Semi-solid balanced audio cable

Abstract

Audio cables including a conductor spirally wrapped in a non-conductive thread to centrally position the conductor within a channel comprising mostly air include a first conductor having a first diameter, and a non-conductive thread spirally wrapped around the center conductor, the non-conductive thread having a second diameter. A first jacket surrounds the center conductor and thread, having an inner diameter approximately equal to the first diameter plus twice the second diameter. A second conductor surrounds the first jacket and/or the center conductor and thread. In many implementations, the first diameter is less than the second diameter. A radially symmetric filler comprising a plurality of arms may form a corresponding plurality of channels.

Claims

1. An audio cable, comprising: a filler comprising a plurality of arms forming a corresponding plurality of channels, each having a first cross-sectional area; a plurality of first conductors, each approximately centered within a corresponding channel, and each having a second cross-sectional area; a plurality of non-conductive threads, each spirally wrapped around a conductor of the plurality of first conductors, and each having a third cross-sectional area; and a first jacket surrounding the filler, conductors, and threads; wherein a sum of the second cross-sectional area of each first conductor and the third cross-sectional area of each thread is equal to less than 30% of the first cross-sectional area of each channel.

2. The audio cable of claim 1, wherein the filler is radially symmetric.

3. The audio cable of claim 1, further comprising a plurality of second jackets, each surrounding a first conductor and corresponding thread and supported within a channel by adjacent arms of the filler.

4. The audio cable of claim 3, wherein each first conductor has a first diameter, each thread has a second diameter, and each of the plurality of second jackets has an inner diameter approximately equal to the first diameter plus twice the second diameter.

5. The audio cable of claim 1, wherein each first conductor has a first diameter, each thread has a second diameter, and the first diameter is between 40-60% of the second diameter.

6. The audio cable of claim 1, wherein each thread has a circular cross-section.

7. The audio cable of claim 1, wherein each arm of the filler terminates in a broadened region such that each channel has an approximately pentagonal border.

8. The audio cable of claim 1, wherein each channel between the filler and the corresponding first conductor is filled by the corresponding thread by less than 30%.

9. The audio cable of claim 1, further comprising a second conductor surrounding the first jacket.

10. The audio cable of claim 9, wherein the second conductor comprises a conductive braid or conductive foil.

11. The audio cable of claim 9, wherein the second conductor comprises a conductive foil.

12. The audio cable of claim 11, wherein the second jacket comprises an inner plastic layer and an outer textile layer.

13. The audio cable of claim 9, further comprising a second jacket surrounding the second conductor.

14. The audio cable of claim 1, wherein each channel contains air.

15. The audio cable of claim 1, wherein the first jacket has a circular cross-section.

16. The audio cable of claim 1, further comprising an electrical connector having a first portion attached to at least one of the plurality of first conductors and a second portion attached to a second at least one of the plurality of first conductors.

17. The audio cable of claim 1, wherein the plurality of non-conductive threads are each spirally wrapped around the corresponding first conductor with a first lay direction; and wherein the filler is twisted in a second, opposing lay direction.

18. An audio cable, comprising: a jacket; a filler positioned within the jacket, the filler comprising a plurality of arms forming a corresponding plurality of channels; a plurality of non-conductive threads, each configured in a spiral within a corresponding channel of the plurality of the channels; and a plurality of first conductors, each in contact with a thread and approximately centered within a corresponding channel of the plurality of channels; wherein an inner diameter of each channel is larger than the sum of a diameter of the thread and the diameter of the first conductor positioned within said channel.

19. The audio cable of claim 18, further comprising a second conductor surrounding the jacket.

20. The audio cable of claim 19, wherein the plurality of first conductors comprises a first diagonally opposed pair of conductors and a second diagonally opposed pair of conductors; and further comprising a connector having a first portion connected to the first diagonally opposed pair of conductors, and a second portion connected to the second diagonally opposed pair of conductors.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1A is a cross section of an embodiment of a semi-solid coaxial audio cable;

(2) FIG. 1B is a cutaway side view of the embodiment of a semi-solid coaxial audio cable of FIG. 1A;

(3) FIG. 2 is a chart of percentage of air void compared to center conductor diameter for a fixed inner diameter of a tube for the embodiments of semi-solid coaxial audio cables of FIGS. 1A-1B;

(4) FIG. 3A is a cross section of an embodiment of a semi-solid audio cable incorporating a filler;

(5) FIG. 3B is a cross section of an embodiment of the filler of FIG. 3A; and

(6) FIG. 3C is a cutaway side view of a the embodiment of a semi-solid audio cable incorporating a filler of FIG. 3A.

