GB2418524A - Multi stranded conductor core with a dual insulation system. - Google Patents

Abstract

A cable has a multi stranded conductor core 11, 13, 15 whereby at least one strand 11 is plated in a material with a different relative conductivity value such as silver. The conductor core is surrounded by a dual insulation system which comprises a first insulating layer 17 formed from a foam structured material surrounding the multi stranded core; and a second insulating layer 19 disposed around the said first insulating layer, the said second being a solid structure material. Preferably the foam layer is a material of polyethylene foamed with a gas such as air. Preferably the core strands are made from copper. The cable structure may also be constructed to form twisted or parallel cables sheathed by an overall jacket 21.

Description

24i 8524 Partially plated, stranded conductor and dual insulation system

electrical cable

Technical Field

The present invention relates to a cable that exhibits high phase velocity and low propagation delay with Improved direct current, low frequency and high frequency resistance for transmitting a broad frequency spectrum of signals for certain appficatons ncludmg, but not hmited to, audio frequency and audio frequency harmomc loudspeaker signals.

More specifically this Invention relates to a cable composing a finely stranded conductor consisting of plated and non-plated strands, with a dual layer, low dissipation, low dielectric coefficient insulation In an arrangement such that said cable demonstrates low propagation delay with Improved large signal current carrying capacity.

Background of the invention

The evolution of high fidelity audio reproduction has lead to an Increase in the sophistication of audio playback systems that enable reproduction of acoustic detail to a far greater accuracy and clarity than has previously been attainable.

In order for the audio reproduction system components to work and interact together to provide the overall high level of performance of the audio reproduction system, the components such as, but not limited to, amphfiers and loudspeakers require interconnection cables that give electrical connectivity between them with mmimal frequency related A.C. and DC electrical resistance, minimal reactive impedance, mimmal distortion and minimal electrical parasitic Influence on the currents and voltages that flow between the components.

The ability of the ear to detect relatively small phase and amphtude inaccuracies in audio signals and the effect this has on the perception of a sound source's position, sound field and the overall authenticity of the audio Images generated from an audio reproduction systems is surprisingly outstanding.

The Hass effect demonstrates how amplitude, relative timing and relative phase of the fundamental, harmonic and Fourier components of an audio signal provide the cues which the human brain Interprets and constructs spatial, positional and drectunal information with.

The three dimensional acoustic effect created by the human bran's Interpretation of the relative amplitude, among and phase of the fundamental, harmonic and Fourier components of a compound acoustic signal Is often referred to as the 'sound stage', 'staging', 'mage'or the 'sound field'.

The significance of fundamental, hannomc and Founer component's relative amplitude, phase and timing in audio signal is highlighted by the fact that many audio reproduction systems depend upon and manipulate these parameters to create and alter the apparent direction and position of sound sources and to provide a spatial Impression of the sound field. A signal with fundamental harmonic accurate relative phase and amphtude nl'ormaton Is referred to as a phase and amphtude coherent signal.

Loss of stable and correct relative phase and amplitude relationship of audio signal fundamental frequencies and component harmonics and the introduction of phase delays In a signal causes degradation of the audio spatial and directional Information and its perceived authenticity. This is acutely apparent In highly accurate and sensitive modern audio reproduction systems where phase and amplitude related distortions are mamlest as loss of the spatial Information and alteration of the Impression of the sound's three dimensional Image and sound field. This is especially apparent when hstening to sounds that are rich In harmonic Information that construct the compound sound and acoustic Image, such as a saxophone or human voice, and even more so with recorded 'clean' sounds that do not have added electronic effects, such as reverberation, that tend to mask sound source directionally.

Typically loss of phase and amplitude coherence of harmonics and Fourier components that are out of the basic 20Hz to 20kH audio band Is manifest by loss of clarity and stability and natural authenticity of the sound, often being referred to as a 'herd' or 'indistinct' sound.

The undesired effects of digital clock nstabhty, often referred to as Jitter, bears witness to how perceived sound Is distorted by alteration to harmomcs and Fourier components In the audio signal that occur at frequencies considerably higher than the basic 20Hz to 20kHz fundamental audio frequency band.

Loss ot phase and amplitude coherence often results from lack of close electrical coupling of audio system components. For example reactive load components such as loudspeaker covers and crossover networks need to be closely coupled to the controlling source dnver, i.e. the amplifier. Resistance or Impedance m this coupling introduces electrical damping, which diminishes the amplifier's control over the loudspeaker's component parts and dmimshes the amplfier's ability to arrest vibrations and resonance in reactive load components. The damping introduced by resistance or Impedance Inherent in the couphng introduces phase delays to the signal that lead to loss of critical fundamental, harmonic and Fourier component phase and amphtude coherence.

