Abstract:
An acoustic resistor or damper and method of manufacturing the same is disclosed. The damper has mesh material and mounting material attached to the mesh material. The mounting material defines an open region for transmission of sound through the mesh material, and has a mounting surface for mounting the damper on a surface surrounding an acoustic port or tube. The mounting surface is located on a plane different from the mesh material, thereby shielding the mesh material from adhesive applied between the mounting surface and the surface surrounding the acoustic port or tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     N/A 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND OF THE INVENTION 
     The use of acoustic resistance in transducers and sound channels is well known. In the case of a sound tube, for example, a resistance equal to its characteristic impedance will completely damp the length resonances, leaving a smooth frequency response. This is recently taught, for example, by the inventor in his chapter describing use of dampers entitled (“Earmold Design: Theory and Practice,” Proceedings of 13th Danavox Symposium, pp. 155-174, 1988). In the case of microphones and receivers, acoustic resistance can be used to smooth resonance peaks and improve the sound quality (as described by Killion and Tillman in their paper “Evaluation of High-Fidelity Hearing Aids,” J. Speech Hearing Res., V. 25, pp. 15-25, 1982). In the case of earplugs, acoustic resistance can be used in cooperation with other acoustic elements to produce high fidelity earplugs such as used by musicians in symphony orchestras (as cited in the following: Carlson, 1989, U.S. Pat. No. 4,807,612; Killion, 1989, U.S. Pat. No. 4,852,683; Killion, Stewart, Falco, and Berger, 1992, U.S. Pat. No. 5,113,967). 
     One problem, however, with available acoustic resistors, commonly called dampers or damping elements, is their cost. When produced with adequately tight tolerance such as to +/−20% or better, the most popular damping elements (Knowles BF-series plugs, Carlson and Mostardo, 1976, U.S. Pat. No. 3,930,560) cost $0.60 each even in very high quantities. This has been relatively stable over the life of the U.S. Pat. No. 3,930,560 and has been independent of whether the actual damping element is a cloth mesh, perforated metal (typically electroformed), or the like. 
     Another problem with available acoustic resistors is their design. FIG. 1 illustrates a typical early prior art acoustic resistor design. Resistor (damper)  100  is comprised of a flat piece of cloth (e.g., silk) punched into a cloth disc  101 . Cloth disc  101  is mounted on a flat surface over an acoustic port or tube  103 . Typically, non-corrosive rubber-like adhesive  105 , for example, is used between a bottom surface of cloth disc  101  and a top surface of the structure that forms port or tube  103 . Portions of the adhesive  105  typically wick into areas of the open region of cloth disc  101 , as shown by reference numerals  107  and  109 . 
     FIGS. 2A and 2B illustrate a later prior art acoustic resistor design. FIG. 2A is a side view of a damper  200 , which is comprised of a flat piece of metal  203  that has perforated holes  205  in the middle. The perforated holes  205  form the open region of the damper  201 . FIG. 2B is another review of the damper of FIG.  2 A. As can be seen, the damper  201  is generally comprised of a perforated center section  207  (i.e., the open region) and a solid outer ring  209 . 
     Like damper  100 , damper  200  is mounted on a flat surface over an acoustic tube or port (not shown). Adhesive is likewise used between a surface of the solid outer ring  209  and a top surface of the structure that forms the tube or port. Again, portions of the adhesive wick into the perforated center section  207 , partially deforming the open region of the damper  200 . 
     In both cases, this wicking effect causes a change in the diameter of the open region of the damper, which consequently causes a change in the resistance of the damper. A 2% change in the diameter of the open region of the damper causes an approximately 4% change in the resistance of the damper. Because the diameter of the port or tube of prior art devices was typically large, however, changes in the diameter of the damper as such had at least a tolerable adverse effect on damper performance. 
     As the port and tube diameters of hearing improvement and audiometric devices become smaller and smaller, however, the adverse effect of adhesive wicking becomes more pronounced. In order to obtain tight tolerances of resistance values as port and tube diameters decrease, it is desirable to more tightly control the open region of the damper by eliminating adhesive wicking. On the other hand, in order to provide inexpensive assembly, adhesive is generally used. The combination of small dampers and the use of adhesive, however, causes highly variable results. 
     Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the present invention set forth in the remainder of the present application with reference to the drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     The problems and drawbacks of the prior art are addressed by the damper of the present invention. The damper comprises a mesh material and a mounting material that is attached to the mesh material. The mounting material defines an open region of the mesh material through which sound is transmitted. The mounting material has a mounting surface that is located on a different plane than the mesh material. This configuration enables adhesive to be used between the mounting surface of the damper and a corresponding mounting surface surrounding an acoustic opening, without effecting the resistance of the mesh material in the open region. 
