Abstract:
An acoustic damper for covering a housing inlet of a transducer is disclosed. The damper includes a mesh panel and a non-mesh periphery. The non-mesh periphery of the damper is adhesively attached to the housing of the transducer wherein the mesh panel covers the inlet. The non-mesh periphery of the damper inhibits the adhesive from wicking into the mesh panel. The damper is adaptable for attachment of a film. The film is capable of cooperating with a backplate to form a motor assembly of the transducer.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Patent Application entitled, “Acoustic Transducer with Improved Acoustic Damper,” Serial No. 60/184,807, filed Feb. b  24 ,  2000 . 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to acoustic transducers, and, more particularly, to acoustic dampers for acoustic transducers.  
         BACKGROUND OF THE INVENTION  
         [0003]    Transducers, and particularly microphones, are typically utilized in hearing aids. Generally, electret transducers comprise a housing having an opening, inlet, that communicates with the interior of the housing. An electret motor assembly including a diaphragm adjacent a charged plate having an electret material formed thereon is mounted within the housing to define acoustic chambers on opposite sides of the motor assembly.  
           [0004]    An acoustic signal enters one of the chambers via the inlet of the housing, allowing the diaphragm to respond thereto. Air pulsations created by the vibrations of the diaphragm pass from one acoustic chamber to the other acoustic chamber.  
           [0005]    The electret material on the charged plate is operably connected to electronic circuitry to permit electroacoustical interaction of the diaphragm and electret material on the backplate to create an electrical signal representative of the acoustic signal. As is known, the converse operation may be provided by the transducer in that an electrical signal may be applied to the electret on the backplate to cause the diaphragm to vibrate and thereby to develop an acoustic signal that can be coupled out of the acoustic chamber.  
           [0006]    Common in microphones, a port tube extends from or is integral with the inlet of the housing and provides acoustic resistance to the acoustic signal before it reaches the diaphragm. However, it is preferable that a hearing aid have the smallest dimensions possible, and a port tube increases the overall size of the microphone.  
           [0007]    An acoustic transducer in accordance with the present invention provides an inexpensive and simple solution to eliminate the drawbacks of the prior acoustic transducers.  
         SUMMARY OF THE INVENTION  
         [0008]    One embodiment of the present invention is directed to an acoustic damper for a transducer. The transducer comprises a housing having an inlet. The damper has a mesh panel and non-mesh periphery wherein the mesh panel covers the inlet. The non-mesh periphery of the damper is attached to the housing with an adhesive. The non-mesh periphery inhibits the adhesive from wicking into the mesh panel.  
           [0009]    Another embodiment of the present invention includes a film operably attached to the non-mesh periphery of the damper. The film and the damper form a diaphragm assembly. The interior of the film is free to move without touching the mesh panel. The diaphragm assembly is adaptable for cooperating with a backplate to form a motor assembly.  
           [0010]    One object of the present invention is to provide an acoustic damper having a reduced dimension for a transducer.  
           [0011]    Another object of the present invention is to provide a diaphragm assembly having an acoustic damper, the diaphragm assembly capable of being adapted to a motor assembly of a transducer. 
       
    
    
       [0012]    Other features and advantages of the present invention will be apparent from the specification taken in conjunction with the following drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a partial cross-sectional view of an acoustic transducer of the present invention;  
         [0014]    [0014]FIG. 2 is a cross-sectional view of the acoustic transducer of FIG. 1 taken along line A-A;  
         [0015]    [0015]FIG. 3 is a cross-sectional view of the acoustic transducer of FIG. 1 taken along line B-B;  
         [0016]    [0016]FIG. 4 is a plan view of an acoustic damper of the present invention;  
         [0017]    [0017]FIG. 5 is a left side view of the acoustic damper of FIG. 4;  
         [0018]    [0018]FIG. 6 is a bottom side view of the acoustic damper of FIG. 4;  
         [0019]    [0019]FIG. 7 is a cross-sectional view of an alternative embodiment of the present invention; and,  
         [0020]    [0020]FIG. 8 is a cross-sectional view of an alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.  
