JP6527828B2 - General purpose silencer - Google Patents

Description

  The present invention relates to a general-purpose silencer, and more particularly to a general-purpose silencer that can obtain a sufficient reduction effect for low frequency sound of 100 Hz or less.

There are various noise sources around the house such as cooling towers, pumping pumps in buildings, and heat pump units for blowers and hot water supply facilities. In the case of housing-related equipment, they are often installed in eaves of houses, and residents including neighboring housing may be affected by noise from housing-related equipment over a long period of time. In addition, in daily life, there are also possibilities of being affected by noise for a certain period of time by various mechanical equipment used for construction and road construction.
The sound emitted from such equipment is generated by various factors such as vibration of machine parts and pulsation of transfer fluid handled by the equipment, but the noise contains sounds of various frequencies and the frequency called low frequency sound is 100 Hz It often contains the following sounds:

The audible range for human beings is said to be 20 Hz to 20 kHz, and infrasound at 20 Hz or less appears as rattles of fixtures in the house, and low frequency noise at 20 Hz or more causes sleep disorder etc. The effects appear as psychological effects such as headaches and dizziness, which may affect daily life.
For this reason, noise measures are required for equipment that is a noise source. As a general noise countermeasure, it is carried out that a vibration-proof rubber is put under the equipment, or a soundproof cover is provided around the equipment which becomes a noise source. However, in the case of low frequency sound, the soundproofing cover has a small effect of soundproofing and tends to leak outside. In addition, a blower and a heat pump unit of a hot water supply facility can not be sealed with a soundproof cover because of air flow and heat exchange, and effective noise countermeasures are more difficult.

In order to reduce low frequency noise, it is effective to use a silencer such as a resonance type silencer, but an expansion type silencer etc. is often attached outside the cover, and the silencer itself tends to be large. There is a problem of In addition, since the resonance type silencer changes the target frequency and the amount of reduction depending on the extension, volume, and installation position of the muffling portion, there is a problem that careful design before manufacturing the silencer is necessary.
If the sound frequency of the noise source is specified, a silencer using an acoustic pipe that is relatively simple in structure and easy to design is also effective for reducing low frequency sound.

  Patent Document 1 discloses an ultra-low circumference in which the opening end of a quarter-wave acoustic resonator having one end opened and the other end closed at a corner where the sound pressure level of the sound insulation chamber is high is directed toward the corner A sound absorbing resonator for wave sound is disclosed. The resonator here corresponds to an acoustic tube, and when ultra low frequency sound enters a resonator whose one end is open and the other end is closed, the other low frequency sound is closed at a portion of 1⁄4 wavelength from the open end And when it returns to the aperture end, it overlaps with the original very low frequency sound by a half wavelength, so that the original very low frequency sound and the reflected very low frequency sound cancel each other, The principle of effectively reducing the sound pressure is applied.

  As described above, it is effective to combine low frequency noise with an acoustic tube with an enclosure that covers the periphery of a noise source like a sound insulation room, but it is useful for various devices used in housing related equipment, construction work and road construction. The mechanical equipment is often not installed in the sound insulation room as described in Patent Document 1. Also, as described above, there are many mechanical equipments that can not be attached with a cover that completely covers the periphery.

Patent Document 2 discloses an ultra low frequency sound reducing device integrally provided with a soundproof house that effectively reduces ultra low frequency sound even when an opening is required. Also in this case, although it is described that it is desirable that the infrasound reducing device provided in the opening is a tubular of constant cross section having a quarter wavelength of the infrasound, details regarding the soundproof house are disclosed. Absent.
Even if a cover or a soundproof house is installed to cover equipment that becomes a noise source, in the case of housing-related equipment etc., due to the structure of the building and the relationship with the next house, a sufficient installation location can not be secured, In some cases, it may not be possible to configure a simple shape such as providing a part.
Compact and effective including the soundproof cover, even for machinery that can not be completely covered with the soundproof cover such as heat pump units of hot water supply equipment, etc. A silencer that reduces low frequency noise is desired.

Japanese Patent Application Publication No. 08-229507 JP 2011-221073 A

  The present invention has been made in view of the problems in the above-described conventional low-frequency sound reduction apparatus, and the object of the present invention is a general-purpose silencer that can obtain a sufficient reduction effect for low-frequency sound of 100 Hz or less. To provide.

