Patent Publication Number: US-7711136-B2

Title: Microphone array in housing receiving sound via guide tube

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/742,033, filed on Dec. 2, 2005, and U.S. Provisional Application No. 60/748,276, filed on Dec. 7, 2005. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a microphone array in a housing receiving sound via guide tubes. 
   2. Description of the Related Art 
   A microphone array includes a number of microphones disposed in tandem. A simple example is shown in  FIG. 1 , wherein the microphone array  10  includes two microphones  11  and  12  placed side by side. Directivity of the microphone array  10  can be achieved by manipulating the signal received by the two microphones  11  and  12 . Assuming the two microphones  11  and  12  are omni-directional and having the same characteristics, the directivity of the microphone array  10  depends on vector {right arrow over (d)} from one microphone  11  to the other microphone  12 . 
   The above-mentioned microphones  11  and  12  are conventionally placed in an open space to achieve directivity. Most electronic devices (cellular phones, personal digital assistants, etc.), however, have plastic or metal housings, acting as acoustic isolators which block audio signals, thus increasing the difficulty of microphone placement. Furthermore, the majority of electronic elements including microphones are conventionally surface-mounted on printed circuit boards (PCBs), thus limiting the directivity of the microphone array. As illustrated by  FIG. 2 , microphones  11 ′ and  12 ′ are disposed in a housing  20 . The housing  20  acts as an acoustic isolator preventing the microphones  11 ′ and  12 ′ from receiving external sound. Furthermore, the distance d 1  between the microphones  11 ′ and  12 ′ on the PCB  21  is limited by the available space on the PCB  21  and in the housing  20 , generally being less than the desired distance (d 1 &lt;d). Furthermore, the direction of the microphone array, as designated by vector {right arrow over (d 1 )}, is always parallel to the PCB  21 . Such a direction, however, does not necessarily target the desired sound source during operation of the electronic device. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention provides a microphone array in a housing of an electronic device, capable of preventing the described problems. 
   The electronic device includes a housing, a plurality of microphones, and a plurality of guide tubes. The plurality of microphones are disposed in the housing. The plurality of guide tubes extend from the housing toward the plurality of microphones, whereby the plurality of microphones in the housing are capable of receiving external sound via the guide tubes. 
   The electronic device may further include a plurality of acoustically isolated chambers disposed in the housing preventing sound transmission therebetween, wherein the plurality of microphones are disposed in the plurality of chambers in a one-to-one manner. 
   The housing may have a plurality of acoustic openings, with the plurality of guide tubes extending from the plurality of acoustic openings to the plurality of chambers. The acoustic openings may be provided on the top, bottom, or sides of the housing. 
   The plurality of acoustic openings may be separated by a first distance, and the plurality of microphones separated by a second distance less than the first distance. 
   The plurality of microphones may include unidirectional microphones, omni-directional microphones, or combinations thereof. 
   The guide tubes may be equal in length. 
   The guide tubes may differ in length. 
   The electronic device may be a cellular phone, an audio recorder, a personal digital assistant (PDA), or other device. 
   The electronic device may further include a circuit board, with the plurality of microphones mounted on the same side of the circuit board, or on opposite sides of the circuit board. 
   The plurality of microphones may be placed side-by-side. 
   The plurality of microphones may be placed back-to-back, in alignment or out of alignment. 
   A detailed description is given in the following embodiments with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
       FIG. 1  is a schematic diagram of a microphone array; 
       FIG. 2  is a schematic view of a microphone array disposed in a housing of an electronic device; 
       FIG. 3  depicts an electronic device in accordance with an embodiment of the invention; 
       FIG. 4  depicts an electronic device in accordance with another embodiment of the invention; 
       FIG. 5  depicts an electronic device in accordance with another embodiment of the invention; 
       FIG. 6  depicts an electronic device in accordance with another embodiment of the invention; 
       FIG. 7A  depicts an electronic device in accordance with another embodiment of the invention; 
       FIG. 7B  depicts a microphone array disposed in a chamber of the electronic device of  FIG. 7A ; and 
       FIG. 8  depicts an electronic device in accordance with another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
   Referring to  FIG. 3 , an electronic device in accordance with an embodiment of the invention comprises a housing  30 , a printed circuit board (PCB)  31 , a plurality of microphones  35  and  36 , a plurality of chambers  32  and  33 , and a plurality of guide tubes  37  and  38 . All of the elements  31 ,  32 ,  33 ,  35 ,  36 ,  37 , and  38  are disposed in the housing  30 . 
   In this embodiment, the microphones  35  and  36 , disposed in the chambers  32  and  33  in a one-to-one manner, are omni-directional. The guide tubes  37  and  38  are equal in length and extend from the chambers  32  and  33  to the acoustic openings  301  and  302  of the housing  30 . Thus, the microphones  35  and  36  are capable of receiving external sound via the guide tubes  37  and  38 . The chambers  32  and  33  are acoustically isolated from each other to prevent sound transmission therebetween. 
   The microphones  35  and  36  are placed side-by-side and surface-mounted on the same side of the PCB  31 . The microphones  35  and  36  constitute a microphone array  34 . The directivity of the microphone array  34  is determined by the acoustic openings  301  and  302  rather than the microphones  35  and  36 . Such an arrangement is advantageous in achieving the directivity of the microphone array  34  since the acoustic openings  301  and  302  can be separated by a distance d 2  greater than the microphones  35  and  36 . In this embodiment, the acoustic openings  301  and  302  are provided at the top of the housing  30 . 
