muffler

Abstract

To provide a muffler capable of muffling sound waves in a wide frequency range with a relatively simple structure.SOLUTION: The sound deadening device 100 includes a pair of shielding plates side 10a1 and side 10b1 forming a first space side SP1 therebetween by forming surfaces on sides facing each other as parabolic recessed surface side 10a and side 10b, and a sound guide tube (cylindrical part) 20 forming a second space side SP2 by being formed in a cylindrical shape with both ends opened. The pair of shielding plates 10a and 10b are disposed so that focal points F determined by the parabolic shape coincide with each other, the sound guiding tube 20 is inserted into one of the pair of shielding plates 10a and 10b, and one end portion side (opening end 21) of both ends of the sound guiding tube 20 is provided in the first space SP1.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a silencer. [Background technology]

[0002] A conventional silencer has been disclosed in which open pipes penetrating between two partition plates that separate the interior of a cylindrical portion are distributed over the entire surface to form phase difference chambers, and the open pipes have openings that open into the phase difference chambers (see Patent Document 1 below).This silencer has a phase difference chamber and an interference chamber arranged in series, with the aim of silencing sound waves over a wide range of frequencies. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-132024 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the silencer disclosed in Patent Document 1 requires a large number of open pipes, and openings must be provided in the open pipes so that they communicate with the phase difference chamber, resulting in a problem of a complex configuration.

[0005] The present invention has been made in view of the above problems, and has an object to provide a silencer that can silence sound waves over a wide range of frequencies with a relatively simple configuration. [Means for solving the problem]

[0006] In order to solve the above problems, the silencer of the present invention comprises a pair of shielding plates whose opposing surfaces are formed as parabolic concave surfaces to form a first space between them, and a cylindrical portion which is formed in a cylindrical shape with both ends open to form a second space, wherein the pair of shielding plates are arranged so that the focal points determined by the parabolic shapes coincide, the cylindrical portion is inserted into one of the pair of shielding plates, and one end side of the cylindrical portion is provided within the first space. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a silencer that can silence sound waves over a wide range of frequencies with a relatively simple configuration. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 10 is a diagram for explaining the properties of a parabolic reflector. [Figure 2] FIG. 10 is a diagram for explaining the properties of a parabolic reflector. [Figure 3] FIG. 1 is a diagram for explaining the principle of the present invention. [Figure 4] 1 is a perspective view showing an example of a silencer according to an embodiment of the present invention; [Figure 5] FIG. 5 is a cross-sectional view of the silencer shown in FIG. [Figure 6] 1 is a perspective view showing an example of a silencer according to an embodiment of the present invention; [Figure 7] 1 is a perspective view showing an example of a silencer according to an embodiment of the present invention; [Figure 8] 1 is a cross-sectional view showing an example of a silencer according to an embodiment of the present invention. [Figure 9] 1 is a cross-sectional view showing an example of a silencer according to an embodiment of the present invention. [Figure 10] 1 is a cross-sectional view showing an example of a silencer according to an embodiment of the present invention. [Figure 11] 1 is a cross-sectional view showing an example of a silencer according to an embodiment of the present invention. [Figure 12]1 is a cross-sectional view showing an example of a silencer for a ventilation opening that uses the silencer of the present embodiment. [Figure 13] 1 is a cross-sectional view showing an example of a silencer for a ventilation opening that uses the silencer of the present embodiment. [Figure 14] 1 is a cross-sectional view showing an example of a silencer for a ventilation opening that uses the silencer of the present embodiment. [Figure 15] 1 is a perspective view of a noise reduction mask using the silencer of the present embodiment, as viewed obliquely from the front. FIG. [Figure 16] FIG. 1 is a perspective view of a noise reduction mask using the silencer of the present embodiment, viewed obliquely from behind. [Figure 17] FIG. 17 is a cross-sectional view of the sound-absorbing mask shown in FIGS. 15 and 16. [Figure 18] FIG. 17 is a diagram showing an example of how the sound-absorbing mask shown in FIGS. 15 and 16 is worn. [Figure 19] FIG. 17 is a diagram showing an example of how the sound-absorbing mask shown in FIGS. 15 and 16 is worn. [Figure 20] 1 is a perspective view showing an example of a silencer for a musical instrument that uses the silencer of the present embodiment. [Figure 21] FIG. 21 is a cross-sectional view of the silencer for a musical instrument shown in FIG. 20. [Figure 22] 21A and 21B are diagrams illustrating an example of use of the silencer for a musical instrument shown in FIG. 20. [Figure 23] 1 is a perspective view of a speaker rear silencer using the silencer of the present embodiment, as viewed obliquely from the front. FIG. [Figure 24] 1 is a perspective view of a silencer for use behind a speaker, which uses the silencer of the present embodiment, as viewed obliquely from behind. [Figure 25] FIG. 25 is a cross-sectional view of the silencer for use behind a speaker shown in FIGS. 23 and 24. [Figure 26] FIG. 25 is a perspective view showing a state in which a speaker unit is attached to the silencer for use behind the speaker shown in FIGS. 23 and 24. [Figure 27] FIG. 27 is a cross-sectional view of the silencer for use behind a speaker shown in FIG. 26. [Figure 28] 10A and 10B are diagrams illustrating an example of use of a silencer for the rear of a speaker. [Figure 29] 10A and 10B are diagrams illustrating an example of use of a silencer for the rear of a speaker. [Figure 30] 10A and 10B are diagrams illustrating an example of use of a silencer for the rear of a speaker. [Figure 31] 10A and 10B are diagrams illustrating an example of use of a silencer for the rear of a speaker. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the principle of the present invention will be described with reference to the drawings, and then an embodiment based on the principle of the present invention will be described.

