JPWO2012008419A1 - Sound equipment - Google Patents

Abstract

Provided is an acoustic device that can always exhibit good listening performance in a state where a sound-insulating earplug is attached to the ear canal. The acoustic device 1 includes a bone conduction speaker 24 that applies acoustic vibration to the earplug 21. The earplug 21 includes a sound-insulating flexible earplug body 22 that is inserted into the ear canal, and a fixed cap body 23 that is provided at the end 22 a of the earplug body 22 on the side opposite to the insertion side. The cap body 23 has a vibration receiving surface 23 a that receives vibrations in contact with the vibration output surface 24 a of the bone conduction speaker 24. The vibration output surface 24a is a concave spherical surface, and the vibration receiving surface 23a is a convex spherical surface. The curvature radius R1 of the vibration receiving surface 23a is 2 mm or more and 10 mm or less, and the curvature radius R2 of the vibration output surface 24a is larger than the curvature radius R1 of the vibration reception surface 23a.

Description

  The present invention relates to an acoustic device that is used in a state where a sound-insulating earplug is attached to an external auditory canal.

  2. Description of the Related Art An acoustic device of a type that listens to sound by pressing a bone conduction speaker (vibration generation source) against an earplug while the earplug is attached to the ear canal is known. (Patent Document 1, Patent Document 2)

Japanese Utility Model Publication No. Hei 6-26328 JP-A-5-207579

  The conventional acoustic device described above is configured to transmit the vibration of the bone conduction speaker to the earplug in a state in which the end surface on the side opposite to the insertion side of the earplug and the vibration surface of the bone conduction speaker are in surface contact with each other. For this reason, in this type of conventional acoustic device, when the vibration surface of the bone conduction speaker is inclined with respect to the end surface of the earplug on the side opposite to the insertion side, the transmission efficiency of vibration decreases due to poor contact between both surfaces. The acoustic performance of can not be demonstrated.

  The problem to be solved by the present invention is an acoustic device that can always exhibit good listening performance with a sound-insulating earplug attached to the ear canal, a contact structure suitable for the acoustic device, an earplug, and an acoustic vibration generator Is to provide.

  In order to solve the above problems, the present invention employs the following technical means.

[Sound device]
The acoustic device of the present invention is an acoustic device having an earplug and an acoustic vibration generating device that applies acoustic vibration to the earplug, wherein the earplug is a sound-insulating flexible earplug body that is inserted into the ear canal. A cap having a fixed shape that covers the end of the earplug on the side opposite to the insertion side, and the cap has a receiving surface that receives vibration in contact with the vibration output surface of the acoustic vibration generator. The vibration output surface is a concave curved surface, the vibration receiving surface is a convex curved surface, the radius of curvature of the convex curved surface is 2 mm or more and 10 mm or less, and the radius of curvature of the vibration output surface is the vibration receiving surface. It is characterized by being equal to or larger than the radius of curvature of the surface.
Here, the “anti-insertion side end” means an end on the side exposed from the ear canal when the earplug is worn (the same applies hereinafter).

  In the acoustic device of the present invention, the fixed part is a member harder than the earplug. The fixed part is preferably formed in a hemispherical shape or a spherical shape. The fixed part is made of metal, plastic, hard rubber, or wood. It is desirable that the earplug has both shape recovery and flexibility. It is desirable that the curvature of the convex curved surface is isotropically constant and the curvature of the concave curved surface is isotropically constant. The radius of the end portion on the side opposite to the insertion side of the earplug is 4 mm to 8 mm.

[Contact structure]
The contact structure of the present invention is a contact structure between an earplug and an acoustic vibration generating device that applies acoustic vibration to the earplug, and the earplug includes a sound-insulating flexible earplug body that is inserted into the external ear canal and the earplug. A cap having a fixed shape provided on the end of the earplug on the side opposite to the insertion side, the cap body having a vibration receiving surface that receives the vibration in contact with the vibration output surface of the acoustic vibration generator. The vibration output surface is a concave curved surface, the vibration receiving surface is a convex curved surface, the curvature radius of the convex curved surface is 2 mm or more and 10 mm or less, and the curvature radius of the vibration output surface is the vibration receiving surface. It has the characteristic that it is equal to or larger than the radius of curvature.

