Abstract:
An apparatus for reducing noise emitted by an electronic or other device and such devices incorporating the noise reducing apparatus. A mechanism for acoustically filtering undesired noise from an electronic device, particularly noise generated by a cooling mechanism is disclosed. In a preferred embodiment, noise is filtered at least in part with an appropriately dimensioned compressible air space. The noise reducing or filtering mechanism may be utilized with portable and non-portable computers, stereos, entertainment equipment and other devices.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to noise suppression or filtering in an electronic device. While applicable to all electronic devices, the present invention is particularly applicable to portable electronic devices because of their size and physical feature constraints.  
         BACKGROUND OF THE INVENTION  
         [0002]    There has been a continual effort to develop new features and improve existing features performed by electronic devices. The features may include, but are not limited to, communication, document production, information storage and retrieval, navigation, entertainment, etc. This effort has been at least in part promoted by advances in integrated circuit technology that have produced more powerful processing circuitry. As the complexity of integrated circuits increased, however, the need to adequately cool these devices also increased. While various approaches have been brought forth, cooling by electric fan is the most common technique for integrated circuit and overall electronic device cooling.  
           [0003]    While beneficial as a cooling mechanism, conventional fans are disadvantageous in that they produce audible noise at frequencies that are unpleasant to the human ear. While a problem in desk top environments, such as in a desk top computer, the problem is more acute in portable electronic devices. One reason for this is that components are more tightly coupled in a portable device leading to thermal build up. In addition, due to their limited size and weight it is generally more difficult to design new features (such as noise suppression) into a portable device.  
           [0004]    Hence a need exists for suppressing or reducing noise generated by the cooling mechanism of an electronic device.  
         SUMMARY OF THE INVENTION  
         [0005]    Accordingly, it is an object of the present invention to reduce or filter noise generated by a cooling mechanism of an electronic device.  
           [0006]    It is another object of the present invention to reduce or filter noise generated by a cooling mechanism of a portable electronic device.  
           [0007]    It is another object of the present invention to provide noise reduction that filters out frequencies that are unpleasant to a human ear.  
           [0008]    It is also an object of the present invention to create a mechanism or structure in a cooling mechanism output path that absorbs, compresses or otherwise attenuates sound waves of particular frequencies.  
           [0009]    These and related objects of the present invention are achieved by use of a acoustic filter apparatus of an electronic device as described herein.  
           [0010]    The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of an electronic device having noise suppression in accordance with the present invention.  
         [0012]    [0012]FIG. 2 is a partial perspective view of an electronic device cooling system in accordance with the present invention.  
         [0013]    [0013]FIG. 3 is a graph of sound power level (SPL) versus frequency.  
         [0014]    [0014]FIG. 4 is a side view of the cooling system and other componentry of FIG. 2 in accordance with the present invention.  
         [0015]    [0015]FIG. 5 is an equivalence acoustic circuit diagram for the configuration of FIGS. 2 and 4 in accordance with the present invention.  
         [0016]    [0016]FIG. 6 is a diagram illustrating the parameters M A  and C A  for the embodiment of FIGS. 2 and 4 in accordance with the present invention.  
         [0017]    [0017]FIG. 7A is a perspective view of an alternative embodiment of a cooling system noise suppression mechanism in accordance with the present invention.  
         [0018]    [0018]FIG. 7B illustrates a perspective cross-sectional view of the compressible air chamber of FIG. 7A in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring to FIG. 1, a perspective view of an electronic device having noise suppression in accordance with the present invention is shown. As illustrated in FIG. 1, the electronic device is a portable computer, such as a notebook computer. This embodiment, however, is a representative embodiment and it should be recognized that the present invention is applicable to any electronic device, including audio receivers, amplifier units, etc., in which it is desired to reduce noise.  
