CN108836631B

CN108836631B - Ear muff

Info

Publication number: CN108836631B
Application number: CN201810597317.6A
Authority: CN
Inventors: 黄礼范
Original assignee: Shanghai Chaoyin Acoustics Technology Co ltd
Current assignee: Shanghai Chaoyin Acoustics Technology Co ltd
Priority date: 2018-06-11
Filing date: 2018-06-11
Publication date: 2021-01-01
Anticipated expiration: 2038-06-11
Also published as: CN108836631A

Abstract

An earmuff, comprising: at least one ear cup further comprising a housing comprising a quasi-vertical end distal to the ear side and approximately parallel to the ear and a quasi-horizontal end approximately perpendicular to the ear; the housing has a receiving cavity; a metamaterial spacer is arranged in the accommodating cavity and comprises a frame and a thin sheet arranged in the frame; the number of the metamaterial spacers is at least one. The earmuffs are simple and light in structure, comfortable to wear, capable of effectively isolating and absorbing low-frequency noise transmitted into ears of people, and meanwhile, voice communication distributed at high frequency cannot be influenced.

Description

Ear muff

Technical Field

The embodiment of the invention relates to a noise protection structure, in particular to an earmuff.

Background

Industrial modernization has greatly increased production efficiency, however the accompanying electromechanical noise presents a considerable health hazard to industrial workers. Measures to reduce noise damage are typically to wear earmuffs or earplugs. These products are generally classified into two broad categories, active and passive. The active noise protection device collects noise frequency spectrum information through the sensor, and controls the built-in micro loudspeaker to generate sound waves in a phase opposite to that of noise to form energy offset, so that the purpose of noise reduction is achieved. But the application range is limited due to the problems of complex structure, lower reliability and higher manufacturing cost. The passive noise protection device has good protection effect in a high frequency band (such as above 1500 Hz), and the protection requirement of the noise in the frequency band can be met by wearing the earplug. However, the noise protection effect for the low frequency band (e.g. below 500 Hz) generated by most mechanical equipment is not ideal. In order to improve the noise protection effect of a low frequency band, the wall thickness of a shell of an ear cup has to be increased as much as possible in the prior art, and meanwhile, the depth of the ear cup is increased to fill more sound absorption materials, so that a product becomes heavy, and the wearing comfort is greatly sacrificed. Moreover, because the noise with higher frequency is cut down too much, and the important voice information carried by the frequency band is blocked, the voice communication among workers becomes difficult.

Therefore, an earmuff with a simple and light structure is needed for low-frequency noise protection, so that low-frequency noise transmitted into ears of a person can be greatly reduced, and voice communication cannot be influenced.

Disclosure of Invention

The embodiment of the invention solves the problem of how to provide an earmuff which is simple in structure, light and thin and can effectively isolate and absorb low-frequency noise.

In order to solve the above problems, embodiments of the present invention provide an earmuff, comprising at least one ear cup, the at least one ear cup further comprising a shell, the shell comprising a quasi-vertical end away from the ear side and approximately parallel to the ear and a quasi-horizontal end approximately perpendicular to the ear; the housing has a receiving cavity; a metamaterial spacer is arranged in the accommodating cavity and comprises a frame and a thin sheet arranged in the frame; the number of the metamaterial spacers is at least one.

Specifically, the casing is filled with sound absorbing material, sound absorbing material surrounds the metamaterial spacer set up in the casing.

Specifically, the accommodating cavity is divided into at least two cavities by the metamaterial partition, and sound absorption materials are filled in at least one cavity.

Specifically, the metamaterial spacer is connected with the shell through a connecting structure.

Specifically, the connecting structure is a welding spot, a welding seam or a rivet piece.

Specifically, the metamaterial spacer is connected with at least one of the quasi-vertical end or the quasi-horizontal end of the shell through the connecting structure.

Specifically, one end of the connecting structure is connected with the frame of the metamaterial spacer, and the other end of the connecting structure is connected with the shell.

Specifically, the connecting structure is one or a combination of a loose-leaf hinge, a reed hinge, a transition ring and a supporting leg.

Specifically, the connecting structure is a columnar supporting leg, one end of the columnar supporting leg is connected with the frame of the metamaterial spacer, the other end of the columnar supporting leg is connected with the shell, and the number of the supporting legs is at least two.

Specifically, the connecting structure is a columnar supporting leg, one end of the columnar supporting leg is connected with the thin sheet of the metamaterial spacer, and the other end of the columnar supporting leg is connected with the shell.

Specifically, the connecting structure is a transition ring, the frame of the metamaterial spacer is nested on the inner edge of the transition ring, and the outer edge of the transition ring is connected with the shell.

Specifically, the inner edge of the transition ring comprises a step platform, and the frame of the metamaterial spacer is nested in the step platform.

Specifically, the inner edge of the transition ring comprises a groove, and the frame of the metamaterial spacer is nested in the groove.

Specifically, the transition ring is made of a sound absorption material.

Specifically, the shape of the outer contour of the metamaterial spacer is the same as the shape of the inner contour section of the shell where the metamaterial spacer is matched with the inner contour section of the shell.

Specifically, the shape of the outer contour of the metamaterial spacer is different from the shape of the inner contour of the housing where the metamaterial spacer is matched with the housing, and the shape of the outer contour of the metamaterial spacer is an ellipse, a circle, a triangle, a rectangle, a pentagon or a hexagon.

Specifically, the area enclosed by the outer contour of the metamaterial spacer accounts for 30% -100% of the area of the inner contour section of the shell where the metamaterial spacer is matched with the metamaterial spacer.

Specifically, the metamaterial diaphragm is provided with a plurality of cavities, and the accommodating cavity of the shell is divided into a plurality of cavities.

Specifically, at least one of the plurality of chambers is filled with a sound absorbing material.

Specifically, each of the plurality of metamaterial spacers is connected with the housing through a connecting structure.

Specifically, at least one part of the plurality of metamaterial spacers is connected with each other through a connecting structure, and at least one piece of the connected metamaterial spacers is connected with the shell through the connecting structure.

In the earmuff as described in any of the above, a first chamber is formed between the quasi-vertical end and the metamaterial spacer closest thereto, the quasi-vertical end of the shell is provided with at least one opening communicating with the first chamber, and the at least one opening forms at least one helmholtz resonator with the first chamber, the metamaterial spacer and the connecting structure; the metamaterial diaphragm has an anti-resonance frequency that coincides with a resonance frequency of the at least one Helmholtz resonator.