[0010] As shown in Figure 1, a parabolic reflector having a parabolic concave surface (reflective surface) has the property of reflecting sound waves incident from a specific direction and concentrating them at the focal point of the parabolic reflector. The sound waves concentrated at the focal point are diffused radially from the focal point. Furthermore, as shown in Figure 2, a parabolic reflector has the property of reflecting the sound waves diffused radially at the focal point, converting them into parallel rectilinear waves. This property is the same regardless of the position on the parabolic reflector where the sound is reflected. Here, the shape (cross-sectional shape) of the concave surface of the parabolic reflector is expressed by the following formula (1). In other words, the focal position is determined by the shape of the concave surface of the parabolic reflector. However, the Y coordinate at the end of the parabolic reflector is assumed to be smaller than the Y coordinate "f" of the focal position. y=x 2 / 4f ···(1) x: X coordinate of the concave surface y: Y coordinate of the concave surface f: Focus position (0,f)

[0011] The principle of the present invention utilizes the properties of the parabolic reflector described above, and as shown in Figure 3, two parabolic reflectors are arranged facing each other and with their focal points coinciding. In this state, if a sound source is arranged at the focal point, the sound waves reflected by one of the parabolic reflectors will become parallel, linear waves and will be incident on the other parabolic reflector. After being reflected by the other parabolic reflector, the sound waves pass through the focal point and are reflected again by one of the parabolic radiators. By repeating this process, the sound waves continue to reflect between the two parabolic reflectors. At this time, the sound waves attenuate according to the distance they travel, so as they continue to reflect, they gradually attenuate and are eventually silenced. Since sound waves basically travel in a straight line, by utilizing this principle, sound waves of a wide range of frequencies can be silenced without being affected by the frequency of the sound waves.

