Abstract:
A vented tweeter with a low profile particularly suited for automotive applications where the mounting depth is limited. The tweeter comprises a motor with a central air passage extending through it and a lateral air chamber formed around it. Radial channels on the top of the motor connect the air gap in the motor with the central air passage, and radial channels under the motor connect the central air passage with the lateral air chamber. As the diaphragm oscillates, air can move back and forth between the air gap around the magnet and lateral space outside the motor. This configuration substantially increases the volume of air that can be acted on by the diaphragm without significantly increasing the length of the assembled tweeter or compromising the power of the motor. To enhance the power of the motor, a secondary magnet can be included above the top plate.

Description:
FIELD OF THE INVENTION 
   The present invention relates to speaker assemblies generally and, in particular, to tweeters. 
   BACKGROUND OF THE INVENTION 
   In the field of automotive sound systems, there is a continuing effort to improve the low range performance of high frequency speakers, or tweeters. Generally, the quality of low range sound in tweeters is enhanced by increasing the air space behind the diaphragm. This can be done by providing an air chamber at the rear of the housing, which extends the length or depth of the speaker. However, this is not a viable design option for tweeters in automotive sound systems because tweeters usually are installed in door panels and dashboards where the available mounting depth is limited. 
   The present invention provides a design for an automotive tweeter that offers a low profile in combination with improved low range characteristics. This is accomplished by providing an air chamber that is lateral to the motor instead of behind it. 
   SUMMARY OF THE INVENTION 
   The present invention comprises a tweeter comprising a housing formed of a rear wall and a sidewall, the sidewall extending forwardly from the rear wall and terminating in an open front end. The rear wall and sidewall form a motor receiving space in the housing. A motor is mounted in the motor receiving space of the housing. The motor comprises a permanent magnet assembly and an annular gap extending around the permanent magnet assembly. The motor is characterized by an air passage extending through it. A diaphragm is movably supported over the open end of the housing and forms a forward air chamber between the motor and the diaphragm. The forward air chamber is continuous with the air passage through the motor and the annular gap around the magnet assembly. A voice coil assembly is movably supported in the annular gap in the motor and operatively engaged with the diaphragm. The voice coil assembly, the motor and the diaphragm are cooperatively adapted to reproduce high frequency sounds. 
   The tweeter further comprises an air chamber lateral to the motor between the motor and the sidewall of the housing. The lateral air chamber is in communication with the air passage through the motor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side perspective sectional view of a fully assembled tweeter constructed in accordance with the present invention. The voice coil and leads have been omitted to simplify the illustration. 
       FIG. 2  is an exploded side elevational view of the tweeter in  FIG. 1  with a coaxial mounting cup. 
       FIG. 3  is an exploded side elevational view showing the tweeter of  FIG. 1  with a flush mounting cup. 
       FIG. 4  is an enlarged side sectional view of the tweeter of  FIG. 1  with the mounting flange and grill removed to better illustrate the lateral venting system. 
       FIG. 5  is a frontal perspective view of the housing of the tweeter. 
       FIG. 6  is a frontal perspective view of the motor with the second permanent magnet removed and top plate positioned over the first or primary permanent magnet. 
       FIG. 7  is a frontal perspective view of the motor showing the second permanent magnet atop the top plate and the radial air channels on the frontal surface of the second magnet. 
       FIG. 8  is a rear perspective view of the back panel of the yoke of the motor showing the radial air channels thereon. 
       FIG. 9  is a frontal perspective view of the motor assembly in the housing with a damper or plug adhered to the top of the second magnet. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference now to the drawings generally and to  FIG. 1  in particular, there is shown therein a tweeter constructed in accordance with a preferred embodiment of the present invention and designated generally by the reference numeral  10 . The external components of the tweeter include a housing  12 , which receives the internal working components. The housing  12  comprises a body  14  formed by a closed rear wall  16  and a sidewall  18  extending forwardly of the rear wall. As used herein, “forward” and “frontal” refer to the end of the tweeter in which the sound is emitted, and “rearward” and “back” refer to the end of the tweeter opposite the forward or front end. The sidewall  18  terminates in an open front end  20 . The rear wall  16  is closed except for small openings  22  for the electrical leads (not shown in  FIG. 1 ). 
   The body  14  of the housing  12  preferably is formed into two sections, a first body portion  24  forming the forward end of the tweeter  10  and a second body portion  26  forming the rearward end of the tweeter  10 . The first body portion  24  has a generally cylindrical shape with external threads  28 . The second body portion  26  also preferably is generally cylindrical with external threads  30 . In this embodiment, the second body portion  24  is connected to the first body portion by a rearwardly tapering frusto-conically shaped connecting portion  32 . 
   Internally, the first body portion  24  and the connecting portion  32  form a motor receiving space  34 , as is also seen in  FIG. 5 , discussed hereafter. The second or rear body portion  26  forms a rear air chamber  36 . The housing  12  may be integrally formed of plastic or other lightweight, moldable, non-conductive material. 
