formed by a plurality of pieces 4A to 4E extending from the vertical wall surface 1B. Each piece 4A thru | or 4E in this embodiment has an angle (theta) of 45 degrees with respect to the wall surface 1B, and it extends at equal intervals mutually.
Therefore, the distance d between the centers of the flow paths 3A to 3D formed between the pieces 4A to 4E is set to be equal in the adjacent flow paths. Further, in the present embodiment, since the angle θ of 45 ° with respect to the wall surface 1B and the virtual discharge surface R2 described later extend to 90 ° with respect to the virtual entry surface R1, the adjacent flow paths The path difference ΔL between the channel lengths L1 to L4 between 3A to 3D is d√2. When the path difference ΔL between the flow path 3C and the flow path 3D is expressed using the center distance d, the path difference ΔL between the flow path 3C and the flow path 3D on the virtual approach surface R1 side and the virtual discharge surface R2 side is D × SIN45 ° to d / √2 respectively. Therefore, the path difference ΔL between the flow path 3C and the flow path 3D is (d / √2) × 2 = d√2.

  The flow path length L includes a virtual approach surface R1 that is a region into which the sound wave S output from the sound source 2 enters and a virtual discharge surface (virtual outflow surface) that is a region from which the sound wave S that has entered the flow channels 3A to 3D is emitted. ) This is a distance obtained by connecting R2s with a line passing through the center of each flow path. Here, the virtual approach surface R1 is represented by a straight line passing through the base ends of the pieces 4A to 4E. The virtual discharge surface R2 is represented by a straight line passing through the free ends of the pieces 4A to 4E, and the angle formed by the virtual entry surface R1 and the virtual discharge surface R2 in the present embodiment is a right angle as described above.

In this embodiment, since the path difference ΔL of the flow path length L between the adjacent flow paths 3A to 3D is d√2, the path difference ΔL is determined based on the sound wave S input from the virtual approach surface R1. When the frequency corresponds to a half wavelength of the frequency f, the sound waves output from the flow paths 3A, 3B and 3B, 3C and 3C, 3D adjacent to each other are output as sound waves of opposite phase (phase difference = 180 °). Is done. In addition, the sound waves emitted from the flow paths 3A to 3D formed by the pieces 4A to 4E extending at equal intervals have the same amplitude. That is, the path difference ΔL between the channel lengths L of the adjacent channels 3A to 3D is equal to the channel length at which sound waves emitted from the sound source S through the plurality of channels 3A to 3D have the same amplitude and opposite phase. L. By configuring in this way, the sound waves emitted from the flow paths 3A to 3D interfere so as to cancel each other, so that the emitted sounds can be reduced. In particular, the effect of canceling out sound waves due to interference can be maximized by setting the same amplitude and opposite phase.
Since the sound waves output from the respective flow paths 3A to 3D as the sound waves having the same amplitude and opposite phase interfere with each other and cancel each other, the specific frequency component input from the virtual approach surface R1 is removed.
Therefore, since the air discharged from the virtual discharge surfaces R2 of the flow paths 3A to 3D is released to the outside with the specific frequency removed, unpleasant noise does not reach. That is, a sound having a specific frequency component is muted.
When the inclination angle with respect to the wall surface is 45 °, the specific frequency f depends on the center-to-center distance d of each of the flow paths 3A to 3D, as shown in the following formula. It is possible to freely adjust the specific frequency f to be silenced by changing the path difference ΔL of the path length L. Since the path difference ΔL of the flow path length L is d√2, the specific frequency f is expressed by dividing the velocity of the sound wave (sound speed) by the wavelength λ of the specific frequency f. Since the flow path is formed so that the path difference ΔL of the flow path length L is a half wavelength of the specific frequency f, the wavelength λ of the specific frequency f is equal to the path difference ΔL = d√2 of the flow path length L. 2 times. If the speed of sound is c, the specific frequency f is expressed as f = c / (2√2 × d). Therefore, the center distance d can be set by d = c / (f × 2√2).