[0012] Next, an embodiment based on the principles of the present invention will be described. As shown in Fig. 4, a silencer 100 of this embodiment includes a pair of shielding plates 10a, 10b and a sound guide tube 20. The pair of shielding plates 10a, 10b correspond to the two parabolic reflectors described above (see Fig. 3). As shown in Fig. 5, the pair of shielding plates 10a, 10b have opposing surfaces formed as parabolic recessed surfaces 10a1, 10b1, thereby forming a first space SP1 between them. The pair of shielding plates 10a, 10b are also arranged via a support member 30. By being arranged via the support member 30, the pair of shielding plates 10a, 10b are adjusted so that their focal points F coincide with each other. The support member 30 is, for example, a columnar member, and a plurality of support members 30 are provided at equal intervals around the periphery of each of the shielding plates 10a, 10b. The support member 30 may be an annular member that extends continuously along the periphery of each of the shielding plates 10a, 10b. When the support member 30 is configured as an annular member, in order to ensure breathability, a plurality of circular slits 30a may be provided in the wall surface of the support member 30 along the periphery of the support member 30 as shown in Fig. 6, or a plurality of oval slits 30b may be provided in the wall surface of the support member 30 along the periphery of the support member 30 as shown in Fig. 7.

[0013] The sound conduit (cylindrical portion) 20 is used to draw sound waves from outside the first space SP1 to the focal point F. As shown in FIG. 5 , the sound conduit 20 is formed in a cylindrical shape with both ends open, thereby forming a second space SP2 inside the cylinder. The sound conduit 20 is also arranged in a state where it is inserted through the lower shielding plate 10b of the pair of shielding plates 10a, 10b. Therefore, the second space SP2 communicates with the first space SP1. The sound conduit 20 is also arranged so that the position of the center of the opening of the open end 21, which is arranged in the first space SP1, coincides with the focal point F. Note that the sound conduit 20 does not necessarily have to be arranged so that the position of the center of the opening of the open end 21 coincides with the focal point F, and it may also be arranged so that the open end 21 is positioned closer to the lower shielding plate 10b. In this way, by including the sound conduit 20, the silencer 100 can draw sound waves from outside the first space SP1 to the focal point F, and can muffle the drawn sound waves by repeatedly reflecting them off the pair of shielding plates 10a, 10b. Therefore, according to the silencer 100, even with a relatively simple configuration consisting of the pair of shielding plates 10a, 10b and the sound conduit 20, it is possible to muffle sound waves of a wide range of frequencies.

[0014] Here, as shown in FIG. 5 , the sound waves radiated from the open end 21 of the sound conduit 20 do not strictly coincide with the sound waves radiated from the point sound source located at the focal point F. For this reason, if sound waves are radiated from the open end 21 directly to the upper shielding plate 10a, the traveling direction of the sound waves reflected by the upper shielding plate 10a will not be stable, and the sound waves will no longer continue to reflect between the pair of shielding plates 10a, 10b as in the principle described above, which may result in a deterioration in sound silencing performance. Therefore, in order to prevent a deterioration in sound silencing performance, the silencer 100 may be provided with a small shielding plate 40 that collects the sound waves radiated from the open end 21 of the sound conduit 20 at the focal point F and then enables the sound waves to be radiated to the shielding plate 10 (for example, the lower shielding plate 10b). As shown in FIG. 8 , the small shielding plate 40 is a shielding plate having a parabolic recessed surface 40a, similar to the pair of shielding plates 10a, 10b. The small shielding plate 40 is arranged in a predetermined position using a support member 50 that is adjusted so that the focal point of the small shielding plate 40 coincides with the focal point F of the pair of shielding plates 10a, 10b. In other words, the small shielding plate 40 is arranged in a position closer to the open end 21 of the sound conduit 20 than the upper shielding plate 10a. In this way, the small shielding plate 40 is arranged in a position closer to the open end 21 of the sound conduit 20 than the upper shielding plate 10a. By arranging the small shielding plate 40 at a position closer to the open end 21 of the sound conduit 20 than the small shielding plate 40a, it becomes easier to collect the sound waves radiated from the open end 21 of the sound conduit 20 at the focal point F. This makes it possible to solve the problem that the sound waves radiated from the open end 21 of the sound conduit 20 do not coincide with the sound waves radiated from the point sound source located at the focal point F. As a result, it is possible to suppress a decrease in sound absorbing performance. The shape (cross-sectional shape) of the recessed surface 40a of the small shielding plate 40 is expressed by the above-mentioned formula (1). Furthermore, as long as there is no geometric interference with the sound conduit 20, the Y coordinate at the end of the small shielding plate 40 does not need to be a value smaller than the Y coordinate "f" of the focal point F (focal position).