  In the contact structure of the present invention, the fixed portion is a member that is harder than the earplug. The fixed part is preferably formed in a hemispherical shape or a spherical shape. The fixed part is made of metal, plastic, hard rubber, or wood. It is desirable that the earplug has both shape recovery and flexibility. It is desirable that the curvature of the convex curved surface is isotropically constant and the curvature of the concave curved surface is isotropically constant. The radius of the end portion on the side opposite to the insertion side of the earplug is 4 mm to 8 mm.

[Earplug]
The earplug of the present invention has a sound-insulating flexible earplug body that is inserted into the ear canal and a cap body that is provided so as to cover the end portion on the opposite side of the earplug body. An earplug that is vibrated by contact with an output surface and transmits acoustic vibrations to the external auditory canal, wherein the cap body has a receiving surface that receives vibration in contact with the vibration output surface at the tip, The vibration output surface is a concave curved surface, the vibration receiving surface is a convex curved surface, and the curvature radius of the convex curved surface is 2 mm or more and 10 mm or less.

In the earplug of the present invention, the cap body has a circular concave portion or an annular sleeve portion on the side opposite to the vibration receiving surface, and the end portion on the opposite side of the earplug body is the concave portion or the sleeve portion. It is desirable to be inserted into and fixed to.
Examples of the shape of the cap body include a spherical shape or a hemispherical shape.
When the shape of the cap body is hemispherical, the recess or the sleeve portion is formed at the center of the flat portion of the hemispherical cap body.

  In the earplug of the present invention, the fixed portion is a member harder than the earplug body. The fixed part is preferably formed in a hemispherical shape or a spherical shape. The fixed part is made of metal, plastic, hard rubber, or wood. It is desirable that the earplug has both shape recovery and flexibility. The radius of the end portion on the side opposite to the insertion side of the earplug is 4 mm to 8 mm. The radius of the joint portion between the fixed portion and the end portion on the non-insertion side of the earplug body is equal to or larger than the radius of the end portion on the antiinsertion side of the earplug body.

[Acoustic vibration generator]
The acoustic vibration generator of the present invention is an acoustic vibration generator that applies acoustic vibrations by contacting the earplug of the present invention, wherein the vibration output surface is a concave curved surface, and the curvature radius of the vibration output surface is the vibration receiving surface. It is characterized by being equal to or larger than the radius of curvature of the surface.
In the acoustic vibration generating device of the present invention, an opening may be provided in the center of the vibration output surface, and a vibration output portion of an acoustic vibration generating source that vibrates the vibration output surface may be provided facing the outside from the opening. .

The acoustic device of the present invention always exhibits good listening performance in a state where a sound-insulating earplug is attached to the ear canal.
According to the contact structure of the present invention, the acoustic device of the present invention can be realized.
The earplug of the present invention is suitable for the earplug of the acoustic device of the present invention. The earplug of the present invention can be easily manufactured by providing a cap body on the end of the earplug body opposite to the insertion side. By using a commercially available earplug with high sound insulation as the earplug, the earplug of the present invention can be realized while utilizing the high sound insulation and safety of the earplug as they are.
The acoustic vibration generator of the present invention is suitable for the acoustic vibration generator of the acoustic apparatus of the present invention.

Side view showing an example of earplug configuration Side view showing an example (use state) of the acoustic device Front view showing an example of the configuration of the acoustic device (A) is a sectional view showing a state where the earplug and the bone conduction speaker are in contact with each other without inclination. (B) is a sectional view showing a state where the earplug and the bone conduction speaker are in contact with each other in an inclined posture. (A)-(D) are side views showing other embodiments of earplugs Sectional drawing which shows another example of an earplug

  Hereinafter, embodiments of the present invention will be described.

[Constitution]
FIG. 1 is a cross-sectional view showing an embodiment of an earplug.
The earplug 21 shown in FIG. 1 is a sound-capable earplug body 22 that is flexibly deformed and inserted into the external auditory canal, and a fixed cap body 23 provided on the opposite end 22a of the earplug body 22 on the opposite side. And have. The cap body 23 has a vibration receiving surface 23a at the tip. The vibration receiving surface 23a is a convex curved surface (in this example, a hemispherical surface) having a constant curvature. The radius of curvature R1 of the vibration receiving surface 23a is selected from a range of 2 mm to 10 mm.