         [0022]    A microphone, generally designated  10 , for a hearing aid (not shown) adapted to be disposed within an ear canal is illustrated in FIGS.  1 - 3 . The microphone  10  is disposed within a housing  12  having a housing wall  14 . A sound inlet slot  16  extends through the housing wall  14 . The sound inlet slot  16  is covered by a damping screen  18 , as further explained below. An electret assembly  20  is disposed within the housing  12 , as is conventional circuitry integrated into a thick film transistor  15 .  
         [0023]    A port inlet tube, when attached to the housing of a microphone provides acoustic resistance to incoming sound. The port inlet tube also provides an impediment to foreign matter entering the housing  12 . With the port tube removed, the sound inlet slot  16  is left exposed to undamped acoustics and foreign matter that will find its way into the housing  12 . However, it is sometimes preferred to remove the port inlet tube to reduce the size of the microphone  10 .  
         [0024]    The present invention provides a damping screen  18  placed over the sound inlet slot  16  to provide an acoustic resistance and a barrier to foreign matter. The damping screen  18  is a preferably a mesh material and has apertures that allow sound to pass through it. A glue is used to hold the damping screen  18  in place. However, a varying amount of glue may be unintentionally placed on the damping screen  18  over the sound inlet slot  16 . By capillary action or other effects, the glue can also “wick” into the damping screen  18  over the sound inlet slot  16 . If the glue adhering the damping screen  18  to the housing  12  is also present in the area over the sound inlet slot  16 , the acoustic effects of the damping screen  18  are altered and the microphone&#39;s response to acoustic vibration impaired.  
         [0025]    In order to prevent glue from entering the damping screen  18  over the sound inlet slot  16 , the present invention forms the damping screen  18  with a non-mesh portion  24  along the periphery of a mesh portion  22 . Glue adhesive is then applied to the non-mesh portion  24  in order to secure the damping screen  18  to the housing  12 . In a preferred embodiment, a thickness A of the non-mesh portion  24  is greater than a thickness B of the mesh portion  22 . While it is preferred that the non-mesh periphery  24  be continuous (in order to maximize glue area), it is within the scope of the present invention to provide a non-mesh portion that surrounds only a portion of the periphery of the mesh portion  22 .  
         [0026]    The mesh portion  22  and non-mesh portion  24  are preferably formed as a single unit from electroformed nickel. However, it is within the scope of the present invention to form the mesh portion  22  and the non-mesh portion  24  as two separate units, such as by forming the non-mesh portion  24  around the periphery of the mesh portion  22  of a different material.  
         [0027]    The mesh portion  22  is formed such that it provides apertures that exhibit the level of acoustic resistance desired for the microphone in which it is placed. This is accomplished by varying the number, size and spacing of apertures within the mesh. However, a damping screen  18  that provides little or no acoustic resistance is within the scope of the present invention. In this instance the damping screen  18  would act as an acoustically transparent barrier to foreign matter.  
         [0028]    In an another embodiment described in FIG. 7, there is shown a simplified drawing of a microphone  40  having a housing  42  defining a sound inlet slot  44 . In this configuration, an acoustic damper  46  is formed having a mesh portion  48  and a non-mesh portion  50  as in the previous embodiment. In addition, a film  52  of an electret assembly (not shown) is attached to the non-mesh portion  50  and spaced apart from the mesh portion  48 . In this manner, the film  52  will not touch the acoustic damper  46  in its normal range of travel and will perform in a conventional manner.  
         [0029]    In this embodiment, the film  52  operably attached to the acoustic damper  46  forms a diaphragm assembly  56 . The diaphragm assembly  56  is adhesively attached to the housing  42  by glue  54 . The diaphragm assembly  56  is adaptable for cooperation with a backplate  58  to form an electret motor assembly  60 . FIG. 8. The film  52  of the diaphragm assembly  56  is metallized to create an electrically active portion, i.e., movable electrode, of the diaphragm assembly. A frame  62  is utilized to space the diaphragm assembly  56  apart from the backplate  58 , thus enabling the diaphragm assembly and the backplate to function as the motor assembly  60 . The film  52 , together with the backplate  58 , determines the capacitance of the motor assembly  60 . Acoustic signals, facilitated by conduits  64  in the frame  62  and the inlet  44 , will affect the motor assembly; thus varying the capacitance. Additionally, an amplifier can be electrically connected to the motor assembly.  
         [0030]    While the specific embodiment has been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.