(7) In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawings are not shown to scale, and sizes of various components and features of the drawings may be different in various embodiments.

DETAILED DESCRIPTION

(8) Signal velocity in a coaxial cable is affected by self inductance due to skin effect and the dielectric material between the conductors. The former may be minimized by using smaller gauge wires, while the latter may be minimized by removing as much of the dielectric material as possible, as air has a dielectric constant nearly equal to that of vacuum.

(9) In some implementations of a semi-solid coaxial cable, a center conductor may be spirally wrapped with a non-conductive thread. The thread may support a jacket and keep the conductor centered within the cable, while providing an air void around the conductor. The jacket may be surrounded by a conductive braid or another conductor, and in many implementations, other outer jacket. In order to keep the conductor centered, the inner diameter of the inner jacket is roughly equal to the conductor diameter plus twice the thread diameter.

(10) FIG. 1A is across section of an embodiment of a semi-solid coaxial audio cable 100. In brief overview, a center conductor 102 is spirally wrapped by a non-conductive thread 104. The thread supports an inner jacket 106 and centers the center conductor 102 within a tube 108, which may comprise mostly air. The inner jacket 106 may be surrounded by an outer conductor 110, which may itself be surrounded by an outer jacket 112.

(11) Still referring to FIG. 1A and in more detail, a coaxial cable 100 includes a center conductor 102 and an outer conductor 110. Conductors 102, 110 may be of any conductive material, such as copper or oxygen-free copper (i.e. having a level of oxygen of 0.001% or less) or any other suitable material, including Ohno Continuous Casting (OCC) copper or silver. As shown, center conductor 102 may be approximately centered within cable 100. To provide uniformity of skin depth for signals in the audible band from 20 Hz to 20 kHz, the center conductor 102 may be very small, such as less than 20 AWG.

(12) A thread 104 may be spirally wrapped around center conductor 102 to position the center conductor within the tube 108 and support inner jacket 106. To keep the center conductor 102 centered, the SUM of the diameter of conductor 102 and twice the diameter of thread 104 are approximately equal to the inner diameter of inner jacket 106. In practice, center conductor 102 may be distorted from a straight line during the spiral wrapping of thread 104, leading to variations in capacitance between inner conductor 102 and outer conductor 110. Larger diameter conductors 102 may reduce this distortion, at the expense of greater self-inductance and skin effect at high frequencies. Accordingly, many implementations may use as narrow a center conductor 102 as possible that has minimal distortion from a center position within the coaxial cable, responsive to material stiffness and tensile strength. In some implementations, the conductor 102 may be less than 20 AWG, such as 24 AWG, 25 AWG, 26 AWG, or any other such size.

(13) Thread 104 may comprise any type or form of non-conductive material, including fluorinated ethylene propylene (FEP) or polytetrafluoroethylene (PTFE) Teflon®, high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), or any other type of insulating and/or low dielectric constant material. As shown, thread 104 may have a circular or substantially circular cross section, resulting in nearly zero contact between thread 104 and conductor 102 (for theoretical infinitely stiff thread 104 and conductor 102). This may further reduce propagation velocity reductions due to interactions of the dielectric material of thread 104 and conductor 102. Thread 104 may have a degree of twist or lay selected as a compromise of providing sufficient support for jacket 106 while maximizing the percentage of air in tube 108 per unit length. For example, in some implementations, thread 104 may make a complete circle around conductor 102 once per centimeter, once per inch, once per two inches, or any other such length.

(14) Turning briefly to FIG. 1B, illustrated is a cutaway side view of the embodiment of a semi-solid coaxial audio cable of FIG. 1A. As shown, thread 104 may spirally wrap around inner conductor 102. Thread 104 may have a clockwise or counter-clockwise wrap.

