Abstract:
An earmuff ( 3 ) includes a disc-shaped elastomeric pressure-equalizing element ( 6 ) that lies between an inner end of a cup ( 4 ) and an outer face of an annular element ( 7 ). The elastomeric element ( 6 ) is found to provide a more consistent blocking of environmental sound. The cup inner end has a radial projection  15  that projects into a recess  19 , and the elastomeric element is bent to lie between the projection and the walls of the recess.

Description:
CROSS REFERENCE  
       [0001]     This is a continuation-in-part of PCT/SE2005/001724 filed 16 Nov. 2005, which claimed priority from Swedish patent application NO. 0402799-1 filed 17 Nov. 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to an earmuff comprising a cup-shaped cap, which has an edge portion defining an opening, and an annular element which is arranged to extend along said edge portion, the cup-shaped cap and the annular element being secured to one another by a locking means.  
       BACKGROUND OF THE INVENTION  
       [0003]     A common type of hearing protector comprises two earmuffs and a headband connecting the earmuffs to one another.  
         [0004]     A conventional earmuff usually comprises a cup-shaped cap, an annular bottom plate, a padded sealing ring which is connected to the bottom plate and arranged to abut against a user&#39;s head, and stuffing which can be made of foam plastic and is positioned in the cap. The cup-shaped cap and the annular bottom plate are tightly fixed to each other by a conventional snap lock. A conventional snap lock is provided, for instance, by the cap being provided with a projection extending along the opening portion of the cap. The projection is formed on the inside of the opening portion of the cap. The bottom plate has a connecting portion which is arranged to extend a certain distance into the opening portion of the cap. The connecting portion has on the outside a circumferential groove. The groove cooperates with the projection to tightly hold the cap and the bottom plate together.  
         [0005]     However, it has been found that two earmuffs which have been manufactured in the same way according to the description above have a tendency to exhibit different damping properties for sound in different frequency ranges. Differences in damping mean that a first earmuff damps sound within a certain frequency range quite well while at the same time a second earmuff damps sound within the same frequency range relatively poorly.  
         [0006]     This means in turn that there is a risk that the two earmuffs in one and the same hearing protector exhibit different sound damping capacities, which means that a user catches a certain sound in one way by one ear and in another way by the other ear. This is a drawback since a user has difficulty in determining the direction of sound, which may cause danger on a shop floor.  
         [0007]     Owing to the difference, it is also difficult to adjust an earmuff to a specific purpose. To adjust an earmuff to a specific purpose means, for instance, satisfying a requirement that the capacity of damping sound in a certain frequency range be improved. The problem is, among other things, that different earmuffs of the same type damp, as mentioned above, sound in a certain frequency range to different degrees. An adjustment of an earmuff so that it has a good capacity of damping sound in a first frequency range means, in practice, that it is necessary to accept an inferior damping capacity in a second frequency range. The difference in the damping capacity of different earmuffs of the type described above can very well be in the same order as the distance between said first and second frequency ranges.  
       SUMMARY OF THE INVENTION  
       [0008]     In view of that stated above, an object of the present invention is to provide an improved earmuff.  
         [0009]     A special object of the invention is to provide earmuffs which have a consistent sound damping capacity. By consistent sound damping capacity is meant, for instance, that two earmuffs which are of the same type and have been manufactured in the same way have essentially the same sound damping capacity. A further object of the invention is to provide an earmuff which has improved sound damping capacity.  
         [0010]     Another object of the invention is to provide a basic construction of an earmuff which allows great freedom in design.  
         [0011]     To achieve at least one of the above objects, and also other objects that will be evident from the following description, an earmuff as claimed in claim  1  is provided according to the invention, preferred embodiments being stated in the dependent claims.  
         [0012]     In particular an earmuff is provided, comprising a cup-shaped cap, which has an edge portion defining an opening, and an annular element which is arranged to extend along said edge portion, the cup-shaped cap and the annular element being secured to one another by a locking means. The earmuff is characterized in that it further comprises at least one pressure-equalizing means, which is arranged between and in contact with the cup-shaped cap and the annular element.  
         [0013]     As a result, an improved earmuff is provided, in which tension or pressure between the cup-shaped cap and the annular element is distributed substantially uniformly around the opening portion of the cap. Effects of differences with respect to geometry, rigidity or the like which, for instance, arise in manufacture and which would result in differences in the transmission of sound between the cap and the annular element are eliminated to a great extent owing to the pressure-equalizing means. A particular advantage of the inventive earmuff is that two earmuffs achieve a similar sound damping capacity. A further advantage is that the earmuff can be adjusted to different surroundings and to sound in specific frequency ranges. It also brings the advantage that a user perceives sound in the same way by both ears, which is advantageous since it will be easier to identify where a source of sound is positioned.  
         [0014]     It should be noted that annular is not necessarily limited to a circular shape, but the ring shape defines an element which extends around a central opening. The ring shape can be more or less square or have other shapes. The annular element can be formed with different cross-sectional shapes depending on what other components it is arranged to cooperate with.  