   The guide tubes  37  and  38  are equal in length, thus, the delay in sound propagating through the guide tubes  37  and  38  is equal. In some cases, however, the lengths of the guide tubes cannot be equal due to design constraints by the location of the PCB or the shape of the housing.  FIG. 4  depicts an electronic device in accordance with another embodiment of the invention, wherein the same reference will be used for elements identical or similar to those shown in  FIG. 3 . In  FIG. 4 , the guide tubes  37 ′ and  38 ′ are not equal in length. 
   Referring to  FIG. 5 , an electronic device in accordance with another embodiment of the invention comprises a housing  40 , a printed circuit board (PCB)  41 , a plurality of microphones  45  and  46 , a plurality of chambers  42  and  43 , and a plurality of guide tubes  47  and  48 . All of the elements  41 ,  42 ,  43 ,  45 ,  46 ,  47 , and  48  are disposed in the housing  40 . 
   In this embodiment, the microphones  45  and  46  are omni-directional and disposed in the chambers  42  and  43  in a one-to-one manner. The guide tubes  47  and  48  are equal in length and extend from the chambers  42  and  43  to the acoustic openings  401  and  402  of the housing  40 . Thus, the microphones  45  and  46  are capable of receiving external sound via the guide tubes  47  and  48 . The chambers  42  and  43  are acoustically isolated from each other to prevent sound transmission therebetween. 
   The microphones  45  and  46  are surface-mounted on opposite sides of the PCB  41  (i.e. back-to-back) and placed in alignment. The microphones  45  and  46  constitute a microphone array  44 . The directivity of the microphone array  44  is determined by the acoustic openings  401  and  402  rather than the microphones  45  and  46 . In this embodiment, the acoustic openings  401  and  402  are provided at the bottom of the housing  40 . 
   Referring to  FIG. 6 , an electronic device in accordance with another embodiment of the invention comprises a housing  50 , a printed circuit board (PCB)  51 , a plurality of microphones  55  and  56 , a plurality of chambers  52  and  53 , and a plurality of guide tubes  57  and  58 . All of the elements  51 ,  52 ,  53 ,  55 ,  56 ,  57 , and  58  are disposed in the housing  50 . 
   The microphones  55  and  56  are omni-directional and disposed in the chambers  52  and  53  in a one-to-one manner. The guide tubes  57  and  58  extend from the chambers  52  and  53  to the acoustic openings  501  and  502  of the housing  50 , wherein the acoustic openings  501  and  502  are provided at the bottom of the housing  50 . Thus, the microphones  55  and  56  are capable of receiving external sound via the guide tubes  57  and  58 . The chambers  52  and  53  are acoustically isolated from each other to prevent sound transmission therebetween. 
   In this embodiment, the chambers  52  and  53  are separated from the bottom of the housing  50  by different distances. Thus, the guide tubes  57  and  58 , extending from the acoustic openings  501  and  502  of the housing  50  to the chambers  52  and  53 , are not equal in length. 
   The microphones  55  and  56  are surface-mounted on opposite sides of the PCB  51  and not placed in alignment. The microphones  55  and  56  constitute a microphone array  54 . The directivity of the microphone array  54  is determined by the acoustic openings  501  and  502  rather than the microphones  55  and  56 . 
   Referring to  FIGS. 7A and 7B , an electronic device in accordance with another embodiment of the invention comprises a housing  60 , a plurality of microphones  65  and  66 , a chamber  62 , a port  63 , and a guide tube  67 . All of the elements  62 ,  63 ,  65 ,  66 , and  67  are disposed in the housing  60 . There are two ports, one is at the end of the guide tube  67  and the other  63  is in front of the microphone facing the front of the electronic device. 
   The microphones  65  and  66  are omni-directional, disposed in the chamber  62 , and constitute a microphone array  64 . The guide tube  67  extends from the chamber  62  to the acoustic opening  601  of the housing  60 , wherein the acoustic opening  601  is provided at the rear of the housing  60 . Thus, the microphones  65  and  66  are capable of receiving external sound via the guide tube  67  and the port  63 . 
   In this embodiment, the chamber  62  and the microphones  65  and  66  therein are arranged at an inclined angle to the rear of the housing  60 . 
     FIG. 8  depicts an electronic device in accordance with another embodiment of the invention, wherein a microphone array  74  comprising microphones  75  and  76  is disposed in the housing  70  of the electronic device. External sound is introduced to a tunnel  77  and then to the microphones  75  and  76 . 
   In the invention, the guide tubes allow a microphone array to receive external sound. Although the microphone array is disposed in a housing, the quality of audio signals received by the microphone array is not influenced by such disposition. Furthermore, the directivity of the microphone array is determined by the acoustic openings of the housing rather than the microphones on a PCB. Thus, directivity of the microphone array and capability thereof to satisfy practical demands is achievable and flexible. It is understood that the invention is applicable to a variety of electronic devices including a cellular phone, an audio recorder, a personal digital assistant (PDA), and others. 
   In the embodiments, the microphone array includes omni-directional microphones. It is understood, however, that the microphone array can include uni-directional microphones, omni-directional microphones, or combinations thereof. 
   It is understood that the acoustic openings can be provided on the top, bottom, or sides of the housing of the electronic device. 
   While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.