     The mesh material may be, for example, cloth, metal, polyester, nylon or silk. The mounting material may be emulsion or double-sided tape, for example. 
     In an emulsion embodiment, the damper may be manufactured by applying a photosensitive emulsion over the mesh material and exposing the emulsion through a photographic mask. The exposed emulsion is washed away, leaving an open region of mesh and a surround of emulsion. The surround of emulsion (and mesh) is then mechanically punched to generate a “doughnut” damper, or any other desired shape, having an open region of mesh defined by surrounding emulsion. 
     In a double-sided tape embodiment, the damper may be manufactured by applying a sheet of perforated double-sided tape to a mesh material. The double-sided tape surrounding the perforation is then mechanically punched to generate a finished damper product (after removal of the double-sided tape backing), having an open region of mesh defined by surrounding double-sided tape. 
     Other aspects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 illustrates a typical early prior art acoustic resistor design. 
     FIGS. 2A and 2B illustrate a later prior art acoustic resistor design. 
     FIG. 3A is a cross-sectional view of an acoustic resistor or damper according to the present invention. 
     FIG. 3B is a cross-sectional view of the acoustic resistor or damper mounted on a flat surface and over an acoustic port or tube. 
     FIG. 4 is a cross-section view of an alternate embodiment of the acoustic resistor or damper of FIG.  3 A. 
     FIGS. 5A-5C are top views of various contemplated shapes that the acoustic resistor or damper of the present invention may take to fit a number of different applications. 
     FIG. 6 is a cross-sectional view of another alternate embodiment of the acoustic resistor or damper of the present invention. 
     FIGS. 7A and 7B are cross-sectional views of embodiments of an acoustic resistor or damper assembly of the present invention, for mounting on or within an acoustic port or tube. 
     FIG. 8 is a side view illustrating an emulsion/mesh combination used in connection with manufacture of one embodiment of the damper of the present invention. 
     FIG. 9 is a top view of a matrix of nearly finished dampers manufactured according to one embodiment of the method of the present invention. 
     FIG. 10A is a top view of an exemplary finished damper product. 
     FIG. 10B is a perspective view of an exemplary finished damper product. 
     FIGS. 11A and 11B illustrate one embodiment of a “peel, stick and punch” process for making a double-sided tape version of the damper of the present invention. 
     FIGS. 12A and 12B illustrate one potential finished product that may be made using the process discussed with respect to FIGS. 11A and 11B. 
     FIGS. 13A and 13B are top and side cross-sectional views, respectively, of an alternate double-sided tape embodiment. 
     FIGS. 14A and 14B are top and side cross-sectional views, respectively, of another alternative double-sided tape embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3A is a cross-sectional view of an acoustic resistor or damper according to the present invention. Damper  300  comprises a mesh material  301  and a mounting material  303 . The mesh material  301  may be, for example, cloth, metal, polyester, nylon, or silk, and may have a thickness chosen to suit the particular application. In one hearing aid application, a thickness of approximately 0.003 inches was found to be acceptable. The mounting material  303  may be, for example, emulsion, double-sided tape, or foam, and may also have a thickness chosen to suit the particular application. In the hearing aid application mentioned above, a thickness of approximately 0.002 inches was found to be acceptable. In another application, a thickness of approximately 0.020 was found acceptable. Mounting material  303  is mounted or attached to mesh material  301 , forming open region  306  of the damper  300 . 
     FIG. 3B is a cross-sectional view of the acoustic resistor or damper  303  mounted on a flat surface and over an acoustic port or tube  305 . Adhesive  307  is used between the flat surface and mounting material  303 . Adhesive  307  may, for example, be epoxy. 
     As can be seen from FIG. 3B, the surface of the mounting material  303  that receives the adhesive  307  is on a different plane than mesh material  301 . Thus, the open region  306  of the damper  300  is positioned away from the adhesive  307 . Any wicking of the adhesive  307  occurs in the mounting material  303 , and consequently the open region is not affected. This configuration enables tight tolerances of the resistance values from one specimen to the next. 
     FIG. 4 is a cross-section view of an alternate embodiment of the acoustic resistor or damper of FIG.  3 A. Acoustic resistor or damper  400  is similar to damper  300  of FIG. 3A, except that mounting material  403  of FIG. 4 is mounted or attached on both sides of mesh material  405 . This enables adhesive to be used on both sides of the damper  400 , if desired for a particular mounting configuration, without affecting the open region  406  of damper  400 . 