         [0015]     Said at least one pressure-equalizing means is arranged in an engaging surface between the cup-shaped cap and the annular element of said locking means. By the pressure equalizing means being arranged in an engaging surface, it will provide a pressure-equalizing sound transmission between the cap and the annular element, which adds to consistent transmission of sound.  
         [0016]     The engaging surface defines a geometric band extending along the opening and having a width, the pressure equalizing means being arranged to extend along the opening along a first portion of the width of the engaging surface. By the pressure-equalizing means extending along the opening, consistent force transmission is obtained along the entire circumference of the cap and the annular element.  
         [0017]     The cup-shaped cap and the annular element can, along a second portion of the width of the engaging surface, abut directly against each other, which brings the advantage of obtaining a dimensionally stable contact between the cap and the annular element.  
         [0018]     The pressure-equalizing means may comprise an annular element, which brings the advantage that the pressure equalizing means can be manufactured in a simple manner. By annular is meant that the pressure-equalizing means has in the longitudinal direction the shape of a ring. This also means that the pressure-equalizing means helps to ensure tightness in the connection between the cup-shaped cap and the annular element. Thus the tolerances in the manufacture of the cup-shaped cap and the annular element can be increased.  
         [0019]     The pressure-equalizing means may comprise an elastic insert, which means that the pressure-equalizing means can be manufactured in a simple and inexpensive manner. In addition, the elastic insert may help to maintain tension in the locking means.  
         [0020]     The elastic insert can be made of a polymer material, which brings the advantage that it can be manufactured in a simple and inexpensive manner.  
         [0021]     To fasten the cup-shaped cap and the annular element to one another in a simple, inexpensive and time-effective manner, the locking means may comprise a snap lock.  
         [0022]     By snap lock is meant a lock comprising two parts. In locking, one of the parts is pressed onto the other part and snaps, by temporary elastic deformation, onto this other part and locks the two parts relative to one another. In a preferred embodiment, a snap lock is provided by the cap being provided with a projection which extends along the opening portion of the cap. The projection is formed on the inside of the opening portion of the cap. The annular element has a flange which is arranged to extend a certain distance into the opening portion of the cap. The flange has on its outside a circumferential recess. The recess cooperates with the projection to tightly hold the cap and the annular element together.  
         [0023]     The pressure-equalizing means can be arranged in said recess. The location of the pressure-equalizing means brings the advantage that it simplifies mounting since it easily retains its position in the recess. It also brings the advantage that the pressure-equalizing means is located in the position in which the greatest power transmission between the cap and the annular element usually occurs.  
         [0024]     The elastic insert can have a circular, square, triangular or H-shaped cross-section. The elastic insert can have a homogeneous or hollow cross-section, such as a tube of various cross-sectional shapes.  
         [0025]     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     A preferred embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings.  
         [0027]     Components having a similar function have been given the same reference numerals throughout the text.  
         [0028]      FIG. 1  is a side view of a hearing protector comprising two inventive earmuffs.  
         [0029]      FIG. 2  is an exploded view of an inventive earmuff.  
         [0030]      FIG. 3  is a cross-sectional view of the earmuff in  FIG. 1  along line I-I, without the sealing ring.  
         [0031]      FIG. 4  is a cross-sectional view of an enlarged part of  FIG. 3 .  
         [0032]      FIG. 5  is an enlarged view of a portion of  FIG. 4 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]      FIG. 1  illustrates a hearing protector  1  comprising a headband  2  and two earmuffs  3 . The earmuffs  3  are connected to the respective ends of the headband  2 . In use, a user (not shown) places an earmuff  3  over each ear, the headband  2  holding the earmuffs  3  in place on the user&#39;s head.  
         [0034]      FIG. 2  shows that the earmuff includes a ring  5  of stuffing material that blocks sound and that fits into a rigid cap  4 . The cap  4  has an inner (I) part  10  that previously directly abutted a rigid annular element  7 . A radial projection  15  ( FIG. 5 ) on the cap inner part  10  snaps into a radial recess  19  in a part  11  of the annular element. The radial projection  15  and radial recess  19  each extends at least partially radial to the earmuff axis  30 . It appears that this construction previously left a small gap through which sound could pass, with the frequency of sound that could pass depending on the exact shape and size of the gap.  
         [0035]     In the present invention, applicant places an elastomeric disc  6  (an elastomer is a material with a Young&#39;s modules of elasticity of under 50,000 psi) in the space between the flat cap end  10  and a flat surface of annular element  7 . Also, part of the elastomeric disc lies between the projection  15  and recess  19 . When the cap  4  and annular element  7  are snapped together, the elastomeric ring is compressed. This seals the space between the cap end and the annular element. It is found that the presence of the compressed elastomeric disc, or pressure equalizing means, results in blocking sounds of all frequencies, far more uniformly than in the prior art when the elastomeric ring was not used. As a result, the amplitude of sound of all frequencies that reach the wearer&#39;s two ears, is much more equal than in the prior art. This avoids a condition in which the wearer cannot determine the direction from which a sound came.  
         [0036]     The elastomeric disc, or ring-shaped member lies between flat facewise-adjacent surfaces  12 ,  32  of the cap inner end  10  and of the annular member  7 .  