The general-purpose silencer according to the present invention made to achieve the above object has a soundproof cover covering a sound source, and an acoustic pipe for reducing the sound emitted from the sound source, and the sound source needs to take in outside air. In the case of an appliance, the soundproof cover comprises an open end having at least one open end, and the acoustic tube comprises a hollow tube having a closed end closed at one end and an open end at the other end. There are provided a plurality of tube lengths corresponding to 1⁄4 wavelength of the plurality of different frequency sounds emitted from the sound source, the respective sound tubes are movable in the soundproof cover, and the sound tubes resonate The opening is disposed at a position where the sound pressure reducing effect of the sound of frequency is maximized in the soundproof cover, and the diameter (D) of the soundproof cover is the sound of the frequency at which the acoustic tube resonates. Wavelength (λ Characterized in that a relation of D <0.59λ to.

It is preferable that the acoustic pipe is formed in a straight pipe shape or a folded shape provided with a folded portion.
The acoustic tube is configured to make the tube length 1/4 wavelength of the sound from the sound source according to the change with time of the frequency of the sound from the sound source or the change of the wavelength of the sound from the sound source accompanying the temperature change in the soundproof cover. It is preferable to provide a sliding portion for adjusting to a corresponding tube length.

  The acoustic tube further includes a microphone for observing a sound pressure level, an actuator for driving the sliding portion, and a control unit for controlling the operation of the actuator based on a sound observed from the microphone, the control unit including: A tube length corresponding to a quarter wavelength of the sound wavelength of the sound pressure frequency high level according to the sound frequency high in the sound pressure level among the sound emitted from the sound source observed by the microphone It is preferable to have a function to control the actuator so that

According to the general-purpose silencer of the present invention, the soundproof cover having one or both ends opened to cover the low frequency sound source to form the main conduit, and the sound is produced at the most effective place in the main conduit. Since the pipe is installed, a sufficient reduction effect can be obtained for low frequency sound of 100 Hz or less while securing the air flow path.
Further, according to the general-purpose silencer according to the present invention, since the acoustic pipe has a folded shape having a folded back portion, the shape of the soundproof cover can be given freedom, and a compact soundproof cover fitted to the installation space Can be provided.
Furthermore, according to the general-purpose silencer according to the present invention, since it has a means for adjusting the pipe length of the acoustic pipe in accordance with the change of the sound frequency of the noise source and the change of the sound wavelength due to the temperature change The sound pressure peak of low frequency sound can also be effectively reduced.

FIG. 2 schematically illustrates the structure of a general purpose silencer according to an embodiment of the present invention. FIG. 5 schematically illustrates the structure of a general purpose silencer according to another embodiment of the present invention. It is a figure which shows the reduction effect of the sound pressure level by an acoustic pipe measured by model experiment. FIG. 2 schematically shows the structure of an acoustic tube of a general purpose silencer according to an embodiment of the present invention. Fig. 5 schematically shows the structure of an acoustic tube according to a second embodiment of the present invention. Fig. 5 schematically shows the structure of an acoustic tube according to a third embodiment of the present invention. Fig. 5 schematically shows the structure of an acoustic tube according to a fourth embodiment of the present invention; It is a figure for demonstrating the structure which combined the means to adjust a pipe | tube length with the acoustic pipe of FIG.

Next, a specific example of the embodiment for carrying out the general purpose silencer according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view of a general-purpose silencer according to an embodiment of the present invention, and FIG. 2 is a schematic view of a general-purpose silencer according to another embodiment of the present invention. .
Referring to FIG. 1, the general-purpose silencer 1 has a soundproof cover 100 with an open end 102 having at least one end open and a quarter wave of low frequency sound provided so as to arrange at least one end inside the soundproof cover 100. And an acoustic pipe 200 having a pipe length corresponding to
In addition, the soundproof cover 100 and the acoustic pipe 200 which comprise the general purpose type silencer 1 can be made into not only a straight pipe shape but a curved pipe shape having curvatures of various magnitudes, and each cross section has a constant cross section As long as it is tubular, any cross-sectional shape may be used, and it may be a cylindrical tube or a rectangular tube.

