Abstract:
Certain embodiments of a noise canceling microphone with acoustically tuned ports are disclosed herein. In one aspect of the invention, the noise canceling microphone may comprise a housing, a transducer for converting received energy received into electrical signals, where the transducer is located in the housing, a front and rear sound pathways to a front and rear sound openings in the transducer, where the front and rear sound pathways may be located on opposite sides of the housing and may be displaced 180 degrees off a vertical axis. The noise canceling microphone may further comprising a boom for supporting the noise canceling microphone, where the boom may be deformed to place the noise canceling microphone near the mouth of the user. For example, the boom may be deformed to place the noise canceling microphone at least ten millimeters away from the edge of the mouth of the user.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE  
       [0001]     This application makes reference to, claims priority to, and claims the benefit of U.S. Provisional Patent Application 60/507,629 (Attorney Docket number 15226US01), filed on Sep. 30, 2003 and entitled “Noise Canceling Microphone With Acoustically Tuned Ports,” the complete subject matter of which is hereby incorporated herein by reference in its entirety. 
     
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     [Not Applicable] 
       SEQUENCE LISTING  
       [0003]     [Not Applicable] 
       MICROFICHE/COPYRIGHT REFERENCE] 
       [0004]     [Not Applicable] 
       BACKGROUND OF THE INVENTION  
       [0005]     Conventional omni-directional microphones are configured to convert changes in the sound pressure of an acoustic wave to mechanical vibrations of a microphone diaphragm. The microphones are typically positioned on a boom and may be located anywhere along the boom—from in front of the user&#39;s mouth to as far back as being close to the ear. When picking up the user&#39;s voice, a conventional omni-directional microphone will also pick up various background noises, such as working equipment, vibration noises, wind noise, breathing noise, and/or other voice chatter noises. Such noises may entirely drown out the user&#39;s voice, especially when the microphone is located back and away from the user&#39;s mouth.  
         [0006]     Noise cancellation in a microphone may be provided by the use of a close-talking microphone design, wherein the pressure difference between the sound at the front and the rear ports or inlets of the microphone as the user speaks provides a microphone output that is often greater than the microphone output for more distant sounds. Even though the design of conventional close-talking microphones may reduce the pick up of extraneous noise, their overall noise reduction characteristics are not optimal.  
         [0007]     Conventional omni-directional microphones have poor noise reduction capabilities and achieved noise attenuation levels are usually very low. In order to achieve acceptable noise attenuation levels, the conventional microphones will need to be placed in a very close proximity to the sound source, e.g., the user&#39;s mouth. When a microphone is located in front of the user&#39;s mouth, however, popping sounds accompany the plosives in the speech, causing increased noise characteristics.  
         [0008]     Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     Certain embodiments of the invention may be found in a noise canceling microphone with acoustically tuned ports. In one aspect of the invention, the noise canceling microphone may comprise a housing, a transducer for converting received energy received into electrical signals, where the transducer is located in the housing, a front and rear sound pathways to a front and rear sound openings in the transducer, where the front and rear sound pathways may be located on opposite sides of the housing and may be displaced 180 degrees off a vertical axis. The noise canceling microphone may further comprise a boom for supporting the noise canceling microphone, where the boom may be deformed to place the noise canceling microphone near the mouth of the user.  
         [0010]     For example, the boom may be deformed to place the noise canceling microphone at least ten millimeters away from the edge of the mouth of the user. The noise canceling microphone may also comprise one or more electric wire leads for communicating the electric signals outside the housing. The front and rear sound pathways may be mechanically tuned, for example by changing the acoustic mass and/or acoustic volume of the front and rear sound pathways, such that no electric tuning may be required. The acoustic mass and/or acoustic volume may be changed by changing at least one of the length and the area of the front and rear sound pathways. The noise canceling microphone may further comprise a single-directional microphone in the housing where the single-directional microphone may convert sound energy received into electrical signals. The noise canceling microphone may also comprise a head-set coupled to the boom.  
         [0011]     In another aspect of the invention, the noise canceling microphone may comprise a housing, a transducer for converting received energy into electrical signals, where the transducer is located in the housing, a front and rear sound pathways to a front and rear sound openings in the transducer, where the front and rear sound pathways may be positioned and mechanically tuned such that the noise canceling microphone may provide a reduction of external acoustic noise of greater than 15 dB. The noise reduction may comprise at least 18 dB at 300 Hz.  
