EP3249947A1

EP3249947A1 - Bass reflex port and acoustic device

Info

Publication number: EP3249947A1
Application number: EP17172712.6A
Authority: EP
Inventors: Koji Okazaki; Hideto Matsuda; Akira Miki
Original assignee: Yamaha Corp
Current assignee: Yamaha Corp
Priority date: 2016-05-25
Filing date: 2017-05-24
Publication date: 2017-11-29
Anticipated expiration: 2037-05-24
Also published as: CN107438212A; JP6709537B2; CN107438212B; EP3249947B1; JP2017212606A

Abstract

A bass reflex port includes a tubular member. A rigidity of a part of a wall surface of the tubular member is smaller than that of a remaining part of the tubular member. A rigidity of a wall surface of at least one end portion of the tubular member in an axis direction of the tubular member is smaller than that of a wall surface of a central portion of the tubular member in the axis direction.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a bass reflex port and an acoustic device such as a bass reflex speaker.

2. Description of the Related Art

A bass reflex speaker that enhances the volume of a low-pitched sound by using the sound emitted from a speaker unit to the back side of a housing of the bass reflex speaker has conventionally been proposed. In the bass reflex speaker, a bass reflex port that communicates the inside and the outside of the housing (enclosure) with each other is provided. In the bass reflex speaker, an unusual sound (noise) is caused from the bass reflex port. Therefore, various technologies to reduce the unusual sound caused from the bass reflex port have been proposed.
JP-UM-A-56-63182 discloses a speaker system in which a sound absorbing material such as glass wool is attached to at least one opening of a bass reflex port. According to this technology, the generation of air whirl at the opening of the bass reflex port is suppressed by the sound absorbing material, thereby reducing the unusual sound.
JP-UM-A-58-173989 discloses a bass reflex cabinet for a speaker in which a buffer material such as urethane is provided at a free end opposite to a fixed end fixed to a housing in a bass reflex port. The free end is fixed to nowhere. According to this technology, vibration at the free end of the bass reflex port becomes difficult to occur, thereby reducing the unusual sound.
However, even though the technology disclosed in JP-UM-A-56-63182 or JP-UM-A-58-173989 is used, the unusual sound caused from the bass reflex port because of air flowing in the bass reflex port cannot be sufficiently reduced.

