Abstract:
A ported electroacoustical device uses the action of the port to provide cooling airflow across a heat producing device. The device includes a loudspeaker enclosure including a first acoustic port, and an acoustic driver, mounted in the loudspeaker enclosure. The device also includes a heat producing device. The acoustic driver and the acoustic port are constructed and arranged to coact to provide a cooling, substantially unidirectional airflow across the heat producing device, thereby transferring heat from the heat producing device.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to porting and heat removal in acoustic devices, and more particularly to heat removal from ported acoustic enclosures. 
   It is an important object of the invention to provide an improved apparatus for porting. It is another object to remove undesired heat from an acoustic device. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the invention, an electroacoustical device, comprises a loudspeaker enclosure including a first acoustic port, an acoustic driver mounted in the loudspeaker enclosure; and a heat producing device. The acoustic driver and the acoustic port are constructed and arranged to coact to provide a cooling, substantially unidirectional airflow across the heat producing device, thereby transferring heat from the heat producing device. 
   In another aspect of the invention, an electroacoustical device includes an acoustic enclosure, a first acoustic port in the acoustic enclosure, an acoustic driver mounted in the acoustic enclosure for causing a first airflow in the port. The first airflow flows alternatingly inward and outward in the port. The device further includes a heat producing device. The acoustic port is constructed and arranged so that the first airflow creates a substantially unidirectional second airflow. The device also includes structure for causing the unidirectional airflow to flow across the heat producing device. 
   In another aspect of the invention, a loudspeaker enclosure having an interior and an exterior includes a first port having a first end having a cross-sectional area and a second end having a cross-sectional area, wherein the first end cross-sectional area is greater than the second end cross-sectional area. The first end abuts the interior, and the second end abuts the exterior. The enclosure also includes a second port. The first port is typically located below the second port. 
   In another aspect of the invention, a loudspeaker includes an electroacoustical transducer and a loudspeaker enclosure. The loudspeaker enclosure has a first port having an interior end and an exterior end, each having cross-sectional area. The exterior end cross-sectional area is larger than the interior end cross-sectional area. The device also includes a second port having an interior end and an exterior end. The first port is typically located above the second port. 
   In another aspect of the invention, a loudspeaker enclosure includes a first port having an interior end and an exterior end, each having a cross-sectional area. The first port interior end cross-sectional area is smaller than the first port exterior end cross-sectional area. The enclosure also includes a second port having an interior end and an exterior end, each end having a cross-sectional area. The second port interior end cross-sectional area is larger than the second port exterior end cross-sectional area. 
   In another aspect of the invention, an electroacoustical device, for operating in an ambient environment includes an acoustic enclosure, comprising a port having an exit for radiating pressure waves; an electroacoustical transducer, positioned in the acoustic enclosure, for vibrating to produce the pressure waves; a second enclosure having a first opening and a second opening; wherein the port exit is positioned near the first opening so that the pressure waves are radiated into the second enclosure through the first opening; a mounting position for a heat producing device in the first opening, positioned so that air flowing into the opening from the ambient environment flows across the mounting position. 
   In another aspect of the invention, an electroacoustical device includes a first enclosure having a port having a terminal point for an outward airflow to exit the enclosure to an ambient environment and for an inward airflow to enter the enclosure. The device also includes an electroacoustical transducer, comprising a vibratile surface for generating pressure waves resulting in the outward airflow and the inward airflow. The device also includes a second enclosure having a first opening and a second opening. The port terminal point is positioned near the first opening and oriented so that the port terminal outward flow flows toward the second opening. The port and the electroacoustical transducer coact to cause a substantially unidirectional airflow into the first opening. 
   In another aspect of the invention, an electroacoustical device, for operating in an ambient environment includes an acoustic enclosure. The enclosure includes a port having an exit for radiating pressure waves. The electroacoustical device further includes an electroacoustical transducer, positioned in the acoustic enclosure, to provide the pressure waves. The device also includes an elongated second enclosure having a first extremity and a second extremity in a direction of elongation. There is a first opening at the first extremity and a second opening at the second extremity. The port exit is positioned in the first opening so that the pressure waves are radiated into the second enclosure through the first opening toward the second opening. The device also includes a mounting position for a heat producing device in the elongated second enclosure, positioned so that air flowing into the opening from the ambient environment flows across the mounting position. 