[0015] The method of arranging the small shielding plate 40 is not particularly limited. As shown in FIG. 8, it may be arranged so that it is suspended from the recessed surface 10a1 of the upper shielding plate 10a using a single support member 50. Alternatively, as shown in FIG. 9, it may be arranged so that it is suspended from the recessed surface 10a1 of the upper shielding plate 10a using a plurality of (e.g., three) support members 50. As shown in FIG. 10, the small shielding plate 40 may be arranged by being supported by a plurality of (e.g., three) support members 50 erected from the recessed surface 10b1 of the lower shielding plate 10b. As shown in FIG. 11, the small shielding plate 40 may be arranged by being supported by a plurality of (e.g., three) support members 50 erected from the open end 21 of the sound conduit 20. It is desirable that the support members 50 be as thin and as few in number as possible within the permissible strength so as not to obstruct sound waves.

[0016] Next, a silencer 100A for ventilation openings that uses the silencer 100 of this embodiment will be described. The silencer 100A for ventilation openings is a silencer for silencing sounds output in soundproof spaces such as soundproof rooms and breeding cages. In describing the silencer 100A for ventilation openings, the same components as those in the silencer 100 described above will be given the same reference numerals, and descriptions thereof will be omitted.

[0017] 12, the ventilation opening silencer 100A is designed to be used by inserting the open end 22 of the sound conduit 20, which is opposite to the open end 21 disposed in the first space SP1, into a ventilation opening (not shown) in a soundproof space. As a result, sound waves generated in the soundproof space pass through the sound conduit 20 and are radiated from the open end 21 into the first space SP1 between the pair of shielding plates 10a, 10b. The sound waves radiated into the first space SP1 are attenuated as they are repeatedly reflected between the pair of shielding plates 10a, 10b, and are ultimately silenced. In this way, the ventilation silencer 100A comprises a pair of shielding plates 10a, 10b that form the first space SP1, and a sound conduit 20 that forms the second space SP2, the pair of shielding plates 10a, 10b are arranged so that their focal points F coincide, the sound conduit 20 is inserted into one of the pair of shielding plates 10a, 10b (the lower shielding plate 10b), and one of the two ends of the sound conduit 20 (open end 21) is provided within the first space SP1, so that the silencer 100A for a ventilation opening can silence sound waves of a wide range of frequencies despite its relatively simple configuration.

[0018] As shown in FIG. 12 , the silencer for ventilation openings 100A includes a fan 60 within the sound conduit 20, i.e., within the second space SP2. The fan 60 is a fan for discharging air within the soundproof space to the outside. However, the fan 60 is not an essential component of the silencer for ventilation openings 100A. The dashed arrows in FIG. 12 indicate the flow of air being discharged from the soundproof space. As shown by the arrows, the air within the soundproof space passes through the sound conduit 20 and is then discharged between the pair of shielding plates 10a, 10b. In this way, the silencer for ventilation openings 100A includes the fan 60, which allows the air within the soundproof space to be ventilated. Furthermore, as described above, the silencer for ventilation openings 100A has a relatively simple configuration and can reduce air resistance compared to conventional silencers with a serpentine structure, eliminating the need for a powerful fan as in the past. Therefore, the silencer for ventilation openings 100A can also solve the problem of wind noise caused by the inclusion of the fan 60. Furthermore, since the silencer for ventilation opening 100A has a relatively simple configuration as described above, the installation space can be significantly reduced.

[0019] 12, the fan 60 is disposed in a position close to the open end 21 inside the sound conduit 20, but the location of the fan 60 is not particularly limited. Specifically, as shown in FIG. 13, the fan 60 may be disposed in a position close to the open end 22 inside the sound conduit 20. In this case, the open end 22 side of the sound conduit 20 is located outside the first space SP1, and the diameter of the location where the fan 60 is to be installed can be made larger, making it easier to install the fan. Also, as shown in FIG. 14, the fan 60 may be disposed above the upper shielding plate 10a of the pair of shielding plates 10a, 10b. In this case, the ventilation opening silencer 100A and the fan 60 are housed in a box-shaped housing B, and air discharged from between the pair of shielding plates 10a, 10b is discharged to the outside of the housing B by the fan 60.

