Abstract:
A speaker comprises a diaphragm, a drive assembly for producing movement of said diaphragm responsive to an applied electrical signal to generate audible sounds, and at least one mechanical dampener applied to a surface of the speaker to dissipate energy when the dampener is impacted by said diaphragm.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to speakers and, more particularly, to a dampening mechanism for a speaker with small dimensions suitable for use in portable electronic devices. 
         [0002]    Advances in communication and manufacturing technologies have resulted in mobile devices, such as mobile telephones and personal digital assistants, becoming increasingly smaller in size. One consequence of these size reductions is that less space is available for speakers and other components. While consumers prefer mobile devices with small form factors, consumers still expect high quality audio output from their mobile devices. Therefore, there is great interest among manufacturers in finding ways to reduce the size of speakers while maintaining high quality audio output. 
         [0003]    In speakers with a movable diaphragm, the diaphragm needs space to move back and forth. As speakers become smaller, designers must be concerned that the diaphragm will contact the housing or other elements within the speaker at the outer limits of the diaphragm excursion. Contact between the diaphragm and other components in the speaker produces sound distortions which affect the perceived quality of the sound. To avoid this problem, designers often limit the signal level to limit the excursion of the diaphragm. This solution is undesirable because the excursion problem may occur only in a limited band near the resonance frequency of the diaphragm. 
       SUMMARY 
       [0004]    The present invention relates to a speaker for portable electronic devices, such as cellular telephones, personal digital assistants (PDAs), and audio players. The speaker comprises a diaphragm and a drive assembly to vibrate the diaphragm responsive to an applied electrical signal to produce audible sounds. A mechanical dampener is disposed adjacent to the diaphragm. The mechanical dampener limits the movement of the diaphragm and dampens the impact of the diaphragm to minimize sound distortion. The mechanical dampener may be applied to one or more surfaces of the speaker that are likely to be impacted by the diaphragm. 
         [0005]    The mechanical dampener allows the speaker to be operated at a high gain over the entire usable frequency band. For frequencies near the resonance of the diaphragm, where the excursion of the diaphragm is greatest, the diaphragm may contact the mechanical dampener. In this case, the mechanical dampener softens the effect of the impact to minimize sound distortion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a cross sectional view of a speaker according to one exemplary embodiment of the invention. 
           [0007]      FIG. 2  illustrates an exemplary mobile electronic device including a speaker as shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Referring now to the drawings,  FIG. 1  illustrates the main elements of a speaker  10  according to one exemplary embodiment of the invention. Speaker  10  comprises a housing  12 , a diaphragm  22  that vibrates to produce audible sounds, a suspension member  24  to flexibly suspend the diaphragm  22  within the housing  12 , and an electromagnetic drive assembly  26  to produce vibrations of the diaphragm  22  responsive to an applied electrical signal. The electromagnetic drive assembly  26  comprises an electromagnetic coil  28  and magnet  30 . The electromagnetic coil  28  connects to the diaphragm  22  and is disposed within a magnetic field generated by the magnet  30 . Sound is produced by varying the direction of the current flowing through the electromagnetic coil  28 . These current variations cause the electromagnetic coil  28  and diaphragm  22  to move back and forth to generate audible sounds. 
         [0009]    The housing  12  of the speaker  10  comprises a frame  14  and a front plate  16 . In the exemplary embodiment, the housing  12  encloses the diaphragm  22  and the electromagnetic drive assembly  26 . The frame  14  includes a back wall  14   a  and a side wall  14   b . The front plate  16  covers and protects the diaphragm  22 . 
         [0010]    The magnet  30  mounts to the back wall  14   a  at the approximate center of the frame  14 . The suspension member  24  comprises an elastic ring that is secured at its outer edge to a shoulder formed in the side wall  14   b  of the frame  14 . A spider  34  connects at one end to the frame  14  and at the opposite end to the electromagnetic coil  28 . The function of the spider  34  is to provide a restoring force to the diaphragm  22  after the diaphragm  22  is move by the electromagnetic coil  28 . 
         [0011]    The front plate  16  may include one or more openings  18  to allow air to enter into and exit from the housing  12  on the front side of the diaphragm  22  as the diaphragm  22  moves back and forth. An opening  20  may also be formed in the back wall  14   a  of the frame  14  to allow air to enter into and exit from the housing  12  on the back side of the diaphragm  22 . In the exemplary embodiment shown, the opening  20  aligns with a central opening  32  in the magnet  30 . Air on the back side of the diaphragm  22  enters and exits the housing  12  on the back side of the diaphragm  22  though the central opening  32  in the magnet  30 . 