     The acoustic resistors or dampers of FIGS. 3A and 4 may be formed into any shape, and may have nearly any desired dimensions to enable use with nearly any size or shape acoustic port or tube. For example, FIGS. 5A-5C are top views of various contemplated shapes that the acoustic resistor or damper of the present invention may take to fit a number of different applications. More specifically, FIG. 5A is a “doughnut” or generally circular shape, which may be used with, for example, generally circular port openings. FIG. 5B is a generally rectangular shape, which may be used with, for example, generally rectangular port openings. FIG. 5C is a “corner” shape, which may be used in an application in which the acoustic port opening is located on a corner. Of course, any number of other shapes may also be used and are contemplated by the present invention. 
     FIG. 6 is a cross-sectional view of another alternate embodiment of the acoustic resistor or damper of the present invention. Damper  600  may be, for example, a formed disc made from metal via a photo etching process. Damper  600  comprises an open region  601  and an adhesive portion or surface  603 . The open region  601  may comprise a plurality of perforated holes  605 , for example. Like the embodiments of FIGS. 3A and 4 discussed above, the mounting surface  603 , as a result of the forming, is located on a different plane than the open region  601 . Consequently, adhesive may be used between the mounting surface  603  and a flat surface surrounding the acoustic port or opening (not shown) without affecting the open region  601 . 
     FIGS. 7A and 7B are cross-sectional views of embodiments of an acoustic resistor or damper assembly of the present invention, for mounting on or within an acoustic port or tube. Damper assembly  700  of FIG. 7A comprises a body piece  701  and a damper piece  703 . Damper piece  703  may be, for example, that described above with respect to FIG. 3A or FIG. 4, and body piece  701  may be molded from plastic. Damper piece  703  is mounted on an end surface of body piece  701 , and the assembly  700  is inserted as a unit into an acoustic port or tube (not shown). 
     Similarly, damper assembly  710  of FIG. 7B comprises a body piece  711  and a damper piece  713 . Again damper piece  713  may be, for example, that described above with respect to FIG. 3A or FIG. 4, and body piece  711  may be molded from plastic. In the embodiment of FIG. 7B, however, body piece  711  includes a recess  715  and a mounting surface  717  for receiving and mounting the damper piece  713  within the body piece  711 . Once the damper piece  713  is mounted within the body piece  711 , the damper assembly  710  is inserted as a unit on or into an acoustic port or tube (not shown). The damper piece  713  can be sealed within the body piece  711  by several means. For, example, the sides of body piece  711  defining the recess  715  may be crimped. Alternately, a sealing collar (not shown) can be pressed into the recess  715  and against the damper piece  713 . Otherwise, adhesive can be used. 
     The damper assembly embodiments of FIGS. 7A and 7B may be used as a lower cost replacement for insertion-type prior art dampers, such as, for example, the cup-like acoustic resistor found in U.S. Pat. No. 3,930,560 mentioned above. 
     As mentioned above with respect to FIGS. 3A and 4, the mounting material may be made of a number of different materials, such as double-sided tape or emulsion. In an emulsion embodiment, a thick photosensitive emulsion is applied over the resistance material and then exposed through a photographic mask so as to allow washing out of the emulsion in the desired resistance area (i.e., the “open region” discussed above) leaving a surround of thick emulsion. The desired form or shape (e.g., the “doughnut” shape discussed above) is then punched or cut out to produce the finished damper product. 
     More specifically, a photographic mask is prepared that defines the inner diameter of the desired opening (i.e., the “open region” discussed above). Any shape or size of the open region may be selected depending on the application (as mentioned above), and the selected shape and size is replicated (typically by a photographic “step and repeat” process). Cloth or mesh material is then obtained having the desired resistance value, and is mounted on a frame (such as a silk screen frame, for example). Emulsion is then applied to the cloth. The emulsion can be applied to the top (or bottom) of the screen only (to obtain the configuration shown in FIG.  3 A), or to both the top and bottom of the screen (to obtain the configuration shown in FIG.  4 ). 
     FIG. 8 is a side view illustrating the resulting emulsion/mesh combination at this stage of the process. Combination  800  comprises emulsion  801  and cloth weave  803 . The cloth weave  803  may have a thickness of approximately 0.0025 to 0.003 inches (dimension A in FIG.  8 ), and may be comprised of double twill polyester. The emulsion may have an approximately flat surface  805  (for mounting), and may be approximately 0.005 inches thick (dimension B in FIG.  8 ). 