Referring to FIG. 2, the general-purpose silencer 2 includes the soundproof cover 110 and an acoustic pipe 200 provided so as to arrange at least one end inside the soundproof cover 110 and has substantially the same configuration as the general-purpose silencer 1. However, the soundproof cover 110 is different from the general-purpose silencer 1 in that the soundproof cover 110 is not linearly extended from the sound source 50 emitting low frequency sound which is noise but has a bent structure extending vertically upward through the bent portion. Do.
The low frequency sound of interest is a compressional wave propagating in the air, and when propagating in the duct, it travels along the duct, so the main duct need not necessarily be straight. Therefore, the soundproof cover 110 is provided with a bent portion. The shape of the soundproof cover is not limited to this, and may be a curved or bent structure. With the structure having the bent portion, the bent portion and the folded portion, the general-purpose silencer can be easily installed even in a limited space between buildings.
Here, the soundproof covers (100, 110) of the general-purpose silencers 1 and 2 are provided with an open end having at least one end open so as to correspond to a device requiring intake of external air such as a heat pump unit of a hot water supply facility If the device does not require ventilation, the soundproof cover (100, 110) may be a closed structure closed at both ends.

The general-purpose type silencer is efficient by the soundproof cover guiding low frequency sound emitted from the sound source as noise in one direction and installing the opening of the acoustic pipe in the position of the soundproof cover where the most muffling effect can be obtained. Equipment that reduces low frequency sound.
For this reason, the soundproof cover 100 is installed so as to surround the sound source 50 that generates low frequency sound that is noise and to form a main pipeline that propagates the low frequency sound in one direction.

  The soundproof cover (100, 110) may not necessarily have a closed outer periphery, such as a cylindrical tube, and may cover the two side walls vertically installed on the ground and the upper ends of these side walls. It is good also as a structure connected with a board and constituting a main pipeline by the soundproof cover which consists of a side wall and a top plate, and the ground. Furthermore, instead of the ground, a wall of a structure such as a building may be used, and a main conduit may be configured with a soundproof cover in which three wall surfaces are connected in a U-shape and the wall of the structure. .

  Sound propagating in the duct changes in sound pressure level along the length of the duct. Further, as the diameter of the conduit increases, sound pressure distribution also occurs in the radial direction. As described above, the general-purpose silencer (1, 2) places the opening of the acoustic pipe 200 at the position where the muffling effect is the most effective. The 200 openings need to be aligned three-dimensionally. Therefore, it is important to configure the diameter of the soundproof cover (100, 110) so that the radial sound pressure distribution can be ignored.

The wavelength (λ) of the sound propagating through the pipe and the diameter (D) of the pipe are D <0.59 λ (1)
The sound propagating in the duct can be regarded as a plane wave, in which case the sound pressure distribution in the duct is constant in the radial direction of the duct and changes only in the longitudinal direction. In addition, the diameter here is not the outer diameter of a pipe line but an internal diameter.
Based on this relationship, the diameter (D) of the soundproof cover (100, 110) is set to satisfy the equation (1) for the wavelength (λ) of the low frequency sound emitted from the sound source 50. Accordingly, the acoustic tube 200 can be installed at a position where an effective muffling effect can be obtained only by adjusting the position along the length direction.

In addition, the distance (L) from one end to the other end of the soundproof cover (100, 110), that is, the propagation distance of sound propagating in the soundproof cover (100, 110) is an important factor for obtaining a sufficient silencing effect. It becomes. When determining the relationship between the sound propagation distance and the installation position of the sound tube effective for muffling, it is necessary to consider the influence exerted by both ends of the soundproof cover, so the dominant frequency of the sound source is the resonance frequency of the soundproof cover. It is necessary to consider separately when there is a match and when it does not match. In the following, the relationship between the sound propagation distance and the effective installation position of the acoustic tube will be described by taking the case where one end of the soundproof cover is open and the case where both ends are open as an example.
Here, the distance (L) from one end to the other end of the soundproof cover (100, 110) corresponds to the length of the soundproof cover 100 in the case of a linear shape without bending as in the soundproof cover 100. In the case of a shape with a bend, it has a length following the shape of the soundproof cover, along the line connecting the center points of the cross sections of the soundproof cover.

First, the case where the dominant frequency of the sound source coincides with the resonant frequency of the soundproof cover will be described.
The length (l) at which resonance occurs for the wavelength (λ) of the low frequency sound emitted from the sound source is
In the case of a structure in which one end of the soundproof cover is open and the other end is closed,
l = (λ / 4) (2n + 1), (n = 0, 1, 2, 3 ...) ... (2)
Expressed by the formula
In the case of a structure in which both ends of the soundproof cover are open,
l = (λ / 2) · n, (n = 1, 2, 3 ···) (3)
It becomes.