         [0020]    Electronic device  10  preferably includes a display  12  and may include speakers  14  or other output devices including, but not limited to, an information panel or the like (with or without light emitting diodes, etc.) for an audio receiver or related devices. Electronic device  10  also preferably includes a keypad  16  and a pointing mechanism  18  (e.g., a touch pad, track ball, mouse, joy stick, etc., for a computer implementation) or other input devices. Processing circuitry  22  and memory  24  are shown in phantom lines as is cooling system  30  which is discussed in more detailed below. The exhaust of cooling mechanism  30  exits the electronic device through exhaust openings  51 .  
         [0021]    Referring to FIG. 2, a partial perspective view of an electronic device cooling system in accordance with the present invention is shown. Cooling system  30  preferably includes a cooling mechanism  32  and a noise suppression mechanism or structure  40  (hereinafter referred to as open “noise reduction mechanism  40 ”) that suppresses or reduces noise created by the cooling mechanism preferably by acoustic filtering. In a preferred embodiment, the cooling mechanism is an electric fan of the type known in the art for cooling electronic devices and components therein. As such, cooling mechanism  32  is also referred to herein as fan  32  (though the cooling mechanism may be other than a fan without deviating from the present invention).  
         [0022]    Fan  32  is preferably coupled to a heat sink  34 . A circuit board  25  with a heat producing integrated circuit such as processing circuitry  22  is positioned proximate heat sink  34 . Arrow A indicates that the circuit board and processing logic are preferably positioned underneath the heat sink (from the perspective of FIG. 2). Heat sink  34  is preferably formed of an inexpensive, lightweight material that has good thermal conductive properties. Die cast aluminum is an example of such a material.  
         [0023]    Fan  32  has an input  31  and a plurality of output openings  33  which are coupled via ducts to exhaust openings  51 . The ducts  36  are preferably separated by dividers  38  and their top surface (not shown in FIG. 2) may be provided by the housing of electronic device  10  as shown in FIG. 4. While dividers and a plurality of openings  51  are shown, it should be recognized that a singular duct and opening  51  or other arrangements could be provided.  
         [0024]    An attenuation orifice  41  is provided in each duct for the purpose of connecting the duct to a compressible air chamber or volume  45  (shown in FIGS. 4 and 6). The arrangement of the attenuation orifice and compressible air chamber serves to dissipate or attenuate noise at undesirable frequencies. Suitable dimensions for the ducts and the compressible air chamber to achieve a desired noise suppression are discussed below.  
         [0025]    Referring to FIG. 3, a graph of sound power level (SPL) versus frequency is shown. Studies of the human ear have shown that the range of human hearing is approximately from 20 Hz to 18 KHz. Studies have further shown that humans are less sensitive to frequencies from 20 to 350 Hz than from 350 Hz to 18 KHz. Thus, if a low pass acoustic filter can be established for the fan or other cooling mechanism of an electronic device, than that device will produce significantly less objectionable noise.  
         [0026]    Equations related to designing for noise suppression include the following. Equation no. 1 indicates that the cutoff frequency of such a low pass filter is inversely proportional to the square root of M A  times C A , where M A  is the acoustic mass and C A  is the acoustic compliance as defined by Leo L. Beranek in his book entitled “Acoustics” published by the Acoustic Society of America (1954,1993). The American Institute of Physics has accepted Beranek&#39;s work as a standard in the acoustics field. Equation no. 1 provides:  
           f   0 =1/( 90  ( M   A   C   A ) ½ )  Eq. 1  
         [0027]    where  
           M   A =(ρ 0 1)/(π a   2 );  Eq. 2  
           C   A   =V/ (ρ 0   C   2 );  Eq. 3  
         [0028]    and  
         1=1′+2(0.85 a ).  Eq. 4  
         [0029]    In these equations, ρ 0  and C are physical constants having the following values:  
         ρ 0 =1.18 Kg/m3 (density of air);  Eq. 5  
         [0030]    and  
           C= 345,000 mm/s (speed of sound).  Eq. 6  
         [0031]    The design parameters of cooling system  30  (i.e. for noise suppression mechanism  40 ) include  1 ′=length of the exhaust ducts, 1=effective length of duct corrected for air loading of flanged opening, a=equivalent radius of the exhaust ducts (a cross-sectional area indicator) and V=volume of the compressible air chamber.  