     Next, the emulsion is exposed through the mask to ultraviolet light, and the exposed emulsion is washed away to define those portions of the emulsion to be removed from the cloth. With appropriate changes to the photographic mask, either a positive or negative resist may be used. In other words, a matrix of nearly finished dampers (inner diameters only) results. FIG. 9 is a top view illustrating an example of such a matrix for a “doughnut” shape damper. Matrix  900  comprises emulsion  901  and a plurality of cloth areas  903  (i.e., open regions discussed above). 
     Finally, the damper outer diameter (see reference numeral  905  in FIG. 8) is mechanically punched out (or cut out using a laser, for example) to achieve the finished damper product. This is done for each of the open regions shown in the matrix  900 , to produce a plurality of finished damper products. 
     FIG. 10A is a top view, and FIG. 10B is a perspective view, of an exemplary finished damper product. Damper  1000  comprises an emulsion mounting portion  1001  and an open mesh region  1003 . Damper  1000  may have, for example, an inner diameter (defining the open mesh region  1003 ) of approximately 0.044 to 0.054 inches, and an outer diameter of approximately 0.078 inches. 
     As mentioned above, the dampers shown in FIGS. 3A and 4 may also have a mounting material comprising double-sided tape. FIGS. 11A and 11B illustrate one embodiment of a “peel, stick and punch” process for making a double-sided tape version of the damper of the present invention. First, a sheet of perforated double-sided tape  1101  is applied to a sheet of cloth or metal mesh  1103 . The perforations  1104  in the double-sided tape  1101  define the inner diameter of a plurality of unfinished dampers. Next, a mechanical punch (reference numeral  1105  in FIG. 11B) is used to punch through the double-sided tape  1101  and the cloth or metal mesh  1103 , defining the outer diameter and creating the finished product. 
     FIGS. 12A and 12B illustrate one potential finished product that may be made using the process discussed above with respect to FIGS. 11A and 11B. FIG. 12A is a top view and FIG. 12B is a side cross-sectional view. Damper  1200  comprises a mounting portion  1201  made of double-sided tape and a screen or mesh portion  1203  made of polyester, for example. The damper  1200  may have an inner diameter of approximately 0.045 inches and an outer diameter of approximately 0.120 inches, for example. 
     In an alternate embodiment, the finished damper of FIGS. 12A and 12B may instead be made by a different process. Specifically non-perforated double-sided tape is applied directly to a sheet of cloth or metal mesh. A laser beam is then used to cut the inner diameter through the double-sided tape (but not the cloth or metal mesh), and the resulting slug is removed. Finally, a mechanical punch (such as shown in FIG. 11B) is used to punch through the double-sided tape and the cloth or metal mesh, defining the outer diameter and creating the finished product. 
     FIGS. 13A and 13B are top and side cross-sectional views, respectively, of an alternative double-sided tape embodiment. Similarly as discussed above with respect to FIG. 4, damper  1300  of FIGS. 13A and 13B comprises double-sided tape  1301  attached to both sides of cloth or mesh material  1303 . The processes discussed above with respect to FIGS. 11A and 11B, with slight modification, may be used to manufacture the finished product shown in FIGS. 13A and 13B. For example, two perforated sheets of double-sided tape may be attached to the mesh or screen (one on each side), before the punch process is undertaken. 
     FIGS. 14A and 14B are top and side cross-sectional views, respectively, of another alternative double-sided tape embodiment. FIGS. 14A and 14B are similar to FIGS. 13A and 13B, except that a sheet of foam is placed on each side of the double-sided tape, and an additional piece of double-sided tape is placed on a surface of one of the foam sheets. Specifically, as can be seen from FIG. 14B, damper  1400  comprises a polyester cloth  1401 , double-sided tape  1403  and  1405  on respective sides of the polyester cloth  1401 , foam  1407  and  1409  on respective sides of the double-sided tape  1403  and  1405 , and finally a further piece of double-sided tape  1411  on the other surface of foam  1409 . Again, the processes discussed above respecting the other double-sided tape embodiments may be used, with slight modification, to produce the finished product shown in FIGS. 14A and 14B. 
     The dampers of the present invention permit tight tolerances of the resistance values even when adhesives are used. In addition, the dampers of the present invention can be made in large numbers relatively easily and inexpensively. In fact, Applicant believes that the dampers of the present invention can be manufactured and sold at a price that is orders of magnitude cheaper (e.g., 5 cents) than the prior art (e.g., 60 cents). 
     Many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as described hereinabove.