PITCH CARBON COMPOSITE COMPONENTS FOR LOUDSPEAKERS

Abstract: Loudspeaker components, and loudspeakers made with such components, are embedded with directionally thermally conductive fibers, such as pitch-based carbon fibers. The fibers are arranged so that they conduct heat away from the voice coil to the speaker frame or a dedicated heat sink. The components that can have thermally conductive fibers embedded in them include the former tube, the voice cone, and the spider.

Description: PITCH CARBON COMPOSITE COMPONENTS FOR LOUDSPEAKERS Background of the Invention This invention relates to loudspeaker components made from pitch-based carbon fiber composite materials. More particularly, this invention relates to loudspeaker components incorporating pitch-based carbon fibers as thermal conduction paths for heat dissipation. A typical loudspeaker includes a cone (typically paper) , a permanent magnet, and a voice coil situated within the field of the permanent magnet. When signals are input into the voice coil, the coil functions as an electromagnet, with its field strength varying in accordance with the input signal. The varying magnetic field of the voice coil interacts with the field of the permanent magnet, causing the voice coil to move relative to the permanent magnet. The voice coil is mechanically coupled to the cone, and therefore movement of the coil results in vibrations in the cone, which cause corresponding vibrations in the surrounding air, producing the desired sound output. The voice coil is typically wound around a tube known as a bobbin, former, or former tube. The best loudspeakers are at most about 6% efficient, meaning that 94% of the applied power is dissipated by heating of the voice coil. This can cause charring or burning of the former tube and even the cone. In addition, as the voice coil heats up, its impedance increases, thereby further reducing efficiency and increasing heat dissipation. It is therefore important to be able to remove heat from the voice coil. One known attempt to remove heat from the voice coil involves making the former tube from aluminum, which can be thermally connected to a suitable heat sink. However, aluminum is electrically conductive, causing two problems. First, although the voice coil wire is electrically insulated, the aluminum tube must be electrically insulated to prevent short- circuiting the voice coil in the event of wire insulation failure. This requires finding an electrical insulation material that is thermally conductive, to avoid negating the thermal conductivity of the aluminum, as well as capable of withstanding the operating temperatures of the voice coil. Second, the electromagnetic field of the voice coil gives rise to eddy currents in the conductive aluminum, affecting speaker efficiency. In addition, aluminum former tubes have traditionally been made very thin, and have been known to melt. Also, as a metal, aluminum has a relatively high coefficient of thermal expansion, which can cause distortion of the speaker structure with corresponding effects on speaker performance. Alternatively, it is known to make the former tube from a polyimide film such as that sold under the trademark KAPTON ® by E.I. du Pont de Nemours and Company, of Wilmington, Delaware. This film is resistant to charring, and has a lower coefficient of thermal expansion than aluminum, but is not effective in removing heat. Therefore, while the former tube may not burn, the voice coil nevertheless heats up and loses efficiency. It would be desirable to be able to provide a loudspeaker former tube that is resistant to charring and that conducts heat away from the loudspeaker voice coil. It would also be desirable to be able to provide a loudspeaker cone that is resistant to charring and that conducts heat away from the loudspeaker voice coil. It would further be desirable to be able to provide a thermal conduction path in any loudspeaker component for dissipating heat from the loudspeaker voice coil. Summary of the Invention It is an object of this invention to provide a loudspeaker former tube that is resistant to charring and that conducts heat away from the loudspeaker voice coil. It is also an object of this invention to provide a loudspeaker cone that is resistant to charring and that conducts heat away from the loudspeaker voice coil. It is a further object of this invention to provide a thermal conduction path in any loudspeaker component for dissipating heat from the loudspeaker voice coil. In accordance with the present invention, there is provided a heat-dissipating component for a loudspeaker. The heat-dissipating component includes a carrier and at least one directionally thermally conductive fiber embedded in the carrier. A loudspeaker according to the invention has a voice coil having a longitudinal axis, and a heat-dissipating component according to the invention in thermally conductive relationship with the voice coil, with the at least one directionally thermally conductive fiber embedded in the carrier having at least a first portion in thermally conductive relationship with the voice coil. The heat-dissipating component can be any component including, but not limited to, a former tube, a voice cone, or an integral former tube and voice cone. Brief Description of the Drawings The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: FIG. 1 is a perspective view of a heat- dissipating former tube according to the present invention with a voice coil wound therearound; FIG. 2 is a cross-sectional view of the heat- dissipating former tube of FIG. 1, taken from line 2-2 of FIG. 1; FIG. 3 is a perspective view of a sheet containing directionally thermally conductive fibers that can be used to form the heat-dissipating former tube of FIG. 1; FIG. 4 is a perspective view of a heat- dissipating voice cone according to the present invention; FIG. 5 is a plan view of a sheet containing directionally thermally conductive fibers that can be used to form the heat-dissipating voice cone of FIG. 4; FIG. 6 is a cross-sectional view of a loudspeaker incorporating heat-dissipating components according to the invention; FIG. 6A is an enlarged view of