Abstract:
The present disclosure describes implementations of audio cables including a conductor spirally wrapped in a non-conductive thread to centrally position the conductor within a channel comprising mostly air, reducing propagation delay and self-inductance compared to cables utilizing non-air dielectric materials that completely surround the conductor. A coaxial cable includes 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.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority to and the benefit of U.S. Provisional Application 61/920,618, entitled “Semi-Solid Balanced and Unbalanced Audio Cables,” filed Dec. 24, 2013, the entirety of which is hereby incorporated by reference. 
     
    
     FIELD 
       [0002]    The present application relates to audio cables. In particular, the present application relates to audio cables having a semi-solid region around a conductor. 
       BACKGROUND 
       [0003]    Audio cables for interconnecting equipment, commonly referred to as interconnects, typically carry signals of 1 volt or less, including signals as low as 0.25 millivolts. These low-level signals can be easily distorted by capacitive, inductive, and dielectric effects. Additionally, as audio signals typically cover a wide frequency range of 10 octaves from 20 Hz to 20 kHz, propagation velocity of a signal through the interconnect may vary widely, depending on dielectric material. Specifically, the characteristic impedance of a cable Z 0  is defined as: 
         [0000]        Z   0 =[( R+j 2π fL )/( G+j 2π fC )] 1/2  
 
         [0000]    with resistance R, conductance G, inductance L, capacitance C, imaginary unit j, and frequency f. Within the typical human audible range of around 20 Hz to 20 kHz, R is typically much larger than j2πfL and j2πfC is typically much larger than G, so the cable impedance can be simplified as: 
         [0000]        Z   0   =[R/j 2π fC]   1/2  
 