   In still another aspect of the invention, an electroacoustical device includes a first enclosure having a port having a terminal point for an outward airflow to exit the enclosure and for an inward airflow to enter the enclosure. The device also includes an electroacoustical transducer, having a vibratile surface, mounted in the first enclosure, for generating pressure waves resulting in the outward airflow and the inward airflow. The device also includes a second enclosure having a first opening and a second opening. The port terminal point is positioned with the port terminal point in the second enclosure, oriented so that the port terminal outward flow flows toward the second opening. The port and the electroacoustical transducer coact to cause a substantially unidirectional airflow into the first opening. 
   According to an aspect of the invention, there is a loudspeaker enclosure having a loudspeaker driver and a port tube formed with a vent intermediate its ends constructed and arranged to introduce leakage resistance into the port tube that reduces the Q of at least one standing wave excited in the port tube when acoustic energy is transmitted therethrough. Venting may occur into the acoustic enclosure, into the space outside the enclosure, to a different part of the port tube, into a small volume, into a closed end resonant tube, or other suitable volume. 
   Other features, objects, and advantages will become apparent from the following detailed description, when read in connection with the accompanying drawing in which: 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is diagrammatic view of a prior art device; 
       FIG. 2  is a diagrammatic view of a device according to the invention; 
       FIGS. 3A and 3B  are views of the device of  FIG. 2 , illustrating the workings of the device; 
       FIGS. 4A-4I  are diagrammatic views of embodiments of the invention; 
       FIG. 5  is a partial blowup of a loudspeaker incorporating the invention; 
       FIGS. 6A and 6B  are a diagram of another embodiment of the invention and a cross section viewed along line B-B, respectively; 
       FIG. 7  is a diagrammatic view of an implementation of the embodiment of  FIGS. 6A and 6B . 
       FIG. 8  is a diagrammatic representation of a loudspeaker enclosure with a vented port tube according to the invention; 
       FIG. 9  shows a form of the invention with the port tube vented outside the enclosure; 
       FIG. 10  shows a form of the invention with the port tube vented to another portion of the port tube; 
       FIG. 11  shows a form of the invention with the port tube vented into a small volume; 
       FIGS. 12 and 13  show forms of the invention with the port tube vented into a closed end resonant tube; 
       FIG. 14  shows standing wave patterns in the port tube; and 
       FIG. 15  shows a form of the invention with the vent asymmetrically located and loaded by closed end tubes of different lengths. 
   

   DETAILED DESCRIPTION 
   With reference now to the drawing and more particularly to  FIG. 1 , there is shown a cross section of a prior art loudspeaker. A loudspeaker  110  includes an enclosure  112  and an acoustic driver  114 . In the enclosure  110  are two ports  116  and  118 , positioned so that one port  118  is positioned above the other. Ports  116  and  118  are flared. The upper port  118  is flared inwardly, that is, the interior end  118   i  has a larger cross-sectional area than the exterior end  118   e . The lower port is flared outwardly, that is, the exterior end  116   e  has a larger cross-sectional area than the interior end  116   i.    
   Referring now to  FIG. 2 , there is shown a cross sectional view of a loudspeaker according to the invention. Loudspeaker  10  includes an enclosure  12  and an acoustic driver  14  having a motor structure  15 . In the enclosure are two ports,  16  and  18 , positioned so that one port  16  is positioned lower in the enclosure  12  than the other port  18 . Lower port  16  is flared inwardly, that is, interior end  16   i  has a larger cross-sectional area than the exterior end  16   e . Upper port  18  is flared outwardly, that is, exterior end  18   e  has a larger cross-sectional area than the interior end  18   i . For purposes of illustration and explanation, the flares of port  16  and  18  are exaggerated. Actual dimensions of an exemplary port are presented below. In the enclosure there are heat producing elements. The heat producing elements may include the motor structure  15  of the acoustic driver, or an optional heat producing device  20 , such as a power supply or amplifier for loudspeaker  10  or for another loudspeaker, not shown, or both. Optional heat producing device  20  may be positioned lower than upper port  18  for better results. It may be advantageous to remove heat from motor structure  15 , positioning it lower than upper port  18  for better results. 