the portion of FIG. 6 circumscribed by circle A; and FIG. 7 is a cross-sectional view of an integrated heat-dissipating former tube and voice cone according to the invention. Detailed Description of the Invention The present invention solves the problem of voice coil heat dissipation in loudspeakers by relying on directionally thermally conductive fibers -- i.e., fibers that conduct heat primarily only along their lengths, with substantially less heat conduction in the transverse direction. Thus, if a number of such fibers are arranged parallel to one another and touching each other, and a heat source is placed in thermal conductive relationship with an end of one fiber, heat will be conducted primarily to the other end of that fiber, with substantially less heat conducted to neighboring fibers, even though the fibers are touching. Many types of directionally thermally conductive fiber can be used — e.g., metal-coated fibers, or metallic substrate fibers such as tungsten fibers coated with boron. However, one particularly preferred type of directionally thermally conductive fiber that can be used in the present invention is a pitch-based carbon fiber such as that available from Mitsubishi Chemical America Inc., of San Jose, California, under the designation K13710, or from Amoco Performance Products, Inc., of Alpharetta, Georgia, under the designations KllOOx and P-120. While PAN- based (i.e., polyacrylonitrile-based) carbon fibers are well-known for their use in structural "graphite" composite materials, pitch-based carbon fibers are also available and have the property of being directionally thermally conductive. The fibers can be arranged as desired and then impregnated with a resin to form a carrier, or "prepreg," in which the fibers are embedded. The resin can be a thermoplastic, thermosetting, ceramic or silicone resin, and may be, e.g., a thermoplastic resin such as polyether sulfone, polyimide, polyether-i ide, or poly-ether ether ketone (otherwise known as "PEEK") , or thermoset resin such as an epoxy, a phenolic resin, a bismaleimide such as that sold by the assignee hereof under the trademark CYCOM ® 5250-4, or a cross-linking polyimide which may be of either the addition or condensation cure type. The resulting carrier may be rigid, in which case it must be formed into the desired shape before it sets. Alternatively, the carrier may be flexible in the direction transverse to the fiber direction, but it preferably should still be rigid in the fiber direction to withstand structural compression loads when the cone is pushed forward. The resin preferably also is chosen so that even if it does heat up to voice coil operating temperatures, it preferably will not char. For use as a former tube, the carrier preferably should be able to withstand steady-state operating temperatures of about 500°F (about 260°C) , and peak temperatures of about 600°F (about 315°C) . A carrier embedded with directionally thermally conductive fibers as described can be formed into a cylinder to serve as a voice coil former tube according to the invention. Pitch-based carbon fibers are electrically as well as thermally conductive. Therefore, if pitch-based or other electrically conductive fibers are used, then in order to minimize or substantially prevent eddy currents during voice coil operation, the fibers preferably should be aligned substantially parallel to the longitudinal axis of the former tube, which substantially coincides with, or is at least substantially parallel to, the longitudinal axis of the voice coil. In the resulting carrier, the fibers are substantially parallel to one another, and also minimizes the length of the thermal conduction path. The portions of the fibers under the voice coil, which could be substantially the entire length of each fiber if the former tube is not substantially longer than the voice coil, are in thermally conductive relationship with the voice coil, allowing the fibers to carry away heat in their direction of thermal conductivity. The ends of the fibers remote from the voice coil •— which could be only the extreme ends if substantially all of each fiber is in thermal contact with the voice coil — could be left to radiate heat to the ambient air. More effectively, however, a heat sink could be provided in thermal conductive relationship with the fibers, preferably with the remote ends. The heat sink could be an existing part of the speaker — e.g., the metallic frame, the dust cap or dome at the end of the former tube, or the whizzer on the dome (if provided) — or a part provided specifically to serve as a heat sink. The wire used in the voice coil is electrically insulated, normally by an insulating varnish. However, it is preferable that the pitch- based carbon fibers, if used, be electrically insulated from the voice coil. Pitch-based carbon fibers are electrically conductive, as discussed above, and if the coil insulation fails in a way that does not short- circuit the voice coil, one would not want the former tube to cause a short circuit. Most preferably, the entire former tube is electrically insulated from the voice coil by a layer of nonwoven fiberglass mat, or by a woven fiberglass scrim. However, other electrically insulating materials can be used, provided they can withstand the operating temperatures of the voice coil. The former tube should contain at least one directionally thermally conductive fiber, and preferably contains many fibers. The number of fibers used can be determined by calculating the amount of heat to be dissipated as a function of the heat transfer capacity of a single fiber. In addition, different types of fiber have different heat transfer capacity. For example, the Mitsubishi K13710 fiber identified above has a thermal conductivity of about 140 W/m-K, while the Amoco KllOOx fiber identified above has a thermal conductivity of about 1100 W/m-K, both as measured for the fiber alone in the fiber direction. The thermal conductivity of a sheet made from fibers impregnated with resin will be less by about 50% because of the lower conductivity of the resin. The carrier used to make the former tube preferably has a cured ply thickness