         [0037]     An earmuff  3  is shown in more detail in  FIGS. 2-4 , to which reference is now made. The earmuff  3  comprises a cup-shaped cap  4 , stuffing material  5 , a pressure equalizing means  6 , an annular element  7  and a sealing ring  8 . The stuffing material  5  is arranged in the cavity of the cup-shaped cap  4 . A farther side, the side facing away from a user, of the annular element  7  is fixed to the cup-shaped cap  4  by a locking means  9  in the form of a snap lock  9 . The snap lock  9  comprises a first and a second part  10 ,  11 . The first part  10  is positioned on the cup-shaped cap  4  and the second part  11  is positioned on the annular element  7 . The pressure-equalizing means  6  is positioned in an engaging surface between, and is in contact with, both the first and the second part  10 ,  11  of the snap lock  9 , see  FIG. 3  and  FIG. 4 . The sealing ring  8  is fixed by a second snap lock (not shown) to a front side, the side facing a user, of the annular element  7 .  
         [0038]     The cap  4  is in the form of a cup and has an edge portion  12  which defines an opening  13  of the cap. As shown in  FIG. 2  and  FIG. 3 , the opening  13  of the cap  4  defines a space which resembles a space as enclosed by a half-sphere.  
         [0039]     On the outside of the cap  4 , that is the side facing away from the user and from the enclosed space, two fastening means  14  are positioned. The fastening means  14 , which can be, for instance, two pins, are arranged to fasten the headband  2  to the cap  4 .  
         [0040]     On the inside of the cap  4 , that is the side facing a user and the enclosed space, the first part  10  of said snap lock  9  is positioned. The first part  10  comprises a projection  15  which extends around the inside of an opening portion  16  of the cap  4 . The opening portion  16  has an engaging surface which in the assembled state is adapted to engage and abut against on the one hand the pressure equalizing means  6  and, on the other, a corresponding engaging surface of the second part  11  of the snap lock  9 .  
         [0041]     In the example shown, the projection  15  and the cap  4  are made in one piece of a polymer material. It will be appreciated that the parts can be separately made and subsequently assembled in a suitable manner, for instance by welding or gluing.  
         [0042]     The annular element  7  has a front side and a rear side, the front side being the side facing the sealing ring  8  and thus also a user, and the rear side being the side facing the cap  4  and thus also facing away from a user. The annular element  7  which is called bottom plate has a through hole  17  extending from the front side to the rear side.  
         [0043]     The second part  11  of the snap lock  9  is formed on the rear side of the annular element  7 . The second part  11  extends as a circumferential flange  18  around the annular element  7 . The second part  11  has an extent corresponding to the shape of the opening  13  of the cup-shaped cap  4 . A recess  19  is formed on the side of the flange  18  which faces away from the through hole  17 . The recess  19  has a shape supplementary to the projection  15  of the cup-shaped cap  4 . On the same side as the recess  19 , the flange  18  has an engaging surface. In  FIGS. 2-4 , the surface of the recess  19  is included in the engaging surface, which in the assembled state is in contact with the pressure-equalizing means  6  and the engaging surface of the cap  4 . It should be mentioned that the second part  11  can be formed with a smaller height relative to corresponding parts according to prior art, which brings the advantage that the requirements as to the shape of the cap  4  are reduced.  
         [0044]     The pressure-equalizing means  6  consists in the shown example of an annular flexible insert  6 . The insert  6  is circular. The insert  6  is arranged between the cup-shaped cap  4  and the annular element  7 . The insert  4  is in contact with both the cup-shaped cap  4  and the annular element  7  in the respective engaging surfaces. The location of the pressure-equalizing means  6  between the cup-shaped cap  4  and the annular element  7  results in the pressure between the first and the second part  10 ,  11  of the snap lock  9  being equalized. The pressure-equalization results in the effect of any irregularities in the first and the second part  10 ,  11  of the snap lock  9  being eliminated or in any case reduced. The pressure-equalizing means  6  also brings the advantage that the tolerances in the manufacture of the cup-shaped cap  4  and the annular element  7  can be increased, which results in reduced costs of manufacture. The reason for this is that the pressure-equalizing means  6  also helps to provide a seal between the cap  4  and the annular element  7 .  
         [0045]     The pressure-equalizing means  6  is positioned in the recess  19  of the second part  11  of the annular element  7 , which is illustrated in  FIG. 3  and  FIG. 4 . In the mounted state, the projection  15  of the snap lock  9  of the cap  4  presses the pressure-equalizing means  6  against the walls of recess  19  of the snap lock  9  of the annular element  7 .  
         [0046]     It will be appreciated that the present invention is not limited to the embodiments described above and that a person skilled in the art can modify the above-described earmuff within the scope of the invention as defined in the claims.  
         [0047]     For instance, it is possible to place the elastic insert also outside the recess which is adapted to provide the snap lock function. In such an embodiment, the flange of the annular portion is advantageously provided with a further groove which is adapted to accommodate the annular elastic insert.  
         [0048]     Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.