   In operation, a surface, such as cone  13 , of acoustic driver  14  is driven by motor structure  15  so that the cone  13  vibrates in the direction indicated by arrow  17 , radiating sound waves, in this case to the exterior  24  of the enclosure and the interior  22  of the enclosure. In driving the acoustic driver cone, the motor structure  15  generates heat that is introduced into enclosure interior  22 . Sound waves radiated to the interior  22  of the enclosure result in sound waves radiated out through ports  16  and  18 . In addition to the sound waves radiated out through the ports, there is a DC airflow as indicated by arrow  26 . The DC airflow is described in more detail below. The DC airflow transfers heat away from motor structure  15  and optional heat producing element  20  through upper port  18  and out of the enclosure, thereby cooling the motor structure  15  and the optional heat producing element  20 . 
   Referring to  FIGS. 3   a  and  3   b , the loudspeaker of  FIG. 2  is shown to explain the DC airflow of  FIG. 2 . As the loudspeaker  10  operates, the air pressure P i  inside the enclosure alternately increases and decreases relative to the pressure P o  of the air outside the enclosure. When the pressure P i  is greater than pressure P o , as in  FIG. 3   a , the pressure differential urges the air to flow from the interior  22  to the exterior  24  of the enclosure. When the P i  pressure is less than the pressure P o , as in  FIG. 3   b , the pressure differential urges the air to flow from the exterior  24  to the interior  22 . For a given magnitude of pressure across the port, there is more flow if the higher pressure end is the smaller end than if the higher pressure end is the larger end. When the airflow is from the interior to the exterior, as in  FIG. 3   a , there is more airflow through outwardly flaring port  18  than through inwardly flaring port  16 , and there is a net DC airflow  31  toward outwardly flaring port  18 , in the same direction as convective airflow  32 . When the airflow is from the exterior to the interior, as in  FIG. 3   b , there is more airflow through inwardly flaring port  16  than through outwardly flaring port  18 , and there is a net DC airflow  31  away from inwardly flaring port  16  toward outwardly flaring port  18 . Whether P i  pressure is less than or greater than the pressure P o , there is a net DC airflow in the same direction. Therefore, as interior pressure P i  cycles above and below P o , during normal operation of loudspeaker  10 , there is a DC airflow flowing in the same direction as the convective DC airflow  32 , and the DC airflow can be used to transfer heat from the interior of the enclosure  24  to the surrounding environment. 
   A loudspeaker according to the invention is advantageous because there is a port-induced airflow that is in the same direction as the convective airflow, increasing the cooling efficiency. 
   Empirical results indicate that thermal rise of a test setup using the configuration of  FIG. 1  was reduced by about 21% as compared to the thermal rise with no signal to the acoustic driver  114 . With the configuration of  FIG. 2 , the thermal rise was reduced by about 75% as compared to the thermal rise with no signal to acoustic driver  14 . 