  The earplug 22 has both shape recovery and flexibility. The radius of the non-compressed side end 22a of the earplug 22 is 4 mm to 8 mm. The shape of the earplug 22 is a columnar shape. The shape of the cap body 23 is hemispherical. A circular recess is formed in the center of the flat portion of the cap body 23, and the end 22a opposite to the insertion side of the earplug 22 is inserted into this recess and fixed by adhesion. The cap body 23 is a member harder than the ear plug body 22. The cap body 23 is made of metal, plastic, hard rubber, or wood.

2 and 3 show examples of acoustic devices. FIG. 2 is a side view showing a use state. FIG. 3 is a front view of the earphone constituting the acoustic device.
The acoustic device 1 includes an earphone (attachment body) 11 that is detachably attached to a user's head.
The earphone 11 includes a first bone conduction speaker (acoustic vibration generator) 24R and a second bone conduction speaker (acoustic vibration generator) 24L. The first bone conduction speaker 24R comes into contact with the cap body 23 of the first ear plug 21R attached to the ear canal of one (right ear) of the user. The second bone conduction speaker 24L comes into contact with the cap body 23 of the second ear plug 21L attached to the external ear canal of the other (left ear) of the user.
The earphone 11 has an arcuate or substantially horseshoe-shaped headband portion straddling the back of the user when worn, and an arch shape extending from one end of the headband portion 11A to the root of one ear of the user. A first ear hook portion 11B (R) that extends, and a second ear hook portion 11B (L) that extends in an arch shape so as to straddle the root of the other pinna of the user from the other end of the headband portion 11A, A first arm portion 11C (R) extending from the first ear hook portion 11B (R) to one ear hole of the user, and a second arm portion extending from the second ear hook portion 11B (L) to the other ear hole of the user. 11C (L). The tip portions of both arm portions 11C (R) and 11C (L) are bent inwardly in an L shape.
Then, the first bone conduction speaker 24R is at the tip of the bent portion of the right arm portion 11C (R), and the second bone conduction speaker 24L is at the tip of the bent portion of the left arm portion 11C (L). Are provided respectively. The first arm portion 11C (R) is rotatably connected to the first ear hook portion 11B (R). The second arm portion 11C (L) is a second ear hook portion 11B.
(L) is rotatably connected.

The first bone conduction speaker 24R and the second bone conduction speaker 24L include an electroacoustic transducer (acoustic vibration generation source) 26 that converts an audio signal (electrical signal) transmitted from an external device (not shown) into acoustic vibration. (See FIG. 4). Examples of the electroacoustic transducer 26 include a piezoelectric speaker, an electrostatic transducer, an electromagnetic transducer, a dynamic transducer, and the like.

  The earplugs 21R and 21L are attached to the ear canal by picking the cap body 23 with a finger and inserting the earplug body 22 into the ear canal from the insertion side end face 22a side. The outer peripheral surface of the earplug 22 is in close contact with the inner surface of the ear canal over the entire circumference. By wearing the earplugs 21R and 21L, the external ear canal of the wearer is kept in a quiet environment in which noise from the outside is blocked (for example, an environment having a noise level that is approximately 20 dB to 30 dB lower than the external noise level). be able to.

4A and 4B show a contact structure between the earplugs 21R and 21L and the bone conduction speakers 24R and 24L.
The bone conduction speakers 24R and 24L have vibration output surfaces 24a that come into contact with the vibration receiving surfaces 23a of the earplugs 21R and 21L. The vibration output surface 24a is a concave curved surface (in this example, a concave spherical surface) whose curvature is isotropically constant, and its curvature radius R2 is larger than the curvature radius R1 of the vibration receiving surface 23a (R2> R1). .

[Action]
In the acoustic device 1, the first ear plug 21R is attached to one (right) external ear canal of the user, and the second ear plug 21L is attached to the other (left) external ear canal of the user. The vibration output surface 24a of the bone conduction speaker 24R is the vibration receiving surface 23a of the cap body 23 of the first ear plug 21R, and the vibration output surface 24a of the second bone conduction speaker 24L is the vibration reception surface 23a of the cap body 23 of the second ear plug 21L. To be used in contact with each other. When the vibration receiving surface 23a and the vibration output surface 24a are not in contact with each other, the vibration output surface 24a only vibrates, and no vibration is generated in the earplugs 21R and 21L.

