Abstract:
A noise attenuation device comprising a first tube for receiving an acoustic signal, a first housing defining a first cavity between a first surface and a second surface, the first tube being coupled to the first housing at the first surface for conducting the acoustic signal into the first cavity, wherein one end of the first tube contacts the first surface at a first region with a first area, a second housing defining a second cavity between a first surface and a second surface, and a second tube coupled between the second surface of the first housing and the first surface of the second housing for conducting the acoustic signal between the first cavity and the second cavity, wherein one end of the second tube contacts the second surface of the first housing at a second region with a second area, wherein the first tube, the first housing and the second tube form a filter structure and the area of the first surface of the first housing is greater than the first area and the area of the second surface of the first housing is greater than the second area.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to a noise attenuation device and, more particularly, to an acoustic transducer device for noise attenuation. 
         [0002]    Remarkable technological advances render the prevalence of various electronic products. Consumer electronic products, especially portable multi-media products, may provide real-time audio and video contents of interest. Most of the multi-media products are generally equipped with at least one speaker to give off sounds. However, since users may not clearly hear the sounds from speakers due to ambient noise, consequently, headphones or earphones, which may be capable of attenuating ambient noise, are widely used in conjunction with speakers for audio signal transmission. 
         [0003]    A headphone may be designed to surround and cover the outer ears of a user to isolate ambient noise. For example, headphones may be devised to exert force against the ears so as to seal the ears tight and provide noise isolation. However, the pressure on the ears of a user may cause a phenomenon of autophony, which may make the user uneasy or uncomfortable. Furthermore, some headphones may have a large size and thus may cause inconvenience to their users. 
         [0004]    Earphones are able to fit the auditory canals of ears so that ambient noise may be blocked outside. Moreover, a noise reduction circuit may be used in an earphone to compensate for noise at a low frequency range from approximately 16 Hertz (Hz) to 1 kilohertz (kHz). Nevertheless, such a noise reduction circuit may not process noise at a high frequency range over approximately 1 kHz. High-frequency noise, however, may also be sensed by the ears and interfere with audio signals of interest. 
         [0005]    Therefore, it may be desirable to have an acoustic transducer device that is able to efficiently transmit audio signals and attenuate ambient noise. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Examples of the present invention may provide a noise attenuation device comprising a first tube for receiving an acoustic signal, a first housing defining a first cavity between a first surface having an area and a second surface having an area, the first tube being coupled to the first housing at the first surface for conducting the acoustic signal into the first cavity, wherein one end of the first tube contacts the first surface at a first region with a first area, a second housing defining a second cavity between a first surface and a second surface, and a second tube coupled between the second surface of the first housing and the first surface of the second housing for conducting the acoustic signal between the first cavity and the second cavity, wherein one end of the second tube contacts the second surface of the first housing at a second region with a second area, wherein the first tube, the first housing and the second tube form a filter structure and the area of the first surface of the first housing is greater than the first area and the area of the second surface of the first housing is greater than the second area. 
         [0007]    Some examples of the present invention may also provide a noise attenuation device comprising a noise processing device comprising a first tube for receiving an acoustic signal, a first housing defining a first cavity between a first surface having an area and a second surface having an area, the first tube being coupled to the first housing at the first surface for conducting the acoustic signal into the first cavity, wherein one end of the first tube contacts the first surface at a first region with a first area, a second housing defining a second cavity between a first surface and a second surface, and a second tube coupled between the second surface of the first housing and the first surface of the second housing for conducting the acoustic signal between the first cavity and the second cavity, wherein one end of the second tube contacts the second surface of the first housing at a second region with a second area, wherein the area of the first surface of the first housing is greater than the first area and the area of the second surface of the first housing is greater than the second area so as to attenuate noise in the second cavity, a first microphone, a speaker electrically coupled to the second housing, and a signal processing circuit electrically coupled to the first microphone and the speaker. 