   Referring to  FIGS. 4A-4I , several embodiments of the invention are shown. In  FIG. 4A , lower port  16  is a straight walled port, and the upper port is flared outwardly. In  FIG. 4B , upper port  18  is a straight walled port, and the lower port is flared inwardly. The embodiments of  FIGS. 4A and 4B  have an airflow similar to the airflow of the embodiment of  FIGS. 2 and 3 , but the airflow is not as pronounced. In  FIG. 4C , it is shown that the ports  16  and  18  can be on different sides of the enclosure  12 ; if the enclosure has curved sides, the ports  16  and  18  can be at any point on the curve.  FIG. 4D  is a front view, showing that acoustic driver  14  and the two ports  16  and  18  may be non-collinear. The position of the acoustic driver  14  and alternate locations shown in dashed lines, and the position of ports  16  and  18  and alternate locations shown in dashed lines show that the acoustic driver  14  need not be equidistant from ports  16  and  18  and that the acoustic driver need not be vertically centered between ports  16  and  18 . In the embodiment of  FIG. 4E , the outwardly flaring upper port  18  is in the upper surface, facing upward, and the inwardly flaring lower port  16  is in the lower surface. If the lower port  16  is in the lower surface as in  FIG. 4E , the enclosure would typically have legs or some other spacing structure to space lower port  16  from surface  28  on which loudspeaker  10  rests.  FIG. 4F  shows that the port walls need not diverge linearly, and that the walls, in cross section, need not be straight lines. The embodiment of  FIG. 4G  shows that the divergence need not be monotonic, but can be flared both inwardly and outwardly, so long as the cross sectional area at the exterior end  18   e  of the upper port  18  is larger than the cross sectional area at the interior end  18   i , or so long as the cross sectional area at the exterior end  16   e  of the lower port  16  is smaller than the cross sectional area at the interior end  16   i , or both. Flaring a port in both directions may have acoustic advantages over straight walled ports or ports flared monotonically. In  FIGS. 4H and 4I , the invention is incorporated in loudspeakers with more complex port and chamber structures, and with an acoustic driver that does not radiate directly to the exterior environment. Third port  117  of  FIG. 5  is used for acoustic purposes. The operation of the embodiments of  FIGS. 4H and 4I  causes interior pressure P i  to cycle above and below exterior pressure P o , resulting in a net DC airflow as in the other embodiments, even though acoustic driver  14  does not radiate sound waves directly to the exterior of the enclosure. Aspects of the embodiments of  FIGS. 4A-4I  can be combined.  FIGS. 4A-4I  illustrate some of the many ways in which the invention may be implemented, not to show all the possible embodiments of the invention. In all the embodiments of  FIGS. 4A-4I , there are an upper port and a lower port, and either the upper port has a net outward flare, or the lower port has a net inward flare, or both. 
   Referring now to  FIG. 5 , there is shown a partially transparent view of a loudspeaker incorporating the invention. The cover  30  of the unit is removed to show internal detail of the loudspeaker. The embodiment of  FIG. 5  is in the form of  FIG. 4I . The reference numerals identify the elements of  FIG. 5  that correspond to the like-numbered elements of  FIG. 4I . Acoustic driver  14  (not shown in this view) is mounted in cavity  32 . Openings  19  help reduce standing waves in the port tube as described below. The variations in the cross sectional areas of ports  16  and  18  are accomplished by varying the dimensions in the x, y, and z directions. Appendix 1 shows exemplary dimensions of the two ports  16  and  18  of the loudspeaker of  FIG. 5 . 
   Referring to  FIGS. 6A and 6B , there are shown two diagrammatic views of another embodiment of the invention. In  FIG. 6A , ported loudspeaker  10  has a port  40  that has a port exit  35  inside airflow passage  38 . In one configuration port  40  and airflow passage  38  are both pipe-like structures with one dimension long relative to the other dimensions, and with openings at the two lengthwise ends; port exit  35  has a cross-sectional area A s  smaller than the cross-sectional area A of the airflow passage  38 ; and port exit  35  is positioned in the airflow passage so that the longitudinal axes are parallel or coincident. Some considerations for the shape, dimensions, and placement of port  40 , port exit  35 , and airflow passage  38  are presented below. Positioned inside airflow passage  38  is heat producing device  20  or  20 ′, shown at two locations. In an actual implementation, the heat producing device or devices can be placed at many other locations in airflow passage  38 . 
   When acoustic driver  14  operates, it induces an airflow in and out of the port  40 . When the airflow induced by the operation of the acoustic driver is in the direction  36  out of the port  40 , as shown in  FIG. 6A , the port and airflow passage act as a jet pump, which causes airflow in the airflow passage  38  in the same direction as the airflow out of the port, in this example in airflow passage opening  42 , through the airflow passage in direction  45  and out airflow passage opening  44 . Jet pumps are described generally in documents such as at the internet location 
   http://www.mas.ncl.ac.uk/˜sbrooks/book/nish.mit.edu/2006/Textbook/Nodes/chap05/node16.html a printout of which is attached hereto as Appendix 2. 