         [0012]     The front and rear sound pathways may be positioned and mechanically tuned such that at least 15 dB noise reduction may be achieved without inserting-user-noticeable high frequency noise. The noise canceling microphone may further comprise a boom for supporting the noise canceling microphone, where the boom may be deformed to place the noise canceling microphone near the mouth of the user. For example, the boom may be deformed to place the noise canceling microphone at least ten millimeters away from the edge of the mouth of the user. The noise canceling microphone may also comprise one or more electric wire leads for communicating the electric signals outside the housing.  
         [0013]     The front and rear sound pathways may be mechanically tuned, for example by changing the acoustic mass and/or acoustic volume of the front and rear sound pathways, such that no electric tuning may be required. The acoustic mass and/or acoustic volume may be changed by changing at least one of the length and the area of the front and rear sound pathways. The noise canceling microphone may further comprise a single-directional microphone in the housing where the single-directional microphone may convert sound energy received into electrical signals.  
         [0014]     These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.  
     
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0015]      FIG. 1A  is a diagram illustrating a frequency response of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention.  
         [0016]      FIG. 1B  is a diagram illustrating a frequency response of a conventional noise canceling microphone with noise reduction characteristics that can be compared to those of the noise canceling microphone of  FIG. 1A , in accordance with an embodiment of the invention.  
         [0017]      FIG. 2  is an illustration of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention.  
         [0018]      FIG. 3  is an exemplary illustration of a noise canceling microphone with acoustically tuned ports mounted on a boom, in accordance with an embodiment of the invention.  
         [0019]      FIG. 4A  is a diagram illustrating on-axis frequency response of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention.  
         [0020]      FIG. 4B  is a diagram illustrating a 90-degree rotation frequency response of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention.  
         [0021]      FIG. 4C  is a diagram illustrating a 180-degree rotation frequency response of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Aspects of the invention may be found in a noise canceling microphone with acoustically tuned ports. By changing the acoustic volume and/or acoustic mass within front and rear sound pathways in the noise canceling microphone, a noise reduction which is higher than conventional noise canceling microphones may be achieved.  
         [0023]      FIG. 1A  is a diagram illustrating a frequency response of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention. In an exemplary aspect of the invention, noise attenuation levels may be measured in a noise canceling microphone with acoustically tuned ports mounted on one side of the face and may be compared to those of a reference microphone mounted on the opposite side of the face. Referring to  FIG. 1A , the reference microphone&#39;s frequency response may be given a value of zero, as illustrated by the graph line  100 .  
         [0024]     Graph line  101  may represent the frequency response of the exemplary noise canceling microphone with acoustically tuned ports, relative to that of the reference microphone, when the exemplary noise canceling microphone is ten millimeters back from the sound source, such as the edge of the user&#39;s mouth. Graph line  102  may represent the response of the exemplary noise canceling microphone relative to that of the reference microphone, when the exemplary noise canceling microphone is placed as described above and the source of sound is that of a diffuse or reverberant field. The difference between response curves  101  and  102  illustrate the noise canceling property of the exemplary noise canceling microphone with acoustically tuned ports of  FIG. 1A .  
         [0025]      FIG. 1B  is a diagram illustrating a frequency response of a conventional noise-canceling microphone with noise reduction characteristics that can be compared to those of the noise canceling microphone of  FIG. 1A , in accordance with an embodiment of the invention. Referring to  FIG. 1B , the reference microphone&#39;s frequency response may be given a value of zero, as illustrated by the graph line  103 . Graph line  104  may represent the frequency response of the conventional noise canceling microphone relative to that of the reference microphone, when the conventional microphone of  FIG. 1B  is in the same position as the noise canceling microphone with acoustically tuned ports of  FIG. 1A , or ten millimeters from the edge of the user&#39;s mouth. Graph line  105  may represent the frequency response of the conventional noise canceling microphone, relative to that of the reference microphone, when the conventional microphone is placed ten millimeters from the edge of the user&#39;s mouth and the source of the sound is that of a diffuse or reverberant field.  
         [0026]     Referring to  FIGS. 1A and 1B , the frequency response characteristics of the conventional noise canceling microphone and the noise canceling microphone with acoustically tuned ports may be represented by graph lines  104  and  101 , respectively. In addition, the response of the conventional noise canceling microphone and the noise canceling microphone with acoustically tuned ports to a diffuse noise field may be represented by graph lines  105  and  102 . In this manner, by comparing the frequency response characteristics of the conventional noise canceling microphone and the noise canceling microphone with acoustically tuned ports with their respective response to a diffuse noise field, may reveal an average of approximately 5 dB superior noise rejection. In addition, the noise canceling microphone with acoustically tuned ports may yield nearly flat acoustic close talking (in-situ) response throughout the entire bandwidth, as reflected by graph line  101 .  