[0020] Next, a noise-absorbing mask 100B using the silencer 100 of this embodiment will be described. The noise-absorbing mask 100B is a mask for preventing the voice of a user wearing the noise-absorbing mask 100B from being heard by people around them when holding a web conference at work, on the go, at home, etc., in other words, a mask for silencing the voice of the user. In describing the noise-absorbing mask 100B, components similar to those of the silencer 100 described above will be assigned the same reference numerals and descriptions thereof will be omitted.

[0021] As shown in Figures 15 and 16, the sound-absorbing mask 100B is shaped to cover the area around the user's mouth (but not the eyes or nose), so the edges of each of the pair of shielding plates 10a, 10b are cut to form a horizontally long rectangle with rounded edges. The upper and lower slits SL1 and the side slits SL2 formed by these cuts each serve as an air vent. As shown in Figures 16 and 17, the sound-absorbing mask 100B has an air vent 10b2 formed in the center of the rear shielding plate 10b, and the sound conduit 20 is connected to this air vent 10b2. This rear shielding plate 10b corresponds to the lower shielding plate 10b of the silencer 100 shown in Figures 4 and 5. As a result, sound (sound waves) emitted by a user wearing the sound-absorbing mask 100B enters through the ventilation opening 10b2, passes through the sound conduit 20, and is radiated into the first space SP1 between the pair of shielding plates 10a, 10b from the open end 21. The sound (sound waves) radiated into the first space SP1 is attenuated as it is repeatedly reflected between the pair of shielding plates 10a, 10b, and is ultimately silencing. In this way, the sound absorption mask 100B comprises a pair of shielding plates 10a, 10b that form the first space SP1 and a sound conduit 20 that forms the second space SP2, the pair of shielding plates 10a, 10b are arranged so that their focal points F coincide, the sound conduit 20 is inserted into one of the pair of shielding plates 10a, 10b (the rear shielding plate 10b), and one end (open end 21) of the sound conduit 20 is provided within the first space SP1, thus having a relatively simple configuration, yet capable of silencing sound waves of a wide range of frequencies. Furthermore, with the sound absorption mask 100B, since upper and lower slits SL1 and side slits SL2 are provided, it is possible to ensure sufficient breathability compared to conventional sound absorption masks (for example, see JP 2022-153249 A).

[0022] The noise-absorbing mask 100B also includes a cushion member 70 surrounding the periphery of the ventilation hole 10b2 formed in the rear shielding plate 10b. The cushion member 70 is made of a soft material such as silicone rubber and fits snugly around the user's mouth when the noise-absorbing mask 100B is worn. Therefore, the provision of the cushion member 70 in the noise-absorbing mask 100B prevents sound emitted by the user wearing the noise-absorbing mask 100B from leaking to the outside before it is guided into the first space SP1 through the ventilation hole 10b2. The noise-absorbing mask 100B also includes a small wireless microphone 80 located near the ventilation hole 10b2 formed in the rear shielding plate 10b and at a predetermined position within the area surrounded by the cushion member 70. The wireless microphone 80 is used to collect sound emitted by the user wearing the noise-absorbing mask 100B.

[0023] When the noise reduction mask 100B is to be used continuously, the user may be able to maintain the state in which the noise reduction mask 100B is worn by using a headband 90 attached to the noise reduction mask 100B, as shown in Fig. 18. Also, as shown in Fig. 19, the user may be able to maintain the state in which the noise reduction mask 100B is worn by using a cover mask 91 that can cover the noise reduction mask 100B itself.

[0024] Next, a description will be given of a musical instrument silencer 100C that uses the silencer 100 of this embodiment. The musical instrument silencer 100C is a silencer that enables a person to practice playing a musical instrument at a low volume that does not disturb those around them. In describing the musical instrument silencer 100C, the same components as those in the silencer 100 described above will be given the same reference numerals, and their description will be omitted.

