Abstract:
A speaker has a magnet assembly, a basket and a voice coil mounted in the flux gap of the magnet assembly. A spider mounts the voice coil to align it. A sound radiator, for producing sound, is connected by a connector to the voice coil. An isolator extends across the basket, between the sound radiator and the voice coil, to isolate the voice coil mechanically from the exterior, while permitting free movement of the connector. This then enables the voice coil to be connected to and driven by an amplifier connected to a relatively high voltage electrical supply.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to loud speakers, and more particularly is concerned with loudspeakers commonly classified as subwoofers and intended to reproduce sound in just a low frequency range. Subwoofers are usually used as part of a speaker system including other speakers intended to produce other audio frequencies, so as to provide a complete range of frequencies covering the entire range of frequencies audible to the human ear.  
       BACKGROUND OF THE INVENTION  
       [0002]     Presently, many consumers and purchasers of audio systems expect such systems both to adequately reproduce frequencies down to quite low frequencies and to reproduce such low frequencies at relatively high power levels. In other words, consumers enjoy and appreciate bass or low frequency sounds. To meet this demand, current sound systems typically provide a separate, stand-alone subwoofer. Unlike higher frequencies, it is not critical to provide any dimensional or stereo aspect to low frequency sound, and it is acceptable to provide a single subwoofer; in contrast, speakers for other frequencies are usually provided either in pairs, for a stereo sound system or in a larger number to provide a surround sound effect.  
         [0003]     A further common requirement in the market place is that such subwoofers should be relatively small and compact. A requirement for compact subwoofers and high sound output require the subwoofer to have a relatively large power.  
         [0004]     A further complication is that design codes in major industrial countries, including United States and Canada, usually require that any live components not be readily accessible by the user. These codes typically include tests to determine if an enclosure can be penetrated by a user, e.g. by dropping weights of a specified size and shape on the speaker cones, probing speaker enclosures with a simulated finger. It is also common to include a minimum “creepage” discharge distance or length. This requires that there be a minimum distance between any live components and the exterior of a speaker enclosure or parts that provide an electrical connection to the exterior, including any paths between surfaces of fitted components and the like.  
         [0005]     For simple, low power applications, passive subwoofers can be provided, which do not incorporate any separate amplifier. Where any significant power level is required, it is not practical to supply this power as an audio signal from a separate amplifier. Rather, the only practical approach is to supply the audio signal at a low power level to the subwoofer, and then to amplify this signal within the subwoofer to generate necessary power level. However, this then introduces the requirement to supply electrical power to the subwoofer and, consequently, the subwoofer itself may not meet the requirements for electrical isolation of any live components if this issue is not properly addressed.  
         [0006]     This places severe design constraints on manufacturers of such subwoofers. One typical approach would be to provide an isolation transformer between the power line and the amplifier within the subwoofer. This would then enable the live components to be isolated from the accessible parts of the subwoofer, thereby simplifying the overall design in compliance with design codes. However, for a subwoofer of any reasonable power, for example of the order of a few hundred watts or higher, it can quickly be determined that the size of the necessary transformer would be quite large and expensive. This then takes up some considerable space within the subwoofer enclosure also.  
         [0007]     A power transformer can be eliminated if other means of isolation are provided. One solution to this problem is to provide a grille or mesh, formed from metal or other durable material, covering the exterior of a speaker. For various reasons, this is not preferred. It adds to the bulk and external dimensions of the speakers, which can in turn limit the internal volume. Any such metal grille is usually considered unsightly and unattractive, and hence rejected for marketing reasons.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is based on the realization that, particularly, but not exclusively, for subwoofers of significant power levels, it is desirable to eliminate the need for any power transformer, and further that it is possible to do this while complying with codes governing isolation of electrically live components.  