Hereinafter, experimental examples using the sound reduction mechanism will be described.
FIGS. 3A to 3C show the frequency of the sine sound emitted from the sound source 2 with respect to the opening 3 that does not include the pieces 4A to 4E of the wall surface 1B as a comparative example of the sound reduction mechanism at intervals of about 3000 Hz to 1000 Hz. The sound pressure distribution is shown when the frequency is changed to about 5000 Hz (every octave). FIG. 3D shows a rotation of 15 ° from the vertical direction of the wall 1B to the direction of one wall 1B at a distance of 0.3 m from the center of the opening 3 when the frequency of the sine sound is about 4000 Hz. The results of measuring the wind speed are shown.
4A to 4C show the sound pressure when the target frequency to be reduced is 4000 Hz and the frequency of the sine sound emitted from the sound source 2 is changed from about 3000 Hz to every 1000 Hz (every octave) from about 5000 Hz. Distribution is shown. FIG. 4D shows a rotation of 15 ° from the vertical direction of the wall 1B to the direction of one wall 1B at a distance of 0.3 m from the center of the opening 3 when the frequency of the sine sound is about 4000 Hz. The results of measuring the wind speed are shown.

  In the experiment, the opening width was set to 0.13 m, and the sound source 2 was spaced from the wall surface 1B by 0.5 m. Further, in the pieces 4A to 4E in FIG. 4, the center-to-center distance d was set to 0.03 m so as to correspond to 4000 Hz, and inclined by 45 ° with respect to the wall surface 1B. The measurement area of the sound wave S emitted from the opening 3 is a 1 m × 1 m area separated by 0.1 m from the wall surface 1B, and microphones are arranged every 5 cm in the vertical and horizontal directions in the area via the flow paths 3A to 3D. Each of the sound pressure distributions of the sound waves S emitted was investigated.

The experimental results will be described below.
As shown in FIGS. 3A to 3C, in the opening 3 that does not have the pieces 4A to 4E, the region in which the sound pressure increases is separated from the wall surface 1B as the frequency increases. Isotropically spreading. In particular, when the frequency exceeds 4000 Hz, directivity in which a region with a high sound pressure extends in a direction perpendicular to the wall surface 1B appears. Moreover, as shown in FIG.3 (d), the wind direction discharge | released from the opening part 3 has faced the perpendicular direction with respect to the wall surface 1B along the area | region where a sound pressure is large.

  On the other hand, when the pieces 4A to 4E are provided in the opening 3 so as to reduce the sound wave having a frequency of about 4000 Hz, as shown in FIG. 4B, the sound is emitted through the pieces 4A to 4E. In the sound wave, the spread of the sound pressure distribution is smaller than that in the case of only the opening (FIG. 3B), and the sound waves emitted from the flow paths 3A to 3D interfere with each other and cancel each other, thereby reducing the sound pressure. I understand that Further, by providing the pieces 4A to 4E in the opening 3 so as to reduce the frequency of about 4000 Hz, about 3000 Hz and about 5000 Hz, which are about 4000 Hz before and after the reduction target (FIGS. 4A and 4C). It can be seen that the sound pressure of the emitted sound wave is also reduced compared to)).

From the above results, at about 4000 Hz, which is the silencing target in the present embodiment, the sound waves S of the same amplitude emitted from the flow paths 3A to 3D interfere with each other so as to cancel each other, so that the wall portions 1B from the pieces 4A to 4E. It was found that quietness can be obtained except during the period up to. That is, by applying a louver structure corresponding to the above-mentioned pieces 4A to 4E to an outlet of an air conditioner such as an air conditioner, what is the direction of the wind emitted from the outlet shown in FIG. Silence can be imparted regardless.
In the present embodiment, the frequency of the sound wave S emitted from the sound source 2 has been described as about 4000 Hz. However, the paths of the adjacent channel lengths L1 to L4 of the pieces 4A to 4E according to the frequency at which the sound wave S is desired to be reduced. The target frequency can be reduced by setting the interval d so that the difference ΔL becomes λ / 2.