of at most about 0.006 in (about 0.15 mm), including the insulating layer, at least in the portion of the tube underlying the coil. The coil normally has a thickness of between about 0.040 in (about 1 mm) and about 0.050 in (about 1.25 mm), so that the former tube can be about that thick where it extends beyond the coil toward the voice cone. That allows for a greater volume for heat dissipation. The fiberglass scrim or cloth used for insulation can be 106-style plain weave fiberglass cloth having a 56-by-56 count per square inch, a weight of about 0.73 oz/yd 2 (about 24.8 g/m 2 ) and a thickness of about 0.0014 in (about 0.036 mm), or 104-style plain weave fiberglass cloth having a weight of about 0.569 oz/yd 2 (about 19.3 g/m 2 ) and a thickness of about 0.0018 in (about 0.046 mm). If a nonwoven fiberglass mat is used for insulation, it preferably has a weight of about 0.6 oz/yd 2 and a thickness of about 0.0021 in (about 0.053 mm). Therefore, the carrier containing the directionally conductive fibers can have a thickness of between about 0.0039 in (about 0.107 mm) and about 0.0046 in (about 0.117 mm). For the preferred embodiment using pitch-based carbon fibers, such a carrier is preferably formed as a sheet and preferably has a weight per unit area of between about 2.34 oz/yd 2 (about 80 g/m 2 ) and about 4.13 oz/yd 2 (about 140 g/m 2 ) . Assuming 35% resin content, the weight per unit area would be about 3.04 oz/yd 2 (about 103 g/m 2 ). Several layers of such a sheet can be built up in the portion of the former tube, if any, that extends beyond the coil (normally there is such a portion) . E-glass insulation, such as 120-style plain weave fiberglass having a weight of about 3.16 oz/yd 2 (about 107 g/m 2 ) and a thickness of about 0.0035 in (about 0,089 mm) preferably is added to outside of the tube to protect the tube-to-cone joint from thermal failure. A strip of polyimide film or E-glass, such as 112-style plain weave fiberglass having a weight of about 2.12 oz/yd 2 (about 72 g/m 2 ) and a thickness of about 0.0036 in (about 0.091 mm), or equivalent, preferably is added to the inside of the former tube to electrically insulate the lead wire from shorting out the voice coil to the former tube. One can make certain assumptions to simplify the calculation of the conduction of heat away from the voice coil along the fiber direction (not including radiation or convection effects) . First, one can assume that all heat loss occurs at the ends of the fibers. Second, one can assume that heat transfer is linear and that thermal conductivity does not diminish with increasing temperature (although in fact it does) . Third, one can assume a steady-state operating temperature of about 450°F (about 232 °C or about 505°K) and an ambient temperature of about 80 °F (about 27 °C or about 300°K) , for a temperature gradient of about 205°K. For ease of analysis, one can assume further that the former tube includes 100%, by volume, of the directionally thermally conductive fibers, oriented parallel to the longitudinal axis of the former tube. In fact, as stated above, the thermal conductivity of an actual sheet will be about 50% of that calculated, because of the lower conductivity of the resin in which the fibers are embedded. If the former tube has an inner diameter of 3 in (7.62 cm) and a length of 3 in (7.62 cm), with a wall thickness under the voice coil of 0.006 in (0.152 mm) and a wall thickness beyond the voice coil of 0.040 in (1.02 mm), and the voice coil occupies 1 in (2.54 cm) along the length of the former tube, then the former tube can be divided for calculational purposes into an inner tube with a length of 3 in (7.62 cm) and a thickness of 0.006 in (0.152 mm), and an outer tube with a length of 2 in (5.08 cm) and a thickness of 0.034 in (0.864 mm). The cross-sectional area of the inner tube is the area of an annulus having an inner diameter of 3 in (7.62 cm) and an outer diameter of 3.012 in (7.65 cm) : A λ = 7T(3.012/2) 2 - π(3/2) 2 = π(1.506 2 - 1.5 2 ) = 0.056 in 2 (3.612X10 -5 m 2 ) . The cross sectional area of the outer tube is the area of an annulus having an inner diameter of 3.012 in (7.65 cm) and an outer diameter of 3.080 in (7.82 cm): A 2 = π(3.080/2) 2 - π(3.012/2) 2 = π(1.540 2 - 1.506 2 ) = 0.325 in 2 (2.10X10 -4 m 2 ) The heat flux in the fiber direction (Q" x ) is given in watts per square meter (W/m 2 ) by the following equation: Q" x = K(ΔT/L) , where: K is the thermal conductivity (in W/m-K), ΔT is the temperature gradient (in °K) , and L is the fiber length (in meters) . For K = 140 W/m-K (e.g., in the case of Mitsubishi K13710 fiber described above) , the heat lux would be: Q" = (140 X 205)/(3 X 0.0254) = 376,640.4 W/m 2 through the inner tube and: Q" = (140 X 205)/(2 X 0.0254) = 564,960.6 W/m 2 through the outer tube. Total heat conducted, which is the product of area times heat flux, would be: Q = (376,640.4 X 3.612xl0 ~5 ) + (564,960.6 X 2.10X10 "4 ) = 13.6 + 118.6 = 132.2 W. For K = 1100 W/m-K (e.g., in the case of Amoco KllOOx fiber described above) , the heat flux would be: Q" = (1100 X 205)/(3 X 0.0254) = 2,959, 317.6 W/m 2 through the inner tube and: Q" = (1100 X 205)/(2 X 0.0254) = 4,438,976.4 W/m 2 through the outer tube. Total heat conducted, which is the product of area times heat flux, would be: Q = 2,959,317.6 X 3.612xl0 ~5 + 4,438,976.4 x 2. lOxlO -4 = 106.9 + 932.2 = 1,039.1 W. Accordingly, once the heat flux for a particular type of fiber is known, the number or density of fibers that should be used can be calculated based on the required heat dissipation and the known cross-sectional area per fiber. Of course, the total cross-sectional area of the structure to be impregnated with fibers is a limiting factor, as the total fiber cross-sectional area cannot exceed the cross-sectional area of the structure and typically is at most about 50% of that total cross-sectional area. Because the voice cone of the loudspeaker is mechanically coupled to the voice coil, it is usually also in thermally conductive relationship with the voice coil, subjecting it to the possibility of charring as described above, and also making it available for the removal