It is thus desirable to mimmse the undesirable effects of coupling between components In an audio reproduction system and to mnimise any undesired electrical interaction between the components and the coupling medium Itself. To achieve this it is necessary to have an Interconnection electric cable that exhibits high velocity ratio with low resistive and reactive Impedances.

Therefore, an electrical cable Is sought which electrically links equipment Including, but not limited to, audio reproduction system components with mammal undesired effect on how the components work and interact together. The sought after cable Is often referred to m the high fdehty audio media as being transparent' end being 'fast', meaning that electrically it has mimmal capacitance, Inductance and resistance and has a low propagation delay with high velocity ratio and exhibits mimmal audio and high frequency energy dissipation in both conductor and Insulation.

A Prior art method of constructing the above described sought alter cable has been to use stranded conductors In order to provided a large conductor surface area for Improved 'skin effect' high frequency transmission conduction. A disadvantage of this method is that it is found to add 'parasitic' elements to the sound quality due to inter strand reactions.

A prior art method to reduce the fore mentioned inter strand reactions has been to insulate the individual strands of the conductors; - this Is often referred to as Lltz wire. The disadvantage of this technique is that virtually all of the additional conductor surface area gained for 'skin effect' high frequency transmission Is In immediate contact with insulation dielectric which, by the nature of dielectrics, increases the propagation delay of the cable. This is further accentuated as, typically, practical size restrictions and the small scale of the Insulation required does not allow for the msulaton to be formed with foamed material or by using other techniques that reduce undesired insulation dielectric effects.

Another prior art method for attaimng low propagation delay is to provide a large surface area for skin effect conduction by forming conductors mto flat foil or ribbon form conductors and using these types of conductors m conjunction with an insulation system that offers low delectoc constant. This method has the disadvantage of provdmg a reduced total conductive cross sectional area relative to other non-flat conductor types which results In a relatively increased resistive for the higher energy, low frequency audio and the close to direct current signals. The effect of this Is significant because generally the majority of audio energy Is transmitted below 500 Hz, and resistive loading causes both signal attenuation and an increased electrical damping factor between connected system components at lower frequencies.

Another disadvantage of this prior art is the large fiat surface of the cable offers a large electrically exposed surface for electromagnetic interference to be mduccd onto and transmitted from.

Another disadvantage of this prior an is that flat, foil and ribbon type cables cannot be successfully twisted together in groups m order reduce electromagnetic linked interference and transmission by way of phase cancellation.

Reduction of many al the undesirable effects that cable has on the way high fidelity audio system components interact is reduced by Increased conductor conductivity. Copper is a commonly used material as it has one of the best conductivties of all metals, it is not expensive and it Is commonly available. The use of other materials with better conductivity than copper has not been commercially practicable because of the relative high cost of these rarer materials, particularly silver, which has the highest conductivity of all metals. Further, the Improvement In overall conductivity of conductors formed wholly from silver Instead of copper is very marginal relative to the cost differences, with copper having a relative conductivity of 100 and silver with a relative conductivity of approximatlylO6.

A prior art technique for Improving high frequency conductivity of copper conductors Is to plate the conductors with a lower resisuvty conductor such as silver. A disadvantage of plating one conducting material with another Is that this establishes an electrical bunion that exhibits undesirable effects due to the transition from skin effect transmission m the plated surface to lower l'requency transmission in the Inner material.

What is required Is an electrical cable which can conduct high level loudspeaker currents and provide improved audio frequency and audio high frequency harmonuc signal transmission with low propagation delays, minimal phase delays and minimal parasitic electrical Interference.

It Is an objective of the present invention to provide a conductor and Insulation arrangement which eliminates the aforementioned deficenees Inherent In the cables of the prior art while providing Improved transmission of high frequency signals that may be additionally conveyed at high power levels.

It Is another objective of the present invention to provide an electrical transmission cable which is capable ot transmitting high power audio frequency and audio frequency harmonic signal currents more efficiently and with improved mimmal electrical distortion, mammal interference and mammal parasitic electrical colourabon.

It Is another objective of the present Invention to provide an electrical transmission cable which is capable of transmitting audio frequency and audio frequency harmonic signal currents with stable and correct relative phase and amphtude relationship between audio signal fundamental frequencies and component harmomcs.