SUMMARY OF THE INVENTION

This invention is made in view of the above-described circumstances, and an object thereof is to reduce the unusual sound caused because of air flowing in the bass reflex port.
This invention provides a bass reflex port including a tubular member characterized in that a rigidity of a part of a wall surface of the tubular member is smaller than that of the remaining part. Moreover, this invention provides an acoustic device provided with the bass reflex port.
When air flows in the bass reflex port, a pressure distribution occurs in the enclosure (outside the bass reflex port) and in the bass reflex port, and an air pressure difference is caused between the inside and the outside of the bass reflex port. In the bass reflex port according to this invention, a portion with low rigidity on the wall surface moves according to the air pressure difference. As a result, the bass reflex port (particularly, the portion with low rigidity on the wall surface of the bass reflex port) is deformed. When the bass reflex port is deformed according to the air pressure difference, the shape of the inner wall surface on the portion with low rigidity randomly changes at each position and each moment. Thereby, the flow velocity distribution of the air in the vicinity of the inner wall surface of the bass reflex port is disordered, so that the position and the timing where a whirl occurs change randomly. Since the position and the timing where a whirl occurs do not concentrate but are dispersed, in the present bass reflex port, the growth of the whirl can be suppressed, so that the unusual sound caused due to the whirl can be reduced. That is, according to the acoustic device provided with the present bass reflex port, the unusual sound caused because of air flowing in the bass reflex port can be reduced.
According to the technology disclosed in JP-UM-A-56-63182, a sound absorbing material is attached to the bass reflex port, and according to the technology disclosed in JP-UM-A-58-173989, a buffer material is attached to the bass reflex port. According to the technologies disclosed in JP-UM-A-56-63182 and JP-UM-A-58-173989, the bass reflex port is not deformed, so that the position and the timing where a whirl occurs cannot be dispersed. On the contrary, in the present bass reflex port, the position and the timing where a whirl occurs can be dispersed as described above, so that the growth of the whirl can be suppressed. For this reason, according to the present bass reflex port, compared with the bass reflex ports disclosed in JP-UM-A-56-63182 and JP-UM-A-58-173989, the unusual sound caused from the bass reflex port because of air flowing in the bass reflex port can be sufficiently reduced.
Moreover, according to the technologies disclosed in JP-UM- A-56-63182 and JP-UM- A-58-173989 , since the position and the timing where a whirl occurs cannot be dispersed, even if the unusual sound is reduced, only the sound of a specific frequency according to the material characteristic and placement position of the sound absorbing material and the buffer material is reduced. On the contrary, in the present bass reflex port, the position and the timing where a whirl occurs are dynamically changed according to the air pressure difference that changes from moment to moment. For example, at a certain time, a whirl occurs at a position, closer to the center, on the end portion of the bass reflex port, and at another time different therefrom, a whirl occurs at a position, closer to the open end, on the end portion of the bass reflex port. The frequency of the sound attributed to the whirl at the position, closer to the center, on the end portion of the bass reflex port and the frequency of the sound attributed to the whirl at the position, closer to the open end, on the end portion of the bass reflex port are different. As described above, in the present bass reflex port, since the position and the timing of occurrence of the whirl are dispersed, the unusual sound attributed to the concentration of occurrence of the whirl at a specific position and timing never becomes conspicuous, so that the unusual sounds of a plurality of frequencies in a predetermined frequency range like a continuous spectrum can be reduced. From this point, according to the present bass reflex port, the unusual sound caused from the bass reflex port because of air flowing in the bass reflex port can also be sufficiently reduced compared with the bass reflex ports disclosed in JP-UM-A-56-63182 and JP-UM-A-58-173989.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the structure of an acoustic device including a bass reflex port according to a first embodiment of this invention.
FIG. 2 is a cross-sectional view showing the structure of the bass reflex port.
FIG. 3 is a side view showing the structure of the bass reflex port.
FIG. 4 is a cross-sectional view showing the structure of a bass reflex port 30A of an acoustic device 1A provided with the bass reflex port 30A according to a second embodiment of this invention.
FIG. 5 is a cross-sectional view showing the structure of a bass reflex port 30B of an acoustic device 1 B provided with the bass reflex port 30B according to a third embodiment of this invention.
FIG. 6 is a cross-sectional view showing the structure of a bass reflex port 30C of the acoustic device 1C provided with the bass reflex port 30C according to a fourth embodiment of this invention.
FIG. 7 is a cross-sectional view showing the structure of a bass reflex port 30D of an acoustic device 1 D provided with the bass reflex port 30D according to a fifth embodiment of this invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, referring to the drawings, embodiments of this invention will be described.