         [0008]    Examples of the present invention may further provide a noise attenuation device comprising at least one first tube for receiving an acoustic signal, a first housing defining a first cavity between a first surface having an area and a second surface having an area, the at least one first tube being coupled to the first housing at the first surface for conducting the acoustic signal into the first cavity, wherein one end of each of the at least one first tube contacts the first surface of the first housing at a first region with a first area, a second housing defining a second cavity between a first surface and a second surface, and at least one second tube coupled between the second surface of the first housing and the first surface of the second housing for conducting the acoustic signal between the first cavity and the second cavity, wherein one end of each of the at least one second tube contacts the second surface of the first housing at a second region with a second area, wherein the area of the first surface of the first housing is greater than a sum of the first area of each of the at least one first tube and the area of the second surface of the first housing is greater than a sum of the second area of each of the at least one second tube to attenuate noise over a predetermined frequency level. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    The foregoing summary as well as the following detailed description of the preferred embodiments of the present invention will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It is understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
           [0010]      FIG. 1A  is a diagram illustrating an assembly of a noise attenuation device in accordance with an example of the present invention; 
           [0011]      FIG. 1B  is an exploded view of the noise attenuation device described and illustrated with reference to  FIG. 1A ; 
           [0012]      FIG. 1C  is a perspective view of portions of the noise attenuation device illustrated in  FIG. 1A ; 
           [0013]      FIGS. 1D ,  1 E and  1 F each show a side view and a rear view of a noise attenuation device in accordance with an example of the present invention; 
           [0014]      FIG. 1G  is a schematic diagram illustrating a portion of a noise attenuation device in accordance with another example of the present invention; 
           [0015]      FIG. 2A  is a cross-sectional diagram of a noise attenuation device in accordance with an example of the present invention; 
           [0016]      FIG. 2B  is a cross-sectional diagram of a noise attenuation device in accordance with another example of the present invention; 
           [0017]      FIG. 3A  is a schematic diagram of a noise attenuation device in accordance with an example of the present invention; 
           [0018]      FIG. 3B  is a schematic block diagram of a signal processing circuit in accordance with an example of the present invention; 
           [0019]      FIG. 4A  is a plot showing experimental results of the frequency response each of noise attenuation devices with different arrangements; 
           [0020]      FIG. 4B  is a plot showing experimental results of the frequency response each of noise attenuation devices of different sizes; and 
           [0021]      FIG. 4C  is a plot showing experimental results of the frequency response each of noise attenuation devices with different chamber designs. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Reference will now be made in detail to the present examples of the invention illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like portions. It should be noted that the drawings are in simplified form and are not drawn to precise scale. In reference to the disclosure herein, for purposes of convenience and clarity only, directional terms such as inner, outer, upper and lower, are used with respect to the accompanying drawings. Such directional terms used in conjunction with the following description of the drawings should not be construed to limit the scope of the invention in any manner not explicitly set forth in the appended claims. 
         [0023]      FIG. 1A  is a diagram illustrating an assembly of a noise attenuation device  1  in accordance with an example of the present invention. Referring to  FIG. 1A , the noise attenuation device  1  may include a first tube  101 , a first housing  102 , a second tube  103 , a second housing  104 , an earplug  105 , a microphone  106 , a speaker  107  and a third tube  108 . The first housing  102  and the second housing  104  respectively define therein a first cavity “A” and a second cavity “B”. The first tube  101  may be coupled to the first housing  102 , which in turn may be coupled to the second tube  103  and then the second housing  104 . The earplug  105  may include an inner cavity “C” to tightly surround and encompass the circumference of the third tube  108 , and one or more opening  105 - 1  to contact the ear canal of a user. Accordingly, an audio channel extending from a first end  101 - 1  of the first tube  101  through the first cavity A, the second tube  103 , the second cavity B and the third tube  108  to the opening  105 - 1  of the earplug  105  may be formed in the noise attenuation device  1 . The microphone  106  and the speaker  107  may be disposed near the second housing  104 . In the present example, the microphone  106  may be disposed under the second housing  104 . Furthermore, the speaker  107  may be disposed between the first housing  102  and the second housing  104 . 
         [0024]      FIG. 1B  is an exploded view of the noise attenuation device  1  described and illustrated with reference to  FIG. 1A . Referring to  FIG. 1B , the speaker  107  may include a speaker body  107 - 1  and a speaker chamber  107 - 2 , which in turn may respectively serve as a receiver and a back chamber for the speaker  107 . In the present example, one or more first opening  14 - 1  may be provided in the second housing  104  to receive acoustic signals from the speaker  107 . The acoustic signals may then be transmitted through the cavity B and the third tube  108  toward the earplug  105 . Furthermore, when the microphone  106  is disposed under the second housing  104  as illustrated in  FIG. 1A , one or more second opening  14 - 2  may be provided in the second housing  104  to facilitate the microphone  106  to receive the acoustic signals in the cavity B. In another example of the present invention, the microphone  106  may be disposed on an outer wall of the second housing  104 . In yet another example of the present invention, the microphone  106  may be disposed within the second housing  104 . In still another example, more than one microphone  106  may be used to receive the acoustic signals in the cavity B. 