In the earmuff as described in any of the above, at least one mass plate or at least one confining body is placed on at least one surface of the thin sheet for adjusting the antiresonance frequency of the metamaterial spacer.

In particular, at least one opening is formed in the sheet and in the at least one mass sheet or in the at least one constraining body, the at least one opening penetrating the sheet and the at least one mass sheet or the at least one constraining body.

Specifically, the mass plate is oval, circular, triangular, rectangular, pentagonal or hexagonal.

Specifically, the constraining body is an ellipse, a circle, a triangle, a rectangle, a pentagon or a hexagon.

Compared with the prior art, the technical scheme of the embodiment of the invention has the following advantages:

the earmuff adopts the metamaterial spacer utilizes the metamaterial spacer to effectively insulate sound in the anti-resonance state generated at the low frequency band, and further reduces the wall thickness requirement of the shell and the depth dimension requirement of the earmuff, so that the earmuff is light and thin in structure and convenient to wear and use. And the metamaterial spacer can not increase the sound insulation of a higher frequency band while improving the sound insulation effect of a low frequency band, and ensures that the voice information contained in the higher frequency band can be clearly transmitted into human ears.

Further, the metamaterial spacer is connected with the shell through the connecting structure, when the connecting structure is in flexible connection, the metamaterial spacer comprises two mass-spring vibration systems, namely the metamaterial spacer is regarded as one mass-spring vibration system, the metamaterial spacer is regarded as a mass, and the flexible connecting structure is regarded as a spring. On one hand, the anti-resonance corresponding frequencies of the two 'mass-spring' vibration systems are usually different, so that the sound insulation bandwidth of the earmuff can be widened; on the other hand, the mechanical impedance of the metamaterial spacer can be adjusted and supplemented by adopting diversified connection structures, and the degree of freedom of design is increased.

Further, the quasi-vertical end of the housing is provided with at least one opening communicating with the first chamber, and the metamaterial diaphragm comprises at least one opening or is introduced into at least one opening through the connecting structure. On one hand, the static pressure born by the ears of a person is balanced with the static pressure outside the earmuffs, so that the influence of the pressure difference on the anti-resonance frequency of the metamaterial spacer is reduced while the wearing discomfort is avoided; on the other hand, increase the heat-sinking capability of ear muff avoids appearing wearing the phenomenon that the ear muff leads to perspiring for a long time.

Further, the quasi-vertical end of the shell is provided with at least one opening communicated with the first cavity, and the opening, the first cavity and the metamaterial spacer form a Helmholtz resonator. The helmholtz resonator has near perfect sound absorption characteristics when the anti-resonance frequency of the metamaterial diaphragm coincides with the resonance frequency of the helmholtz resonator. So that the earmuff has excellent low-frequency sound absorption performance.

Drawings

FIG. 1 is a schematic view of an earmuff according to an embodiment of the invention;

FIG. 2 is an exploded view of the metamaterial spacer of FIG. 1;

FIG. 3 is a schematic view of another earmuff according to an embodiment of the invention;

FIG. 4 is a schematic illustration of one embodiment of the present invention in which a metamaterial spacer is attached to a housing;

FIG. 5 is a schematic view of another embodiment of the present invention in which a metamaterial spacer is attached to a housing;

FIG. 6 is a schematic view of another embodiment of the present invention in which a metamaterial spacer is attached to a housing;

FIG. 7 is a schematic view of another embodiment of the present invention in which a metamaterial spacer is attached to a housing;

FIG. 8 is a schematic view of another embodiment of the present invention in which a metamaterial spacer is attached to a housing;

FIG. 9 is a schematic view of another embodiment of the present invention in which a metamaterial spacer is attached to a housing;

FIG. 10 is a schematic view of another embodiment of the present invention in which a metamaterial spacer is attached to a housing;

FIG. 11 is a schematic view of a housing opening according to an embodiment of the present invention;

FIG. 12 is a schematic view of an alternative configuration of the housing opening in accordance with an embodiment of the present invention;

FIG. 13 is a schematic diagram of the structure of a metamaterial spacer in one embodiment of the present invention;

FIG. 14 is a schematic view of the structure of a metamaterial spacer opening in one embodiment of the present invention;

FIG. 15 is a schematic diagram of an apparatus for testing acoustic performance of earmuffs in accordance with an embodiment of the present invention;

fig. 16 is a microphone sound pressure level spectrum at the position of the ear where the earmuff shown in fig. 15 is worn on the artificial head.

Detailed Description

In order to design a low-frequency noise protection earmuff with a light and thin structure, the embodiment of the invention combines the metamaterial spacer with the earmuff shell, and effectively improves the low-frequency sound insulation and absorption performance of the earmuff by designing the mechanical impedance matching relationship of the metamaterial spacer and the shell. In order to make the aforementioned objects, features and advantages of the embodiments of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below.

In some embodiments of the invention, an earmuff is contemplated comprising at least one ear cup, the ear cup further comprising a shell; the shell comprises a quasi-vertical end which is far away from the side of the ear and is approximately parallel to the ear and a quasi-horizontal end which is approximately vertical to the ear; the shell is provided with a containing cavity; a metamaterial spacer is arranged in the accommodating cavity; the metamaterial spacer comprises a frame and a thin sheet arranged in the frame; the number of metamaterial spacers is at least one.

In some embodiments of the invention, the metamaterial spacers are connected to at least one of the quasi-vertical ends or the quasi-horizontal ends of the housing by a connection structure.

Referring to fig. 1, fig. 1 is a schematic diagram of an earmuff 10 according to an embodiment of the invention. The earmuff 10 comprises two ear cups 11, the ear cups 11 further comprise a shell 111; the housing 111 has a receiving cavity 112; a metamaterial spacer 12 is arranged in the accommodating cavity 112; the housing 111 includes a quasi-vertical end 1111 away from the ear side and approximately parallel to the ear and a quasi-horizontal end 1112 approximately perpendicular to the ear. The metamaterial diaphragm 12 divides the receiving cavity 112 into a first chamber 1121 and a second chamber 1122. In some embodiments, the metamaterial spacer 12 is connected to the shell 111 of the ear cup 11 by a connection structure 13.

To connect the two ear cups 11 together, the earmuff 10 of fig. 1 further comprises a headband 14 connecting the ear cups 11. To increase the comfort of the wearer, the earmuff 10 in fig. 1 further comprises a sponge cushion 15.