FIG. 1 is a cross-sectional view showing the structure of an acoustic device 1 including a bass reflex port 30 according to a first embodiment of this invention. The acoustic device 1 emits a sound responsive to an acoustic signal supplied from an external device, specifically, the acoustic device 1 is a bass reflex speaker. The acoustic device 1 has an enclosure 10 which is a housing of the acoustic device 1, the bass reflex port 30 and a speaker unit 20 formed of a diaphragm, a voice coil and the like.
The enclosure 10 is a hollow structure (typically, a rectangular parallelepiped) formed of a plurality of plate members. The speaker unit 20 is fixed to a plate member 12 of the plate members constituting the enclosure 10. This plate member 12 functions as a baffle surface. The plate member 12 has a circular opening 14 passing through the plate member 12. While the enclosure 10 in the present embodiment is formed of a plurality of plate members, the enclosure 10 may be a resin molded product by injection molding or the like. Moreover, while the opening 14 is provided on the plate member functioning as a baffle surface (that is, the plate member 12) in the acoustic device 1 in the present embodiment, the opening 14 may be provided on a surface other than the baffle surface such as the back surface or a side surface of the enclosure 10. Moreover, the shape of the opening 14 is not limited to a circle and may be a different shape.
The bass reflex port 30 is a hollow and substantially cylindrical tube, and is disposed in the enclosure 10. Both ends of the bass reflex port 30 are open. One open end of the bass reflex port 30 is fixed to the rim of the opening 14 of the plate member 12. The other open end of the bass reflex port 30 is located in the enclosure 10. The space in the enclosure 10 and the space outside the enclosure 10 are communicated through the bass reflex port 30 and the opening 14. For this reason, the air inside and outside the enclosure 10 passes in the bass reflex port 30.
In the present specification, the line as the center of the tube in the bass reflex port 30 will be referred to as tube axis. Moreover, in the present specification, of both ends of the bass reflex port 30, the one fixed to the rim of the opening 14 will be referred to as external side, and the one that is open in the enclosure 10 will be referred to as internal side. Moreover, in the present specification, at each end of the bass reflex port 30, a region predetermined in the tube axis direction from the open end will be referred to as end portion. Moreover, a region predetermined in the tube axis direction in the center of the bass reflex port 30 in the tube axis direction will be referred to as central portion.
FIG. 2 is a cross-sectional view showing the structure of the bass reflex port 30. The bass reflex port 30 includes a first tube 32, a second tube 34 and a sheet member 36. The first tube 32 is a tubular member of a cylindrical shape (hereinafter, referred to as tubular shape) in which the inside diameter and the outside diameter are maintained substantially constant from one end to the other end thereof. The first tube 32 is, for example, a paper tube shaped from a paper material such as recycled paper. The constituent material of the first tube 32 is not limited to paper and may be resin or the like.
The second tube 34 is a tubular member of a straight tube shape having an inside diameter substantially equal to the outside diameter of the first tube 32. The material forming the second tube 34 is, for example, a synthetic resin. The length of the second tube 34 is shorter than that of the first tube 32. A flange 35 is provided on one end of the second tube 34.
The first tube 32 has its one end side accommodated in the second tube 34, and is fixed to the second tube 34 with an appropriate frictional force between the outer wall surface of the first tube 32 and the inner wall surface of the second tube 34. Under a condition where the first tube 32 is fixed to the second tube 34, the other end side of the first tube 32 protrudes to the outside of the second tube 34 from the end opposite to the end of the second tube 34 where the flange 35 is provided. The flange 35 of the second tube 34 is fixed to the rim of the opening 14 of the plate member 12 (baffle surface).
The first tube 32 is provided with the sheet member 36 protruding in the extending direction of the first tube 32 from an end 33 of the first tube 32 opposite to the baffle surface. The material forming the sheet member 36 is, for example, felt, and the rigidity of the sheet member 36 is smaller than that of the first tube 32. The sheet member 36 extends over in a circumferential direction (radial direction) of the first tube 32, and forms a tube disposed in a position where the first tube 32 is extended.
The sheet member 36 is provided so as to cover over the end 33 of the first tube 32. More specifically, the sheet member 36 is partly fixed to the inner wall surface of the first tube 32. In the example of FIG. 2, the sheet member 36 is fixed over the entire inner wall surface of the first tube 32. The sheet member 36 extends so as to protrude from the end 33 of the first tube 32 in the extending direction of the first tube 32, is folded back in such a manner that a space 38 is formed by the end 33 of the first tube 32 and the sheet member 36, and has the end of extension thereof fixed to the outer wall surface of the first tube 32. An example of the method of fixing the sheet member 36 to the first tube 32 is a method using double-faced tape. A binding band or the like may be wound as a complement in order that the portion of the sheet member 36 pasted to the outer wall surface of the first tube 32 does not peel off. As described above, in the bass reflex port 30, the sheet member 36 is fixed in such a manner as to protrude in the extending direction from the end 33 of the first tube 32. Thereby, in the bass reflex port 30, the folded-back portion of the sheet member 36 is the internal side end of the bass reflex port 30.
The portion, accommodated in the second tube 34, of the first tube 32 (more precisely, including the sheet member 36 fixed to the inner wall surface of the first tube 32) and the second tube 34 constitute the wall surface of the external side end portion of the bass reflex port 30. The portion, protruding from the second tube 34, of the first tube 32 (more precisely, including the sheet member 36 fixed to the inner wall surface of the first tube 32) constitutes the wall surface of the central portion of the bass reflex port 30. The portion, protruding from the first tube 32, of the sheet member 36 constitutes the wall surface of the internal side end portion of the bass reflex port 30. Since the rigidity of the sheet member 36 (felt) is smaller than that of the first tube 32 (paper tube) in the bass reflex port 30, the rigidity of the wall surface of the internal side end portion of the bass reflex port 30 is smaller than that of the wall surface of the central portion thereof. For this reason, in the bass reflex port 30, the wall surface of the internal side end portion is readily deformed.
In the bass reflex port 30, the sheet member 36 is folded back at the internal side end. For this reason, at the folded-back portion, the bass reflex port 30 has, although slightly, a flare shape where the area of the region surrounded by the sheet member 36 increases toward the internal side end.
FIG. 3 is a side view showing the structure of the bass reflex port 30. On the portion of the sheet member 36 serving as the outer wall surface (in other words, the outer layer portion of the sheet member 36 folded back into two layers), a cutout 39 in the extending direction of the first tube 32 is provided more than one in number in the circumferential direction. For this reason, at the time of manufacture of the bass reflex port 30, the sheet member 36 fixed to the inner wall surface is neatly folded back toward the outer wall surface of the first tube 32, and easily fixed to the outer wall surface of the first tube 32. On the other hand, on the bass reflex port 30, a cutout like the cutout 39 of the portion serving as the outer wall surface is not provided on the portion serving as the inner wall surface of the sheet member 36 (in other words, the inner layer portion of the sheet member 36 folded back into two layers).
The above is the structure of the acoustic device 1 having the bass reflex port 30.
When the air in the enclosure 10 vibrates by the vibration of the diaphragm of the speaker unit 20, an air pressure distribution occurs in the enclosure 10 (outside the bass reflex port 30) and in the bass reflex port 30. This air pressure distribution changes from moment to moment according to the vibration of the diaphragm of the speaker unit 20. In the acoustic device 1, since such an air pressure distribution occurs, an air pressure difference is caused between the inside and the outside of the bass reflex port 30. Typically, a difference is caused between the air pressure in the bass reflex port 30 and that in the enclosure 10. And the air inside and outside the enclosure 10 passes in the bass reflex port 30.
As described above, in the bass reflex port 30, the rigidity of the wall surface of the internal side end portion is smaller than that of the wall surface of the central portion. For this reason, in the bass reflex port 30, the internal side end portion with low rigidity (particularly, the sheet member 36) moves randomly in the radial direction, the circumferential direction and the tube axis direction of the bass reflex port 30 and in a synthetic direction of these directions according to the air pressure difference. As a result, the bass reflex port 30 (particularly, the sheet member 36) is deformed. When the bass reflex port 30 is deformed according to the air pressure difference, the shape of the inner wall surface on the internal side randomly changes at each position and each moment. Thereby, the flow velocity distribution of the air in the vicinity of the inner wall surface of the bass reflex port 30 is disordered, so that the position and the timing where a whirl occurs change randomly. That is, in the bass reflex port 30, the position and the timing where a whirl occurs according to the air pressure difference do not concentrate but are dynamically dispersed. For this reason, in the bass reflex port 30, the growth of the whirl can be suppressed compared with the conventional bass reflex port.
As described above, according to the bass reflex port 30, since the growth of the whirl can be suppressed by dynamically dispersing the position and the timing where the whirl occurs, an unusual sound caused due to the whirl can be sufficiently reduced compared with the conventional bass reflex port. That is, according to the acoustic device 1 provided with the bass reflex port 30, the unusual sound caused because of air flowing in the bass reflex port 30 can be sufficiently reduced.
In the bass reflex port 30 of the present embodiment, the position and the timing where a whirl occurs dynamically change according to the air pressure difference that changes from moment to moment. For example, at a certain time, a whirl occurs at a position, closer to the center, on the end portion of the bass reflex port 30, and at another time different therefrom, a whirl occurs at a position, closer to the open end, on the end portion of the bass reflex port 30. The frequency of the sound attributed to the whirl at the position, closer to the center, on the end portion of the bass reflex port 30 and the frequency of the sound attributed to the whirl at the position, closer to the open end, on the end portion of the bass reflex port 30 are different. As described above, in the bass reflex port 30 of the present embodiment, since the position and the timing of occurrence of the whirl are dispersed, the unusual sound attributed to the concentration of occurrence of the whirl at a specific position and timing never becomes conspicuous, so that the unusual sounds of a plurality of frequencies in a predetermined frequency range like a continuous spectrum can be reduced. From this point, according to the bass reflex port 30 of the present embodiment, the unusual sound caused from the bass reflex port because of air flowing in the bass reflex port can also be sufficiently reduced compared with the conventional bass reflex port.
In the bass reflex port 30 of the present embodiment, the sheet member 36 protrudes from the end 33 of the first tube 32 in such a manner that the space 38 is formed. Thereby, the wall surface of the internal side of the bass reflex port 30 can be made to have a softness desirable for appropriately deforming it according to the air pressure difference.
On the sheet member 36 of the bass reflex port 30 of the present embodiment, the cutouts 39 are provided on the portion serving as the outer wall surface. In the bass reflex port 30, since these cutouts 39 are provided, compared with a case where the cutouts 39 are not provided, not only an advantage is obtained in that the sheet member 36 is easily fixed to the first tube 32 but also an advantage is obtained in that the unusual sound reduction effect can be enhanced since the sheet member 36 is readily deformed.
While felt is cited as a preferred example of the sheet member 36 in the present embodiment, the sheet member 36 is not limited to felt but may be a sheet resin or the like. In short, any mode may be adopted as long as the sheet member 36 is made of a material lower in rigidity than the material of the first tube 32. Moreover, while the sheet member 36 is fixed to the entire inner wall surface of the first tube 32 in the present embodiment, the sheet member 36 may be fixed to a part of the inner wall surface of the first tube 32. Moreover, the folded-back sheet member 36 may be fixed to the entire outer wall surface of the first tube 32 instead of being fixed to a part of the outer wall surface of the first tube 32.