         [0027]     In one aspect of the invention, a noise canceling microphone with acoustically tuned ports may be utilized in microphone head-set applications, for example, as well as applications utilizing voice-recognition techniques. In addition, a noise canceling microphone with acoustically tuned ports may also be utilized during a two-way conversation in a vehicle with 100 dB SPL vehicle noise, for example.  
         [0028]     In another aspect of the invention, a noise reduction of approximately 12 dB at 1000 Hz and nearly 20 dB at 300 Hz and 8 dB at 3000 Hz may be achieved, as evidenced from a comparison of the frequency response characteristics of an exemplary noise canceling microphone with acoustically tuned ports, as represented by graph line  101 , with the noise response of a reference microphone, as represented by graph line  102 . The conventional noise canceling microphone, on the other hand, may achieve only 8 dB noise rejection at 1000 Hz, only approximately 10 dB noise reduction at 300 Hz, and only 2 dB noise rejection at 3000 Hz, as illustrated by graph lines  104  and  105 .  
         [0029]     In another aspect of the invention, an exemplary noise canceling microphone with acoustically tuned ports may be adapted to achieve noise reduction of at least 20 dB greater than a conventional omni-directional microphone tested under similar circumstances. For example, a conventional microphone manufactured by Jabra and tested under similar circumstances as the exemplary noise canceling microphone with acoustically tuned ports, may be characterized with a −9 dB noise reduction at 1 kHz, or 21 dB less noise reduction than the exemplary noise canceling microphone with acoustically tuned ports.  
         [0030]      FIG. 2  is an illustration of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention. a Referring to  FIG. 2 , the noise canceling microphone with acoustically tuned ports  200  may comprise a microphone housing  208 , a front port  201 , a rear port  202 , an internal microphone  203  with a front side  209  and a back side  210 , a front entry canal  204 , a rear entry canal  205 , and microphone electric wire leads  206  and  207 . The front side  209  and the back side  210  of the internal microphone  203  may comprise a front inlet  214  and a rear inlet  215 , respectively.  
         [0031]     The front port  201  is the port closer to the sound source, such as a user&#39;s mouth. In an exemplary aspect of the invention, in order to achieve higher microphone sensitivity, the front port  201  may be situated on the same horizontal plane as the sound source is. The rear port  202  may be situated on the same horizontal plane as the front port  201  and the sounds source are. However, the rear port  202  may be offset one hundred and eighty degrees off a vertical axis from the front port  201 , so that the rear port may be located on the opposite side of the microphone housing  208 .  
         [0032]     The front entry canal  204  may connect the front port  201  with the front inlet  214  of the internal microphone&#39;s front side  209 . The back entry canal  205  may connect the back port  202  with the rear inlet  215  of the internal microphone&#39;s back side  210 . In another aspect of the invention, there may be no active electric tuning utilized with the noise canceling microphone with acoustically tuned ports. In this regard, the ports  201  and  202  may be acoustically tuned by changing the acoustic volume and/or the acoustic mass of the cavities formed by the front entry canal  204  and the back entry canal  205 .  
         [0033]     The acoustic mass M may be determined by the equation M=0.0016×(L/A), where L is the length and A is the area of the front entry canal  204  or the back entry canal  205 . The acoustic volume V may be determined by the equation V=L×A. The volumes and ratio of acoustic mass to volume may be selected independently in order to optimize overall performance. The acoustic volumes of the canal cavities formed by the front entry canal  204  and the back entry canal  205  may be optimized to obtain high noise reduction level and close-talking sensitivity. While a single-directional microphone cartridge may be utilized as the internal microphone  203 , the present invention is not limited in this manner and other types of microphone cartridges may be utilized within the noise canceling microphone with acoustically tuned ports  200 .  