(15) Returning to FIG. 1A, as discussed above, thread 104 and conductor 102 may be surrounded by an inner jacket 106, forming a tube 108 comprising mostly air. In some implementations, other gases than air may be employed, including oxygen-free gases to reduce oxidation of conductor 102, such as nitrogen. Jacket 106 may be of any type or form of material, including FEP, PTFE, HDPE, LDPE, PP, rubber, plastic, fabric, or any other type of non-conductive material. Because jacket 106 is adjacent to conductor 110, jacket 106 may be selected from materials having a low dielectric constant (e.g. 1-3) relative to air, to reducing capacitance between conductors 102, 110. The insulation may also have a high dielectric strength, such as 400-4000 V/mil, allowing thinner walls and similarly reducing the amount of dielectric material by expanding the size of tube 108. For example, in some implementations, the jacket 106 may have an inner diameter of less than 0.1 inches, and an outer diameter of less than 0.2 inches. In some such implementations, the jacket 106 may have an outer diameter of less than 0.15, 0.14, or 0.13 inches.

(16) Jacket 106 may be surrounded by an outer conductor 110. As shown, in many implementations, outer conductor 110 may have a cross section of a toroid. As discussed above, outer conductor 110 may comprise any type and form of conductor, including copper or oxygen-free copper or any other suitable material, including Ohno Continuous Casting (OCC) copper or silver. In some implementations, outer conductor 110 may comprise a braid of many individual narrow gauge wires, providing flexibility with low direct current resistance. Specifically, when unbalanced audio cables are used as interconnects, the signal grounds of attached components are linked. Any ground level differences between the components will allow a “new” signal current to flow between component inputs and outputs. The unwanted ground current is multiplied by the shield resistance and produces a “signal” that may have a level similar to the s all signal levels of moving coil (MC) devices, such as phonograph transducers. In practice, it may be difficult to ensure that different components are at the same electrical ground level. Accordingly, to remove the unwanted ground current noise, it shield resistance may be reduced through the use of large outer conductors 110 or heavy braids.

(17) In some implementations, an outer jacket 112 may surround outer conductor 110. As with inner jacket 106, outer jacket 112 may be of any type or form of material, including FEP, PTFE, HDPE, LDPE, PP, rubber, plastic, fabric, polyvinyl chloride (PVC), or any other type of jacket material or combinations of such materials. For example, in one embodiment, an outer jacket 112 may comprise a textile inner jacket and PVC outer jacket for durability. The outer PVC jacket may be clear or tinted in various embodiments. In other embodiments, the jacket may comprise a nylon outer jacket over a PVC jacket for further increased durability. In some embodiments, jacket 112 may be flame resistant or designed to produce a plenum- or riser-rated cable. Frequently, jacket 112 may be printed, imprinted, silk screened, or otherwise labeled with model numbers, types, distance markings, or any other such data.

(18) In some implementations not illustrated, a shield may be provided between outer conductor 110 and outer jacket 112, such as a foil shield or other such shield, to further reduce direct current resistance of the outer conductor and/or reduce electrostatic interference.

(19) For a fixed inner diameter of inner jacket 106, the amount of air void within tube 108 is related to the ratio of the diameter of the conductor 102 to the diameter of the thread 104, but not in a linear relationship. Instead, the percentage of air void is proportional to the total area inside the inner jacket 106 minus the sum of the area of the conductor 102 and the area of the thread 104, or:

(20) $\begin{array}{c}\%\mathrm{air}=\mathrm{area}\mathrm{of}\mathrm{air}\text{/}\mathrm{area}\mathrm{inside}\mathrm{jacket}106\\ =[\mathrm{area}\mathrm{inside}\mathrm{jacket}106-(\mathrm{area}\mathrm{of}\mathrm{conductor}102+\\ \mathrm{area}\mathrm{of}\mathrm{thread}104)]\text{/}\mathrm{area}\mathrm{inside}\mathrm{jacket}106\\ =[\pi *{\left(\mathrm{jacket}106\mathrm{inner}\mathrm{diameter}\text{/}2\right)}^{.Math.}2-(\pi *[\mathrm{conductor}\\ {102\mathrm{diameter}\text{/}2)}^{.Math.}2]+\pi *{\left[\mathrm{thread}104\mathrm{diameter}\text{/}2\right]}^{.Math.}2)]\text{/}\\ \left[\pi *{\left(\mathrm{jacket}106\mathrm{inner}\mathrm{diameter}\text{/}2\right)}^{.Math.}2\right]\\ =[\pi *{\left(\mathrm{jacket}106\mathrm{inner}\mathrm{diameter}\text{/}2\right)}^{.Math.}2-(\pi *[\mathrm{conductor}\\ {102\mathrm{diameter}\text{/}2]}^{.Math.}2+\pi *[((\mathrm{jacket}106\mathrm{inner}\mathrm{diameter}-\\ {\mathrm{conductor}102\mathrm{diameter})\text{/}2)\text{/}2]}^{.Math.}2)]\text{/}[\pi *(\mathrm{jacket}\\ {106\mathrm{inner}\mathrm{diameter}\text{/}2)}^{.Math.}2]\end{array}$
This function 202 is illustrated in the chart 200 of FIG. 2 with percentage of air within tube 108 compared to center conductor 102 diameter for the embodiments of semi-solid coaxial audio cables of FIGS. 1A-1B. The example values shown are for a fixed inner diameter of jacket 106 equal to 0.098 inches. However, the same relationship holds for any jacket diameter, such that the percentage of air space is maximized when the conductor 102 diameter is equal to 50% of the thread 104 diameter, with 80% air within the tube 108 at point 204. For example, as illustrated, air percentage is maximized with conductor diameter of 0.0196 inches and thread diameter of 0.0392 inches, with jacket inner diameter of (0.0196+2*(0.0392)) or 0.098 inches. The percentage of air approaches this value asymptotically, so variations in conductor 102 and thread 104 diameters are acceptable. For example, in some implementations, the percentage of air may be above approximately 70%; or, in other words, the thread and conductor may fill less than 30% of the channel. However, as the wire size increases from peak 204 in region 208, capacitance between the inner and outer conductors increases. Accordingly, in some implementations, inner conductor diameters of less than 50% of the thread diameter, corresponding to region 206, may be utilized to provide acceptably low capacitance with high propagation velocity. Thus, in various implementations, the diameter of inner conductor may be between 40-60% of the thread diameter, and in many implementations, the diameter may be between 40-50% of the thread diameter.

(21) Accordingly, a coaxial cable constructed according to the implementations discussed herein provides high propagation velocity across the audible band with low self-inductance due to the removal of dielectric material and low capacitance due to the maintained geometry and spacing between conductors. For example, in some implementations, capacitance may be less than 12 pF/foot. Inductance may also be low, with many implementations having inductance of less than 0.15 μH/foot. Propagation velocity may be greater than 80% of c, with many implementations having propagation velocity greater than 8.5% or 88% of c. The cable may, in many implementations, be terminated with a connector or connectors, such as an RCA or phono-type connector, spade or ring connector, or any other type of connector, or may be connected to a terminal block, binding posts, or other such connections.

(22) Although discussed primarily in terms of cables having a round cross section, with outer conductors or jackets having toroidal cross sections, in some implementations, the same techniques may be applied to cables having other cross sections. For example, in one such implementation in which the cable is a “flat” cable having a rectangular cross section, the center conductor may have a rectangular profile, and the thread may be wrapped around the center conductor to support an inner jacket having a similar, larger rectangular cross section, while maintaining an air channel between the inner jacket and the center conductor.

(23) Additionally, the combination of inner conductor and thread may be utilized as a subcomponent of a balanced audio cable. A plurality of units, each comprising a conductor and spirally wrapped thread, may be provided to carry opposing polarities or legs of a signal to be summed to reject common mode interference. In one implementation, four units may be provided in a star-quad configuration with diagonally opposing pairs wired together as a single leg. The average position of each leg is therefore in the center of the cable, maximizing common mode rejection. A filler or spacer may be provided between the four units, channels for each unit formed between adjacent arms of the filler. The filler may maintain the geometry of the units in a square, even in the presence of external physical forces that would otherwise distort the units into a trapezoid or other shape. Additionally, by maintaining the spacing of the units, capacitance between the signal legs is reduced compared to star-quad cables without fillers, due to the increased inter-conductor distance.