  The bone conduction speakers 24R and 24L convert the input audio signals (electric signals) into acoustic vibrations. That is, the bone conduction speakers 24R and 24L vibrate the left and right vibration output surfaces 24a according to the input audio signal (electrical signal). When the vibration output surface 24a of the bone conduction speaker 24R on the right ear side vibrates, the vibration is transmitted to the cap body 23 of the earplug 21R attached to the right ear canal, and the vibration output of the bone conduction speaker 24L on the left ear side. As the surface 24a vibrates, the vibration is transmitted to the cap body 23 of the earplug 21L attached to the left ear canal. The vibrations of the cap bodies 23 are transmitted to the earplug bodies 22 of the earplugs 21R and 21L. When the earplug body 22 vibrates, sound (sound using air as a medium) is emitted from the insertion-side end surface 22a of the earplug body 22 into the ear canal, and is transmitted to the eardrum as sound. The vibration of the earplug 22 is transmitted to the auditory organ such as the eardrum using the skin of the ear canal or the like as a medium. The ratio (sound volume ratio) of the sound using air as a medium and the sound using skin as a medium (volume ratio) can be adjusted by appropriately selecting the materials, dimensions, and the like of the ear plug body 22 and the cap body 23.

  The vibration output surface 24a of the bone conduction speakers 24R and 24L made of a hard member and the cap body 23, which is a member harder than the ear plug body 22, are brought into contact with each other, so that the vibration of the vibration output surface 24a is applied to the ear plug 21. Therefore, the vibration transmission efficiency between the two is much higher than the vibration transmission efficiency between a conventional earplug made of only a soft material and a bone conduction speaker. The vibration output surface 24a does not need to be in strong pressure contact with the vibration receiving surface 23a of the cap body 23, but only needs to be in contact therewith. The contact pressure between them can be adjusted by appropriately selecting the rigidity (elasticity) of the arm portions 11C (R) and 11C (L) of the earphone 11.

[effect]
The acoustic device 1 has a vibration receiving surface (curvature constant isotropically constant) of the cap body 23 provided at the end 22a on the opposite side of the earplug body 22 with the earplugs 21R and 21L attached to the left and right external auditory canals. Of the left and right bone conduction speakers 24R, 24L of the earphone 11 and a part of the vibration output surface (concave curved surface having a constant isotropic curvature) 24a is in contact with the earphone 11. Therefore, even if the bone conduction speakers 24R and 24L are inclined with respect to the ear plug body 22 (see FIG. 4B), the contact failure does not occur as in the prior art. The vibrations 24R and 24L are always transmitted to the earplugs 21R and 21L with high efficiency. Therefore, it is possible to always exhibit good listening performance.

  Further, according to the acoustic device 1, the ear plugs 21R and 21L vibrate the cap body 23 of the ear plugs 21R and 21L in a state where the user's external ear canal is kept in a quiet environment in which noise from the outside is blocked. You can listen to the audio. Therefore, extremely high listening performance can be exhibited even under high noise.

[Others]
In the above example, the arm portions 11C (R) and 11C (L) are rotatably connected to the ear hook portions 11B (R) and 11B (L), but the arm portions 11C (R) and 11C By configuring the outer shell of (L) with a member that can be freely deformed and can be autonomously held in the changed posture, the posture or shape of the arm portions 11C (R) and 11C (L) can be made variable. May be.

  In the above example, the earplugs 21R and 21L provided with the columnar earplug body 22 have been described. However, the earplug body 22 may have a bullet shape (substantially columnar shape with a narrow end on the insertion side). Good.

  Further, the form of the earphone 11 is not limited to the form shown in FIGS. The earphone 11 in the above example includes two bone conduction speakers 24R and 24L for the right ear and the left ear, but is a single-ear type acoustic device including only one of the bone conduction speakers 24R or 24L. It is also possible. However, even when a single-ear type acoustic device is used, it is desirable to attach earplugs to both ears. This is to protect both ears from noise.

  5A to 5D show other embodiments of the earplug 21. FIG. The earplug 21 of (a) includes a hemispherical cap body 23. The earplug 21 of (b) includes a substantially spherical cap body 23. The earplug 21 of (c) is provided with a partial spherical cap body 23. The earplug 21 of (d) includes a flat sphere (spheroid) cap body 23. (A)-(c) The cap body 23 of any earplug 21 has a vibration receiving surface 23a formed of a convex curved surface having an isotropic curvature. The internal structure of the cap body 23 may be a solid structure or a hollow structure.