For example, when the frequency of the low frequency sound emitted from the sound source 50 is 50 Hz, the wavelength (λ) of this sound is 6.9 m, so the distance (L) in the structure where one end is open and the other end is closed is The distance (L) in the case of a structure in which the both ends are 1.7 m, 5.2 m, etc. calculated by the equation (2), is 3.4 m in length calculated by the equation (3) , 6.9 m ....
Strictly speaking, there is an influence of the open end, and since the effective length of the conduit becomes longer than the actual dimension, it is necessary to shorten the actual dimension of the conduit length of the soundproof cover. Specifically, the distance (L) from one end to the other end of the soundproof cover 100 is the diameter (D) at one open end with respect to the length calculated by the equation (2) or (3) Make the length setting after taking into account the shortening correction by about 0.3 times the length of.

As described above, in the case of a soundproof cover having a length at which resonance occurs with respect to the wavelength (λ) of low frequency sound at a prominent frequency, the sound pressure distribution generated in the soundproof cover is maximized in order to maximize the sound pressure reduction effect. On the other hand, it is most effective to install the acoustic pipe with the opening of the acoustic pipe aligned with the position where the sound pressure level is maximum.
Specifically, when the dominant frequency of the sound source matches the resonance frequency of the soundproof cover, in the structure of the soundproof cover where one end is open and the other end is closed, the closed end corresponds to the antinode of vibration The sound pressure level becomes maximum, and in addition to this closed end, (n / 2) times (n = 1, 2, 3) of the wavelength (λ) of low frequency sound from the closed end in the soundproof cover. The sound pressure level is also maximized at a position separated by a length corresponding to. That is, from the closed end of the soundproof cover, including the closed end, the position of (n / 2) (n = 0, 1, 2, 3 ...) times the wavelength (λ) of the low frequency sound The pressure level is at the maximum position. Therefore, the opening of the acoustic tube is installed at the position where the sound pressure level is maximum.

On the other hand, when the dominant frequency of the sound source matches the resonant frequency of the soundproof cover, in the structure where both ends of the soundproof cover are open, the sound pressure level becomes minimum at both open ends, and within the soundproof cover The sound pressure level becomes maximum at the position of ((2 n -1) λ / 4) times (n = 1, 2, 3 ...) times the wavelength (λ) of the wave sound. Therefore, the opening of the acoustic tube is installed at the position where the sound pressure level is maximum.
Although the sound pressure level is amplified in the soundproof cover due to the resonance occurring in the soundproof cover, the sound pipe muffling effect also increases, and as a result, the sound pressure level does not install the soundproof cover nor the sound pipe It is surely reduced than the sound pressure level of
Thus, by placing the opening of the acoustic tube at an appropriate position, when the dominant frequency of the sound source matches the resonance frequency of the soundproof cover, the muffling effect of the acoustic tube is much larger than when it does not match. Become.

Next, the case where the dominant frequency of the sound source does not coincide with the resonant frequency of the soundproof cover will be described.
Depending on the installation location, the soundproof cover can not be set to a length at which resonance occurs with respect to the wavelength (λ) of the low frequency sound which is the dominant frequency. In such a case, the position of the acoustic pipe that can most effectively reduce the sound pressure level does not necessarily coincide with the position where the sound pressure level is maximum, and is as simple as in paragraphs [0024] and [0025] above. Not required.

If the dominant frequency of the sound source does not match the resonant frequency of the soundproof cover, the relationship between the position of the sound pipe and the sound pressure level synthesized in the soundproof cover under the condition that the sound pipe is installed in the soundproof cover It is necessary to apply the sound propagation theory in a one-dimensional sound field taking into account the boundary conditions, and to examine the position of the acoustic pipe where the reduction effect of the synthetic sound pressure level becomes large.
Assuming that the distance from the closed end of the soundproof cover to the opening of the acoustic pipe is represented by l ₁ , according to the sound propagation theory, l ₁ is l ₁ = (2 n -1) λ / 4 (n = 1,2, 3 ...) ... (4)
The sound pressure level takes a maximum value when. That is, the effect of reducing the sound pressure level is smaller than at other positions.
Furthermore, assuming that the open end of the soundproof cover represents the distance to the opening of the acoustic pipe by _{l 2,} by the sound propagation theory, _{l 2} is _{l 2 = (n-1)} λ / 2 (n = 1, 2, 3 ...) ... (5)
At the time, the sound pressure level takes a maximum value, and the reduction effect of the sound pressure level becomes smaller than at other positions.
Therefore, the installation position of the opening of the acoustic tube, the distance l ₂ from (4) Distance l ₁ and (5) the open end of the soundproof cover which is calculated by the formula from the closed end of the soundproof cover which is calculated by the formula It is desirable to avoid the position where the reduction effect of the sound pressure level synthesized in the soundproof cover is small.