         [0009]     In accordance with a first aspect of the present invention, there is provided a speaker comprising: 
        a magnet assembly defining a magnetic flux gap;     a voice coil mounted in the flux gap extending parallel to an axis of the speaker;     a sound radiator;     a connector, connecting the voice coil to the sound radiator, to drive the sound radiator; and     an isolator mounted between the sound radiator and the magnet assembly, to at least restrict access to electrically conductive parts the speaker that might become live while not restricting movement of the voice coil and the sound radiator.        
 
         [0015]     Preferably, the speaker includes a basket, with the magnet assembly and the isolator mounted to the basket, and with a spider provided between the basket and voice coil to align the voice coil.  
         [0016]     The isolator can include a central portion including a plurality of openings permitting free movement of air through the isolator.  
         [0017]     The connector can comprises a voice coil extender including a generally circular base portion and the plurality of leg portions extending from the base portion, or the connector can comprise an extension of a bobbin of the voice coil.  
         [0018]     The sound radiator advantageously has a generally planar exterior surface for generating sound, and can include a plurality of ribs on a rear face thereof, to reinforce the planar exterior surface.  
         [0019]     The present invention also provides an isolator for use in a speaker, the isolator comprising: 
        a central portion including a plurality of openings permitting free passage of air therethrough and a plurality of apertures for leg portions of a connector connecting, in use, a voice coil and a sound radiator, and permitting free movement of the leg portions therethrough; and     a peripheral portion including a mounting flange.        
 
         [0022]     For some applications it may be possible to have a single leg portion and just one aperture in the isolator. Also, for use with passive drivers, there is not need to provide any apertures as there is no connection to any leg portions required.  
         [0023]     It is also possible for some applications that the active driver could be provided with a different structure, and that the isolator would only be needed for the passive drivers. In such a case, the isolator would not need any apertures for leg portions or the like, but instead would simply need openings to permit free movement of air.  
         [0024]     A further aspect of the present invention provides a voice coil extender comprising a base portion for connection to a voice coil and a plurality of legs extending generally parallel to one another away from the base portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:  
         [0026]      FIG. 1   a  is a view of a horizontal cross-section through a subwoofer in accordance with the present invention;  
         [0027]      FIG. 1   b  is a view of a horizontal cross-section similar to  FIG. 1   b , and showing an alignment tool;  
         [0028]      FIG. 2  is a perspective view of elements of the subwoofer of the present invention, showing the main elements of the active driver, except for a flat sound radiator;  
         [0029]      FIG. 3  is a perspective view showing the active driver and the amplifier;  
         [0030]      FIG. 4  is a perspective view showing the arrangement of the active and passive sound radiators in the enclosure;  
         [0031]      FIG. 5  is a further perspective view showing details of a trim piece;  
         [0032]      FIG. 6  is a perspective view showing a voice coil extender in accordance with the present invention;  
         [0033]      FIG. 7  is a perspective view showing a voice coil extender, a voice coil and a spider in combination;  
         [0034]      FIG. 8  is a perspective view showing the combination of elements of  FIG. 7  and including a mounting and alignment tool;  
         [0035]      FIG. 9  is a perspective view showing the combination of the voice coil extender and the voice coil, mounted to a sound radiator and its surround;  
         [0036]      FIG. 10  is a perspective view showing the complete woofer, including the mounting and alignment tool and with the sound radiator removed;  
         [0037]      FIG. 11  is a perspective view showing the complete woofer;  
         [0038]      FIG. 12  is a perspective view of the isolator from the front;  
         [0039]      FIG. 13  is a perspective view of the isolator from the rear;  
         [0040]      FIG. 14  is a perspective view showing the mounting and alignment tool; and  
         [0041]      FIG. 15  is a perspective view of the rear of the sound radiator of a passive radiator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]     In the figures, a subwoofer in accordance with the present invention is indicated generally by the reference  10 . The subwoofer  10  has an enclosure  12 , and in the disclosed embodiment, the enclosure  12  is of a generally cubic shape. However, it will be understood that any suitable shape of enclosure can be used; the enclosure need not necessarily comprise purely flat surfaces, and any flat surfaces are not restricted to always being perpendicular to one other.  