of heat from the voice coil in accordance with the invention. Thus, in accordance with the invention, directionally thermally conductive fibers can be embedded in the cone. Each fiber preferably would have one end near the central longitudinal axis of the cone adjacent the voice coil, while the other end would extend preferably to the edge of the cone, where preferably it would be in thermally conductive relationship with a heat sink, which could be the speaker frame. The cone could be made by making a sheet as described above and then forming a cone in the same manner as conventional voice cones. Although there is less of a problem with eddy currents in the voice cone as compared to the voice coil, it is still preferable that the fibers not cross one another, and it is also desirable to minimize the length of the thermal conduction path. Therefore each fiber in the voice cone preferably extends from at or near the center of the cone substantially radially to the edge of the cone. By "substantially radially" is meant that even though the fiber may not extend from the longitudinal axis of the cone (e.g., because the cone is truncated) , and even though the cone is not a flat circular structure, the fiber extends along a line that would project onto a radius of a circle that is perpendicular to the cone longitudinal axis, or that extends substantially parallel to such a line even when it does not extend from the axis. (Because the voice cone usually is a truncated cone, normally not having an apex, the fibers generally would not extend from the actual axis of the cone.) In another embodiment, the former tube and the voice cone are formed as a single integrated structure, resembling a funnel. Such a structure would probably be more difficult to make than simply forming the carrier as a sheet as described above and rolling it into a tube or forming a cone, instead requiring the molding of the fiber-bearing resin carrier into the required shape. However, an integrated former tube/ voice cone structure may be able to dissipate more heat than the combination of a separate former tube and a separate voice cone. This is because the directionally thermally conductive fibers could be arranged to extend from one end of the former tube to the other end, then smoothly into the voice cone and radially toward the edge, without a break at the former tube/voice cone interface. Transfer of heat to the former tube is always efficient because the former tube, by definition, is in direct contact with the voice coil. However, if the two heat-dissipating components are made separately, heat transfer to the voice cone, which might be less directly connected to the voice coil, might be less efficient than heat transfer to the former tube. However, if the thermally conductive fibers extend continuously — i.e., without a gap in each fiber — from the former tube portion of the structure to the voice cone portion of the structure, then heat transfer to the voice cone will be as efficient as heat transfer to the former tube. While the invention can be used to greatest advantage in connection with the former tube and the voice cone of a loudspeaker, other speaker components can also be embedded with one or more directionally thermally conductive fibers for the purpose of carrying heat away from the voice coil. For example, the "spider" used to align the former tube in position in the loudspeaker, which is in contact with the former tube, can be embedded with one or more thermally conductive fibers, which also can be terminated at a suitable heat sink. The invention will now be described with reference to FIGS. 1-7. It should be noted that the dimensions, and particularly the diameters, of the directionally thermally conductive fibers are exaggerated for purposes of illustration. FIGS. 1 and 2 show schematically a former tube 10 according to the invention against which a voice coil 11 is wound (voice coil 11 would normally have more turns and layers of turns than shown in FIGS. 1 and 2, as well as leads (not shown) to which the input signal is applied) . Although voice coil 11 is shown as being wound against (around) the outside of former tube 10, it could also be wound against the inside of former tube 10. Ends of directionally thermally conductive fibers 13 as described above are visible at the end of former tube 10, and fibers 13 themselves are seen in phantom embedded in the portion of former tube 10 not covered by voice coil 11. As can be seen, fibers 13 are preferably substantially parallel to one another and to longitudinal axis 14 of former tube 10 and voice coil 11. As explained above, when fibers 13 are electrically as well as thermally conductive, as in the case of pitch-based carbon fibers, the parallel arrangement minimizes or substantially prevents the formation of eddy currents. Electrically insulating layer 20, seen in FIG. 2 between voice coil 11 and former tube 10, prevents short-circuiting of voice coil 11 by conductive fibers 13 in the event of a failure of the insulation of coil 11 (in such a way that the coil turns themselves are not short-circuited but do contact former tube 10) . Layer 20 can be any electrically insulating material that can withstand the heat generated by voice coil 11. Preferably, layer 20 is a fiberglass scrim as described above. If the resin carrier 21 in which directionally thermally conductive fibers 13 are embedded cures as a substantially rigid solid, then former 10 must be formed as a tube before the resin sets, unless the resin is of a type that can be re- melted for forming purposes. Alternatively, the resin may when cured be flexible in the direction transverse to the fiber direction, but substantially rigid in the fiber direction to withstand the structural compression load as the voice coil is moved by the magnetic field, particularly at low frequencies. When such a flexible resin carrier is provided, it can be formed as a sheet 30, as seen in FIG. 3, whose edges 31 can be joined in any suitable manner at seam 15 of former tube 10. Although edges 31 are shown butted together at seam 15, they can also be overlapped (not shown). The turns of voice coil 11 preferably