FIG. 3 is a view showing the reduction effect of the sound pressure level by the acoustic pipe, which was measured in the model experiment.
In FIG. 3 (a), a cylindrical tube with a length of 2 m and a diameter of 200 mm with one end closed and the other end opened is regarded as a soundproof cover, a sound source is installed at the closed end of the cylindrical tube, and the distance from the sound source The result of having measured the sound pressure level distribution in a cylindrical pipe with respect to no in the state with an acoustic pipe with respect to is shown.
In FIG. 3 (b), two acoustic tubes with a diameter of 40 mm are placed in a cylindrical tube regarded as a soundproof cover, and the positions of the openings of the two acoustic tubes are horizontally moved from the closed end of the cylindrical tube toward the open end The sound pressure level is measured at a position outside the cylindrical tube 1 m away from the open end which is the other end of the cylindrical tube, and the sound pressure level against the distance of the opening of the acoustic tube horizontally moved from the closed end of the cylindrical tube Shows the measurement results. The measurement position of the sound pressure level was provided outside the cylindrical pipe 1 m away from the open end of the cylindrical pipe, but outside the cylindrical pipe, the sound pressure level only attenuates as it gets away from the sound source. Even if the sound pressure level is measured at the position, the change in the sound pressure level with respect to the position of the cylindrical tube shows the same tendency as FIG. 3 (b).

First, from the following consideration of FIG. 3A, FIG. 3 shows the measurement result when the sound from the sound source does not resonate with the cylindrical tube, that is, the dominant frequency of the sound source does not match the resonant frequency of the soundproof cover It is clear that it is what is shown.
The frequency of the sound source used in the model experiment is 145 Hz, and in this case, the wavelength (λ) is about 2.4 m, and λ / 4 is about 0.6 m. On the other hand, the minimum value of the sound pressure level distribution in the cylindrical tube shown in FIG. 3A occurs at a distance of about 0.9 m from the closed end of the cylindrical tube, and the distance when the cylindrical tube closed at one end resonates It does not become (λ / 4).
Also, referring to FIG. 3 (a), the sound pressure level has a local minimum value near the position of 1.2 m corresponding to about λ / 2 from the position of 2 m which is the opening end, and can be seen on the opening end side It represents a feature. The position at which the local minimum value in the graph in FIG. 3A is slightly deviated from the position 1.2 m from the opening end toward the opening end, but in the case of an actual acoustic tube, the sound pressure at the opening end This is due to the effect that appears to be longer than the length of the actual acoustic tube.
Next, consider FIG. 3 (b). Referring to the measurement results of the sound pressure level when there is an acoustic tube, as described in paragraph [0027], the sound pressure level increases when the distance l ₁ from the closed end is λ / 4 and 3λ / 4. The reduction effect of the sound pressure level (difference from the measurement result when there is no acoustic pipe) is small. Also, it can be seen that the reduction effect of the sound pressure level is small even at a position where the distance l ₂ from the opening end is λ / 2. This position corresponds to the position at which the sound pressure level in FIG. 3 (a) is minimized. Conversely, it can be seen that the reduction effect of the sound pressure level is large at the midpoint between the positions where the reduction effect of the adjacent sound pressure level is small (when the acoustic pipe opening is at a distance of 1.4 m from the closed end).

As a model experiment of FIG. 3, when one end is closed, the distance l ₂ from the open end, it is replaced by a distance from the closed end in l-l ₂ with the length l of the cylindrical tube it can. Therefore, assuming that the distance from the closed end is l ₃ , the position where the reduction effect of the sound pressure level in equation (5) is small is
l ₃ = l- (n-1) λ / 2 (n = 1,2,3 ...) (6)
Can be represented by
When the resonance frequency of the soundproof cover is not matched, in the structure where one end is closed, the position of the opening of the acoustic tube is given by the position of l ₁ shown by the adjacent equation (4) and the equation (6) When set to the middle position between the position of the l _3, the sound pressure reduction effect is maximized. In the structure in which both ends are opened, the midpoint position between the l ₂ and l ₃ adjoining the distance l ₃ to be replaced in about a distance l ₂ from the open end (5) and (6) The sound pressure reduction effect is the largest and effective setting.