         [0000]    Accordingly, cable impedance at 20 Hz may be drastically different than impedance at 20 kHz, three orders of magnitude higher. 
         [0004]    Dielectric material around a conductor will affect the propagation velocity of signals in the conductor. Specifically, the velocity factor VF or ratio of the velocity of the signal in the conductor to the velocity of a signal in vacuum (i.e. the speed of light, c) is the reciprocal of the square root of the dielectric constant of the material (e.g. 1 for vacuum). Air has a dielectric constant only slightly above that of vacuum (e.g. roughly 1.00059 at standard temperature and pressure). However, conductors surrounded or separated by air may be impractical: such conductors may need to be rigidly fixed in place to avoid short circuits or variations in geometry or spacing, leading to changes in capacitance. Accordingly, many cables employ polyethylene or similar material for structural support. For example, many coaxial cables surround a center conductor with a polyethylene foam, supporting an outer conductor. By using a foam containing a large portion of air, the dielectric constant of the material is reduced compared to solid polyethylene. However, the velocity factor of such cables may still be approximately 80%. As with self inductance or impedance effects, propagation velocity is similarly frequency dependent and, with wide differences between arrival times of low frequency components and high frequency components of an audio signal, can result in audible phase distortion and “smearing”. 
       SUMMARY 
       [0005]    To overcome signal velocity impairments in a cable, narrow gauge conductors may be used to reduce skin effect by ensuring that high frequency signals utilize the full depth of the conductor. For example, with a large diameter (low gauge) copper conductor with a radius measured in millimeters, a low frequency signal at 20 Hz may travel via the entire depth of the conductor, while a high frequency signal at 20 kHz may travel only via a thin layer on the outside of the conductor less than a millimeter in depth. Accordingly, by using conductors with a radius equal to the sub-millimeter skin depth, both low and high frequency signals will travel via the entire conductor. Additionally, the amount of non-air dielectric material surrounding a conductor may be reduced while still maintaining position and structural support by spirally wrapping the conductor with a non-conductive thread or bead of material, or a plastic or dielectric coated thread, with an air void formed between the conductor and a jacket and/or outer conductor supported by the thread. Because the strength of a magnetic field around a conductor is inversely proportional to the square of the distance from the conductor, a polyethylene foam dielectric material creates a gradient of dielectric effect that is strongest immediately adjacent to the conductor, and is thus inferior to even a small air gap around the conductor, which results in a step function for the dielectric effect. The diameter of the thread or bead may be selected to maximize the percentage of air within the jacket and/or outer conductor, resulting in the maximum possible velocity factor, and a minimum of contact between the thread and conductor. 
         [0006]    In one aspect, the present disclosure is directed to a coaxial audio cable. The cable includes 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. In some implementations, 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. 
         [0007]    In some implementations, the audio cable includes a second jacket surrounding the second conductor. In many implementations, the first conductor is approximately centered in the cable. In some implementations, a region between the first jacket and first conductor is filled by the thread by less than 30%. In other implementations, the first diameter is between 40-60% of the second diameter. In still other implementations, the first diameter is between 40-50% of the second diameter. In many implementations, the thread has a circular cross-section. 
         [0008]    In some implementations, the audio cable includes a channel formed by an inner surface of the first jacket, and a sum of the cross-sectional areas of the first conductor and thread is equal to less than 30% of a cross-sectional area of the channel. In a further implementation, the channel contains air. In many implementations, the first diameter is between 40-50% of the second diameter. 
         [0009]    In some implementations of the audio cable, the thread has a circular cross-section. In other implementations, the first jacket has a circular cross-section. In still other implementations, the second conductor includes a conductive braid and/or a conductive foil shield. In many implementations, the audio cable terminates in a connector attached to the first conductor and second conductor. 
         [0010]    In another aspect, the present disclosure is directed to an audio cable with a first conductor, and an inner jacket surrounded by the first conductor. The cable also includes a non-conductive thread configured in a spiral within the inner jacket, and a second conductor in contact with the non-conductive thread and approximately centered within the inner jacket. 
         [0011]    In some implementations, the first conductor has a toroidal cross section. In other implementations, the second conductor is approximately centered within the first conductor. In still other implementations, an inner diameter of the inner jacket is larger than the sum of a diameter of the thread and a diameter of the second conductor. In some implementations, the cable includes an outer jacket surrounding the first conductor. In other implementations, the cable includes a channel formed by an inner surface of the inner jacket, and a sum of the cross-sectional areas of the second conductor and thread is equal to less than 30% of a cross-sectional area of the channel. In a further implementation, the channel contains air. 
         [0012]    The features of unbalanced coaxial cables described herein may also be applied to balanced audio cables. In one such implementation, a non-conductive filler material having a cross-shaped cross section is centered within the cable, with conductors positioned within channels or air voids between each arm of the filler. To maintain positioning of the conductors in the centers of the corresponding channels, each conductor may be spirally wrapped with a non-conductive thread as discussed above in the implementations of unbalanced coaxial cables. Diagonally opposite conductors may be wired together in a configuration sometimes referred to as “star-quad”. Because the position of each conductor is tightly controlled, common mode interference rejection is improved. As discussed above, self-inductance is reduced with the use of smaller individual conductors. However, in typical star-quad configurations, capacitance is increased due to the proximity of the conductors. By spacing the conductors via the filler and air voids, capacitance is significantly reduced. Simultaneously, propagation velocity is maximized to nearly 100% of the theoretical maximum at the interface of the conductor and dielectric through the removal of dielectric material compared to foamed polyethylene cables. As discussed above, by removing dielectric material in the region immediately surrounding the conductor where the magnetic field is strongest, the most significant effects from the dielectric material come from the surrounding jacket, which, being spaced from the conductor by air, results in a dielectric constant that has a step function over distance from the conductor, compared to a gradient as in foamed dielectric cables. 
         [0013]    In one aspect, the present disclosure is directed to a balanced audio cable. The cable includes a radially symmetric filler comprising a plurality of arms forming a corresponding plurality of channels. The cable also includes a plurality of conductors, each approximately centered within a corresponding channel. The cable further includes a plurality of non-conductive threads, each spirally wrapped around a conductor of the plurality of conductors. In some implementations, the cable also includes a jacket surrounding the filler, conductors, and threads. 
         [0014]    In one implementation, the cable includes a plurality of second jackets, each surrounding a conductor and corresponding thread and supported within a channel by adjacent arms of the filler. In a further implementation, each 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. In other implementations, each conductor has a first diameter, each thread has a second diameter, and the first diameter is between 40-60% of the second diameter. In another implementation, each thread has a circular cross-section. In still another implementation, each arm of the filler terminates in a broadened region such that each channel has an approximately pentagonal border. In some implementations, each channel is filled by the corresponding thread by less than 30%. 
         [0015]    In many implementations, the cable includes a second conductor surrounding the jacket, and a second jacket surrounding the second conductor. In some implementations, the second conductor includes a conductive braid, while in other implementations, the second conductor includes a conductive foil. In some implementations, the second jacket includes an inner plastic layer and an outer textile layer. 
         [0016]    In some implementations of the audio cable, a sum of the cross-sectional areas of a first conductor and corresponding thread wrapped around said first conductor is equal to less than 30% of a cross-sectional area of the corresponding channel formed by adjacent arms of the filler. In many implementations, each channel contains air. 
         [0017]    In some implementations of the audio cable, the first jacket has a circular cross-section. In many implementations of the audio cable, the cable terminates in 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. In one such implementations, a first pair of first conductors positioned in diagonally opposing channels is attached to the first portion of the connector and a second pair of first conductors positioned a second set of diagonally opposing channels is attached to the second portion of the connector. In another implementation, a second conductor surrounding the first jacket is attached to a third portion of the connector. In still another implementation, the plurality of non-conductive threads are each spirally wrapped around the corresponding first conductor with a first lay direction; and the filler is twisted in a second, opposing lay direction. 
         [0018]    In still another aspect, the present disclosure is directed to an audio cable include a jacket, and a filler positioned within the jacket, the filler comprising a plurality of arms forming a corresponding plurality of channels. In some implementations, the filler may be radially symmetric. The cable includes a plurality of non-conductive threads, each configured in a spiral within a corresponding channel of the plurality of the channels. The cable also includes a plurality of first conductors, each in contact with a thread and approximately centered within a corresponding channel of the plurality of channels. 
         [0019]    In some implementations, the cable includes a second conductor surrounding the jacket. In other implementations, 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. 
         [0020]    The present disclosure describes methods of manufacture and implementations of semi-solid unbalanced and balanced audio cables. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0021]      FIG. 1A  is a cross section of an embodiment of a semi-solid coaxial audio cable; 
           [0022]      FIG. 1B  is a cutaway side view of the embodiment of a semi-solid coaxial audio cable of  FIG. 1A ; 
           [0023]      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 ; 
           [0024]      FIG. 3A  is a cross section of an embodiment of a semi-solid audio cable incorporating a filler; 
           [0025]      FIG. 3B  is a cross section of an embodiment of the filler of  FIG. 3A ; and 
           [0026]      FIG. 3C  is a cutaway side view of a the embodiment of a semi-solid audio cable incorporating a filler of  FIG. 3A . 
       