         [0032]    Combining equations 1-6 provides that the cutoff frequency, f 0 , is equal to  
         194645 ( a /(1′ V ) ½ .  Eq. 7  
         [0033]    Assuming that the four ducts  36  of the embodiment of FIGS. 2 and 4 have a cross-sectional area of 100 mm 2 , then the equivalent radius for this area if it were circular is r=(π.100) ½  or 5.6 mm. The length of the ducts may be established at 25 mm, thus causing  1 ′ to have a value of 25 mm. If the desired cutoff frequency is set at 316 Hz (e.g., below a 350 Hz limit), then substituting the values of a and  1 ′ into Eq. 6 provides a compressible air chamber volume of 4×10 5  mm. This volume may be achieved, for example, in a chamber that is 10 mm×200 mm×200 mm and a great number of other configurations, including those that are not uniformly dimensioned. Implementation of such a volume in the cooling system discussed with reference to FIG. 2 is now presented.  
         [0034]    Referring to FIG. 4, a side view of the cooling system and other componentry of FIG. 2 in accordance with the present invention is shown. Fan  32  is provided on or proximate a heat sink  34  and processing circuitry  22  is coupled by a thermal joiner  42  to heat sink  34 . Thermal joiner  42  is provided for efficient conduction of heat away from processing circuitry  22  to the heat sink. A plurality of inlet openings  54  are provided in housing cover  53  (not shown in FIG. 2) that is coupled to or formed integrally with the remainder of the housing  52 . One of the attenuation orifices  41  is shown connecting a duct  36  to the compressible air chamber or volume  45 . Volume  45  may have the dimensions of 10 mm in height, 200 mm in width and 200 mm in depth (into the page) to achieve a cutoff frequency (in combination with the duct length and cross-sectional area discussed above) of 316 Hz.  
         [0035]    While volume  45  of FIG. 4 has generally uniform dimensions, it should be recognized that these uniform dimensions are provided in part because they permit easier mathematical analysis than non-uniform dimensions. Nonetheless, the present invention may be implemented with curved, round, punctuated and other non-uniform shapes. Furthermore, the volume may be established from otherwise unused air space in the electronic device. As such it is possible that the volume may contain components including other circuitry therein. Accordingly, a representative circuit board  61  with a component  62  provided thereon is shown in FIG. 4. It should be recognized that while the equations provided herein are helpful in cooling system design (particularly from a mathematical or theoretical perspective), the ultimate selection of component layout and dimensions is preferably established empirically.  
         [0036]    Referring to FIG. 5, an equivalence acoustic circuit diagram for the configuration of FIGS. 2 and 4 in accordance with the present invention is shown. The term C A  refers to the compressible air space while the M A  terms refers to the duct sections before and after the attenuation orifice(s). This equivalence circuit and others like it can be implemented such that the compressible air chamber is accessed by penetrating the heat sink (as shown in FIG. 4) or such that the compressible air chamber is coupled to the output duct(s) other than through the heat sink, i.e., coupled to the top of the duct(s) or provided around the duct(s) as in FIG. 7 below.  
         [0037]    Referring to FIG. 6, a diagram illustrating the parameters M A  and C A  in accordance with the present invention is shown.  
         [0038]    Referring to FIG. 7A, a perspective view of an alternative embodiment of a cooling system noise suppression mechanism in accordance with the present invention is shown. FIG. 7A illustrates one wall of an electronic device housing  152  having a cooling system coupled thereto. Illustrated components include a fan or other cooling mechanism  132 , a heat sink  134  and processing logic  122 . Processing logic  122 , heat sink  134  and fan  132  function in substantially the same manner as components  22 ,  34  and  32  discussed above. In the cooling system of FIG. 7A, however, the compressible air chamber  145  is configured as a hollow disk or the like that is placed around the fan exhaust duct. Attenuation orifice(s)  141  preferably couples duct  136  to the interior of chamber  145 .  
         [0039]    [0039]FIG. 7B illustrates a perspective cross-sectional view of compressible air chamber  145  in accordance with the present invention.  
         [0040]    While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.