Hereinafter, a case where the sound reduction mechanism is used for a ventilation duct having a rectangular cross section will be described as a specific application example of the sound reduction mechanism. For example, the basic model of the ventilation duct is a rectangular cross section having a side of 0.12 m and a plurality of ducts having a pipe length of 0.5 m connected by a bent pipe so as to be orthogonal to each other.
FIG. 5A shows a 4000 Hz reduction model in which a piece is arranged on a bent pipe so as to reduce the sound wave S having a frequency of about 4000 Hz propagating in the ventilation duct, and FIG. 5B shows the inside of the ventilation duct. 1 shows a 5000 Hz reduction model in which one part is arranged at the bent part so as to reduce the sound wave S having a frequency of about 5000 Hz propagating in FIG.
FIG. 6A shows the sound pressure distribution when the 4000 Hz sound wave S is emitted into the air duct in the basic model, and FIG. 6B shows the 4000 Hz sound wave S emitted into the air duct in the 4000 Hz reduction model. The sound pressure distribution is shown. FIG. 7A shows the sound pressure distribution when the 5000 Hz sound wave S is emitted into the ventilation duct in the basic model, and FIG. 7B shows the 5000 Hz sound wave S emitted into the ventilation duct in the 5000 Hz reduction model. The sound pressure distribution is shown.
Hereinafter, changes in the sound pressure distribution of the ventilation duct when the sound wave S is released into the pipe line will be described with reference to FIGS.
As shown in FIGS. 5A and 5B, the ventilation duct uses a bent pipe that changes the direction of the flow path to a right angle in the pipe. In the bent tube, for example, the inner wall 8A and the outer wall 8B that change direction change the direction of the flow path at a right angle with an inclination of 45 ° with respect to the flow path. Therefore, a plurality of wall surfaces are arranged in parallel between the inner wall 8A and the outer wall 8B.
As shown in FIG. 5A, in the 4000 Hz reduction model, three pieces 9A to 9C are arranged between the inner wall 8A and the outer wall 8B of the bent tube, and the inner wall 8A and the outer wall 8B are included. In the channel formed by the pieces 9A to 9C, the pieces 9A to 9C are arranged so that the channel length of the adjacent channel is a half wavelength of the above frequency.
As shown in FIGS. 6A and 6B, the sound wave S propagating through the pipe passes through the pieces 9A to 9C, so that the sound wave S is reduced.

Further, as shown in FIG. 5B, in the 5000 Hz reduction model, four pieces 9A to 9D are arranged between the inner wall 8A and the outer wall 8B, and the piece including the inner wall 8A and the outer wall 8B. In the flow path formed between the portions 9A to 9D, the adjacent flow paths are arranged so that the flow path length is a half wavelength of the above frequency.
As shown in FIGS. 7A and 7B, the sound wave S propagating through the pipes passes through the pieces 9A to 9D, so that the sound wave S is reduced.

That is, according to the frequency of the sound wave S emitted into the pipeline, the noise can be reduced without using a sound absorbing material or the like by arranging the pieces at predetermined intervals in the pipeline. In addition, since the specific frequency can be selectively reduced, when the sound emitted from the sound source is composed of a plurality of frequencies, the frequency that becomes the peak of the frequency in the flow path is reduced. By designing, noise can be effectively prevented.
Therefore, even if the air sent to the outside by the blowing means and the sound generated from the driving mechanism such as a motor for driving the blowing means are sent from the opening 3 in the same direction, the sound sent from the opening 3 Is reduced by mutual interference, and it is possible to suppress unpleasant noises for those who enjoy the air sent out to the outside, neighboring residences, and the like.
In the formation of the flow paths 3A to 3D, the pieces 4A to 4E may be provided at equal intervals to generate a path difference ΔL in the amplitude. The interval between the pieces 4A to 4E may be set so that the emitted sound waves have the same amplitude.

FIG. 8 is a cross-sectional view showing another embodiment of the opening 3.
As shown in the figure, the plurality of flow paths 3A to 3D constituting the opening 3 are formed by a plurality of pieces 4A to 4E extending from the vertical wall surface 1B, as in the above-described embodiment. .
Similarly, each of the pieces 4A to 4E has an angle θ of 45 ° with respect to the wall surface 1B and extends at an equal interval. Therefore, also in this embodiment, the center-to-center distance d of the flow paths 3A to 3D is set to be equal between adjacent flow paths.
On the other hand, in the present embodiment, since the angle θ of 45 ° with respect to the wall surface 1B and the virtual discharge surface R2 extend to 45 ° with respect to the virtual approach surface R1, the adjacent flow paths 3A to 3A are. The path difference ΔL of the channel length L between 3Ds is d / √2.