         [0012]    The speaker  10  illustrated in  FIG. 1  may be used in cellular telephones, personal digital assistants, audio playback devices, and other small electronic devices. The magnet  30  is large relative to the size of the entire speaker assembly, and the coil  28  is disposed at the outer edge of the diaphragm  22 . This design accommodates a larger diaphragm  22  and stronger magnet  30 . The larger diaphragm  22  provides a larger vibrating surface area and therefore greater sensitivity. The stiffness of the diaphragm  22  may be increased to reduce the possibility of unstable vibration modes that could reduce the efficiency and increase the distortion level of the speaker  10 . Using a stiff diaphragm  22  also reduces the travel distance of the diaphragm  22 . 
         [0013]    For use in small electronic devices, it is generally desirable to make the speaker  10  as small as possible. For example, in order to provide a thin profile speaker, the depth of the speaker cavity is typically made as small as possible. Reducing the depth of the speaker cavity may lead to problems when the speaker  10  is operated at maximum sound pressure level. The diaphragm  22  needs space to move back and forth. When this space is small, the diaphragm  22  may come into contact the top of the magnet  30  or the front plate  16  at the outer limits of its excursion. This problem typically occurs in frequency bands near the resonance frequency of the diaphragm  22 . Contact between the diaphragm  22  and these other components may produce a perceptible distortion in the sound. 
         [0014]    According to one exemplary embodiment of the invention, dampeners  40 ,  42  may be applied to the top of the magnet  30  and to the inner surface of the front plate  16  to cushion the impact of the diaphragm  22  against the magnet  30  and front plate  16 . The thickness, density, porosity, and hardness of the dampeners  40 ,  42  may be chosen for a preferred trade-off between total component thickness, transducer sensitivity, and sound quality. One material suitable for use as a dampener with the present invention comprises a microcellular urethane foam material such as PORON®. The dampeners  40 ,  42  may be formed in sheets that are applied to the inside of the front plate  16  and the top of the magnet  30 . The dampeners  40 ,  42  may be secured by a suitable adhesive. 
         [0015]    Dampeners  40 ,  42  allow the speaker  10  to be operated at a high gain over the entire usable frequency band. For frequencies near the resonance of the diaphragm  22 , where the excursion of the diaphragm  22  is greatest, the diaphragm  22  may contact the dampeners  40 ,  42  on the front plate  16  and/or magnet  30 . The dampeners  40 ,  42 , in effect, act like shock absorbers to dampen the impact of the diaphragm  22  when the dampener  40 ,  42  is contacted by the diaphragm  22  and to reduce the amount of sound distortion. 
         [0016]    In one embodiment of the invention, the dampener  42  on the front plate  16  may be provided with apertures  44  that align with the sound apertures  18  in the front plate  16  to allow the passage of air as the diaphragm  22  moves back and forth. The dampening material  40  applied to the top of the magnet  30  may cover or partially cover the exit opening in the center of the magnet  30  to restrict the air flow into and out of the housing  12 . Restricting the air flow provides a mechanism for tuning the speaker assembly. 
         [0017]    The speaker  10  may be made with a thin profile, making it suitable for use in cellular telephones, personal digital assistants, laptop computer, and other portable and hand-held electronic devices.  FIG. 2  illustrates an exemplary mobile electronic device  100  in which the speaker  10  may be used. The mobile electronic device  100  comprises a main control unit  102 , memory  104 , communication interface  106 , and user interface  108 . The main control unit  102  may comprise one or more processors to control overall operation of the mobile electronic device  100 . Memory  104  stores programs and data needed for operation. Communication interface  106  enables the mobile electronic device  100  to communicate with external devices. The communications interface  106  may comprise for example, a cellular transceiver (e.g., GSM, WCDMA, etc.), wireless LAN (e.g., WiFi, WiMAX, etc.) interface, BLUETOOTH interface, other type of wireless interface. The user interface  108  comprises a display  110 , one or more user input device  112 , a microphone  114 , and speaker  116 . The display  110  displays information or viewing by a user. The user input devices  112 , such as a keypad, touch pad, joystick, etc., enable the user to input data and commands to control the mobile electronic device  100 . The microphone  114  converts audible sounds into electrical signals for input top the main control unit  102 . The speaker  116  converts electrical signals into audible sounds that may be heard by the user. Those skilled in the art will appreciate that the speaker  116  may comprise a speaker  10  as shown in  FIG. 1 . 
         [0018]    The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.