(24) Referring now to FIG. 3A, illustrated is across section of an embodiment of a semi-solid audio cable 300 incorporating a filler 301. Cable 300 may include a filler 301 with a cross-shaped cross section providing channels or tubes 308a-308b (referred to generally as channel(s) 308), similar to tube 108 of FIG. 1A. A conductor 302a-302d (referred to generally as conductor(s) 302), similar to conductor 102, may be positioned in the center of each corresponding channel 308a-308d. Each conductor 302a-302d may be spirally wrapped with a corresponding thread 304a-304d (referred to generally as thread(s) 304), similar to thread 104.

(25) As discussed above in connection with FIG. 2, the percentage of air surrounding each conductor 302 within each corresponding channel 308 may be maximized via function 202 discussed above for conductor 302 diameters and thread 304 diameters, to approximately 80% air surrounding each conductor 302 within channel 308 in some embodiments. Accordingly, the performance of the balanced version of the cable with respect to signal propagation velocity and inductance may be substantially similar to the performance of the unbalanced version of the cable discussed above, while enjoying the benefit of increased noise reduction through common mode rejection of electromagnetic interference on the separate legs of the cable. For example, a channel 1308 with a volume of 0.00756 square inches is similar to the 0.00754 square inches volume of the unbalanced cabled with inner jacket inner diameter of 0.098 inches discussed above (albeit in a pentagon or “v-shape”), and may thus utilize a conductor with a diameter of 0.0196 inches and thread with diameter of 0.0392 inches to achieve an approximately 80% air space. For example, the table below shows the results of measurements of capacitance, inductance, and propagation velocity for one such embodiment of a semi-solid balanced cable, along with corresponding measurements for an embodiment of a semi-solid unbalanced cable having similar sizes:

(26) TABLE-US-00001 Unbalanced semi-solid cable Balanced semi-solid cable Chamber 0.00754 square inches 0.00756 square inches volume Conductor 0.0201 inches (24 AWG) 0.0201 inches (24 AWG) diameter Thread 0.0390 inches 0.0400 inches diameter Capacitance 13.7 pF/foot 10.0 pF/foot Inductance 0.157 μH/foot 0.147 μH/foot Velocity of 86.8% of c 87.2% of c Propagation

(27) Returning to FIG. 3A, in some implementations, each unit of a conductor 302 and corresponding thread 304 may be surrounded by a jacket (illustrated in dashed line), while in other implementations, the conductor/thread pairs may not be individually jacketed. In many implementations, an inner jacket 306, similar to inner jacket 106, may surround filler 301 and conductors 302/threads 304. In some implementations, inner jacket 306 may be replaced by a conductive braid and/or foil shield to provide protection from electrostatic interference. In other implementations, a conductive braid and/or foil shield may be placed around inner jacket 306. Signal to ground capacitance due to inner jacket 306 may be reduced compared to typical cables due to the spacing between conductors 302 and the inner jacket 306, supported by filler 301 with conductors 302 centered within each channel.

(28) In many implementations, the cable 300 may include an outer jacket 312 surrounding the inner jacket 306 and/or foil shield, filler 301, and conductors 302/threads 304. Outer jacket 312 may comprise any type and form of material, including FEP, PTFE, HDPE, LDPE, PP, rubber, plastic, fabric, polyvinyl chloride (PVC), or any other type of jacket material or combinations of such materials. For example, in one embodiment, an outer jacket 312 may comprise an inner textile jacket and outer PCV jacket, a PVC and nylon jacket, or any other type and form of material or combination of materials for increased durability. In some embodiments, outer jacket 312 may be flame resistant or designed to produce a plenum- or riser-rated cable. Frequently, outer jacket 312 may be printed, imprinted, silk screened, or otherwise labeled with model numbers, types, distance markings, or any other such data.