In fig. 1, the housing 111 includes a quasi-vertical end 1111 away from the ear side and approximately parallel to the ear and a quasi-horizontal end 1112 approximately perpendicular to the ear. It should be noted that, in order to make the positions of quasi-vertical end 1111 and quasi-horizontal end 1112 easier to understand, the description is made in conjunction with the relative positions of human ears and quasi-vertical end 1111 and quasi-horizontal end 1112 in actual use. It is obvious to the earmuff 10 itself that the human ear is not part of its structure.

In a particular implementation, the metamaterial spacer 12 may be connected to at least one of the quasi-vertical end 1111 or the quasi-horizontal end 1112 of the housing 111 by a connection structure 13. In fig. 1, the metamaterial spacer 12 is attached to the quasi-horizontal end 1112 of the housing 111.

It should be noted that the number of the metamaterial spacers 12 may be one or more, but a first chamber is formed between one metamaterial spacer 12 closest to the quasi-vertical end 1111 and the quasi-vertical end 1111. That is, when the number is one, the metamaterial diaphragm 12 is the closest metamaterial diaphragm 12 to the quasi-vertical end 1111, and the first chamber 1121 is formed therebetween. When the metamaterial spacers 12 are plural in number, a first chamber 1121 is formed between the nearest quasi-vertical end 1111 and the quasi-vertical end 1111.

In some embodiments of the invention, the receiving cavity may be divided into at least two cavities by a metamaterial spacer, at least one cavity being filled with sound absorbing material. In fig. 1, the metamaterial spacer 12 is connected to the quasi-horizontal end 1112 of the housing 111 by a connection structure 13. The first chamber 1121 and the second chamber 1122 are filled with a sound absorbing material to widen the operating frequency range of the earmuff 10. Of course, whether the sound absorbing material is filled in the first cavity 1121 or the second cavity 112 may be selected according to actual needs, or neither the first cavity 1121 or the second cavity 112 may be filled with the sound absorbing material. Here, the working frequency range of the earmuff 10 means that the earmuff 10 has a good sound absorption or sound insulation effect for sound waves in a certain frequency range. The meaning of the operating frequency ranges mentioned in the other embodiments is the same and will not be described further. Specifically, the operating frequency range may be 0Hz to 500 Hz. Thus, the earmuffs 10 can improve the sound insulation effect of the low frequency band, and simultaneously can not increase the sound insulation of the higher frequency band, so that the voice information contained in the higher frequency band can be clearly transmitted into the ears of people.

It should be noted that the metamaterial spacer 12 is not shown in fig. 1 in specific structure, for example, the frame 121 and the sheet 122 thereof can be referred to the description of fig. 2.

The number of the ear cups 11 in the earmuffs 10 may be one or more. When there is one ear cup 11, the head mount for connecting a plurality of ear cups can be omitted. The sponge cushion 15 can increase the comfort of wearing the ear cup 11, and other soft structures can be selected according to actual needs, or the sponge cushion 15 is not used.

As shown in fig. 2, fig. 2 is an exploded view of the metamaterial spacer 12 of fig. 1. Wherein, the metamaterial spacer 12 shown in fig. 2a comprises a frame 121 and a thin sheet 122 attached to the surface of the frame 121, which is a basic structure of the metamaterial spacer 12; the metamaterial spacer 12 shown in fig. 2b comprises two frames, namely a frame 121 and a frame 123 and a thin sheet 122 attached between the frame 121 and the frame 123. By adopting the structural form of the metamaterial spacer 12 shown in fig. 2b, not only the assembly fastness of the thin sheet 122 can be enhanced, but also the assembly freedom of the metamaterial spacer 12 can be increased, for example, the frame 123 and the frame 121 can be assembled with the thin sheet 122 clamped in the middle by riveting, heat bonding and other processes; the metamaterial spacer 12 shown in fig. 2c comprises a frame 121 and two sheets, i.e. a sheet 122 and a sheet 124, attached to the surface of the frame 121. If the constituent materials, thickness dimensions, etc. of the

sheets

122 and 124 are different, more antiresonance states can be introduced into the metamaterial spacer 12, so that the sound insulation band of the earmuff can be widened.

The earmuff 10 with the metamaterial spacer 12 can effectively insulate sound by utilizing the anti-resonance state generated by the metamaterial spacer at low frequency, so that the wall thickness of the shell 111 of the ear cup 11 can be further reduced, and the depth dimension of the ear cup 11 can be reduced, so that the ear cup 11 is lighter and thinner in structure.

In some embodiments of the invention, the metamaterial spacer is connected to the housing by a connection structure. However, the metamaterial spacers may be disposed in the housing by other means without using a connecting structure.

In some embodiments of the invention, the housing is filled with sound absorbing material disposed within the housing surrounding the metamaterial spacer. In this way, the metamaterial spacers can be placed in the receiving cavity of the shell of the earmuff without using connecting structures. For example, the metamaterial spacers 12 of fig. 1 may be encased in sound absorbing material without the use of the attachment structure 13 described previously. The sound absorbing material can broaden the operating frequency of the earmuff 10.

Fig. 3 is a schematic view of another earmuff 20 embodiment of the invention. The earmuff 20 shown in fig. 3 is typically lightweight and lightweight as compared to the earmuff 10 shown in fig. 1. The earmuff 20 comprises two left and right ear cups 21, a sponge cushion 25 for placing the ear cups 21 against the sides of the human ear in use, and a headband 24 for attaching the ear cups 21. Wherein the ear cup 21 comprises a housing 211, a receiving cavity 212 and a metamaterial spacer 22. A metamaterial diaphragm 22 is disposed within the receiving cavity 212 to divide the receiving cavity 212 into a first chamber 2121 and a second chamber 2122. The housing 211 includes a quasi-vertical end 2111 which, in use, is remote from the side of the human ear and approximately parallel to the human ear, and a quasi-horizontal end 2112 which is approximately perpendicular to the human ear. The metamaterial spacer 22 is connected to the quasi-horizontal end 2112 of the housing 211 by a connection structure 23. The first and

second chambers

2121 and 2122 are not filled with a sound absorbing material.

