Patent Publication Number: US-2012027240-A1

Title: Microphone module with helmholtz resonance chamber

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part (CIP) application of patent application Ser. No. 12/758,805 entitled “MICROPHONE MODULE WITH HELMHOLTZ RESONANCE CHAMBER” and filed on Apr. 13, 2010, whose disclosure is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to microphones and, particularly, to a microphone module with Helmholtz resonance chambers. 
     2. Description of Related Art 
     With the continuing development of audio and sound technology, microphones have been widely used in electronic devices such as headsets, mobile phones, computers and other devices providing audio capabilities. 
     A typical microphone defines a resonance chamber therein. The size of the resonance chamber promotes a corresponding mass of air with commensurate quality of low frequency sound transmitted. If the microphone is reduced in size, the size of the resonance chamber of the microphone and the maximum power the microphone can handle are accordingly reduced, resulting in both a reduction in loudness as well as a poorer overall quality of sound. On the other hand, increasing the size of the microphone to increase the size of the resonance chamber is not feasible in many portable device applications. 
     What is needed, therefore, is a microphone module which can address the limitations described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the various views. 
         FIG. 1  is an assembled, isometric view of a microphone module in accordance with an embodiment of the disclosure. 
         FIG. 2  is an exploded, isometric view of the microphone module of  FIG. 1 . 
         FIG. 3  is similar to  FIG. 2 , but viewed from another aspect. 
         FIG. 4  is a cross section of the microphone module of  FIG. 1 , taken along line IV-IV thereof. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a microphone module in accordance with one embodiment of the present disclosure is shown. The microphone module is configured for use in electronic devices such as headsets, mobile phones, computers, and others. The microphone module includes a shell  10 , a circuit board  20  located in the shell  10 , and a microphone  30  located on the circuit board  20 . 
     Referring to  FIGS. 3 and 4 , the shell  10  includes a bottom cover  11 , a top cover  12  engaging the bottom cover  11 , a pair of baffle plates  13  respectively disposed at opposite ends of the bottom and top covers  11 ,  12 , and a faceplate  14  located on the top cover  12 . 
     The bottom cover  11  is semi-enclosed, and includes a bottom wall  111 , two sidewalls  112  extending upwardly from two opposite sides of the bottom wall  111 , respectively, and an engaging wall  116  extending upwardly from an end of the bottom wall  111 . The bottom wall  111  and the sidewalls  112  cooperatively define a receiving chamber  113  therebetween (see  FIG. 4 ). The bottom wall  111  is substantially rectangular. A pair of supporting ribs  114  and a pair of elastically-deformable buckles  115  extend upwardly from the two sidewalls  112 , respectively. The supporting ribs  114  can support the circuit board  20  thereon, and the buckles  115  press the circuit board  20  downwardly towards the supporting ribs  114 , thereby fixing the circuit board  20  within the bottom cover  11 . Each of the sidewalls  112  defines a mounting groove  117  in an inner surface thereof. The mounting grooves  117  communicate with the receiving chamber  113 . Each of the sidewalls  112  forms a step  118  at a top end thereof. An outer side of the step  118  is lower than an inner side of the step  118 . The engaging wall  116  interconnects the two sidewalls  112 . The engaging wall  116  has a height smaller than that of the sidewall  112 . The engaging wall  116  defines a depression  119  in a top face thereof for engaging with the baffle plate  13 . 
     The top cover  12  is also semi-enclosed, and includes a top wall  121  and two sidewalls  122  depending downwardly from two opposite sides of the top wall  121 , respectively. The top wall  121  and the sidewalls  122  cooperatively define a receiving chamber  123  therebetween (see  FIG. 4 ). 
     The top wall  121  is substantially rectangular, and defines a rectangular hole  124  at each of two adjacent corners thereof. The top wall  121  further defines a through hole  127  in a central area thereof. The top wall  121  has an annular flange  128  extending perpendicular to an outer edge of the through hole  127  towards the bottom cover  11 . 
     A distance between outer surfaces of the two sidewalls  122  of the top cover  12  is equal to or slightly less than a distance between inner surfaces of the two sidewalls  112  of the bottom cover  11 . A mounting hook  125  depends from a bottom end of each sidewall  122  of the top cover  12 , and is received in the mounting groove  117  of a corresponding sidewall  112  of the bottom cover  11 , thereby locking the top cover  12  with the bottom cover  11 . 