FIG. 4 is a cross-sectional view showing the structure of a bass reflex port 30A of an acoustic device 1A provided with the bass reflex port 30A according to a second embodiment of this invention. Except for the bass reflex port 30A, the acoustic device 1A is similar to the acoustic device 1 of the first embodiment.
The bass reflex port 30A has a straight tube shape where the area of the region surrounded by the inner wall surface is maintained substantially fixed from the external side end over to the internal side end. The bass reflex port 30A includes a first tube 32A and a second tube 36A. The first tube 32A constitutes the wall surface of the central portion and the wall surface of the external side of the bass reflex port 30A. The second tube 36A constitutes the wall surface on the internal side. The material forming the first tube 32A and the material forming the second tube 36A are the same, and the first tube 32A and the second tube 36A are formed, for example, by integral molding. The thickness of the wall surface of the second tube 36A is smaller than that of the wall surface of the first tube 32A. That is, in the bass reflex port 30A, the rigidity of the wall surface of the internal side end portion is made smaller than that of the wall surface of the central portion by making the thickness of the wall surface of the internal side end portion smaller than that of the wall surface of the central portion.
The bass reflex port 30A is not provided with the sheet member 36 of the first embodiment. However, the bass reflex port 30A is similar to the bass reflex port 30 in that the rigidity of the wall surface of the internal side end portion is smaller than that of the wall surface of the central portion. For this reason, in the bass reflex port 30A, as in the bass reflex port 30, the internal side end portion moves randomly according to the air pressure difference, so that the bass reflex port 30A is deformed. Therefore, in the present embodiment, similar advantages to those of the first embodiment are obtained. In the present embodiment, the rigidity of the wall surface of the internal side end portion of the bass reflex port 30A is made smaller than that of the wall surface of the central portion by forming the first tube 32A and the second tube 36A of the same material and making the thickness of the wall surface of the second tube 36A smaller than that of the wall surface of the first tube 32A. However, if the rigidity of the wall surface of the internal side end portion of the bass reflex port 30A can be made smaller than that of the wall surface of the central portion by making the thickness of the wall surface of the second tube 36A smaller than that of the wall surface of the first tube 32A, the constituent material of the first tube 32A and that of the second tube 36A may be different.