It should be noted that, in the embodiments of the present invention, the metamaterial diaphragm is disposed in the receiving cavity of the casing to form an integral acoustic system with the casing, and the acoustic characteristics of the metamaterial diaphragm are different between the inside and the outside of the casing. Therefore, in order to obtain an ideal noise protection effect, the mechanical impedance matching relationship between the metamaterial spacer and the shell needs to be designed according to the preset low-frequency sound insulation and absorption frequency band and index. Wherein the mechanical impedance of the metamaterial spacer is directly related to the mechanical impedance of the metamaterial spacer itself and the mechanical impedance of the connection structure. In particular, the mechanical impedance of the metamaterial spacers themselves is closely related to their geometric dimensions and the thickness of the thin sheets employed; the mechanical impedance of the connecting structure is related to the geometrical size, the hardness and softness of the material of the connecting structure, and the size of the connecting area. Generally, the larger the cross-sectional area of the metamaterial spacer, the thinner the sheet employed, the more likely the antiresonance state will occur at low frequencies; the thinner the bending deformation direction of the connection structure or the longer the longitudinal deformation direction, the softer the material used and the smaller the area of the connection region, the more likely the antiresonance state occurs at low frequencies. In order to ensure the requirement of external rigidity, the shell is generally made of a hard material, and the geometric shape and the size of the shell are also taken into consideration, so that the impedance can be designed to be extremely small, and therefore, the design of the mechanical impedance of the metamaterial spacer and the mechanical impedance of the connecting structure becomes the key of the design of the acoustic performance of the earmuff. The design concept of the metamaterial spacer mentioned in the foregoing embodiment and the following embodiments is the same, and will not be described in detail later.

The basic structure and various modifications of the metamaterial spacer are easily understood by those skilled in the art, and thus, the embodiment of the present invention is not described in detail. It should be noted that the form and specific structure of the connection structure may be various, and are not limited to the form shown in this embodiment or other embodiments. In a specific implementation, one end of the connecting structure is connected with the frame of the metamaterial spacer, and the other end of the connecting structure is connected with the shell. For example, one end of the connection structure 13 in fig. 1 may be connected to the frame 121 of the metamaterial spacer 12, and the other end is connected to the housing 111.

In some embodiments of the invention, the attachment structure is a combination of one or more of a living hinge, a leaf hinge, a transition ring, and a support foot. Next, a specific structure of the connection structure 13 will be explained.

As shown in fig. 4, fig. 4 is a schematic diagram of a structure of the metamaterial diaphragm 12 connected to the housing 111 according to an embodiment of the present invention. Fig. 4a is a schematic structural view of a metamaterial spacer 12 having a connection structure 13, and fig. 4b is a schematic sectional view of a structure of an ear cup 11. The connecting structure 13 is a cylindrical supporting leg, one end of the cylindrical supporting leg is connected to the frame 121 of the metamaterial spacer 12, the other end of the cylindrical supporting leg is connected to the casing 111, and the number of the supporting legs is four. As shown in fig. 4, the ear cup 11 includes a metamaterial spacer 12 and a connecting structure 13, wherein the metamaterial spacer 12 includes a frame 121 and a thin sheet 122 attached to the surface of the frame 121, the connecting structure 13 is a column-shaped supporting leg, as shown in fig. 4a, 4 column-shaped supporting legs are symmetrically distributed around the center point of the metamaterial spacer, one end of each column-shaped supporting leg is connected to the frame 121, and the other end of each column-shaped supporting leg is connected to a quasi-vertical end 1111 of the housing, as shown in fig. 4 b.

It should be noted that the number of the cylindrical support legs in fig. 4 is at least two, that is, the frame 121 of the metamaterial spacer 12 may be connected to the housing 111 only through two cylindrical support legs.

In some embodiments of the invention, one end of the columnar support foot is connected to the sheet of metamaterial spacer, and the other end is connected to the housing.

As shown in fig. 5, fig. 5 is another structural schematic diagram of the metamaterial diaphragm 12 connected to the housing 111 according to an embodiment of the present invention. Fig. 5a is a schematic structural view of a metamaterial spacer 12 having a connection structure 13, and fig. 5b is a schematic sectional view of a structure of an ear cup 11. The connecting structure 13 is a columnar supporting leg, one end of the columnar supporting leg is connected with the thin sheet 122 of the metamaterial spacer 12, the other end of the columnar supporting leg is connected with the shell 111, and the number of the columnar supporting legs is at least one; the positions of the plurality of columnar supporting feet are centrosymmetric about the center point of the metamaterial spacer 12. As shown in FIG. 5, the ear cup 11 comprises a metamaterial spacer 12 and a connecting structure 13, wherein the metamaterial spacer 12 comprises a frame 121 and a sheet 122 attached to a surface of the frame 121. The connecting structure 13 is also a cylindrical support foot, one of which is shown in fig. 5a, one end of which is attached to the centre of the lamella 122 and the other end of which is attached to the quasi-vertical end 1111 of the housing, see fig. 5 b. Of course, when the number of the supporting legs is plural, the positions of the supporting legs are centrosymmetric with respect to the center point of the metamaterial spacer 12.

It should be noted that, in the connection structure of the column-shaped support foot shown in fig. 4 and 5, the connection manner between the column-shaped support foot and the frame 121 and the shell 111 may be gluing, screwing, welding, riveting, etc., and if the column-shaped support foot and the frame 121 or the sheet 122 are made of the same material, an integral molding process may also be adopted.

In particular implementations, the connecting structure 13 may be a weld, or a rivet piece.

If the connecting structure 13 is a welding spot or a welding seam, the frame 121 of the metamaterial spacer 12 and the shell 111 can be directly welded together to complete the connection.

If the connecting structure 13 is a rivet, the frame 121 of the metamaterial spacer 12 and the shell 111 can be directly riveted together to complete the connection.

In some embodiments of the present invention, the connection structure is a transition ring, the frame of the metamaterial spacer is nested in the inner edge of the transition ring, and the outer edge of the transition ring is connected to the housing.

In an implementation, the inner edge of the transition ring comprises a groove, and the frame of the metamaterial spacer is nested in the groove.

As shown in fig. 6, fig. 6 is another structural schematic diagram of the metamaterial diaphragm 12 connected to the housing 111 according to an embodiment of the present invention. Fig. 6a is a schematic structural view of a metamaterial spacer 12 having a connection structure 13, and fig. 6b is a schematic sectional view of a structure of an ear cup 11. In fig. 6, the connecting structure 13 is a transition ring, the shape of the inner contour of the transition ring is the same as the shape of the outer contour of the metamaterial spacer 12, the inner edge of the transition ring is nested in the rim of the metamaterial spacer 12 by interference fit, and the outer edge of the transition ring is connected with the housing. The inner edge of the transition ring can be seen in the portion indicated by the dashed line a in fig. 6a, and the outer edge of the transition ring can be seen in the portion indicated by the dashed line B in fig. 6 a.