  The sound tube 200 is constituted by a hollow tube closed at one end and opened at the other end, and moved along the length of the soundproof cover (100, 110) in the soundproof cover (100, 110) to adjust the position Install as possible. The sound tube 200 may be composed of a plurality of sound tubes having various lengths, as the sound tube has different frequencies of sound that can be reduced depending on its length.

FIG. 4 is a view schematically showing the structure of an acoustic pipe of a general-purpose silencer according to an embodiment of the present invention, showing the structure of a straight pipe-shaped acoustic pipe.
Referring to FIG. 4, the straight tube-shaped acoustic tube 200 is a hollow tube provided with a closing portion 201 at one end and an opening 202 at the other end. The tube length of the straight tube-shaped acoustic tube 200 is adjusted to 1⁄4 of the sound wavelength (λ) of the frequency to be reduced.

  When a sound of a predetermined frequency emitted from a sound source enters through the opening 202 of the acoustic tube 200 and travels a quarter wavelength which is the tube length and strikes the closing portion 201 of the acoustic tube, it is reflected here and is again opened 202 It is a reflected wave towards When the reflected wave reaches the opening 202, the sound travels from the entrance by a half wavelength corresponding to twice the length of the acoustic pipe and overlaps with the base sound. The waves shifted by 1/2 wavelength cancel each other because the phases are reversed, and the sound is attenuated.

Such sound attenuation effect is not limited to the sound of the predetermined frequency to be reduced, and is effective for the sound of a series of harmonics in which the odd multiple of 1⁄4 wavelength of the sound corresponds to the tube length of the acoustic tube .
For sounds of frequencies other than this, since the shift amount of the wavelength of the reflected wave by the acoustic tube and the base traveling wave is different from the half wavelength of the sound, a sufficient sound reduction effect can not be obtained. Therefore, for synthetic sounds of sounds of various frequencies, it is necessary to adjust the tube length in accordance with the 1⁄4 wavelength of the sound of each frequency component, and a plurality of acoustic tubes having different lengths are required.

The diameter of the acoustic tube 200 also affects the magnitude of the muffling effect. As a result of the experiment, it is obtained that the larger the diameter of the sound tube 200, the larger the muffling effect, and in order to obtain a predetermined muffling effect, 10% or more of the diameter (inner diameter) of the soundproof cover preferable.
Although the acoustic tube 200 of FIG. 4 shows the tube length as a quarter wavelength to simplify the explanation, strictly speaking, the open end correction is required, and the acoustic tube 200 has the diameter (D1) of the acoustic tube 200. Make it shorter by 0.3 times the distance.

By the way, in order for the sound tube to fully exhibit the muffling effect, it is desirable to reverse only the phase while maintaining the sound pressure level of the sound emitted from the sound source. For this reason, it is necessary to avoid the thing of the sound absorption which absorbs a sound, and the thing which permeate | transmits a sound easily as a material used for an acoustic pipe. In general, porous materials are not suitable as materials for acoustic tubes because they are sound absorbing.
It is effective as a material to be used for an acoustic pipe, because the harder the material is, the harder the material is for transmitting sound, the more the sound is transmitted. Thus, it is desirable that the material used for the acoustic tube has a strength sufficient to act as a rigid wall against the air inside. In the case of housing-related equipment such as heat pump type heat exchangers (Eco-Cute), sound pipes made of resin materials such as polyvinyl chloride can provide sufficient silencing effect, but higher sound pressure levels require more rigid materials It becomes. For general applications, it is desirable to select the material used for the acoustic tube according to the sound pressure level of the sound source.

FIG. 5 is a view schematically showing the structure of an acoustic tube according to a second embodiment of the present invention, showing the structure of an acoustic tube 210 having a curved folded shape.
Referring to FIG. 5, the acoustic tube 210 is a hollow tube provided with a closure 201 at one end and an opening 202 at the other end, and it is further arranged to fold the acoustic tube 210 between the closure 201 and the opening 202 And a bent portion 203 which is bent in The length along the center line of the acoustic tube 210 is adjusted to 1⁄4 of the sound wavelength (λ) of the frequency to be reduced. Therefore, the length as the external dimension of the acoustic tube 210 can be made equal to or less than the length corresponding to 1⁄8 wavelength which is 1⁄2 of 1⁄4 wavelength due to the influence of the length of the bent portion.