In the present embodiment, since the path difference ΔL of the channel length L between the adjacent channels 3A to 3D is d / √2, the path difference ΔL is the frequency of the sound wave input from the virtual approach surface R1. In the case where it corresponds to a quarter wavelength of f, the sound waves output from the adjacent channels 3A, 3B and 3B, 3C and 3C, D have the same amplitude and the same phase difference (phase difference). = 90 °).
The sound waves output from the virtual emission surface R2 with the same phase difference from each other interfere with each other in the same phase components of the adjacent sound waves, and the specific frequency components input from the virtual entry surface R1 are the flow paths 3A to 3D. The direction is a predetermined angle α with respect to the extension direction. The angle α at which the sound wave S is directed with respect to the flow paths 3A to 3D includes the path difference ΔL between the adjacent flow paths 3A to 3D, and the center distance e between the adjacent flow paths 3A to 3D on the virtual emission surface R2 side. Determined by. Specifically, the angle α directed with respect to the extending direction of the flow paths 3A to 3D is calculated by the following equation (1).
That is, in-phase components of sound waves emitted through the plurality of flow paths 3A to 3D are separated into the extending direction of the pieces 4A to 4E and the sound emitting direction. In the present embodiment, α = 45 °.
That is, the air discharged from the virtual discharge surfaces R2 of the flow paths 3A to 3D is discharged to the outside in a state where the specific frequency is directed in a direction different from the extending direction of the flow paths 3A to 3D, and thus the flow paths 3A to 3D. There is no unpleasant noise on the extension line. Thus, the sound having the specific frequency component is separated from the air emission direction.
Since the specific frequency f depends on the path difference ΔL between the channel lengths L of the adjacent channels 3A to 3D, each channel 3A to 3D has a phase difference equal to the path difference ΔL between the channel lengths L. , And by setting the distance e between the centers of the adjacent flow paths 3A to 3D on the virtual emission surface R2 side so as to be the angle α desired to be directed, the angle α desired to be directed to the specific frequency f to be separated Can be adjusted freely.
In particular, when the angle θ of the virtual emission surface R2 with respect to the wall surface 1B is 45 °, the center-to-center distance e on the virtual emission surface R2 side can be represented by the center-to-center distance d on the virtual entry surface R1 side, and thus the specific frequency f is Since it depends on the center-to-center distance d of each of the channels 3A to 3D as shown in the following equation, the channel length L is changed by changing the center-to-center distance d, and the in-phase sound wave of the specific frequency f is It is possible to freely adjust the direction of interference.
The angle α directed by the above formula (1) is called a main lobe, and is an angle directed by a region having a large sound pressure at which sound waves emitted from the adjacent flow paths 3A to 3D interfere. Therefore, the main lobe angle α having a large sound pressure can be set by generating a phase difference equal to the sound wave emitted from the adjacent flow paths 3A to 3D. In the sound wave interference, in addition to the main lobe, a region having a directivity having a sound pressure smaller than that of the main lobe called a side lobe is formed. The sound pressure distribution can be calculated by the directivity coefficient H (β, α) shown in the following equation (2).
N indicates the number of flow paths, and λ is the wavelength of the frequency at which the sound wave is desired to be directed. Further, β is an angle when scanning the main lobe and the side lobe with the air emission direction as a reference.

Hereinafter, experimental data when the center distance d is 0.03 m are shown.
Hereinafter, experimental examples will be described.
FIGS. 9A to 9C show the sound pressure distribution when the target frequency desired to be separated from the air flow direction is 4000 Hz and the frequency of the sine sound emitted from the sound source 2 is changed from about 3000 Hz to about 5000 Hz every 1000 Hz. Indicates. FIG. 9D shows a rotation of 15 ° from the vertical direction of the wall 1B to the direction of one wall 1B at a distance of 0.3 m from the center of the opening 3 when the frequency of the sine sound is about 4000 Hz. The results of measuring the wind speed are shown.
In the experiment, the opening length was set to 0.13 m, and the sound source was placed 0.5 m away from the opening wall. Moreover, each piece 4A thru | or 4E set the distance d between centers to 0.03 m so that it might correspond to 4000 Hz, and inclined 45 degrees with respect to the wall surface. The measurement area of the sound wave emitted from the opening was a 1 m × 1 m area separated by 0.1 m from the wall surface having the opening, and microphones were arranged every 5 cm vertically and horizontally in the area to examine the distribution of sound pressure. .