         [0025]      FIG. 1C  is a perspective view of portions of the noise attenuation device  1  illustrated in  FIG. 1A . Referring to  FIG. 1C , the first housing  102  and the second housing  104  may have a cylindrical shape. The first tube  101  may be disposed near or at the center of a first outer wall  102 - 1  of the first housing  102 . The second tube  103  may be coupled between upper portions of the first and second housings  102  and  104 . In an example of the present invention, a second end  101 - 2  of the first tube  101  may contact the outer wall  102 - 1  at a first region “a” with a first area, and a first end  103 - 1  of the second tube  103  may contact a second outer wall  102 - 2  at a second region “b” with a second area. The first outer wall  102 - 1 , the second outer wall  102 - 2  and a sidewall  102 - 3  may together define therein the cavity “A”. In one example, the area of the first outer wall  102 - 1  may be greater than the first area, and the area of the second outer wall  102 - 2  may be greater than the second area. Furthermore, the ratio of the area of the first outer wall  102 - 1  to the first area may range from approximately 30 to 300. The first tube  101  and the second tube  103  may be approximately 1 millimeter (mm) in length but may be longer or shorter. Furthermore, the first housing  102  and the second housing  104  may be approximately 1 mm in width but may be thinner or thicker. The volume of the cavity B enclosed by the second housing  104  may be kept relatively small to facilitate miniature of the noise attenuation device  1 . 
         [0026]      FIGS. 1D ,  1 E and  1 F each show a side view and a rear view of a noise attenuation device in accordance with an example of the present invention. For simplicity, a second housing similar to the second housing  104  in  FIG. 1C  is not illustrated. Referring to the left part of  FIG. 1D , which illustrates a side planar view of an arrangement, the noise attenuation device may include a first tube  111 , a first housing  112  and a second tube  113 . The first tube  111 , the first housing  112  and the second tube  113  may respectively be similar to the first tube  101 , the first housing  102  and the second tube  103  described and illustrated with reference to  FIG. 1C  except that, for example, the first tube  111  may be disposed near an upper portion of the first housing  112  and the second tube  113  may be disposed near a lower portion of the first housing  112 . Referring to the right part of  FIG. 1D , a rear view of the arrangement of the noise attenuation device is illustrated. 
         [0027]    Referring to  FIG. 1E , the noise attenuation device may include a first tube  121 , a first housing  122  and a second tube  123 . The first tube  121 , the first housing  122  and the second tube  123  may respectively be similar to the first tube  101 , the first housing  102  and the second tube  103  described and illustrated with reference to  FIG. 1C  except that, for example, the first tube  121  may be coupled to an upper portion of the first housing  122 . 
         [0028]    Referring to  FIG. 1F , the noise attenuation device may include a first tube  131 , a first housing  132  and a second tube  133 . The first tube  131 , the first housing  132  and the second tube  133  may respectively be similar to the first tube  101 , the first housing  102  and the second tube  103  described and illustrated with reference to  FIG. 1C  except that, for example, the first tube  131  and the second tube  133  may be coupled to a center portion of the first housing  132 . 
         [0029]      FIG. 1G  is a schematic diagram illustrating a portion of a noise attenuation device  1 ′ in accordance with another example of the present invention. Referring to  FIG. 1G , the noise attenuation device  1 ′ may include a first tube  101 ′, a first housing  102 ′, a second tube  103 ′ and a second housing  104 ′. The noise attenuation device  1 ′ may be similar to the noise attenuation device  1  described and illustrated with reference to  FIG. 1A  except that, for example, one or both of the first housing  102 ′ and the second housing  104 ′ may have an irregular shape rather than a cylindrical shape. 
         [0030]      FIG. 2A  is a cross-sectional diagram of a noise attenuation device  2  in accordance with an example of the present invention. Referring to  FIG. 2A , the noise attenuation device  2  may include a first tube  201 , a first housing  202 , a second tube  203 , a second housing  204 , an earplug  205 , a microphone  206 , a speaker  207  and a third tube  208 . The noise attenuation device  2  may be similar to the noise attenuation device  1  described and illustrated with reference to  FIG. 1A  except that, for example, the microphone  206  may be disposed within the second housing  204 . 