(29) FIG. 3B is a cross section of an embodiment of the filler 301 of FIG. 3A. Filler 301 may be of a non-conductive material such as flame retardant polyethylene (FRPE) or any other such low loss dielectric material. As shown, filler 301 may have a cross-shaped cross section with arms 320 radiating from a central point and terminating in enlarged portions or anvils 322 having end surfaces 324 and angled sides 326. Each arm 320 and anvil 322 may surround a channel 308, separating pairs of units of conductors 302 and threads 304, and providing structural stability to cable 300. Angled sides 326 and arms 320 may form four sides of a pentagon enclosing a channel 308. As discussed above, in many embodiments, each channel 308 may have a volume similar to the volume of channels 108 in embodiments of semi-solid unbalanced cables. Accordingly, function 220 discussed above may be used to select conductor 302 and thread 304 sizes to maximize air volume within channels 308. The filler allows a cylindrical shape for optimized ground plane uniformity and stability for improved capacitance stability cross the audio band. By physically separating conductors 302 carrying different polarities of a signal, capacitance may be reduced over cables with physically adjacent insulated conductors. Similarly, by providing structural support for air-filled channels, dielectric material is removed compared to such cables, as discussed above in connection with the unbalanced coaxial cable.

(30) Filler 301 may be of any size, depending on the diameter of the Channels 308 desired. For example, in one embodiment of a cable with an outer diameter of approximately 0.275″, the filler may have an anvil edge to anvil edge measurement of approximately 0.235″. Although shown symmetric, in some embodiments, the anvils 322 may have asymmetric profiles. Similarly, although shown flat, in some embodiments end surfaces 324 may be curved to match an inner surface of a circular jacket of cable 300.

(31) FIG. 3C is a cutaway side view of an embodiment of a portion of a semi-solid audio cable 300 incorporating a filler 301 of FIG. 3A. Outer jacket 312 and/or conductive braid or foil shields are not illustrated. As shown, each pair of conductors 304 and threads 302 may be positioned within channels formed between arms of the filler 301, with position of each conductor in the center of its corresponding channel maintained via the spirally wrapped thread in conjunction with filler 301 and inner jacket 306. In many implementations, the cable 300 may be terminated in a connector, such as an XLR connector, tip-ring-sleeve (TRS) connector, or any other type and form of connector.

(32) Although illustrated in FIG. 3C with different directions of spiral wrapping or “lay” of the thread 304 around conductor 302 (e.g. a clockwise or right hand lay for thread 304a and a counter-clockwise or left hand lay for thread 304d), in many implementations, each thread 304a-304d may have the same direction of spiral or lay. The lay or wrapping may have any length, such as one complete revolution of thread 304 around a conductor 302 per foot, one revolution per yard, two revolutions per foot, six revolutions per foot, or any other such rate. The rate may be selected to maximize air volume within each channel while still supporting each conductor 302.

(33) Furthermore, the overall cable 300 may have a twist or lay, with filler 301 (and conductor/thread pairs) rotated around the axis of the cable along its length (not illustrated). The cable lay may also be of any length, such as one complete revolution per foot, one revolution per yard, two revolutions per foot, six revolutions per foot, or any other such rate. In some implementations, the cable lay may be the same as each thread lay (e.g. right-hand cable lay and right-hand thread lay). In other implementations, the cable lay may be different from the thread lay. For example, in one such implementation, the thread lay may be a right-hand lay, and the cable lay may be a left-hand lay, or vice versa. In such implementations, the reversed direction of the cable lay may serve to “untwist” the threads, reducing tension on each thread around the corresponding conductor. This reduced tension may help maintain the positioning of the conductor within each corresponding conductor, by reducing pressure from the thread that would distort the path of the conductor. In some implementations, the reduced tension may also result in the thread partially losing contact with the conductor, resulting in a small additional channel of air immediately adjacent to the conductor in the region where the magnetic fields are strongest. This may further reduce dielectric effect, as discussed above.

(34) The above description in conjunction with the above-reference drawings sets forth a variety of embodiments for exemplary purposes, which are in no way intended to limit the scope of the described methods or systems. Those having skill in the relevant art can modify the described methods and systems in various ways without departing from the broadest scope of the described methods and systems. Thus, the scope of the methods and systems described herein should not be limited by any of the exemplary embodiments and should be defined in accordance with the accompanying claims and their equivalents.