are bonded to one another, after being wound, by a suitable adhesive (not shown) applied over voice coil 11 as is well known in loudspeaker construction. As shown in FIG. 1, a portion 16 of former tube 10 is not covered by voice coil 11. This portion 16 can be placed in thermal conducting relationship with a heat sink (see below) , or voice coil 11 could extend substantially the full length of former tube 10 and the heat sink can be placed in contact with the ends of directionally thermally conductive fibers 13 at the end of former tube 10. Alternatively, fibers 13 could conduct heat directly into the air by radiation and/or convection at their ends . As stated above, a voice cone 40 (FIGS. 4 and 5) can also be made in accordance with the present invention with directionally thermally conductive fibers 13. Voice cone 40 includes a conical structure 41 made from sheet material similar to sheet 30. Conical structure 41 is typically not a true cone, but is truncated at narrow end 42, which is mounted adjacent voice coil 11 and former tube 10 when assembled into a loudspeaker (see below) , and preferably is covered by dome 44. Nevertheless, voice cone 40 preferably has a central longitudinal axis 43, preferably extending through what would be the apex of the cone. In accordance with the invention, directionally thermally conductive fibers 13 of voice cone 40 must be in thermal conductive relationship (e.g., by direct conduction or by radiation) with voice coil 11 in order to have the desired effect of carrying heat away from voice coil 11. Therefore, fibers 13 preferably should terminate at narrow end 42, and preferably should trace back substantially to axis 43 and what would be the apex of voice cone 40. The remote ends of fibers 13 preferably extend to the edge of the voice cone 40, where they can radiate heat to the ambient air, or can be connected to a suitable heat sink (such as the frame of the loudspeaker) . FIG. 5 shows one embodiment of a fiber- bearing resin carrier in the form of a sheet 50 from which conical structure 41 could be made. Although sheet 50 is shown as a square, it could be made circular. Sheet 50 is formed with its directionally thermally conductive fibers 13 extending substantially from a central point 51. An annular section 52, with an angular sector 53 (here, 45°) missing, is cut from sheet 50 and can be formed into conical structure 41. Of course, as discussed above in connection with former tube 10, conical structure 41 could be formed in its conical shape, particularly where resin 21 is not flexible when cured. FIGS. 6 and 6A show a loudspeaker 60 made from one or more heat-dissipating components according to the invention. Loudspeaker 60 preferably includes frame 61, typically metallic, having an large opening 62 supporting voice cone 40 and a small opening at end 63, opposite end 62, which preferably houses permanent magnet 64, adjacent to which is preferably mounted former tube 10 carrying voice coil 11. A dome 44 preferably covers the opening at end 42 of voice cone 40. Former tube 10 preferably is further supported by a corrugated "spider" 66 — used in many speakers to center voice coil 11 relative to frame 61 -- which preferably is in thermally conductive relationship with frame 61, preferably by direct conduction. Voice coil 11 and former tube 10 preferably are located in an air gap 650 in a magnetic circuit preferably formed by magnet 64 , backing plate and pole piece assembly 640, and top plate 65. Former tube 10 is thus in thermally conductive relationship, by radiation, with top plate 65. Top plate 65 is in turn in thermally conductive relationship, by direct conduction, with frame 61 and magnet 64. Magnet 64, in turn, is in thermally conductive relationship, by direct conduction, with backing plate and pole piece assembly 640. Portions 65 and 640 thus preferably serve as a heat sink to remove heat radiated across gap 650 from former tube 10. Backing plate and pole piece assembly 640 itself preferably is also in thermal conductive relationship, by radiation, with former tube 10, insofar as it is mounted, as shown, partially within former tube 10. Radiation conducted by directionally thermally conductive fibers 13 in former tube 10 to the end of former tube 10 near backing plate and pole piece assembly 640 is preferably radiated to assembly 640, which sinks that heat, and preferably conducts it to magnet 64, in addition to the heat radiated across gap 650. Moreover, top plate 65 is preferably in thermally conductive relationship (e.g., at 63) with frame 61, so that the entire frame 61 preferably functions as a heat sink for heat radiated across gap 650. Heat is also conducted preferably by direct conduction, as discussed above, by spider 66 to frame 61. Voice cone 40 preferably is sufficiently close to voice coil 11 and/or former tube 10 to be in thermal conductive relationship, so that its directionally thermally conductive fibers 13 also can conduct heat from voice coil 11 through surround 67 at end 62 to frame 61 which serves as a heat sink. Surround 67 may itself include directionally thermally conductive fibers (not shown) to increase its conductivity. As an alternative to using portions of loudspeaker 60 as heat sinks, a dedicated heat sink (not shown) can be provided in thermally conductive relationship with directionally thermally conductive fibers 13 in one or more components 10, 20 that contain such fibers 13. Other loudspeaker components can be made incorporating directionally thermally conductive fibers 13 to remove heat from voice coil 11. For example, spider 66 could be made with one or more such fibers 13 to improve its ability to conduct heat to frame 61. In a further embodiment of the invention, the former tube and voice cone could be made as a single unitary piece 70, as shown in FIG. 7. Of course, such a structure could not be made from a flat sheet, and would have to be molded from resin 21 into its final shape, which preferably resembles a funnel. The directionally thermally conductive fibers 13 would preferably be aligned so that they are substantially parallel to longitudinal axis 71 in former tube segment 72 and then extend