         [0031]      FIG. 2B  is a cross-sectional diagram of a noise attenuation device  3  in accordance with another example of the present invention. Referring to  FIG. 2B , the noise attenuation device  3  may include a number of (in the example, two) first tubes  301 , a first housing  302 , a number of (in the example, three) second tubes  303 , a second housing  304 , a microphone  306 , a speaker  307  and a number of (in the example, six) third tubes  308 . The noise attenuation device  3  may be similar to the noise attenuation device  2  described and illustrated with reference to  FIG. 2A  except that, for example, the microphone  306  may be disposed near an upper portion within the second housing  304 . In an example of the present invention, one end  301 - 1  of each of the first tubes  301  may contact an outer wall  302 - 1  of the first housing  302  at a first region (not numbered) with a first area, and one end  303 - 1  of each of the second tubes  303  may contact a second outer wall  302 - 2  of the first housing  302  at a second region (not numbered) with a second area. In one example of the present invention, the area of the first outer wall  302 - 1  may be greater than a sum of the first areas and the area of the second outer wall  302 - 2  may be greater than a sum of the second areas. In another example of the present invention, the ratio of the area of the first outer wall  302 - 1  to the sum of the first areas may range from approximately 30 to 300. Each of the first tubes  301  and the second tube  303  may be approximately 1 mm in length but may be longer or shorter. The first housing  302  and the second housing  304  may be approximately 1 mm in width but may be thinner or thicker. The volume of the chamber enclosed by the second housing  304  may be kept relatively small. The number of the first tubes  301 , the second tubes  303  or the third tubes  308  may vary to fit other applications. 
         [0032]      FIG. 3A  is a schematic diagram of a noise attenuation device  7  in accordance with an example of the present invention. Referring to  FIG. 3A , the noise attenuation device  7  may include a noise processing device  4  and a signal processing circuit  5 . The noise processing device  4 , which may be similar to the noise attenuation devices  1 ,  2  and  3  respectively described and illustrated with reference to  FIGS. 1A ,  2 A and  2 B, may include a first tube  401 , a first housing  402 , a second tube  403 , a second housing  404 , a microphone  406  and a speaker  407 . The microphone  406  may be disposed at an upper portion of the second housing  404 . The noise attenuation device  7  may operate in an environment where noise such as ambient noise may be sensitive to the microphone  406 . Noise may denote the intensity, frequency and duration of undesired sounds from a signal source or multiple sources. Furthermore, ambient noise may denote the all-encompassing noise associated with a given environment, which may be a composite of sounds from many sources near and far. The first tube  401 , the first housing  402 , the second tube  403  and the second housing  404  may function to serve as a low-pass filter to cancel or attenuate high-frequency components of noise higher than, for example, approximately 1 kHz. Furthermore, acoustic signals in the cavity B may be collected by the microphone  406  and then transmitted to the signal processing circuit  5 . The signal processing circuit  5  may also receive audio signals from an electronic product, such as a multi-media device or an audio player, by wired or wireless communication. The signal processing circuit  5  may then process the received audio signals and the acoustic signals from the microphone  406  and generate a control signal for controlling the speaker  407 . 
         [0033]    The noise attenuation device  7  may further include an air-conduction (AC) type microphone  606 , which may receive acoustic signals from a user  777 . Furthermore, the noise attenuation device  7  may include a bone-conduction (BC) type microphone  607  to receive acoustic signals from the user  777 . The received acoustic signals may then be transmitted to the signal processing circuit  5 . 