         [0043]     The subwoofer  10  has an active driver or radiator  14 , otherwise known as a woofer, and two passive radiators  16  and  18 . Again, the combination of active and passive radiators is not critical to the present invention, and it is possible that just one or more active drivers or radiators could be provided with no passive radiators, and also that conventional vents could be provided. Further, where passive radiators are provided, the number of passive radiators  16 ,  18  can be varied, as required.  
         [0044]      FIG. 1  also shows an amplifier  20 , shown schematically, since the details of the amplifier form no part of the present invention. The amplifier  20  is provided with a power supply connection  22  ( FIG. 3 ). The amplifier  20  is thus connected directly to an electrical power supply, which, commonly, is at a voltage of either 120 volts (in North America) or 240 volts (applicable in many other countries) AC. As detailed below, the amplifier  20  has connections  24  to the motor elements of the active driver  14 , so that both the amplifier  20 , and possibly also the active driver  14 , are subject to the voltages of the power supply.  
         [0045]     Turning to details of the active driver  14 , many components can be, to at least some extent, conventional. Thus, the driver  14  includes a magnet  30 , provided with a top plate  32  and a yoke  34 . The top plate  32  and yoke  34  together define an annular gap in which is mounted a voice coil  36 . In known manner, the voice coil  36  is connected to the amplifier  20 , so that the signal from the amplifier  20  drives the voice coil. The magnet  30 , top plate  32  and the yoke  34  form a magnet assembly.  
         [0046]     A basket  40 , usually formed from cast iron, aluminum or an aluminum alloy, has a planar bottom plate  42 , connected to a plurality of spokes  44 . The spokes  44  in turn are connected at their upper ends to an annular mounting flange  46 . Additionally, an intermediate or mounting ring  48  extends between the spokes  44 , to provide further strength to the basket  40 , and is used to mount a spider  66 .  
         [0047]     The voice coil  36  is formed on a cylindrical former or bobbin  38 , that extends up above the actual voice coil  36  itself (It is here noted that references to orientation, such as “top”, “above”, etc. are with reference to the active driver  14  as shown in  FIG. 1  and following common convention. It will be understood that the active driver  14  can, in use, be placed in any orientation). In conventional subwoofers, the upper end of the former  38  is connected to a frusto-conical cone and the former is usually closed off by a dust cap, so as to form the actual sound-producing element or radiator.  
         [0048]     While the strength of the cone in particular, and also possibly the dust cap, are usually very dependent upon the size and power of the speaker and may be quite substantial for large, high powered subwoofers. They are nonetheless almost always not very strong elements. Since the cone necessarily must move to generate the sound, it is highly desirable to maintain the mass of the cone as low as possible. Additionally, the various components are glued together and the glue used is not reliable. For this reason, it is believed that the cone itself and its surround would generally never meet standards for an enclosure, to prevent access to electrically live components. As detailed above, one option is to consider substantial metal grilles or the like on the outside of the speaker. However, for aesthetic and other reasons, these are undesirable.  
         [0049]     In accordance with the present invention, a voice coil extender  50  is connected to the voice coil former  38 , as best shown in FIGS.  6  to  9 . The voice coil extender  50  comprises a base portion  52 , having essentially an annular shallow conical shape. Elongate arcuate leg portions  54  extend outwardly from the base portion  52  and parallel to an axis of the driver  14  and voice coil extender  50 . For some applications, the voice coil extender could comprise an extension of the former or bobbin  38 .  
         [0050]     A central alignment collar  56  is connected by ribs  58  to the base portion  52  and includes arcuate apertures  60  for aligning the various components of the driver  14 , as detailed below.  
         [0051]     Flat surface portions  62  extend between the elongate arcuate portions  54 . The ends of the elongate arcuate portions  54  are cut back to provide connecting end portions  64 .  
         [0052]     In known manner the spider  66  is connected between the voice coil former or bobbin  38  and the mounting ring  48  of the basket  40 . This spider  66  can be of largely conventional construction.  