substantially radially in voice cone segment 73. An advantage of this structure is that a single continuous such fiber 13, as shown, can extend from one end of former tube segment 72 all the way to the far end of voice cone segment 73. Heat conduction and dissipation by the voice cone segment 73 would be improved as compared to the embodiment of FIGS. 4-6 because heat transfer to voice cone segment 73 would occur directly through fibers 13 in thermally conductive relationship with voice coil 11, rather than by conduction across the gap between voice coil 11 and voice cone 40. Thus it is seen that a loudspeaker former tube that is resistant to charring and that conducts heat away from the loudspeaker voice coil, as well as a loudspeaker cone that is resistant to charring and that conducts heat away from the loudspeaker voice coil, has been provided, along with the ability to provide a thermal conduction path in any loudspeaker component for dissipating heat from the loudspeaker voice coil. One skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation, and the present invention is limited only by the claims which follow.

Claims: WHAT IS CLAIMED IS: 1. A heat-dissipating component for a loudspeaker, said heat-dissipating component comprising: a carrier; and at least one directionally thermally conductive fiber embedded in said carrier. 2. The heat-dissipating component of claim 1 comprising a plurality of said directionally thermally conductive fibers. 3. The heat-dissipating component of claim 2 wherein said plurality of said directionally thermally conductive fibers are substantially parallel to one another. 4. The heat-dissipating component of claim 2 wherein each of said directionally thermally conductive fibers extends through said carrier without crossing any other of said directionally thermally conductive fibers. 5. The heat-dissipating component of claim 1 further comprising a heat sink in thermally conductive relationship with said at least one directionally thermally conductive fiber. 6. The heat-dissipating component of claim 1 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 7. The heat-dissipating component of claim 6 wherein said metallic substrate fiber comprises tungsten coated with boron. 8. The heat-dissipating component of claim 6 wherein said carbon fiber comprises pitch-based carbon fiber. 9. The heat-dissipating component of claim 8 further comprising electrical insulation around at least said pitch-based carbon fiber. 10. The heat-dissipating component of claim 1 wherein said carrier comprises a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 11. The heat-dissipating component of claim 10 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether-imide and poly-ether ether ketone. 12. The heat-dissipating component of claim 10 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 13. A loudspeaker comprising: a voice coil having a longitudinal axis; and a heat-dissipating component in thermally conductive relationship with said voice coil, said heat-dissipating component comprising: a carrier, and at least one directionally thermally conductive fiber embedded in said carrier and having at least a first portion in thermally conductive relationship with said voice coil. 14. The loudspeaker of claim 13 wherein said heat-dissipating component comprises a plurality of said directionally thermally conductive fibers, each having at least a respective first portion in thermally conductive relationship with said voice coil. 15. The loudspeaker of claim 14 wherein said plurality of said directionally thermally conductive fibers are substantially parallel to one another and to said longitudinal axis. 16. The loudspeaker of claim 14 wherein said directionally thermally conductive fibers extend substantially radially, substantially from said longitudinal axis. 17. The loudspeaker of claim 13 wherein: each of said at least one directionally thermally conductive fiber has a respective second portion; said loudspeaker further comprising: a heat sink in thermally conductive relationship with at least one of said respective second portion. 18. The loudspeaker of claim 17 wherein said heat sink is in thermally conductive relationship with each said respective second portion. 19. The loudspeaker of claim 13 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 20. The loudspeaker of claim 19 wherein said metallic substrate fiber comprises tungsten coated with boron. 21. The loudspeaker of claim 19 wherein said carbon fiber comprises pitch-based carbon fiber. 22. The loudspeaker of claim 21 further comprising electrical insulation between said pitch- based carbon fiber and said voice coil. 23. The loudspeaker of claim 13 wherein said carrier comprises a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 24. The loudspeaker of claim 23 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether- imide and poly-ether ether ketone. 25. The loudspeaker of claim 23 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 26. A former tube for a loudspeaker voice coil, said former tube comprising: a tubular wall having a longitudinal axis; and at least one directionally thermally conductive fiber embedded in said tubular wall. 27. The former tube of claim 26 comprising a plurality of said directionally thermally conductive fibers. 28. The former tube of claim 27 wherein said plurality of said directionally thermally conductive fibers are substantially parallel to one another and to said longitudinal axis. 29. The former tube of claim 26 further comprising a heat sink in thermally conductive relationship with at least a portion of said at least one directionally thermally conductive fiber. 30. The former tube of claim 26 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 31. The former tube of claim 30 wherein said metallic substrate fiber comprises tungsten coated with boron. 32. The former tube of claim 30 wherein said carbon fiber comprises pitch-based carbon fiber. 33. The former tube of claim 32 further comprising electrical insulation around at least said pitch-based carbon fiber. 