   Referring to  FIG. 6B , when the acoustic driver induced airflow is in the direction  37  into port  40 , there is no jet pump effect. The airflow into the port  40  comes from all directions, including inwardly through airflow passage opening  42 . Since the airflow comes from all directions, there is little net airflow within the airflow passage. 
   To summarize, when the acoustic driver induced airflow is in direction  36 , there is a jet pump effect that causes an airflow in airflow passage opening  42  and out passage opening  44 . When the acoustic driver induced airflow is in the direction  37 , there is little net airflow in airflow passage  38 . The net result of the operation of the acoustic driver is a net DC airflow in direction  45 . The net DC airflow can be used to transfer heat away from heat producing elements, such as devices  20  and  20 ′, that are placed in the airflow path. 
   There are several considerations that are desirable to consider in determining the dimensions, shape, and positioning of port  40  and airflow passage  38 . The combined acoustic effect of port  40  and passage  38  is preferably in accordance with desired acoustic properties. It may be desirable to arrange port  40  to have the desired acoustic property and airflow passage  38  to have significantly less acoustic effect while maintaining the momentum of the airflow in desired direction  45  and to deter momentum in directions transverse to the desired direction. To this end port  40  may be relatively elongated and with a straight axis of elongation parallel to the desired momentum direction. It may be desirable to structure airflow passage  38  to increase the proportion of the airflow is laminar and decrease the proportion of the airflow that is turbulent while providing a desired amount of airflow. 
   Referring to  FIG. 7 , there is shown a mechanical schematic drawing of an actual test implementation of the embodiment of  FIGS. 6A and 6B , the elements numbered similarly to the corresponding elements of  FIGS. 6A and 6B . In the test implementation device the airflow passage  38  and the heat producing device were both parts of a unitary structure. A resistor was placed in thermal contact with at heat sink in a tubular form with appropriate dimensions so it could function as the airflow passage  38 . With current flowing through the resistor and with acoustic driver  14  not operating, the temperature in the vicinity of the heatsink rose 47° C. With the acoustic driver operating at ⅛ power, the temperature in the vicinity of the heatsink rose 39° C. With the acoustic driver operating at ⅓ power radiating pink noise, the temperature in the vicinity of the heatsink rose 25° C. Additionally, the thermal effect of the device at other points in the loudspeaker enclosure was measured. For example, at area  55 , convection heating caused the temperature to rise 30.5° C. with current flowing through the resistor and with acoustic driver  14  not operating. With the acoustic driver operating at ⅓ power, the temperature in the vicinity of the heatsink rose 30.5° C. With the acoustic driver operating at ⅛ power radiating pink noise, the temperature in the vicinity of the heatsink rose 30.5° C. With the acoustic driver operating at ⅓ power radiating pink noise, the temperature in the vicinity of the heatsink rose 21° C. This indicates that if the acoustic driver operates at high enough power, thereby moving more air than when it operates at lower power, the airflow resulting from a loudspeaker according to the invention transfers heat from areas near, but not directly in, the airflow. 
   Referring to  FIG. 8 , there is shown a diagrammatic representation of a loudspeaker enclosure  61  having a driver  62  and a port tube  63  formed with a vent  64  typically located at a point along the length of port tube  63  corresponding to the pressure maximum of the dominant standing wave established in port tube  63  when driver  62  is excited to reduce audible port noise. Acoustic damping material  90 , for example, polyester or cloth, may be positioned in or near vent  64 . 
   This aspect of the invention reduces the objectionability of port noise caused by self resonances. For example, consider the case of increased noise at the frequency for which one-half wavelength is equal to the port length. In this example of self resonance, the standing waves in the port tube generate the highest pressure midway between the ends of port tube  63 . By establishing a small resistive leak near this point with vent  64  in the side of the tube, the Q of the resonance is significantly diminished to significantly reduce the objectionability of port noise at this frequency. The acoustic damping material  90  may further reduce the Q of high frequency resonances. 