         [0053]     Further in accordance with the present invention, there is provided an isolator indicated at  70 . The isolator  70  is largely disc-shaped, and includes an annular mounting flange  72 , that can include raised cylindrical projections ( FIG. 10 ) for engaging openings in a flange of a surround, or for location around that flange. Radially inwardly from the flange  72 , there is a frusto-conical portion  74 , that serves to space a central portion of the isolator  70  inwardly from the enclosure  12 .  
         [0054]     A central portion  76  of the isolator  70  is in the form of a mesh. The mesh or central portion  76  is formed from three sets of parallel ribs  78 , that extend and intersect to form a plurality of triangular openings  80 . Here, triangular openings are each in the form of an equilateral triangle.  
         [0055]     The triangular openings  80  are dimensioned to meet the requirements for a finger-probing test. A common test uses a simulated or artificial finger of specified dimensions, so that the openings  80  are dimensioned to be small enough to prevent penetration of this artificial finger. Triangular openings  80  have been found to be the best shape to give the maximum opening size while meeting this finger test.  
         [0056]     Nonetheless, it will be understood that openings of any shape and size could be used, provided they meet the required regulations or specifications. Thus, the openings need not all be of the same size and shape, and could, for example, be circular, square, etc.  
         [0057]     A central part  82  of the isolator  70  does not have the openings  80 , but instead has arcuate slots  84  for an alignment tool. Additionally, spaced further out radially, arcuate slots  86  are provided for the leg portions  54  of the voice coil extender, these being of sufficiently large dimensions to provide for unrestricted movement of the voice coil extender  50 , and to allow for some lateral movement of the leg portions  54  in the arcuate slots  84 .  
         [0058]     The actual sound-producing element or radiator is indicated at  90 . Unlike conventional subwoofers or speakers which utilize a cone construction, the sound-producing radiator  90  has a planar exterior surface  92  and is generally circular. On the rear of the surface  92 , there is a pattern of ribs  93  serving to reinforce the surface  92 , and dimensioned to ensure that any natural frequency of vibration of the radiator  90  is higher than the frequencies delivered by the subwoofer  10 , so that it will not interfere with the performance of the subwoofer  10 .  
         [0059]     A flexible rubber surround  96  joins an edge of the sound radiator  90  to the enclosure  12 . As shown, the surround  96  has an inner rib  98  that is secured by adhesive within a corresponding circular groove of the sound radiator  90 .  
         [0060]     A radially outer portion of the surround  96  comprises an annular flange  100  and a rib  102 , that engages a corresponding circular groove  104  of the isolator  70 . Note that this rib and groove arrangement is not absolutely essential, but it does facilitate assembly.  
         [0061]     As shown, the annular mounting flange  46  of the basket  40  is secured to the enclosure  12 , for example by screws (not shown), with the flanges  72  and  100  of the isolator  70  and surround  96  sandwiched between the mounting flange  46  and the enclosure  12 . The mounting flange  46  includes, at the outer edge, a lip around the flanges  72  and  100 . This configuration of the various flanges  46 ,  72  and  100  is dimensioned to ensure that requirements for creepage distances between the exterior and the interior of the subwoofer  10  meet appropriate specifications. For this purpose, it is assumed that the surround  96  will be treated as being capable of being torn or penetrated by a user.  
         [0062]     The voice coil extender is connected by its connecting end portions  64  to the sound radiator  90 . The rear side of the sound radiator  90  includes recesses  95  corresponding to the end portions  64 , with the two components being glued together by a suitable adhesive. Further recesses in the central portion are adapted to engage an alignment tool. Preferably, both components are molded from a suitable plastic material. ABS plastic can be used, but any suitable plastic can be used that is sufficiently strong and rigid and that meets any other requirements, e.g. with respect to flammability.  