34. The former tube of claim 33 wherein said electrical insulation extends around said tubular wall. 35. The former tube of claim 26 wherein said tubular wall comprises a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 36. The former tube of claim 35 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether- imide and poly-ether ether ketone. 37. The former tube of claim 35 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 38. A loudspeaker comprising: a heat-dissipating former tube; and a voice coil having a coil longitudinal axis; wherein: said heat-dissipating former tube comprises: a tubular wall having a tube longitudinal axis, and at least one directionally thermally conductive fiber embedded in said tubular wall; and said voice coil is wound against said heat-dissipating former tube with said coil longitudinal axis substantially aligned with said tube longitudinal axis, said voice coil being in thermally conductive relationship with at least a first portion of said at least one directionally thermally conductive fiber. 39. The loudspeaker of claim 38 wherein said tubular wall comprises a plurality of said directionally thermally conductive fibers each having at least a respective first portion in thermally conductive relationship with said voice coil. 40. The loudspeaker of claim 39 wherein said plurality of said directionally thermally conductive fibers are substantially parallel to one another and to said tube longitudinal axis. 41. The loudspeaker of claim 38 further comprising a heat sink in thermally conductive relationship with at least a second portion of said at least one directionally thermally conductive fiber. 42. The loudspeaker of claim 38 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 43. The loudspeaker of claim 42 wherein said metallic substrate fiber comprises tungsten coated with boron. 44. The loudspeaker of claim 42 wherein said carbon fiber comprises pitch-based carbon fiber. 45. The loudspeaker of claim 44 further comprising electrical insulation around at least said pitch-based carbon fiber. 46. The loudspeaker of claim 45 wherein said electrical insulation extends around said tubular wall. 47. The loudspeaker of claim 38 wherein said tubular wall comprises a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 48. The loudspeaker of claim 47 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether- i ide and poly-ether ether ketone. 49. The loudspeaker of claim 47 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 50. A voice cone for a loudspeaker, said voice cone comprising: a substantially conical wall having a longitudinal axis; and at least one directionally thermally conductive fiber embedded in said substantially conical wall. 51. The voice cone of claim 50 comprising a plurality of said directionally thermally conductive fibers. 52. The voice cone of claim 51 wherein said plurality of said directionally thermally conductive fibers extend substantially radially, substantially from said longitudinal axis. 53. The voice cone of claim 50 further comprising a heat sink in thermally conductive relationship with a portion of said at least one directionally thermally conductive fiber. 54. The voice cone of claim 50 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 55. The voice cone of claim 54 wherein said metallic substrate fiber comprises tungsten coated with boron. 56. The voice cone of claim 54 wherein said carbon fiber comprises pitch-based carbon fiber. 57. The voice cone of claim 50 wherein said substantially conical wall comprises a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 58. The voice cone of claim 57 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether- imide and poly-ether ether ketone. 59. The voice cone of claim 57 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 60. A loudspeaker comprising: a heat-dissipating voice cone; and a voice coil having a coil longitudinal axis; wherein: said heat-dissipating voice cone comprises : a substantially conical wall having a cone longitudinal axis, and at least one directionally thermally conductive fiber embedded in said substantially conical wall; and said voice coil is adjacent said heat- dissipating voice cone with said coil longitudinal axis substantially aligned with said cone longitudinal axis, said voice coil being in thermally conductive relationship with a first portion of said at least one directionally thermally conductive fiber. 61. The loudspeaker of claim 60 wherein said substantially conical wall comprises a plurality of said directionally thermally conductive fibers each having at least a respective first portion in thermally conductive relationship with said voice coil. 62. The loudspeaker of claim 61 wherein said plurality of said directionally thermally conductive fibers extend substantially radially, substantially from said cone longitudinal axis. 63. The loudspeaker of claim 60 further comprising a heat sink in thermally conductive relationship with at least a second portion of said at least one directionally thermally conductive fiber. 64. The loudspeaker of claim 60 further comprising a heat-dissipating former tube, said heat- dissipating former tube comprising: a tubular wall having a tube longitudinal axis, and at least a second directionally thermally conductive fiber embedded in said tubular wall; wherein: said voice coil is wound against said heat-dissipating former tube with said coil longitudinal axis substantially aligned with said tube longitudinal axis, said voice coil being in thermally conductive relationship with at least a first portion of said at least a second directionally thermally conductive fiber. 65. The loudspeaker of claim 64 wherein said at least a second directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 66. The loudspeaker of claim 65 wherein said metallic substrate fiber comprises tungsten coated with boron. 67. The loudspeaker of claim 65 wherein said carbon fiber comprises pitch-based carbon fiber. 68. The loudspeaker of claim 64 wherein said tubular wall comprises a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 69. The loudspeaker of claim 64 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether- i ide and poly-ether ether ketone. 