[0025] As shown in FIGS. 20 and 21 , similar to the silencer 100 shown in FIG. 7 , the musical instrument silencer 100C has a plurality of oval slits 30b formed in the wall surface of the support member 30 along the periphery of the support member 30. The musical instrument silencer 100C also has a mounting portion 110 on the outer surface of the rear shielding plate 10b (the surface opposite the recessed surface 10b1). This rear shielding plate 10b corresponds to the lower shielding plate 10b of the silencer 100 shown in FIGS. 4 and 5 . As shown in FIG. 22 , when the musical instrument silencer 100C is in use, the mounting portion 110 is inserted into the horn portion MIa of the musical instrument (e.g., a trumpet) MI, thereby securing the musical instrument MI to the musical instrument MI. The mounting portion 110 also has an air vent 110a formed on the inside thereof, the diameter of which gradually narrows from the open end, and the sound conduit 20 is connected to the air vent 110a. As a result, sound (sound waves) emitted from a musical instrument MI (see FIG. 22) to which musical instrument silencer 100C is attached passes through ventilation hole 110a and sound conduit 20, and is radiated into first space SP1 between the pair of shielding plates 10a, 10b from open end 21. Then, the sound (sound waves) radiated into first space SP1 is attenuated as it is repeatedly reflected between the pair of shielding plates 10a, 10b, and is ultimately silenced. In this way, musical instrument silencer 100C comprises a pair of shielding plates 10a, 10b that form first space SP1, and a sound conduit 20 that forms second space SP2, with the pair of shielding plates 10a, 10b arranged so that their focal points F coincide, with the sound conduit 20 inserted through one of the pair of shielding plates 10a, 10b (the rear shielding plate 10b), and with one of the opposite ends (open end 21) of sound conduit 20 being located within first space SP1, thus providing a relatively simple configuration, yet capable of muffling sounds (sound waves) of a wide range of frequencies. Also, with musical instrument silencer 100C, slits 30b are formed in the wall surface of support member 30, ensuring sufficient breathability, making it possible to reproduce a blowing feel during performance practice that is comparable to that during normal performance.

[0026] Next, a speaker back silencer 100D that uses the silencer 100 of this embodiment will be described. The speaker back silencer 100D is a silencer that absorbs sound (hereinafter referred to as rear sound) that is output to the rear side of a speaker unit 130 (described later). In describing the speaker back silencer 100D, the same components as those in the above-described silencer 100 are given the same reference numerals, and their description will be omitted.

[0027] As shown in Figures 23 and 24, the silencer 100D for use behind a speaker has a cylindrical speaker unit housing portion 120 provided on the outer surface of the front shielding plate 10b (the surface opposite the recessed surface 10b1). This front shielding plate 10b corresponds to the lower shielding plate 10b of the silencer 100 shown in Figures 4 and 5. As shown in Figure 25, the speaker unit housing portion 120 has a sound path 120a formed inside it that is designed so that the diameter gradually narrows from the open end side (hole cut out in a funnel shape), and the sound guide tube 20 is connected to this sound path 120a. As shown in Figures 26 and 27, the speaker unit housing portion 120 has The speaker unit 130 can be housed in this sound path 120a so as to cover the rear side of the speaker unit 130. Furthermore, in the speaker back silencer 100D, a pair of shielding plates 10a, 10b are arranged so that their peripheral edges meet, and the first space SP1 is a closed, highly sealed space. As a result, rear sound (sound waves) emitted from the speaker unit 130 passes through the sound path 120a and the sound conduit 20 and is radiated from the open end 21 into the first space SP1 between the pair of shielding plates 10a, 10b. The rear sound (sound waves) radiated into the first space SP1 is attenuated as it is repeatedly reflected between the pair of shielding plates 10a, 10b, and is ultimately silencing. In this way, the speaker back silencer 100D comprises a pair of shielding plates 10a, 10b that form the first space SP1 and a sound conduit 20 that forms the second space SP2, the pair of shielding plates 10a, 10b are arranged so that their focal points F coincide, the sound conduit 20 is inserted through one of the pair of shielding plates 10a, 10b (the front shielding plate 10b), and one end (open end 21) of the sound conduit 20 is provided within the first space SP1, which is a relatively simple configuration, yet it can muffle (absorb) rear sounds (sound waves) over a wide range of frequencies. Therefore, with the speaker back silencer 100D, it is no longer necessary to place sound-absorbing material inside the enclosure to absorb rear sounds, as in the conventional case, and rear sound can be handled more easily.