   The leak can occur through vent  64  into the acoustic enclosure as shown in  FIG. 8 . Alternatively, the leak can leak into the space outside enclosure  61  through vent  64 ′ of port tube  63 ′ as shown in  FIG. 9 . The port tube  63 ″ could leak through vent  64 ″ to a different part of port tube  63 ″ as shown in  FIG. 10 . Port tube  63 ′″ could leak through vent  64 ′″ into a small volume  65  as shown in  FIG. 11 . The port tube  63 ″″ could leak through vent  64 ″″ into a closed end resonant tube  65 ′. In the embodiments of  FIGS. 9-12 , there may be positioned near the vent  64 ′- 64 ″″ acoustic damping material  90 . 
   An advantage of the embodiments of  FIGS. 11 and 12  is that the disclosed structure may have insignificant impact on the low frequency output. The acoustic damping material  90  may further reduce the Q of high frequency resonances. 
   The structures shown in  FIGS. 9-12  reduce the Q of the self resonance corresponding to the half-wave resonance of the port tube. The principles of the invention may be applied to reducing the Q at other frequencies corresponding to the wavelength resonance, 3/2 wavelength resonance and other resonances. To reduce the Q at these different resonances, it may be desirable to establish vents at points other than midway between the ends of the port tubes. For example, consider the wavelength resonance where pressure peaks at a quarter of the tube length from each end. A vent at these locations is more effective at diminishing the Q of the wavelength resonance than a vent at the midpoint of the tube. Vents at these points and other points may furnish leakage flow to the same small volume for the midpoint vent. Alternatively, each may have dedicated closed end resonant tubes. Still alternatively, they may allow leakage to the inside or outside of the enclosure. To reduce the audible output at a variety of resonances, a multiplicity of vents may be used, including a slot, which can be considered as a series of contiguous vents. 
   There are numerous combinations of venting structures, structures defining volumes for venting, including resonant closed end tubes. 
   Referring to  FIG. 13 , there is shown a schematic representation of an embodiment of the invention for reducing Q of the half-wave resonance of a port tube  73  of length A 1  in enclosure  71  having driver  72  using tube  75  with a closed end of length 0.3 A 1  having its open end at vent  74 .  FIG. 14  shows the standing wave for the half-wave resonance along the length of tube  73 , (in the absence of resonant tube  75 ), showing the pressure distribution  76  and volume velocity distribution  77 . The pressure is at a maximum at point  74 . Energy from the standing wave in the port tube  73  is removed from the port tube at maximum pressure point  74 . The energy may be dissipated by damping material  90  in the resonant tube, significantly reducing the Q of the half-wave resonance. 
   In the resonant tube  75  may be acoustic damping material. The acoustic damping material may fill only a small portion of the resonant tube  75  as indicated by acoustic damping material  90 , or may substantially fill resonant tube as indicated in dotted line by acoustic damping material  90 ′. The acoustic damping material  90  or  90 ′ reduces the Q of high frequency multiples of the half-wave resonant frequency. 
   Referring to  FIG. 15 , there is shown a diagrammatic representation of a port tube  83  with a vent  84  six-tenths of the port tube length s from the left end and four-tenths of the port tube length from the right end terminated in a closed end resonant tube  85  of length 0.5 the length of port tube  83  and diameter d 1  of 3″ and another closed end tube  85 ′ of length 0.25 that of port tube  83  and diameter d 2  of 1.5″. In one or both of closed end resonant tube  85  and closed end resonant tube  85 ′ may be acoustic damping material  90 . As with the embodiment of  FIG. 13 , the acoustic damping material may fill a portion of one or both of closed end resonant tubes  85 ,  85 ′, or may substantially fill one or both of close end resonant tubes  85 ,  85 ′. 
   It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific apparatus and techniques disclosed herein without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques disclosed herein and limited only by the spirit and scope of the appended claims.