The experimental results will be described below.
As shown in FIG. 9A, at about 3000 Hz, a region with a large sound pressure shows directivity along the vertical direction of the wall surface 1B, and the extension direction of the pieces 4A to 4E and the extension direction of the wall surface 1B are the same. A quiet area is formed between them.
Furthermore, as shown in FIGS. 9B and 9C, at about 4000 Hz and about 5000 Hz, a quiet region of sound pressure is formed along the extending direction of the pieces 4A to 4D.
On the other hand, as shown in FIG.9 (d), the direction of the air discharged from the flow path has a sharp directivity in the extending direction of the pieces 4A to 4E. In other words, as shown by the experimental results, it was confirmed that the direction of air flow and the direction of sound travel are separated according to the opening 3 according to the present embodiment. From the above results, it was found that at the target of about 4000 Hz, quietness can be obtained in the extending direction of the pieces 4A to 4E. That is, by applying the louvers corresponding to the pieces 4A to 4E to the outlet of an air conditioner such as an air conditioner as described above, silence can be maintained in the extending direction of the louvers.

In this embodiment, the frequency of the sound wave emitted from the sound source has been described as 4000 Hz. However, the target frequency is set by setting the interval d between the pieces 4A to 4E and the angle θ of the flat plate according to the frequency to be directed. Can be released separately from the direction of air flow.
Therefore, for example, air sent to the outside by the blowing unit and sound generated from a driving mechanism such as a motor that drives the blowing unit are not emitted from the opening in the same direction. It is possible to suppress unpleasant noises from being enjoyed by persons who enjoy the environment and nearby dwellings.
Note that the angle θ of the flat plate with respect to the wall surface 1B need not be limited to 45 °, and may be set according to the directing direction in which the sound wave is directed with respect to the air emission direction.

  As described above, as described in the first and second embodiments, in the sound reduction method according to the present invention, the length of the adjacent channels is set to the sound wave emitted from the sound source through the plurality of channels. It is configured as a channel length that causes a phase difference, and the sound waves emitted from the mutually adjacent channels are made mutually opposite by making the phase difference opposite to the sound waves of the same amplitude emitted from the mutually adjacent channels. Can cancel each other. Further, by configuring a plurality of flow paths having the same amplitude and the same phase difference in the flow paths adjacent to each other, it is possible to separate the interference of sound waves emitted from the flow paths adjacent to each other from the extension direction of the flow paths. it can.

  In the first embodiment and the second embodiment, the flow paths are described as straight lines, but the length of the adjacent flow paths is equal to the sound wave emitted from the sound source through the plurality of flow paths. The flow path may be curved as long as the flow path length is configured. Further, the angle θ of the flat plate need not be limited to 45 °, and may be changed as appropriate according to the direction of air release. In addition, although the sound waves emitted from the plurality of flow paths have the same amplitude, this maximizes the above effect, and the amplitudes may be different. The sound wave S may be a plane wave or a spherical wave.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various modifications or improvements can be added to the above embodiment.

1 housing, 1B wall surface, 2 sound source, 3 opening, 3A thru | or 3D flow path,
4A to 4E One part, d center distance, R1 virtual approach surface, R2 virtual discharge surface.

Claims (5)

A method for reducing sound emitted from an opening that communicates sound generated from a sound source to the inside and outside of a housing,
The opening communicates with the inside and outside of the housing, and is formed as a plurality of channels having equal distances between the centers of the channels adjacent to each other.
A method for reducing sound at a specific frequency, wherein the length of adjacent channels is a channel length that causes a phase difference in sound waves emitted from the sound source through the plurality of channels.   2. The sound reduction method for a specific frequency according to claim 1, wherein the length of the plurality of flow paths is set to a flow path length in which phase differences of sound waves emitted through the flow paths adjacent to each other are equal.   The length of the mutually adjacent flow paths is a flow path length in which sound waves emitted from the sound source through the plurality of flow paths have the same amplitude and opposite phase. Sound reduction method for specific frequency.   The angle of the virtual emission surface connecting the sound emission side end portions in the plurality of flow paths is 45 ° with respect to the virtual entry surface connecting the sound entry side end portions in the plurality of flow paths. The sound reduction method of a specific frequency according to any one of claims 1 to 3.   The angle of the virtual emission surface connecting the sound emission side end portions in the plurality of flow paths is 90 ° with respect to the virtual entry surface connecting the sound entry side end portions in the plurality of flow paths. The sound reduction method of a specific frequency according to any one of claims 1 to 3.