FIG. 5 is a cross-sectional view showing the structure of a bass reflex port 30B of an acoustic device 1B provided with the bass reflex port 30B according to a third embodiment of this invention. Except for the bass reflex port 30B, the acoustic device 1 B is similar to the acoustic device 1 of the first embodiment.
The bass reflex port 30B has, like the bass reflex port 30A of the second embodiment, a straight tube shape from the external side end over to the internal side end. The bass reflex port 30B has a first tube 30B and a second tube 36B. The first tube 30B constitutes the wall surface of the central portion and the wall surface of the external side end portion of the bass reflex port 30B. The second tube 36B constitutes the wall surface on the internal side. The wall surface of the first tube 32B and the wall surface of the second tube 36B have the same thickness. The second tube 36B is formed of a material more flexible than that forming the first tube 32B. The second tube 36B is fixed to the first tube 32B by an adhesive agent or the like. That is, in the bass reflex port 30B, the rigidity of the wall surface of the internal side end portion is made smaller than that of the wall surface of the central portion by making the material forming the wall surface of the internal side end portion more flexible than that forming the wall surface of the central portion.
In the bass reflex port 30B, as in the second embodiment, the sheet member 36 of the first embodiment is not provided. However, the bass reflex port 30B is, like the second embodiment, similar to the bass reflex port 30 of the first embodiment in that the rigidity of the wall surface of the internal side end portion is made smaller than the rigidity of the wall surface of the central portion. For this reason, in the bass reflex port 30B, as in the bass reflex port 30, the internal side end portion moves randomly according to the air pressure difference, so that the bass reflex port 30B is deformed. Therefore, in the present embodiment, similar advantages to those of the first embodiment are obtained.