         [0034]      FIG. 3B  is a schematic block diagram of the signal processing circuit  5  illustrated in  FIG. 3A  in accordance with an example of the present invention. Referring to  FIG. 3B , the signal processing circuit  5  may include power amplifiers  51 - 1  and  51 - 2 , filters  52 - 1  and  52 - 2 , an analog/digital (A/D) converter  53 , a digital/analog (D/A) converter  54  and a signal processing module  55 . The signals from the microphone  406  may be amplified in the power amplifier  51 - 1  and then transmitted to the filter  52 - 1 . The filtered signals may then be converted in the A/D converter  53  and input to the signal processing module  55 . The signal processing module  55  may include but is not limited to a digital signal processing (DSP) module. The signal processing module  55  may include a mixer  553 , a signal generator  551  and a controller  552 . Assuming that the microphone  406  may receive a first signal, of which the high-frequency components may be filtered off by the low-pass filter structure, in response to the first signal, the controller  552  may control the signal generator  551  to generate a default signal to drive the speaker  407 . The speaker  407  may then provide a second signal, for example, an acoustic signal, which may be subsequently received by the microphone  406 . The second signal received by the microphone  406  may be transmitted to the mixer  553  after processed by the power amplifier  51 - 1 , the filter  52 - 1  and the A/D converter  53 . The mixer  553  may combine a converted second signal from the A/D converter  53  and a reference signal from the controller  552  to form a mixed signal. The controller  552  may provide a control signal based on the audio signal from the electronic product, the mixed signal from the mixer  553  and a feedback signal from the signal generator  551 . Once the control signal is determined, the controller may send another reference signal to the mixer  553 . The audio signal from the electronic product and an output signal from the signal generator  551  may be converted in the D/A converter  54 , processed in the filter  52 - 2  and amplified by the power amplifier  51 - 2  before transmitted to the speaker  407 . An amplified signal from the amplifier  51 - 2  may drive the speaker  407  to generate a third signal that may offset the noise signal in the cavity B. The operation in the circuit shown in  FIG. 3B  may be repeated till the controller  552  detects that an output of the mixer  553  may match a predetermined value, which in turn may result in an output signal from the speaker  407  that is able to cancel out the noise in the cavity B. 
         [0035]      FIG. 4A  is a plot showing experimental results of the frequency response each of noise attenuation devices with different arrangements to acoustic signals at various frequencies. Referring to  FIG. 4A , a curve  61  may represent a frequency response of a desirable noise attenuation device, wherein a first housing may have a cross-sectional area of approximately 15×5 mm 2  with a width of approximately 3 mm, and the diameter of a first tube may be approximately 1.5 mm such that the ratio of the cross-sectional area of the first housing to that of the first tube is approximately 33.3. Furthermore, the curves  62 ,  63 ,  64 , and  65  may respectively represent the frequency response in a second housing of the noise attenuation devices described and illustrated with reference to  FIGS. 1C ,  1 D,  1 E and  1 F, given the same size of the first housing and the first tube and the same area ratio. It may be found from  FIG. 4A  that the noise attenuation device illustrated in  FIG. 1F  represented by the curve  65  may have the best noise suppressing effect among the devices at the high-frequency region. 
         [0036]      FIG. 4B  is a plot showing experimental results of the frequency response each of noise attenuation devices of different sizes to acoustic signals at various frequencies. Referring to  FIG. 4B , a first curve  71  and a second curve  72  may represent a frequency response in a first noise attenuation device having a first size and a second noise attenuation device having a second size, respectively. The first and second noise attenuation devices may be similar to the noise attenuation device  1  described and illustrated with reference to  FIG. 1C . In the first noise attenuation device, the first housing may have a cross-sectional area of approximately 15×5 mm 2  with a width of approximately 3 mm, and the diameter of the first tube may be approximately 1.5 mm. In the second noise attenuation device, the first housing may have a cross-sectional area of approximately 20×15 mm 2  with a width of approximately 3 mm, and the diameter of the first tube  101  may be approximately 1.5 mm. Accordingly, the second noise attenuation device may have a greater area ratio than the first noise attenuation device. It may be found from  FIG. 4B  that the second noise attenuation device represented by the curve  72  may have better noise suppressing effect than the first noise attenuation devices because of the larger area ratio. 
         [0037]      FIG. 4C  is a plot showing experimental results of the frequency response each of noise attenuation devices with different chamber designs to acoustic signals at various frequencies. Referring to  FIG. 4C , a first curve  81  may represent a frequency response in a first noise attenuation device with a single chamber, for example, the chamber A, while a second curve  82  may represent a frequency response in a second noise attenuation device with two chambers such as the chambers A and B described and illustrated with reference to  FIG. 2A . It may be found from  FIG. 4C  that the second noise attenuation device represented by the curve  82  may have better noise suppressing effect than the first noise attenuation devices because of the addition of the second chamber B. 
         [0038]    It will be appreciated by those skilled in the art that changes could be made to the preferred embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present application as defined by the appended claims.