   The external components of the tweeter  10  may also include an annular mounting flange  38 . The mounting flange  38  comprises a generally cylindrical sidewall  40  internally threaded to engage the threads  28  of the first body portion  24  of the housing  12 . A laterally extending flange portion  42  extends outwardly from the sidewall  40 . Openings  44  are spaced circumferentially around the flange portion  42  for mounting and removal torque. 
   Still further, external components of the tweeter  10  include a perforate domed grill  46  sized to cover the open front end  20  of the housing  12 . Preferably, the grill  46  includes an edge  48  adapted to be trapped between the open front end  20  of the housing  12  and an inwardly extending shoulder  50  on the mounting flange  38 . 
   As is apparent from  FIG. 1 , the tweeter has a relatively short depth. For example, in a preferred embodiment shown, the diameter of the diaphragm is 40 mm and the overall length of the assembled tweeter is about 25 mm. This allows the tweeter to be installed in a variety of locations in a vehicle, including the dashboard, the front and rear door panels, and A-pillars. 
   Preferably, the housing  12  comprises means by which the tweeter  10  can be mounted in the selected environment. As illustrated in  FIG. 2 , the external threads  30  of the second body portion  26  may be adapted to threadingly engage the internal threads of a coaxial mounting cup  56 . This permits the tweeter  10  to be mounted coaxially. Alternately, a flush mounting cup  58  may be used to mount the tweeter  10  by threading the flush mounting cup to the larger diameter first body portion  22 , as indicated in  FIG. 3 . The flush mounting cup  58  allows the tweeter  10  to be mounted into the mounting surface. 
   Returning to  FIG. 1 , the main internal or working components of the tweeter  10  comprises a motor  62 , a diaphragm  64  and a damper  66  mounted atop the motor under the diaphragm. A voice coil assembly is also included, but is not shown in  FIG. 1 . The motor  62  generally is sized and shaped to be mounted in the motor receiving space  34  in the housing  12 . 
   The motor  62  preferably comprises a supporting member such as the yoke  68 , which may be generally U-shaped. The yoke  68  preferably comprises a back panel  70  and a sidewall  72  extending forwardly of the back panel to form a magnet receiving space  76 . The yoke  68  may be integrally formed of conductive metal such as low carbon steel and preferably 1008 grade steel. 
   The motor  62  also includes a permanent magnet assembly  80 . The permanent magnet assembly comprises at least a first permanent magnet  82  receivable inside the yoke  68  in the magnet receiving space  76 . A top plate  84  is included in the motor  62 , the top plate being receivable in the yoke  68  over the first permanent magnet  82 , as best seen in  FIG. 6 . Although the magnet assembly  80  may consist of a single magnet, such as the magnet  82 , the preferred magnet assembly further comprises a second permanent magnet, such as the magnet  86 . The second permanent magnet  86  preferably is positioned immediately above and resting on the top plate  84 , as seen in  FIG. 7 . 
   Several different types of permanent magnets may be employed in the motor  62 . However, particularly suitable for this purpose are rare earth magnets, and most preferably, the permanent magnets will comprise Neodymium Iron Boron (NdFeB or NIB). 
   As seen in  FIG. 1  and also in  FIG. 4 , the size of the first magnet  82  and the top plate  84  is selected to provide an annular gap  90  extending therearound adapted to receive a voice coil assembly  92  (shown only in  FIG. 4 ). As seen in  FIG. 4 , in this embodiment of the tweeter  10  the diaphragm  64  is domed and is supported by a flexible surround  96  having an inner edge  98  attached to the periphery of the diaphragm and an outer edge  100  supportable on the open front end  20  of the housing  12 . 
   The voice coil assembly  92  preferably comprises a cylindrical former  102  on which a conductor is supported. The conductor comprises a coil portion (not shown) supported on the former  102  and leads  104  (shown only in  FIGS. 2 and 3 ) extending from the coil portion to connect the coil to a signal source (not shown). The upper edge of the former  102  is affixed to the surround  96  near or at its inner edge  98  so that the voice coil assembly  92  is operatively engaged with the diaphragm. 
   When the outer edge  100  of the surround  96  is supported on the open front end  20  of the housing  12 , the diaphragm  64  is movably supported over the open end of the housing forming a forward air chamber  108  between the motor  62  and the diaphragm, and this air chamber is continuous with the annular gap  90 . In addition, the voice coil assembly  92  is movably supported in the annular gap  90 . 
   Thus, the voice coil assembly  92 , the motor  62  and the diaphragm  64  are cooperatively adapted to reproduce high frequency sounds. As used herein, “high frequency” denotes a range between about 1000 Hz and about 22 kHz. 