FIG. 6 is a cross-sectional view showing the structure of a bass reflex port 30C of the acoustic device 1C provided with the bass reflex port 30C according to a fourth embodiment of this invention. Except for the bass reflex port 30C, the acoustic device 1C is similar to the acoustic device 1 of the first embodiment.
The bass reflex port 30C has, like the bass reflex port 30A and the bass reflex port 30B, a straight tube shape from the external side end over to the internal side end. The bass reflex port 30C has a first tube 30C and a second tube 36C. The a first tube 30C constitutes the wall surface of the central portion and the wall surface of the internal side end portion of the bass reflex port 30C. The second tube 36C constitutes the wall surface of the external side end portion. The second tube 36C is fixed to the rim of the opening 14 of the plate member 12 by an adhesive agent or the like. The wall surface of the first tube 32C and the wall surface of the second tube 36C have the same thickness. The second tube 36C is formed of a material more flexible than that forming the first tube 32C. The second tube 36C is fixed to the first tube 32C by an adhesive agent or the like. That is, in the bass reflex port 30C, the rigidity of the wall surface of the external side end portion is made smaller than that of the wall surface of the central portion by making the material forming the wall surface of the external side end portion more flexible than that forming the wall surface of the central portion.
The bass reflex port 30C is similar to the bass reflex ports 30 to 30B of the first to third embodiments in that the rigidity of the wall surface of the end portion of the bass reflex port 30C which is the neighborhood of the boundary between the inside and the outside of the bass reflex port 30C is made smaller than that of the wall surface of the central portion. For this reason, in the bass reflex port 30C, as in the bass reflex port 30, the external side end portion moves randomly according to the air pressure difference, so that the bass reflex port 30C is deformed. Therefore, in the present embodiment, similar advantages to those of the first embodiment are obtained.
For example, the wall surface of the second tube 36C of the bass reflex port 30C is deformable according to the air pressure difference and has a rigidity of a degree where the bass reflex port 30C is maintained so as to be self-sustained with respect to the plate member 12.
The second tube 36C may have a structure in which a first rigidity region having a rigidity smaller than that of the wall surface of the central portion and a second rigidity region having a rigidity higher than that of the first rigidity region are repeated in the circumferential direction of the second tube 36C. According to this embodiment, the portions of the first rigidity region of the second tube 36C move randomly according to the air pressure difference to make the bass reflex port 30C deformable, and by the portions of the second rigidity region of the second tube 36C, the bass reflex port 30C can be maintained so as to be self-sustained.

FIG. 7 is a cross-sectional view showing the structure of a bass reflex port 30D of an acoustic device 1 D provided with the bass reflex port 30D according to a fifth embodiment of this invention. Except for the bass reflex port 30D, the acoustic device 1 D is similar to the acoustic device 1 of the first embodiment.
The bass reflex port 30D is different from the bass reflex port 30 of the first embodiment in that it has a sheet member 36D instead of the sheet member 36. The sheet member 36D is partly fixed to the inner wall surface of the first tube 32, and extends so as to protrude from the end 33 of the first tube 32 in the extending direction of the first tube 32. In the bass reflex port 30D, the end of the protrusion of the sheet member 36D is the internal side end of the bass reflex port 30D. The portion of the sheet member 36D protruding from the first tube 32 constitutes the wall surface of the internal side end portion of the bass reflex port 30D.
In the bass reflex port 30D, the sheet member 36D is not folded back at the internal side end. However, the bass reflex port 30D is similar to the bass reflex port 30 in that the wall surface of the internal side end portion is formed of the sheet member 36D with the sheet member 36D protruding from the end 33 of the first tube 32 to thereby make the rigidity of the wall surface of the internal side end portion smaller than that of the wall surface of the central portion. For this reason, in the bass reflex port 30D, as in the bass reflex port 30, the sheet member 36D on the internal side end portion moves randomly according to the air pressure difference, so that the bass reflex port 30D is deformed. Therefore, in the present embodiment, similar advantages to those of the first embodiment are obtained.

While the first to fifth embodiments of this invention are described above, other embodiments are considered for this invention, for example, as follows:

(1) In the bass reflex ports 30 to 30B and 30D of the first to third and fifth embodiments, the rigidity of the wall surface of the internal side end portion is smaller than that of the wall surface of the central portion, and in the bass reflex port 30C of the fourth embodiment, the rigidity of the wall surface of the external side end portion is smaller than that of the wall surface of the central portion. However, the position where the rigidity is low is not limited to these positions. That is, in the bass reflex port according to this invention, it is necessary only that the rigidity of at least a part of the wall surface be smaller than that of the remaining portion. This is because if the rigidity of at least a part of the wall surface is low, the part with the low rigidity moves according to the air pressure difference, so that the bass reflex port is deformed. And if the part with the low rigidity is deformed, the flow velocity distribution of the air in the vicinity of the inner wall surface of the part with the low rigidity is dynamically disordered, so that the position and the timing of occurrence of a whirl do not concentrate but are dispersed. As described above, by making the rigidity of at least a part of the wall surface of the bass reflex port smaller than that of the remaining part, the unusual sound caused because of air flowing in the bass reflex port can be reduced as in the embodiments.
(2) While it is necessary only that the rigidity of at least a part of the wall surface be smaller than that of the remaining part in the bass reflex port according to this invention, it is preferable that the rigidity of the wall surface of at least one end portion of the bass reflex port be smaller than that of the wall surface of the central portion. The first reason is that the part with the low rigidity moves more easily when the part with the low rigidity is on the end portion than when it is on the central portion. The second reason is that the whirl tends to easily occur on the end portion where air flows out from the bass reflex port compared with on the central portion and the effect of dispersing the position and the timing of occurrence of the whirl is high on the end portion compared with on the center. Moreover, the effect of reducing the unusual sound is higher in the mode where the rigidity of the wall surface of the internal side end portion is smaller than the rigidity of the wall surface of the central portion than in the mode where the rigidity of the wall surface of the external side end portion is smaller than the rigidity of the wall surface of the central portion. The first reason is that the internal side end portion moves easily compared with the external side end portion since the internal side end portion is not supported by the baffle surface. The second reason is that the whirl tends to easily occur on the internal side end portion not continuous with the baffle surface compared with on the external side end portion continuous with the baffle surface and the effect of dispersing the position and the timing of occurrence of the whirl is high. Moreover, the bass reflex port according to this invention is not limited to the mode where the rigidity of the wall surface of one end portion is made smaller than that of the wall surface of the central portion; the rigidities of the wall surfaces of both end portions may be made smaller than that of the wall portion of the central portion.
(3) Specific modes where the rigidity is made low are not limited to the modes of the embodiments. For example, in the bass reflex port 30 of the first embodiment, the cutouts 39 of the sheet member 36 may be provided not only on the portion serving as the outer wall but also on the portion serving as the inner wall. According to this mode, the rigidity of the wall surface of the sheet member 36 is smaller than that of the first embodiment and it is considered that the sheet member 36 is more easily deformed.
(4) The cutouts 39 are provided on the portion serving as the outer wall of the sheet member 36 of the bass reflex port 30 of the first embodiment. However, such cutouts 39 are not essential.
(5) In the bass reflex port, the portion constituting the wall surface of the end portion with low rigidity may be structured so as to be detachably attachable to the central portion with high rigidity.
(6) The bass reflex port 30 of the first embodiment has a straight tube shape except for the folded-back portion of the sheet member 36. However, the internal side end portion of the bass reflex port 30 may have a flare shape from the end 33 of the first tube 32 over to the internal side end. Moreover, not only the internal side end portion of the bass reflex port 30 but the external side end portion of the bass reflex port 30 may have a flare shape. Moreover, not only the one end portion of the bass reflex port 30 but both end portions may have a flare shape. Moreover, in the bass reflex ports 30A to 30D of the second to fifth embodiments, the end portions of the internal and external sides of the bass reflex ports 30A to 30D may similarly have a flare shape.
(7) The wall surface of the end portion of the bass reflex port may have a multilayer structure formed of an inner layer member constituting the inside wall surface and an outer layer member constituting the outer wall surface. In this case, the rigidity of at least the inner layer member is made smaller than that of the wall surface of the central portion so that at least the inner layer member moves according to the air pressure difference to make the bass reflex port deformable.
(8) Technical features of the embodiments may be combined as appropriate.
(9) As well as the provision to the market as the acoustic devices of the embodiments, the bass reflex ports adopted in the acoustic devices of the embodiments may be singly provided to the market. This is because the acoustic devices of the embodiments can be realized by attaching the bass reflex ports to acoustic devices. Moreover, the acoustic devices of the embodiments may be provided to the market in a state of being mounted on musical instruments such as electronic keyboards.

Here, the details of the above embodiments are summarized as follows.