In this way, the overall length can be shortened by adopting the folded shape, and the general-purpose silencer (1, 2) can be installed even in a place where the installation area is limited.
Although FIG. 5 shows that the acoustic tube 210 is U-shaped having a bending portion 203 at a position between the closing portion 201 and the opening 202, the position of the bending portion is closer to the opening 202 from the middle position Alternatively, the side closer to the closing portion 201 may be used. Also, it is not necessary to set the folding angle to 180 ° so as to be U-shaped.

  As described above, the soundproof cover 110 may have a structure having a bent portion or a folded back portion. Therefore, the sound tube 210 may be configured to be folded back in accordance with the shape of the soundproof cover 110. For example, the soundproof cover may be bent and raised upward along the wall surface of the building adjacent to the sound source to reduce the installation area.

FIG. 6 is a view schematically showing the structure of an acoustic tube according to a third embodiment of the present invention, and shows the structure of an acoustic tube 220 having a rectangular folded shape.
Referring to FIG. 6, the acoustic tube 220 is a hollow tube having a closure 201 at one end and an opening 202 at the other end, and further includes a turnaround 204 between the closure 201 and the opening 202.
Since the folded portion 204 has a rectangular shape, the tube on the opening 202 side and the tube on the closing portion 201 can be juxtaposed without providing a gap, and therefore, can be disposed more densely than the acoustic tube 210. The length along the center line of the acoustic tube 220 is adjusted to 1⁄4 of the sound wavelength (λ) of the frequency to be reduced. The acoustic tube 220 may also be structured to be folded back in accordance with the shape of the soundproof cover 110.
Even if it is a curved folded shape like the acoustic tube 210 or a rectangular folded shape like the acoustic tube 220, it is adjusted to 1/4 of the wavelength (λ) of the sound of the frequency for which the tube length is reduced. For example, the muffling effect is similar.

FIG. 7 schematically shows the structure of an acoustic tube according to a fourth embodiment of the present invention.
Referring to FIG. 7, the straight tube-shaped acoustic tube 230 is a hollow tube provided with a closing portion 201 at one end and an opening 202 at the other end. The tube length of the straight tube-shaped acoustic tube 230 is adjusted to 1⁄4 of the sound wavelength (λ) of the frequency to be reduced. The acoustic tube 230 differs from the acoustic tube 200 of FIG. 3 in that it includes a sliding portion 205.

  General purpose silencers (1, 2) are often installed outdoors. Therefore, the temperature of the installation environment also changes with the change of the outside temperature. Since the speed of sound propagating in the air changes with the temperature of the air, the wavelength of the sound changes with respect to the sound having a constant frequency. Even if the tube length of an acoustic tube at one temperature matches one-fourth of the wavelength of the low frequency sound at that temperature, if the temperature changes, the tube length of the acoustic tube and one quarter of the wavelength of the low frequency sound at that temperature It will not match the length of. Therefore, when the temperature changes, the muffling effect of the acoustic pipe also decreases. In order to avoid this, the acoustic tube 230 is provided with a sliding portion 205 so that the tube length can be changed.

  The acoustic tube 230 includes an outer tube 230 b having a closing portion 201 and an inner tube 230 a having an outer shape that fits inside the outer tube 230 b, and the overlapping portion of both is a sliding portion 205. By sliding the inner pipe 230a and the outer pipe 230b in the length direction, the pipe length of the acoustic pipe 230 can be varied.

In one embodiment, based on the change in the wavelength of sound with respect to temperature, corresponding to the change in temperature in the soundproof cover (100, 110), the pipe length of the acoustic tube 230 is set to 1/4 wavelength of the sound from the sound source at that temperature. The slide may be provided with a scale 206 for adjusting to a corresponding tube length. The temperature in the soundproof cover (100, 110) is measured by displaying the value of the scale 206 as a temperature, and the inner pipe 230a or the outer pipe 230b of the acoustic pipe 230 is slid to a position corresponding to the temperature. The pipe length can be set to obtain an optimum muffling effect.
Although the tube length of the acoustic tube 230 may be manually adjusted in this manner, when the temperature change is large in one day, it is necessary to adjust the tube length of the acoustic tube 230 frequently, which takes time and effort.