FIGS. 5A to 5C show examples in which the curvature of the entire tip surface of the cap body 23 is isotropically constant.
As shown in FIG. 5D, the curvature of the entire tip surface of the cap body 23 does not need to be isotropically constant. Moreover, if the curvature of most of the front-end | tip part of the vibration receiving surface 23a is constant, you may change a curvature from the peripheral part. In the example of FIG. 5D, the curvature around the tip of the vibration receiving surface 23a is larger.
By forming a large number of dimples on the surface of the spherical cap body 23 shown in FIG. 5B, the earplug 21 having the cap body 23 simulating the shape of a golf ball is obtained.

It is desirable to use a commercially available earplug having a sound insulation value (NRR) of 20 dB or more (preferably 30 dB or more) as the earplug body 22. By covering and adhering the cap body 23 to one end of a commercially available earplug whose sound insulation and safety have been confirmed by many years of use, the sound insulation and safety of the earplug can be utilized as they are. The earplug 21 of the invention can be realized.
Therefore, by mounting the earplug 21 of the present invention on both ears and mounting the earphone 11 on the outside thereof, while implementing noise disturbance prevention measures in accordance with guidelines for noise disturbance prevention based on the Industrial Safety and Health Law. Voice communication in a noisy work environment is possible.

  The radius of the non-insertion side end 22a of the commercially available sound insulating earplug is about 4 mm for the smallest size and about 8 mm for the largest size. When the minimum thickness of the portion covering the periphery of the end portion 22a of the earplug is 1 mm, the earplug has a radius of 4 mm and a hemispherical cap having a radius of curvature R1 of 6 mm. By covering the body 23, the earplug 21 of the smallest size having the shape shown in FIG. Similarly, by attaching a hemispherical cap body 23 having a radius of curvature R1 of 10 mm to an earplug having a radius of the anti-insertion side end 22a of 8 mm, the earplug 21 of the largest size having the shape of FIG. Is obtained. Even in the case of a hemispherical cap body 23 having a curvature radius R1 of 4 mm, the earplug 21 can be obtained by covering the cap body 23 by slightly compressing the end portion 22a on the side opposite to the earplug. The value of the radius of curvature R1 of the vibration receiving surface 23a of the cap body 23 is theoretically unlimited, but 10 mm is practically the upper limit. If the radius of curvature R1 is further increased to obtain the vibration receiving surface 23a having a sufficient area, the cap body 23 becomes too large with respect to the earplug body 22, and thus the usability, wearing feeling, stability during wearing, etc. are poor. Problem arises.

When the radius of curvature R1 of the vibration receiving surface 23a is less than 3 mm, as shown in FIG. 6, a projection 23c is provided at the center of the main body portion (the portion covering the opposite end portion 22a of the earplug body) 23b of the cap body 23. It is desirable to form the vibration receiving surface 23a at the tip. The tip of the protrusion 23c may be formed in a spherical shape. In the case of the configuration shown in FIG. 6 as well, the earplug 21 of the present invention is realized by directly applying the cap body 23 to one end of a commercially available earplug while adhering to the high sound insulation and safety of the earplug. it can.
However, experience has shown that if the radius of curvature R1 of the vibration receiving surface 23a is smaller than 2 mm, slippage tends to occur between the vibration output surface 24a and the vibration output surface 24a, although this is not necessarily true. If the radius of curvature R2 of the vibration output surface 24a is reduced in accordance with the vibration receiving surface 23a in order to avoid this problem, it is difficult to align the vibration receiving surface 23a and the vibration output surface 24a when the earphone 11 is mounted. Further, the protrusion 23c is essential, and there is a high possibility that the strength is reduced.

In the above example, the curvature of the vibration output surface 24a is assumed to be isotropically constant. However, the curvature of the central portion (the innermost part) of the vibration output surface 24a is made isotropically constant, and the curvature from the periphery thereof is determined. May be changed.
In addition, an opening is provided at the center of the vibration output surface 24a, and the vibration output portion of the electroacoustic transducer 26 in the speakers 24R and 24L is exposed to the outside so as to be substantially flush with the vibration output surface 24a. You may not. According to this configuration, vibration from the electroacoustic transducer 26 can be directly transmitted to the cap body 23 of the earplug 21.