[1] The disclosure provides a bass reflex port comprising:
- a tubular member,
- wherein a rigidity of a part of a wall surface of the tubular member is smaller than that of a remaining part of the tubular member.
[2] For example, a rigidity of a wall surface of at least one end portion of the tubular member in an axis direction of the tubular member is smaller than that of a wall surface of a central portion of the tubular member in the axis direction.
[3] For example, a thickness of the at least one end portion in a radial direction of the tubular member is smaller than that of the central portion in the radial direction being perpendicular to the axis direction.
[4] For example, the at least one end portion and the central portion are formed in a unity piece.
[5] For example, the at least one end portion and the central portion are formed in separated pieces, and a rigidity of a piece for the at least one end portion is smaller than that of a piece for the central portion.
[6] For example, the piece for the at least one end portion is a sheet member.
[7] For example, an inner wall surface of the at least one end portion is flush with an inner wall surface of the central portion, and an outer wall surface of the at least one end portion is continuous with an inner wall surface of the central portion via a stepped part.
[8] For example, a material forming the wall surface of the at least one end portion is more flexible than a material forming the wall surface of the central portion.
[9] For example, the bass reflex port further comprises:
- a sheet member being lower in rigidity than the tubular member,
- wherein the sheet member is fixed to the tubular member and protrudes from one end of the tubular member in an extension direction of the tubular member.
[10] For example, the sheet member is partly fixed to an inner wall surface of the tubular member, extends so as to protrude from an end of the tubular member in the extending direction of the tubular member, and then is folded back so that a space is formed by the end of the tubular member and the sheet member, and an end of the folded sheet member is fixed to an outer wall surface of the tubular member.
[11] For example, a plurality of cutouts extending in the axis direction are provided in the folded sheet member which is fixed to the outer wall surface of the tubular member.
[12] For example, the sheet member is folded so that the space in a cross section area having the axis direction becomes larger as extending in the extending direction.
[13] For example, an acoustic device comprising:
- the bass reflex port according to any one of items [1] to [12]; and
- an enclosure having an opening,
- wherein the bass reflex port is disposed in the enclosure and one end of the bass reflex port is fixed to a rim of the opening.
[14] For example, a rigidity of a wall surface of an end portion close to the opening, among end portions of the tubular member of the bass reflex port is smaller than that of a wall surface of the central portion of the tubular member of the bass reflex port.

Claims

A bass reflex port comprising:
a tubular member,

wherein a rigidity of a part of a wall surface of the tubular member is smaller than that of a remaining part of the tubular member.
The bass reflex port according to claim 1, wherein a rigidity of a wall surface of at least one end portion of the tubular member in an axis direction of the tubular member is smaller than that of a wall surface of a central portion of the tubular member in the axis direction.
The bass reflex port according to claim 2, wherein a thickness of the at least one end portion in a radial direction of the tubular member is smaller than that of the central portion in the radial direction being perpendicular to the axis direction.
The bass reflex port according to claim 2 or 3, wherein the at least one end portion and the central portion are formed in a unity piece.
The bass reflex port according to claim 2 or 3, wherein the at least one end portion and the central portion are formed in separated pieces; and
wherein a rigidity of a piece for the at least one end portion is smaller than that of a piece for the central portion.
The bass reflex port according to claim 5, wherein the piece for the at least one end portion is a sheet member.
The bass reflex port according to any one of claims 2 to 6, wherein an inner wall surface of the at least one end portion is flush with an inner wall surface of the central portion; and
wherein an outer wall surface of the at least one end portion is continuous with an inner wall surface of the central portion via a stepped part.
The bass reflex port according to any one of claims 2, 3, 5, 6 and 7, wherein a material forming the wall surface of the at least one end portion is more flexible than a material forming the wall surface of the central portion.
The bass reflex port according to any one of claims 1, 2, 3, 5 and 8, further comprising:
a sheet member being lower in rigidity than the tubular member,

wherein the sheet member is fixed to the tubular member and protrudes from one end of the tubular member in an extension direction of the tubular member.
The bass reflex port according to claim 9, wherein the sheet member is partly fixed to an inner wall surface of the tubular member, extends so as to protrude from an end of the tubular member in the extending direction of the tubular member, and then is folded back so that a space is formed by the end of the tubular member and the sheet member; and
wherein an end of the folded sheet member is fixed to an outer wall surface of the tubular member.
The bass reflex port according to claim 10, wherein a plurality of cutouts extending in the axis direction are provided in the folded sheet member which is fixed to the outer wall surface of the tubular member.
The bass reflex port according to claim 10 or 11, wherein the sheet member is folded so that the space in a cross section area having the axis direction becomes larger as extending in the extending direction.
An acoustic device comprising:
the bass reflex port according to any one of claims 1 to 12; and

an enclosure having an opening,

wherein the bass reflex port is disposed in the enclosure and one end of the bass reflex port is fixed to a rim of the opening.
The acoustic device according to claim 13, wherein a rigidity of a wall surface of an end portion close to the opening, among end portions of the tubular member of the bass reflex port is smaller than that of a wall surface of the central portion of the tubular member of the bass reflex port.