As shown in FIG. 6, the ear cup 11 comprises a metamaterial spacer 12 and a connecting structure 13, wherein the metamaterial spacer 12 comprises a frame 121 and a sheet 122 attached to a surface of the frame 121. The connecting structure 13 is a transition ring. In fig. 6a, a transition ring with a groove on its inner edge is shown, and in use, the metamaterial spacer 12 is inserted into the groove on the inner edge of the transition ring, and the outer edge of the transition ring is attached to the quasi-horizontal end 1112 of the housing, see fig. 6 b.

It should be noted that, in the connection structure of the transition ring shown in fig. 6, the connection manner with the frame 121 may be an interference fit, and the connection manner with the housing may be gluing, screwing, welding, riveting, interference fit, and the like.

In some embodiments of the present invention, the rim of the metamaterial spacer is nested to the inner edge of the transition ring, and the outer edge of the transition ring is connected to the housing.

In some embodiments of the present invention, the transition ring may also be made of a sound absorbing material.

In some embodiments of the invention, the shape of the outer contour of the metamaterial diaphragm and the shape of the inner contour cross section of the housing where it fits may be the same. In some embodiments of the present invention, the shape of the outer contour of the metamaterial diaphragm may be different from the shape of the inner contour of the housing where the metamaterial diaphragm is engaged, and the shape of the outer contour of the metamaterial diaphragm may be an ellipse, a circle, a triangle, a rectangle, a pentagon or a hexagon.

In some embodiments of the invention, the shell of the ear cup can be an ellipsoidal hemispherical shell, a regular hemispherical shell, a rectangular concave shell, a hemispherical rectangular combined concave shell, or an ergonomically shaped concave shell. The shell with a proper shape can be selected according to actual needs.

In some embodiments of the invention, the area enclosed by the outer contour of the metamaterial spacer occupies 30-100% of the area of the inner contour cross section of the housing where it fits.

In some embodiments of the invention, the attachment structure may be a living hinge or a reed hinge.

Fig. 7 is a schematic view of another structure of the metamaterial diaphragm 12 connected to the housing 111 in one embodiment of the present invention. As shown in FIG. 7, the ear cup 11 (not shown in FIG. 7) includes a metamaterial spacer 12 and a connecting structure 13, wherein the metamaterial spacer 12 includes a frame 121 and a sheet 122 attached to a surface of the frame 121. The connecting structure 13 is a living hinge. In use, the frame 121 of the metamaterial spacer 12 is drilled and the hinge is connected by rivets or screws, and the other end of the hinge is also drilled and connected to the housing by rivets or screws (the part is connected not shown). Only bore 123 is labeled in fig. 7, but it is readily understood that there are four bores in the rim 121 of fig. 7.

Fig. 8 is a schematic view of another structure of the metamaterial diaphragm 12 connected to the housing 111 in one embodiment of the present invention. As shown in FIG. 8, the ear cup 11 (not shown in FIG. 8) includes a metamaterial spacer 12 and a connecting structure 13, wherein the metamaterial spacer 12 includes a frame 121 and a sheet 122 attached to a surface of the frame 121. The connecting structure 13 is a leaf hinge, which is a thin sheet with a bent and folded structure. In use, the rim 121 of the metamaterial spacer 12 is drilled and the leaf hinges are attached by rivets or screws, the other ends of the leaf hinges are also drilled and attached to the housing by rivets or screws (this part of the attachment is not shown).

It should be noted that the hinge and the leaf hinge shown in fig. 7 and 8 are only connected to the frame, and the number of the installation hinges is at least two to ensure the stability of installation.

In a specific implementation, the connecting structure may be made of a rigid material, such as: wood, metal (aluminum, steel, etc.), various resin plastics (PC, ABS, PVC, PP, acryl), composite materials (carbon fiber, glass fiber), etc.; elastic materials may also be selected, for example: rubber, silica gel, latex, EVA, etc. Other hard or elastic materials can be selected according to actual needs.

It should be noted that the flexibility required for the dynamic properties of the connection structure does not only come from the constituent materials. Such as the living hinge and the leaf hinge shown in fig. 7 and 8, respectively, the material of construction may be selected from stiff materials, but the dynamic properties thereof exhibit flexibility, i.e. spring-like properties. In the dynamic category, "rigid" corresponds to "flexible".

In an embodiment of the invention, the connection structure exhibits flexible dynamic properties, and the connection structure has the following effects: (1) compared with a rigid connection structure, the flexible connection structure can further facilitate the metamaterial spacer to have an anti-resonance frequency in a low frequency band, and can relax the thickness requirement of a sheet adopted in the metamaterial spacer, because the boundary condition of the metamaterial spacer is relatively free by adopting the flexible connection structure, namely the boundary constraint of the metamaterial spacer is smaller, the boundary rigidity is smaller; (2) the flexible connection may be combined with the metamaterial spacers into an additional "mass-spring" system. Specifically, the metamaterial diaphragm is regarded as a mass-spring vibration system, the metamaterial diaphragm is regarded as a mass, the flexible connection structure is regarded as a spring, and the mass-spring vibration system is formed. On one hand, the corresponding frequencies of the two 'mass-spring' vibration systems in the anti-resonance state are usually different, so that the sound insulation bandwidth of the earmuff can be widened; on the other hand, the mechanical impedance of the metamaterial spacer can be adjusted and supplemented by adopting diversified connection structures, and the degree of freedom of design is increased. The connection structure (e.g., the connection structure 13 in fig. 1 or the connection structure 23 in fig. 3) in the embodiment of the present invention may be a flexible connection structure, or may be a rigid connection structure, and the related principle is the same as or similar to the principle described above, and will not be described again.

In some embodiments of the present invention, the metamaterial diaphragm has a plurality of chambers dividing the receiving cavity of the housing into a plurality of chambers, and the plurality of chambers may be further filled with a sound absorbing material. The plurality of metamaterial spacers can be connected with the shell independently or mutually attached. The main purposes of adopting a plurality of metamaterial spacers are to increase the sound insulation magnitude of the earmuff and widen the sound insulation bandwidth.

It should be noted that whether the sound absorbing material is filled may be selected according to actual needs, and the number of the chambers in which the sound absorbing material is to be filled may also be selected according to actual needs, that is, at least one of the chambers is filled with the sound absorbing material. The sound absorption material can be used for widening the sound absorption bandwidth of the earmuffs, and the sound absorption material with smaller mass can reduce the mass of the earmuffs and increase the portability of the earmuffs.

Next, the structure of the earmuff having a plurality of chambers will be described in detail.