     The baffle plates  13  are made of elastic material, such as rubber. Each of the baffle plates  13  includes a base  131  and a protrusion  132  protruding inwardly from a central area of the base  131 . The base  131  is rectangular and joined to lateral sides of the top wall  121  of the top cover  12  and the bottom wall  111  of the bottom cover  11 . The protrusion  132  of one baffle plate  13  is received in the depression  119  of the bottom cover  11  and pressed downwardly by a bottom face of the top wall  121  of the top cover  12  and abuts against an outer circumferential face of the flange  128  of the top cover  12 . The protrusion  132  of the other baffle plate  13  is pressed downwardly by the bottom face of the top wall  121  of the top cover  12 . 
     The faceplate  14  includes a top plate  141 , two side plates  142  extending downwardly and respectively from two opposite sides of the top plate  141  towards the bottom cover  11 , and a washer  143  attached to the top plate  141 . 
     The top plate  141  is substantially rectangular, and has an engaging hook  144  depending toward the bottom cover  11  from a bottom face of the top plate  141 . The engaging hooks  144  of the top plate  141  are received in the rectangular holes  124  of the top cover  12  so that the faceplate  14  is fixed to the top cover  12 . 
     The top plate  141  defines a sound hole  147  in a center thereof. The sound hole  147  extends perpendicularly through the top plate  141 , and is aligned with the through hole  127  of the top cover  12 . The sound hole  147  is circular, and has a diameter far less than that of the through hole  127  of the top cover  12 . The top plate  141  has an annular flange  148  extending towards the top cover  12 . The annular flange  148  is disposed around the sound hole  147 . 
     The washer  143  is hollow and made of elastic material such as sponge, rubber, or another suitable material. The washer  143  is adhered to the top plate  141  in the annular flange  148  and a top face of the microphone  30 . In one embodiment, the washer  143  is annular and has a through hole as a sound chamber  149  therein. An outer diameter of the washer  143  is less than the inner diameter of the orienting flange  148 . An inner diameter of the washer  143 , namely, a diameter of the sound chamber  149 , exceeds that of the sound hole  147 . 
     Each of the side plates  142  forms a step  146  at a bottom end thereof. An outer side of the step  146  is lower than an inner side of the step  146 . The steps  146  are matched with the steps  118  of the sidewalls  112  of the bottom cover  11  so that the faceplate  14  can be fittingly engaged with the bottom cover  11 . 
     The circuit board  20  is received in the receiving chamber  113  of the bottom cover  11  of the shell  10 . The circuit board  20  forms a pair of holes  21  therein. 
     The microphone  30  is disposed on the top surface of the circuit board  20 , and electrically connects to the circuit board  20 . In this embodiment, the microphone  30  is an electret condenser microphone (ECM). The microphone  30  is cylindrical with two pins  300  extending downwardly into the two holes  21  of the circuit board  20 . The microphone  30  has an outer diameter less than an inner diameter of the through hole  127  of the top cover  12  of the shell  10 . The microphone  30  defines an acoustic chamber  31  in an interior thereof, and an acoustic hole  37  in a top end thereof. The acoustic hole  37  communicates the acoustic chamber  31  with an exterior. The acoustic hole  37  and the acoustic chamber  31  cooperatively form a first Helmholtz resonance chamber  38  in the microphone  30 . A tuning cloth  39 , made of unwoven cloth, is arranged on the acoustic hole  37 . A bottom surface of the washer  143  is fixed to the tuning cloth  39 . The tuning cloth  39  cooperates with the acoustic hole  37  to improve the sound quality factor and adjust the sound sharpness of the microphone  30 . 
     In the present microphone module, the washer  143  with the sound chamber  149  therein is provided between the microphone  30  and the faceplate  14 , and the sound chamber  149  of the washer  143  and the sound hole  147  of the top plate  141  of the faceplate  14  cooperatively form a second Helmholtz resonance chamber  50  outside of the microphone  30 . The two Helmholtz resonance chambers  38 ,  50  work together to improve sound quantity of the microphone module, i.e., widening the frequency bandwidth of the sound generated by the microphone module, and lowering the lowest resonance frequency of the sound generated by the microphone module. On the other hand, an interior space of the microphone module is adequately used without increasing a volume of the microphone module. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.