FIG. 8 is a view for explaining a structure in which means for adjusting the tube length is combined with the acoustic tube of FIG. Referring to FIG. 8, the acoustic pipe 240 of the general-purpose silencer 3 is similar to the acoustic pipe 230 of FIG. 6 in that it has overlapping sliding portions 205 of the inner pipe 240 a and the outer pipe 240 b. An actuator 300 which slides the outer tube 240b to change the tube length, a microphone 310 for inputting a low frequency sound emitted from a sound source as a sound, and a frequency of a sound input from the microphone 310 are analyzed and analyzed frequency The acoustic tube 230 differs from the acoustic tube 230 in that it includes a control unit 320 that calculates the wavelength (λ) of the sound and controls the actuator 300 so that the tube length of the acoustic tube 240 is a quarter of the wavelength (λ). . The microphone 310 is installed outside the soundproof cover 110 where standing waves are generated in order to measure the dominant frequency.
By providing a mechanism for automatically adjusting the length of the acoustic tube based on the observation of the sound emitted from the sound source 50 in this manner, it is possible to efficiently reduce the sound of the frequency to be reduced. Even when the frequency of the sound fluctuates, it is possible to control the pipe length of the acoustic pipe 240 so as to always obtain the optimum silencing effect.

  The general-purpose silencer 3 also includes a temperature sensor 330 for measuring the temperature in the soundproof cover. Thereby, the control unit 320 analyzes the frequency of the sound input from the microphone 310, and when calculating the wavelength (λ) of the sound from the analyzed frequency, corrects the speed of sound based on the temperature sensed by the temperature sensor, The tube length of the acoustic tube 240 may be controlled so as to always obtain an optimum muffling effect in response to changes in both the frequency of the sound source and the temperature of the acoustic tube. Although FIG. 8 shows that the temperature sensor 330 is installed alone, it may be built in the control unit 320.

  Although the actuator 300 is shown in FIG. 7 as being installed on the extension of the acoustic pipe 240 so as to be directly connected to the closing portion of the outer pipe 240b of the acoustic pipe 240, the actuator 300 and The actuator 300 may be configured to slide the outer tube 240 b via the connection portion in parallel with the acoustic tube 240. It can suppress that the full length of the general purpose silencer 3 becomes long by this.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the technical scope of the present invention. It is possible.

1, 2 and 3 General purpose silencer 50 Sound source 100, 110 Soundproof cover 102 Opening end (Soundproof cover)
200, 210, 220, 230, 240 acoustic tube 201 closing part (acoustic tube)
202 Opening (acoustic tube)
Reference Signs List 203 bending portion 204 turning back portion 205 sliding portion 206 scale 300 actuator 310 microphone 320 control portion 330 temperature sensor

Claims (4)

Soundproof cover covering the sound source,
And an acoustic tube for reducing the sound emitted from the sound source,
In the case where the sound source is a device that requires the intake of external air, the soundproof cover has an open end that is open at least at one end,
The acoustic tube comprises a hollow tube having a closed portion closed at one end and an opening opened at the other end, corresponding to a quarter wavelength of a plurality of different frequency sounds emitted from the sound source A plurality of pipe lengths are provided,
Each of the sound tubes is movable within the soundproof cover, and the opening is provided at a position where the sound pressure reducing effect of the sound of the frequency at which the sound tubes resonate is maximal in the soundproof cover. And
The diameter (D) of the soundproof cover is D <0.59λ with respect to the wavelength (λ) of sound at a frequency at which the acoustic tube resonates.
A general purpose silencer characterized by the relationship of
  The general-purpose silencer according to claim 1, wherein the acoustic pipe is formed in a straight pipe shape or a folded shape provided with a folded portion.   The acoustic tube is configured to make the tube length 1/4 wavelength of the sound from the sound source according to the change with time of the frequency of the sound from the sound source or the change of the wavelength of the sound from the sound source accompanying the temperature change in the soundproof cover. The general-purpose silencer according to claim 1 or 2, further comprising a sliding portion for adjusting to a corresponding pipe length. The acoustic tube further includes a microphone for observing a sound pressure level, an actuator for driving the sliding portion, and a control unit for controlling the operation of the actuator based on sound observed from the microphone.
The control unit adjusts the tube length of the sound tube to 1/1 of the wavelength of the sound having the high sound pressure level according to the sound having the high sound pressure level among the sounds emitted from the sound source observed by the microphone. The general-purpose silencer according to claim 3, having a function of controlling the actuator so as to have a pipe length corresponding to four wavelengths.

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