[0028] The speaker back silencer 100D may be further placed inside an enclosure EC as shown in FIG. 28. This enhances the effectiveness of processing rear sounds emitted from the speaker unit 130. However, if the speaker unit 130 is a high-output speaker unit or a large-diameter speaker unit, a tight sealing on the rear side and a small capacity may suppress the vibration of the speaker unit 130, potentially hindering its intended performance. For this reason, as shown in FIG. 29, slits SL3 may be formed in the periphery of the pair of shielding plates 10a, 10b. The provision of slits SL3 attenuates high-frequency sounds with high directivity within the first space SP1, while low-frequency sounds with low directivity (weak directivity) leak out through the slits SL3. However, as shown in FIG. 30, by providing a bass reflex duct BD in the enclosure EC, the low-frequency sounds output from the front side of the speaker unit 130 can be amplified by Helmholtz resonance. 31, in the case of a 2-way speaker having a high-frequency speaker unit 130A and a low-frequency speaker unit 130B, a speaker rear silencer 100D may be provided only for the high-frequency speaker unit 130A to mute the sound from the rear of the high-frequency speaker unit 130A while not mute the sound from the rear of the low-frequency speaker unit 130B. In such a case, by using a bass reflex duct BD, the low frequencies output to the front side of the low-frequency speaker unit 130B can be amplified by Helmholtz resonance.

[0029] The present invention has been specifically described above based on the embodiments, but the present invention is not limited to the above embodiments and can be modified within the scope of the gist of the present invention. For example, in the above embodiment, examples of use of the silencer 100 include a silencer for ventilation openings 100A, a noise-reducing mask 100B, a silencer for musical instruments 100C, and a silencer for the back of a speaker 100D, but these examples of use are merely examples.

[0030] Furthermore, each of the ventilation opening silencer 100A, the noise absorbing mask 100B, the musical instrument silencer 100C, and the speaker rear silencer 100D may be provided with a small shielding plate 40 (see FIGS. 8 to 11). [Explanation of symbols]

[0031] 100 silencer, 10a shielding plate, 10b shielding plate, 20 sound guide tube, 30 support member, F Focus, SP1 1st space, SP2 2nd space

Claims

1. a pair of shielding plates whose opposing surfaces are formed as parabolic recessed surfaces to form a first space therebetween; a cylindrical portion that is formed in a cylindrical shape with both ends open to form a second space; Equipped with the pair of shielding plates are arranged so that focal points determined by the parabolic shape coincide with each other, and the cylindrical portion is inserted into one of the pair of shielding plates, One end of the cylindrical portion is provided within the first space. A silencer characterized by:

2. the cylindrical portion is disposed so that the position of the center of the opening of the end portion disposed in the first space coincides with the focal point; 2. The silencer according to claim 1.

3. a small shielding plate smaller than the shielding plate; The small shielding plate is arranged so that a focal point determined by the parabolic shape of the small shielding plate coincides with a focal point determined by the parabolic shape of the shielding plate, and is arranged so that a concave surface of the parabolic shape faces an end of the cylindrical portion provided in the first space.

2. The silencer according to claim 1.

4. a pair of shielding plates whose opposing surfaces are formed as parabolic recessed surfaces to form a first space therebetween; a cylindrical portion that is formed in a cylindrical shape with both ends open to form a second space; Equipped with the pair of shielding plates are arranged so that focal points determined by the parabolic shape coincide with each other, and a predetermined opening is formed in one of the pair of shielding plates, One end of the cylindrical portion is connected to the opening, so that the second space communicates with the first space. A silencer characterized by:

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