70. The loudspeaker of claim 64 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 71. The loudspeaker of claim 60 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 72. The loudspeaker of claim 71 wherein said metallic substrate fiber comprises tungsten coated with boron. 73. The loudspeaker of claim 60 wherein said carbon fiber comprises pitch-based carbon fiber. 74. The loudspeaker of claim 60 wherein said substantially conical wall comprises a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 75. The loudspeaker of claim 74 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether- i ide and poly-ether ether ketone. 76. The loudspeaker of claim 74 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 77. A integrated former tube and voice cone for a loudspeaker, said integrated former tube and voice cone comprising: a tubular wall portion having a tube longitudinal axis; a substantially conical wall portion having a cone longitudinal axis substantially aligned with said tube longitudinal axis, said tubular wall portion merging into said substantially conical wall portion; and at least one directionally thermally conductive fiber embedded in, and extending continuously through, said merged tubular and substantially conical wall portions. 78. The integrated former tube and voice cone of claim 77 comprising a plurality of said directionally thermally conductive fibers. 79. The integrated former tube and voice cone of claim 78 wherein said plurality of said directionally thermally conductive fibers are substantially parallel to one another and to said tube longitudinal axis in said tubular wall portion, and extend substantially radially, substantially from said cone longitudinal axis, in said substantially conical wall portion. 80. The integrated former tube and voice cone of claim 77 further comprising a heat sink in thermally conductive relationship with at least a portion of said at least one directionally thermally conductive fiber. 81. The integrated former tube and voice coil of claim 77 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 82. The integrated former tube and voice coil of claim 81 wherein said metallic substrate fiber comprises tungsten coated with boron. 83. The integrated former tube and voice cone of claim 81 wherein said carbon fiber comprises a pitch-based carbon fiber. 84. The integrated former tube and voice cone of claim 83 further comprising electrical insulation around at least said pitch-based carbon fiber. 85. The integrated former tube and voice cone of claim 84 wherein said electrical insulation extends around said tubular wall portion. 86. The integrated former tube and voice coil of claim 77 wherein said tubular wall portion and said substantially conical wall comprise a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 87. The integrated former tube and voice coil of claim 86 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether-i ide and poly-ether ether ketone. 88. The integrated former tube and voice coil of claim 86 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide. 89. A loudspeaker comprising: a heat-dissipating integrated former tube and voice cone; and a voice coil having a coil longitudinal axis; wherein: said heat-dissipating integrated former tube and voice cone comprises: a tubular wall portion having a tube longitudinal axis, a substantially conical wall portion having a cone longitudinal axis substantially aligned with said tube longitudinal axis, said tubular wall portion merging into said substantially conical wall portion, and at least one directionally thermally conductive fiber embedded in, and extending continuously through, said merged tubular and substantially conical wall portions; and said voice coil is wound against said heat-dissipating integrated former tube and voice coil with said coil longitudinal axis substantially aligned with said tube longitudinal axis, said voice coil being in thermally conductive relationship with at least a first portion of said at least one directionally thermally conductive fiber. 90. The loudspeaker of claim 89 wherein said tubular wall portion comprises a plurality of said directionally thermally conductive fibers each having at least a respective first portion in thermally conductive relationship with said voice coil. 91. The loudspeaker of claim 90 wherein said plurality of said directionally thermally conductive fibers are substantially parallel to one another and to said tube longitudinal axis in said tubular wall portion, and extend substantially radially, substantially from said cone longitudinal axis in said substantially conical wall portion. 92. The loudspeaker of claim 89 further comprising a heat sink in thermally conductive relationship with at least a second portion of said at least one directionally thermally conductive fiber. 93. The loudspeaker of claim 89 wherein said at least one directionally thermally conductive fiber is selected from the group consisting of carbon fiber, metal-coated fiber and metallic substrate fiber. 94. The loudspeaker of claim 93 wherein said metallic substrate fiber comprises tungsten coated with boron. 95. The loudspeaker of claim 93 wherein said carbon fiber comprises pitch-based carbon fiber. 96. The loudspeaker of claim 89 further comprising electrical insulation around at least said pitch-based carbon fiber. 97. The loudspeaker of claim 96 wherein said electrical insulation extends around said tubular wall portion. 98. The loudspeaker of claim 89 wherein said tubular wall portion and said substantially conical wall comprise a resin selected from the group consisting of thermoplastic resin, thermosetting resin, ceramic resin and silicone resin. 99. The loudspeaker of claim 98 wherein said thermoplastic resin is selected from the group consisting of polyether sulfone, polyimide, polyether- imide and poly-ether ether ketone. 100. The loudspeaker of claim 98 wherein said thermosetting resin is selected from the group consisting of epoxy, phenolic resin, bismaleimide and cross-linking polyimide.

Inventors: ROGERS SCOTT A, ROGERS, SCOTT, A.
Applicants: CYTEC TECH CORP, CYTEC TECHNOLOGY CORP.
Application year: 1999
Main classification: H04R9
IPC codes: H04R9