         [0063]     With reference to  FIG. 1 , this shows a mounting and alignment tool  110 . This tool  110  includes a planar base  112  and a circular portion  114  dimensioned to form a close fit within the yoke  34 , so as to ensure accurate alignment. The circular portion  114  extends above the yoke  34 , until it abuts the central alignment collar  56  of the voice coil extender  50 , as shown on the left hand side of the collar  56  in  FIG. 1 . As shown on the right hand side of the collar  56  in  FIG. 1 , the mounting and alignment tool  110  includes three arcuate portions  116  that extend through the alignment collar  56  and through the apertures  84  of the central part  82  of the isolator  70 . The arcuate portions  116  then engage the arcuate recesses  97  of the sound radiator  90 . This arrangement ensures that the voice coil extender  50 , secured to the sound radiator  90 , and also the sound radiator  90  itself are both accurately aligned in the radial direction with the motor elements of the subwoofer  10 , comprising the magnet  30 , top plate  32  and yoke  34 . More particularly, as the voice coil extender  50  is attached it the voice coil  36 , this ensures that the voice coil  36  itself is accurately aligned and spaced in the gap between the top plate  32  and yoke  34 , with desired radial spacing.  
         [0064]     Further, the arcuate portions  116  slide through and engage corresponding arcuate slots  84  in the isolator  70 , correspondingly to ensure alignment, in radial direction of the isolator  70 .  
         [0065]     With the mounting and alignment tool  110  in place, the flange  46  of the basket  40  can be secured to the flanges  72  and  100  of the isolator  70  and surround  96 , ensuring proper alignment. Simultaneously, the spider can be attached to the voice coil former  38  and to the ring  48  of the basket, to ensure accurate location of the voice coil  36  in the flux gap with the various elements properly aligned, the alignment tool  110  can then be removed.  
         [0066]     In known manner, the subwoofer  10 , as noted above, also includes the two passive radiators  18 . Each of these passive radiators  18  is provided with a respective isolator  70 . Further, each of them include a respective sound radiator  90  and surround  96 . Here, since there is no basket  40  or the like, the isolator  70  and the flanges of the surround  96  are secured, e.g. by screws and the like to the enclosure  12 .  
         [0067]     In known manner, to give desired characteristics to the passive drivers  16 , each of the sound radiators  90  thereof is provided with a metal disc, dimensioned to give a desired mass to the passive driver.  
         [0068]     To complete the subwoofer  10 , each of the openings in the enclosure  12  for the active and passive drivers  14 ,  16  and  18  can be finished with an annular trim piece  122 . Commonly, this trim piece  122  is an electrical insulator and serves to cover heads of screws or other conductive fasteners that would otherwise be visible on the exterior of the enclosure  12 ; this also serves to prevent unintended access to the screws, which can encourage a user to partially dismantle a subwoofer  10 , and also provides electrical isolation. The screws may be countersunk, so that the annular trim piece  122  can be otherwise flush mounted to the exterior of the enclosure  12 . The trim piece  122  can include cylindrical projections  124  for fitting into holes  126  of the housing  12 . The screws engage the basket and as such must be insulated from the exterior. This construction ensures that the only access to the interior of the speaker is from the bottom, and hence it is then only necessary to put warning labels concerning a potential shock hazard on the bottom of the speaker. These are considered to be unsightly and one would not want them on any visible surface of the speaker. For some designs it may be possible to eliminate the screws and the hence the possible conductive path to the exterior, so that the trim piece  122  is not then necessary.  
         [0069]     It will be understood that while a preferred embodiment of the invention has been described, numerous variations are possible within the scope and spirit of the present invention. While the sound radiator has been shown as a generally planar disc, it will be appreciated that a variety of different sound radiators can be employed. Indeed, a sound radiator could be in the nature of a conventional cone, although this would require an isolator of different configuration, and practically it would be difficult to find space for the isolator. While the voice coil extender has been shown with arcuate legs, connecting it to the sound radiator, it will be understood that the configuration of the voice coil extender can be varied in many respects. For example, it could be provided with generally cylindrical leg portions extending through the isolator. The number of leg portions can be varied, and conceivably it might be possible to have one, central leg if this is of sufficient strength.