In some embodiments of the invention, each of the plurality of metamaterial spacers is connected to the housing by a connection structure. In other embodiments of the present invention, at least a portion of the plurality of metamaterial spacers are connected by a connecting structure, and at least one of the connected metamaterial spacers is connected to the housing by a connecting structure. The connecting structure can be the connecting structure mentioned in any of the above embodiments, such as a supporting leg, a transition ring, a hinge, a leaf hinge, and the like, and other forms of connecting structures can be selected according to actual needs.

Fig. 9 is a schematic view of another structure of the metamaterial diaphragm 12 connected to the housing 111 in one embodiment of the present invention. Fig. 9a is a schematic structural view of a metamaterial spacer 12 having a connection structure 13, and fig. 9b is a schematic sectional view of a structure of an ear cup 11. Two metamaterial spacers, namely a metamaterial spacer 12a and a metamaterial spacer 12b, are shown in fig. 9, and connecting

structures

13a and 13b are also shown in fig. 9, wherein the metamaterial spacer 12a comprises a frame 121a and a sheet 122a attached to the surface of the frame 121a, and the connecting structures 13a are columnar supporting feet; the metamaterial spacer 12b includes a frame 121b and a thin sheet 122b attached to the surface of the frame 121b, and the connecting structure 13b is a transition ring, as shown in fig. 9 a. The metamaterial spacer 12b is connected with the quasi-horizontal end 1112 of the housing 111 through a connecting structure 13 b; the metamaterial spacer 12a is connected to the metamaterial spacer 12b by a connecting structure 13a, wherein one end of the connecting structure 13a is connected to a central region of a sheet 122a of the metamaterial spacer 12a and the other end is connected to a central region of a sheet 122b of the metamaterial spacer 12b, as shown in fig. 9 b.

Fig. 10 is a schematic view of another structure of the metamaterial diaphragm 12 connected to the housing 111 in one embodiment of the present invention. Two metamaterial spacers, namely a metamaterial spacer 12a and a metamaterial spacer 12b, are shown in the ear cup 11 in fig. 10. The shell 111 of the ear cup 11 also has a sound absorbing material 16, which may be a sponge, foam, fabric material, or the like. The sound absorption material 16 is filled in the casing 111 by wrapping the metamaterial spacer 12a and the metamaterial spacer 12 b. In the present embodiment, the two metamaterial spacers divide the receiving cavity 112 of the housing 111 into a plurality of chambers, which are a first chamber 1121, a second chamber 1122, and a third chamber 1123 in order from the quasi-vertical end 111 of the housing.

In some embodiments of the invention, the quasi-vertical end and the metamaterial diaphragm closest thereto form a first chamber, the quasi-vertical end of the housing is provided with at least one opening communicating with the first chamber, and the at least one opening forms at least one helmholtz resonator with the first chamber, the metamaterial diaphragm and the connecting structure; the metamaterial diaphragm has an anti-resonance frequency that coincides with a resonance frequency of the at least one helmholtz resonator.

Even if only one metamaterial diaphragm is provided, at least one opening communicating with the first chamber may be provided at the quasi-vertical end of the housing, and the opening, the first chamber and the metamaterial diaphragm constitute a helmholtz resonator. The anti-resonance frequency of the metamaterial diaphragm coincides with the resonance frequency of the helmholtz resonator.

Fig. 11 is a schematic view of an opening of the housing 111 according to an embodiment of the present invention. Fig. 11a is a schematic sectional view of the ear cup 11, and fig. 11b is a schematic side view of the ear cup 11. In fig. 11, the ear cup 11 comprises a metamaterial spacer 12 and a connecting structure 13, wherein the connecting structure 13 can be selected from any one of the connecting structures described in the previous embodiments or other connecting structures according to actual needs. As shown in fig. 11a and 11b, the quasi-vertical end 1111 (not shown in fig. 11, see fig. 1) of the housing 111 is provided with an opening 17 communicating with the first chamber 1121 (not shown in fig. 11, see fig. 1), and the opening 17, the first chamber 1121 and the metamaterial diaphragm 12 constitute a helmholtz resonator. The interior of the first chamber 1121 may be further filled with a sound absorbing material 16 to improve the sound absorbing performance of the helmholtz resonator. The opening 17 may also be provided with a mesh 171 to protect against accidental finger contact and leakage of the sound absorbing material 16.

The earmuff 10 with the structure shown in fig. 11 can be regarded as a nearly total reflection surface when the metamaterial diaphragm 12 is in an anti-resonance state, and has better sound insulation performance. The structure also comprises a Helmholtz resonator; if the resonance frequency of the Helmholtz resonator coincides with the antiresonance frequency of the metamaterial diaphragm 12, the Helmholtz resonator will have nearly perfect sound absorption characteristics. So that the earmuff 10 has excellent low-frequency sound absorption performance. Meanwhile, the existence of the opening 17 in the shell 111 enables the static pressure born by the ear of a person to be balanced with the static pressure outside the earmuff 10, and reduces the influence of the pressure difference on the anti-resonance frequency of the metamaterial spacer 12 while avoiding the uncomfortable feeling of wearing; on the other hand, the heat dissipation capacity of the earmuffs 10 is increased, and the phenomenon that the earmuffs are worn for a long time to cause sweating is avoided.

Fig. 12 is a schematic view of an opening of another housing 111 according to an embodiment of the present invention. Fig. 12a is a schematic sectional view of the ear cup 11, and fig. 12b is a schematic side view of the ear cup 11. In fig. 12, the ear cup 11 comprises a metamaterial spacer 12 and a connecting structure 13, wherein the connecting structure 13 can be selected from any one of the connecting structures described in the above embodiments or other connecting structures according to actual needs. As shown in fig. 12a and 12b, the quasi-vertical end 1111 (not shown in fig. 11, see fig. 1) of the shell 111 is provided with a plurality of openings 17 communicating with the first chamber 1121 (not shown in fig. 11, see fig. 1), and the plurality of openings 17, the first chamber 1121 and the metamaterial spacers 12 constitute a plurality of helmholtz resonators. The plurality of openings 17 may have different sizes, and the first chamber 1121 may be further filled with a sound absorbing material 16 to improve the sound absorbing performance of the helmholtz resonator. A layer of mesh 171 may also be installed in the plurality of openings 17 to provide protection against inadvertent finger contact and leakage of the sound absorbing material 16.

Compared to fig. 11, the housing 111 in fig. 12 has a plurality of openings 17, and can form a plurality of helmholtz resonators together with the first chamber 1121 and the metamaterial spacer 12, and if the size of the openings 17 is different, the resonance frequencies of these helmholtz resonators are different, and therefore, a sound absorption effect in a wider frequency band can be produced.