         [0034]      FIG. 3  is an exemplary illustration of a noise canceling microphone with acoustically tuned ports mounted on a boom, in accordance with an embodiment of the invention. Referring to  FIG. 3 , the noise canceling microphone with acoustically tuned ports  301  may comprise acoustically tuned front and back ports  302  and  303 . The microphone  301  may be mounted on a boom  305 , which may be part of a head-set. The boom  305  may be deformed so that the distance  306  between the edge of the user&#39;s mouth and the noise canceling microphone with acoustically tuned ports  301  may be changed. In an exemplary aspect of the invention, the boom  305  may be adjusted so that the distance  306  is at least ten millimeters and the noise canceling microphone with acoustically tuned ports  301  provides pop-free performance combined with excellent noise rejection.  
         [0035]     In another aspect of the invention, the position of the microphone with acoustically tuned ports  301  may be changed relative to the sound source, such as the end of the user&#39;s mouth. In this manner, the position of the microphone  301 , as well as the position of the microphone ports and the volume of the canal cavities of the front entry and the back entry, may be optimized so that the highest noise reduction and close-talk sensitivity is achieved compared to a conventional microphone.  
         [0036]      FIG. 4A  is a diagram illustrating on-axis frequency response of a noise canceling microphone with. acoustically tuned ports, in accordance with an embodiment of the invention. In an exemplary aspect of the invention, noise attenuation levels and on-axis frequency response may be measured in a noise canceling microphone with acoustically tuned ports  410  mounted on one side of the face and may be compared to those of a reference microphone mounted on the opposite side of the face.  
         [0037]     Referring to  FIG. 4A , the reference microphone&#39;s frequency response may be given a value of zero, as illustrated by graph line  400 . Graph line  401  may represent the on-axis frequency response of the exemplary noise canceling microphone  410  with acoustically tuned ports, relative to that of the reference microphone. Graph line  402  may represent a frequency response to a testing level of ambient noise as a result of the use of the noise canceling microphone  410 . In this case, the first-microphone inlet  412  is close to the mouth and the second microphone inlet  414  is away from the mouth on the outside of the microphone pod and, as a result, optimal level of noise reduction may be achieved. For example, approximately 10 dB in noise reduction may be achieved at 1000 Hz and approximately 20 dB of noise reduction at 300 Hz.  
         [0038]      FIG. 4B  is a diagram illustrating a 90-degree rotation frequency response of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention. In an exemplary aspect of the invention, noise attenuation levels and 90-degree rotation frequency response may be measured in a noise canceling microphone with acoustically tuned ports  416  mounted on one side of the face and may be compared to those of a reference microphone mounted on the opposite side of the face.  
         [0039]     Referring to  FIG. 4B , the reference microphone&#39;s frequency response may be given a value of zero, as illustrated by graph line  403 . Graph line  404  may represent the 90-degree rotation frequency response of the exemplary noise canceling microphone with acoustically tuned ports  416 , relative to that of the reference microphone. Graph line  405  may represent a frequency response to a testing level of ambient noise as a result of the use of the noise canceling microphone  416 . In this case, the microphone pod of the noise canceling microphone  416  may be turned 90 degrees, so that the rear inlet port  420  faces down and the front inlet port  418  faces up. As a result, noise reduction levels decrease in comparison to the noise reduction levels illustrated on  FIG. 4A . For example, approximately 5 dB in noise reduction may be achieved at 1000 Hz and approximately 10 dB of noise reduction at 300 Hz.  
         [0040]      FIG. 4C  is a diagram illustrating a 180-degree rotation frequency response of a noise canceling microphone with acoustically tuned ports, in accordance with an embodiment of the invention. In an exemplary aspect of the invention, noise attenuation levels and 180-degree rotation frequency response may be measured in a noise canceling microphone with acoustically tuned ports  422  mounted on one side of the face and may be compared to those of a reference microphone mounted on the opposite side of the face.  
         [0041]     Referring to  FIG. 4C , the reference microphone&#39;s frequency response may be given a value of zero, as illustrated by graph line  406 . Graph line  407  may represent the 180-degree rotation frequency response of the exemplary noise canceling microphone with acoustically tuned ports  422 , relative to that of the reference microphone. Graph line  408  may represent a frequency response to a testing level of ambient noise as a result of the use of the noise canceling microphone  422 . In this case, the microphone pod of the noise canceling microphone  422  may be turned 180 degrees, so that the rear inlet port  422  is closest to the face and the front inlet port  424  is away from the face. As a result, noise reduction levels decrease even further in comparison to the noise reduction levels illustrated on  FIGS. 4A and 4B . For example, approximately −2 dB in noise reduction may be achieved at 1000 Hz and approximately  3  dB of noise reduction at 300 Hz.  
         [0042]     While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art, that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.