  In the above example, the case where the radius of curvature R2 of the vibration output surface 24a is larger than the radius of curvature R1 of the vibration receiving surface 23a, that is, R2> R1 is illustrated, but it is also possible to set R2 = R1.

  The acoustic device of the present invention can be used for a hearing aid. That is, a microphone, a driving circuit (including an amplifier circuit, a filter circuit, etc.) for driving a bone conduction speaker in accordance with an output signal of the microphone, a battery, a volume controller (output volume controller) ), Etc., it is possible to realize a hearing aid that is compact and lightweight, has a very good wearing feeling, and exhibits extremely high listening performance even under high noise.

DESCRIPTION OF SYMBOLS 1 Sound apparatus 11 Earphone 21 Earplug 21R 1st earplug 21L 2nd earplug 22 Earplug body 22a Non-insertion side edge part 23 Fixed part 23a Vibration receiving surface (convex curved surface)
24R first bone conduction speaker (acoustic vibration generator)
24L second bone conduction speaker (acoustic vibration generator)
24a Vibration output surface (concave surface)
26 Electroacoustic transducer (acoustic vibration oscillation source)
R1 Radius of curvature of receiving surface R2 Radius of curvature of vibration output surface

Claims (8)

An acoustic device having an earplug and an acoustic vibration generating device that applies acoustic vibration to the earplug,
The earplug has a sound-insulating flexible earplug body that is inserted into the ear canal and a fixed cap body that is provided on the end of the earplug body opposite to the insertion side,
The cap body has a receiving surface that receives vibration in contact with a vibration output surface of the acoustic vibration generating device at a tip portion thereof,
The vibration output surface is a concave curved surface,
The vibration receiving surface is a convex curved surface,
The radius of curvature of the convex curved surface is 2 mm or more and 10 mm or less,
The acoustic device according to claim 1, wherein a curvature radius of the vibration output surface is equal to or greater than a curvature radius of the vibration receiving surface. A contact structure between an earplug and an acoustic vibration generator that applies acoustic vibration to the earplug,
The earplug has a sound-insulating flexible earplug body that is inserted into the ear canal and a fixed cap body that is provided on the end of the earplug body opposite to the insertion side,
The cap body has a receiving surface that receives vibration in contact with a vibration output surface of the acoustic vibration generating device at a tip portion thereof,
The vibration output surface is a concave curved surface,
The vibration receiving surface is a convex curved surface,
The radius of curvature of the convex curved surface is 2 mm or more and 10 mm or less,
A contact structure between an earplug and an acoustic vibration generator, wherein a radius of curvature of the vibration output surface is equal to or greater than a radius of curvature of the vibration receiving surface. It has a sound-insulating flexible earplug inserted into the ear canal and a cap provided on the end of the earplug opposite to the insertion side, and is vibrated by contact with the vibration output surface of the acoustic vibration generator. Earplugs that transmit acoustic vibrations to the ear canal,
The cap body has a receiving surface that receives vibrations in contact with the vibration output surface at its tip.
The vibration output surface is a concave curved surface,
The vibration receiving surface is a convex curved surface,
An earplug, wherein the curvature radius of the convex curved surface is 2 mm or more and 10 mm or less. The cap body has a circular concave portion or an annular sleeve portion on the side opposite to the vibration receiving surface,
The earplug according to claim 3, wherein an end portion on the side opposite to the insertion side of the earplug body is inserted and fixed in the concave portion or the sleeve portion.   The earplug according to claim 4, wherein the cap body has a spherical shape. The shape of the cap body is hemispherical,
The earplug according to claim 4, wherein the concave portion or the sleeve portion is formed at a center of a flat portion of the hemispherical cap body. An acoustic vibration generator for applying an acoustic vibration in contact with the earplug according to any one of claims 4 to 6,
The vibration output surface is a concave curved surface;
The acoustic vibration generating device, wherein a curvature radius of the vibration output surface is equal to or larger than a curvature radius of the vibration receiving surface. Having an opening in the center of the vibration output surface;
The acoustic vibration generator according to claim 7, wherein a vibration output portion of an acoustic vibration generation source that vibrates the vibration output surface is provided facing the outside from the opening.

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