    
    
       [0027]    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 
       [0028]    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. 
         [0029]    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, an another 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. 
         [0030]      FIG. 1A  is a cross 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 . 
         [0031]    Still referring to  FIGS. 1A and 1   n  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. 
         [0032]    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. 
         [0033]    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. 
         [0034]    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. 
         [0035]    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. 
         [0036]    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 small 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. 
         [0037]    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. 
         [0038]    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. 
         [0039]    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: 
         [0000]    
       
         
           
             
               
                 
                   
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         [0000]    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. 
         [0040]    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 85% 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. 
         [0041]    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. 
         [0042]    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, with 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. 
         [0043]    Referring now to  FIG. 3A , illustrated is a cross 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  308   a - 308   b  (referred to generally as channel(s)  308 ), similar to tube  108  of  FIG. 1A . A conductor  302   a - 302   d  (referred to generally as conductor(s)  302 ), similar to conductor  102 , may be positioned in the center of each corresponding channel  308   a - 308   d . Each conductor  302   a - 302   d  may be spirally wrapped with a corresponding thread  304   a - 304   d  (referred to generally as thread(s)  304 ), similar to thread  104 . 
         [0044]    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  308  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: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                 Unbalanced semi-solid 
                 Balanced semi-solid 
               
               
                   
                 cable 
                 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 
                   
                   
                   
               
               
                   
               
             
          
         
       
     
         [0045]    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. 
         [0046]    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. 
         [0047]      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. 
         [0048]    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 . 
         [0049]      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. 
         [0050]    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  304   a  and a counter-clockwise or left hand lay for thread  304   d ), in many implementations, each thread  304   a - 304   d  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 . 
         [0051]    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. 
         [0052]    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.