In some embodiments of the present invention, the metamaterial spacer includes a frame and a thin sheet connected to the frame, at least one mass sheet or at least one constraining body being disposed on at least one surface of the thin sheet for adjusting an anti-resonance frequency of the metamaterial spacer.

In a specific implementation, at least one opening is formed in the sheet, in the at least one mass sheet, or in the at least one constraining body, the at least one opening extending through the sheet, and the at least one mass sheet and the at least one constraining body.

In the embodiment of the present invention, the structural form of the metamaterial spacer has various forms, and is not limited to the structure mentioned in the foregoing example. For example, at least one mass plate or at least one constraining body may be placed on at least one surface of a thin sheet of metamaterial spacers for adjusting the anti-resonance frequency of the metamaterial spacers. As another example, at least one opening may also be included, the at least one opening being located on the sheet of metamaterial spacers. Alternatively, the metamaterial spacer further comprises at least one opening, the at least one opening is located in the at least one mass sheet or the at least one constraining body, and the at least one opening penetrates through the metamaterial spacer. In a specific implementation, the mass plate and the restraint body are oval, circular, triangular, rectangular, pentagonal, or hexagonal. Of course, the shapes of the mass sheet and the restraining body are not limited thereto, and may be selected according to actual needs.

The structure of the metamaterial spacer can be applied to the structure of the earmuff mentioned in the embodiment of the invention, and a proper connecting structure can be selected to connect the metamaterial spacer with the shell of the earmuff according to the structure of different metamaterial spacers. This will be explained next. In some embodiments of the present invention, the metamaterial spacer in any of the above implementations further comprises at least one mass sheet or a constraining body disposed on at least one surface of the thin sheet to adjust the antiresonant frequency of the metamaterial spacer. The structure of the metamaterial spacer and the mass sheets and restraints therein will be described in detail below.

Fig. 13 is a schematic diagram of the structure of a metamaterial spacer 12 in one embodiment of the present invention, as shown in fig. 13. The metamaterial spacer 12 includes at least a frame 121, and a sheet 122, the sheet 122 covering at least one side of the frame 121. As shown in fig. 13a, the metamaterial spacer 12 may further include a mass sheet 123; as shown in fig. 13b, the metamaterial spacer 12 may further include a constraining body 124. Specifically, the mass pieces 123 may be connected to the web 122 by gluing, riveting, integral molding, or the like, two mass pieces 123 being shown in fig. 13 a. The constraining bodies 124 may be rigidly connected to the frame 121 by gluing, riveting, integral molding, etc. and fit over the sheet 122 to constrain the movement of the sheet, two constraining bodies 124 being shown in fig. 13 b.

In some embodiments of the present invention, the metamaterial spacer 12 in any of the above implementations further includes at least one opening in the thin sheet 122, the mass sheet 123, and the restraining body 124. On the one hand, the structural form of the opening on the metamaterial spacer 12 further facilitates heat dissipation; on the other hand, the air spring effect between the metamaterial spacer 12 and the quasi-vertical end 1111 of the housing 111 can be reduced, so that the depth of the first chamber 1121 can be further reduced, and the earmuff with a lighter and thinner structure can be manufactured. The structure of the openings in the metamaterial spacer 12 will be described in detail below.

Fig. 14 is a schematic view of the opening of the metamaterial spacer 12 according to an embodiment of the present invention, as shown in fig. 14. The metamaterial spacer 12 includes at least a frame 121, and a sheet 122, the sheet 122 covering at least one side of the frame 121. As shown in FIG. 14a, the metamaterial spacer 12 may further include an opening 125 in a central region of the sheet 122; as shown in fig. 14b, the metamaterial spacer 12 may further include a mass sheet 123, and an opening 125 penetrating the mass sheet 123 and the thin sheet 122; as shown in FIG. 14c, the metamaterial spacer 12 may also include constraints 124, and openings 125 through the constraints 124 and the sheet 122.

It should be noted that the connecting structure 13 included in the metamaterial spacer 12 in some embodiments of the present invention also has a certain degree of opening, and this structure form that the opening through the connecting structure 13 causes the opening of the metamaterial spacer 12 also facilitates the heat dissipation of the earmuff.

It should be noted that the structure of the metamaterial spacer 12 shown in fig. 13 and 14 can be applied to the earmuffs mentioned in other embodiments of the present invention.

In some embodiments of the present invention, the shape of the mass plate may be an ellipse, a circle, a triangle, a rectangle, a pentagon or a hexagon, and the shape of the mass plate may be selected according to actual needs.

In some embodiments of the present invention, the constraining body is an ellipse, a circle, a triangle, a rectangle, a pentagon or a hexagon, and the shape of the constraining body can be selected according to actual needs.

Fig. 15 is a schematic diagram of an apparatus for testing acoustic performance of an earmuff 30 in an embodiment of the invention. In the figure, the earmuff 30 is worn on the artificial head E02, the loudspeaker E01 generates broadband white noise of 0Hz-1000Hz, and the microphone (not shown in figure 15) positioned at the position of the human ear of the artificial head E02 collects sound pressure level spectrum information. A lower level of collected sound pressure indicates a better noise protection of the earmuff.

In this embodiment, the earmuffs 30 are made of ABS and have a shell thickness of 10 mm; the frame of the metamaterial spacer arranged in the shell is 2mm in thickness, the metamaterial spacer is ABS and is in an oval shape, the long axis of the inner edge is 8mm, the short axis is 5mm, and the frame is 3mm in width; the sheet thickness of the metamaterial spacer is 0.125mm, the material is PC, and the outline shape and the size of the metamaterial spacer are the same as those of the frame of the metamaterial spacer. The metamaterial spacer is rigidly connected with the shell through a step platform in the shell, and the width of the step platform is 3 mm.

Fig. 16 is a microphone sound pressure level spectrum at the position of the human ear where the earmuff 30 shown in fig. 15 is worn at the artificial head E02. In the figure, A01 represents that a metamaterial spacer is not placed; a02 represents the placement of a metamaterial spacer. Through comparison, at 200Hz-600Hz, the noise heard by human ears is reduced by 5dB-10dB by placing the ear muffs of the metamaterial spacers, and the frequency range above 600Hz is slightly changed. This shows that wearing the earmuffs 30 with the placed metamaterial spacers does not affect the voice traffic distributed at higher frequencies while protecting against harmful low frequency noise.