   In accordance with the present invention, the motor  62  is characterized by an air passage extending therethrough and continuous with the forward air chamber  108 . This air passage may take many forms. For example, it may be a single passage or comprise a plurality of passages; such passages may have different shapes and sizes and may be centrally located in the motor or positioned elsewhere. In the preferred embodiment shown herein, the air passage in the motor  62  comprises a single central passage  112  formed by a central bore  114  in the second magnet  86 , a central bore  116  in the top plate  84 , a central bore  118  in the first magnet  82 , and a central bore  120  in the back panel  70  of the yoke  68 , all these central passages being aligned. 
   The central air passage  112  through the motor  62  preferably will be in communication with the annular gap  90  around the motor. This communication may be provided by one or more radial air channels  122  or grooves in the upper surface  124  of the second magnet  86 , as best seen in  FIG. 7 . 
   In addition to the air passage through the motor  62 , the tweeter  10  comprises an air chamber  128  lateral to the motor  62  and between the motor and the sidewall  18  of the housing  12 . Although the lateral chamber  128  may take different forms, a preferred shape is a single annular chamber formed by a space between the sidewall  18  of the housing and the sidewall  72  of the yoke  68 . 
   This lateral air chamber  128  communicates with the air passage  112  through the motor  62 . To this end, one or more air channels are provided between the air passage  112  and the chamber  128 . Preferably, the air channel comprises a plurality of radial channels  130  or grooves formed in the rear surface  132  of the back panel  70  of the yoke  68 , as shown in  FIG. 8 . 
   As indicated, the tweeter  10  of this invention may include an acoustic damper or plug  66 . In the tweeter  10 , the acoustic damper is a dome-shaped plug formed of pressed polyfill. The plug  66  is sized to be supported on the upper surface  124  of the second magnet  86  and adapted to support the oscillating diaphragm  64 . Ideally, the bottom  142  of the plug  66  is provided radial grooves  144  corresponding in size and position to the radial grooves  122  in the second magnet  86  to form part of the communicating passage between the central bore  112  in the motor  62  and the annular gap  90 . 
   Having described the preferred structural components of the tweeter  10 , one preferred method of assembly will be explained. First the motor  62  is assembled. The first magnet  82  is set inside the yoke  68  and the top plate  84  is placed on top of the first magnet. Then, the first magnet  82  is magnetized. Next, the second magnet  86  is magnetized and placed over the top plate  84 . The plug  66  is glued to the top of the second magnet  86  aligning the grooves  144  in the plug with the grooves  122  in the second magnet  86 . 
   Next, a washer  148  ( FIG. 1 ) is glued to the top annular edge  150  of the yoke  68 . The top edge of the coil former  102  is glued to the depending inner edge  98  of the surround  96 , and glue is applied to the top of the washer  148 . Then, the coil/surround assembly is positioned over the motor  62  with the coil former  102  in the annular gap  90  and the outer edge  100  of the surround  96  against the washer  148 . The leads  104  are positioned in notches  152  on the outer aspect of the top edge  150  of the yoke  68 , and through the lateral air chamber  128 . Preferably, the housing  12  will have been formed with longitudinally placed lead grooves  154 , as shown in  FIG. 5  on opposing sides of the housing to accommodate the leads  104 . The ends of the leads  104  are pulled through the openings  22  in the rear wall  16  of the housing  12 . Epoxy is applied over the openings  22  to seal the housing and to fix the leads against the rear wall. 
   Having inserted the motor  62  and secured the leads  104 , an inner flange ring  156  ( FIG. 1 ) is glued over the top of the outer edge  100  of the surround  96 . Finally, the grill  46  is inserted inside the mounting flange  36 , and the grill/mounting flange assembly is screwed down over the threads  28  on the first body portion  24  of the housing  12 . Now the tweeter  10  is ready for installation in a car or other vehicle, using the coaxial mounting cup  56 , the flush mounting cup  58 , or any other suitable mounting device. 
   In operation, the leads  104  from the tweeter  10  are connected to a signal source as part of the installation. Once the signal source is activated, current is supplied to the motor  62  causing reciprocal motion of the diaphragm. Movement of the diaphragm  64  moves the air mass inside the housing  12 . This air mass occupies one continuous dampening enclosure  160  formed by the air gap  90 , the radial passages formed by the grooves  144  in the plug  66  and the matching grooves  122  in the second magnet  86 , the central air passage  112  through the motor  62 , the grooves  130  in the back panel  70  of the yoke  68 , the rear air chamber  36  in the rear or second portion  26  of the housing  12  behind the yoke  68 , and the lateral air chamber  128  surrounding the motor. This significantly increases the volume of air that can be acted on by the diaphragm, thus enhancing the range and sound quality of the tweeter  10  without significantly increases its length. 
   Changes can be made in the combination and arrangement of the various parts and elements described herein without departing from the spirit and scope of the invention as defined in the following claims.