In some embodiments of the present invention, the shell 111 of the earmuff 10 also has a sound-insulating effect, and the shell 111 can be made of a material having a sound-insulating effect, so that the shell 111 can isolate sound waves of a part of frequencies, and the rest of the sound waves penetrating through the shell 111 can be absorbed or reflected by other structures in the shell 111, thereby increasing the sound absorption or isolation effect of the earmuff 10. Of course, other structures within the enclosure 111, such as metamaterial spacers or helmholtz resonators, may isolate or absorb sound waves penetrating the enclosure 111 even though the enclosure 111 does not have a sound insulating effect.

In any of the above embodiments, whether to fill the sound absorbing material may be selected according to actual needs, or the number of the chambers filled with the sound absorbing material may be selected according to implementation needs. The sound-absorbing material can widen the working frequency range of the earmuff.

Those skilled in the art will appreciate that all or part of the steps in the methods of the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer-readable storage medium, and the storage medium may include: ROM, RAM, magnetic or optical disks, and the like.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. An earmuff, comprising:

at least one ear cup further comprising a housing comprising a quasi-vertical end distal to the ear side and approximately parallel to the ear and a quasi-horizontal end approximately perpendicular to the ear;

the housing has a receiving cavity;

the metamaterial wall structure is characterized in that a metamaterial spacer is arranged in the accommodating cavity, and the metamaterial spacer comprises a frame and a thin sheet arranged in the frame; the metamaterial diaphragm is provided with a plurality of chambers which divide the accommodating cavity of the shell into a plurality of chambers.

2. The earmuff of claim 1, wherein the shell is filled with a sound absorbing material disposed within the shell surrounding the metamaterial spacer.

3. The earmuff of claim 1, wherein the receiving cavity is separated by the metamaterial spacer into at least two cavities, at least one cavity being filled with sound absorbing material.

4. The earmuff of claim 1, wherein the metamaterial spacer is connected to the shell by a connecting structure.

5. The earmuff of claim 4, wherein the attachment structure is a weld, or a rivet.

6. The earmuff of claim 4, wherein the metamaterial spacer is connected to at least one of the quasi-vertical or quasi-horizontal ends of the shell by the connecting structure.

7. The earmuff of claim 4, wherein the connecting structure is connected to the rim of the metamaterial spacer at one end and to the shell at the other end.

8. The earmuff of claim 7, wherein the attachment structure is a combination of one or more of a living hinge, a leaf hinge, a transition ring, and a support foot.

9. The earmuff of claim 4, wherein the connecting structure is a cylindrical support leg, one end of the cylindrical support leg is connected to the rim of the metamaterial spacer, the other end of the cylindrical support leg is connected to the shell, and the number of the support legs is at least two.

10. The earmuff of claim 4, wherein the connecting structure is a cylindrical support foot having one end connected to the sheet of metamaterial spacer and the other end connected to the shell.

11. The earmuff of claim 4, wherein the connecting structure is a transition ring, and wherein the rim of the metamaterial spacer nests within an inner edge of the transition ring, and wherein an outer edge of the transition ring connects to the shell.

12. The earmuff of claim 8, wherein the inner edge of the transition ring comprises a step floor, and wherein the rim of the metamaterial spacer nests within the step floor.

13. The earmuff of claim 8, wherein the inner edge of the transition ring comprises a groove, and wherein the rim of the metamaterial spacer nests within the groove.

14. The earmuff of claim 8, wherein the transition ring is made of a sound absorbing material.

15. The earmuff of claim 4, wherein the metamaterial spacers have an outer contour that is the same shape as an inner contour cross-section of the shell where they mate.

16. The earmuff of claim 3, wherein the metamaterial spacers have an outer contour that is shaped differently than an inner contour of the shell where they mate, the outer contour of the metamaterial spacers being oval, circular, triangular, rectangular, pentagonal, or hexagonal.

17. The earmuff of claim 3, wherein the metamaterial spacers have an outer contour that encompasses 30-100% of the area of the inner contour cross-section of the shell where they mate.

18. The earmuff of claim 1, wherein at least one of the plurality of chambers is filled with a sound absorbing material.

19. The earmuff of claim 18, wherein each of the plurality of metamaterial spacers is connected to the shell by a connecting structure.

20. The earmuff of claim 18, wherein at least a portion of the plurality of metamaterial spacers are interconnected by a connecting structure, and wherein at least one of the connected metamaterial spacers is connected to the shell by a connecting structure.

21. The earmuff of any of claims 1-20, wherein the quasi-vertical end and the metamaterial spacer closest thereto form a first chamber, and wherein the quasi-vertical end of the shell is provided with at least one opening communicating with the first chamber, the at least one opening forming with the first chamber, the metamaterial spacer and the connecting structure at least one helmholtz resonator; the metamaterial diaphragm has an anti-resonance frequency that coincides with a resonance frequency of the at least one Helmholtz resonator.

22. The earmuff of any of claims 1-20, wherein at least one mass plate or at least one constraining body is placed on at least one surface of the thin sheet for adjusting the antiresonance frequency of the metamaterial spacer.

23. The earmuff of claim 22, wherein at least one opening is formed in the sheet and in the at least one mass sheet or in the at least one restraint, the at least one opening extending through the sheet and the at least one mass sheet or the at least one restraint.

24. The earmuff of claim 22, wherein the mass pieces are oval, circular, triangular, rectangular, pentagonal, or hexagonal.

25. The earmuff of claim 22, wherein the restraints are elliptical, circular, triangular, rectangular, pentagonal, or hexagonal.

26. The earmuff of claim 11, wherein the inner edge of the transition ring comprises a step floor, and wherein the rim of the metamaterial spacer nests within the step floor.

27. The earmuff of claim 11, wherein the inner edge of the transition ring comprises a groove, and wherein the rim of the metamaterial spacer nests within the groove.

28. The earmuff of claim 11, wherein the transition ring is made of a sound absorbing material.

29. The earmuff of any of claims 26-28, wherein the quasi-vertical end and the metamaterial spacer closest thereto form a first chamber, and wherein the quasi-vertical end of the shell is provided with at least one opening communicating with the first chamber, the at least one opening forming with the first chamber, the metamaterial spacer and the connecting structure at least one helmholtz resonator; the metamaterial diaphragm has an anti-resonance frequency that coincides with a resonance frequency of the at least one Helmholtz resonator.

30. The earmuff of any of claims 26-28, wherein at least one mass plate or at least one constraining body is placed on at least one surface of the thin sheet for adjusting the antiresonance frequency of the metamaterial spacer.