Sununay of the Invention The present invention therefore provides a conductor and Insulation system, which composes an electoral conductor made up of a minimum of a number of strands equal to the total cross sectional conducting area of the conductor measured in square mllmetres multiplied by two hundred, where a maximum of fifty percent of the strands are plated In a material which has a relative conductivity of between 1.01 and 1.2 times higher than the conductor strand material that the plating Is apphed to, and a foamed skin insulation system formed around the conductor, said foamed skin Insulation system comprising a first insulating layer of a flexible dielectric material with a maximum dielechne constant of 3 which is foamed with a minimum ol 60% gas such as, but not limited to, air and a second solid, flexible insulation layer that Is formed around the said first insulating layer.

The conductors of the present invention are charaetensed by having tine strands of which a portion is plated with a higher conductivity material than the base matenal. In one preferred embodiment the strands are made from oxygen free copper and three sbrands out of every seven are plated in silver.

The Insulator system of the present invention Is characterized by a low dielectric constant and a low dissipation factor. The Insulation system of the present invention comprises an inner foamed layer and a sohd outer layer. In one preferred embodiment the inner msulaton layer Is made fonm polyethylene which Is foamed with 85% air content and the outer Insulation layer Is made from sohd polyethylene.

A pluhty of the conductor and Insulator system of the present invention may be used to construct a cable comprising a plurality of the said conductor and Insulation system that can be twisted together or laid together m parallel and may also, but not necessarily, be contained within an overall sheath or Jacket.

Brief description Qf the drawings

FIGURE 1 shows a cross sectional representation of the conductor with the first and secondary layers of Insulation according to a preferred embodiment of the present invention FIGURE 2 shows a pcrspectve of the conductor with the first and secondary layers of Insulation according to the preferred embodiment of the present invention FIGURE 3 shows a cross sectional representation of a cable comprising two conductors contained in one jacket according to another preferred embodiment of the present invention FIGURE 4 shows a cross sectional representation of a cable composing four conductors contained m one Jacket according to another preferred embodiment of the present mention

Detailed description

Refemng to FIG. 1, an electric cable of the present invention composes an electric conductor made up of plated copper strands 1 1 that are twisted together and non-plated strands 13 and 15 that are twisted together.

in a preferred embodiment the strands are arranged and twisted Into groups of either plated strands or non- plated strands. In preferred embodiment twisted groups of silver plated copper strands 11 and twisted groups of non-plated copper strandsl3 are laud up consecutively around a central twisted group of non- plated copper strands 15.

The stranding of the groups 11, 13 and 15 Is uncommonly fine such that the concentration of surface electrical fields and current Is diffused and distributed over the large surface area provided by the fine stranding so as to ehmnate undesirable electrical inter strand reactions.

The stranding Is made adequately fine such that the mass of each stand Is very low so as to cause each strand to have a very high natural mechanical resonance that Is damped by the twist and body of the conductor and Insulation body so as to further ehminated and render Insignificant any undesirable electrical and mechanical inter strand reactions.

Given that the number of strands 'n' m a conductor must be increased by an Inverse square function of the strand radii in order to maintain a constant overall cross sectional area 'A' of the said conductor, as the conductor strand radn tend toward bemg very small, the field concentration on the surface area of each strand rapidly tends toward zero and the field pattern tends toward that of a sohd conductor that has umform conductivity at all frequencies.

In practice a suitable stranding is attuned where the number of strands 'n' exceeds the total conductor cross sectional area of the cable 'A' measured m square mllimetres by a factor of approximately 200; that Is to say; n>200A In a preferred embodiment that has a total conductive cross sectional area A per conductor of between 1.0 and 6 square millmetres, the conduct bundles are made up of very strands of typically 0.035mm radius.

This strand size is as fme as Is practical for reasons of cable tenmmation and commercial availability.

The high frequency attenuation of a conducting cable pair is approximately given by the following equation: Allenuation= 8.68 ( (R/2) C/L) + G/2) IIC) dB /lOOm Where R = high frequency skin resistance in Ohms /lOOm, C= Capacitance in Farads /lOOm L = Inductance in Henrys /lOOm and G = Conductance In Siemens /lOOm The term (R/2) C/L is typically larger than the lenm (G/2)L/C, therefore in order to achieve minimal attenuation, mammal values of R. G and C are sought.

Refemug to Fig. 1, a proportion of the conductor strands 11 are plated with a higher conductivity material than the inner bulk strand material In a preferred embodiment the conductor strand groups 13 and 15 are made from copper and the conductor strand groups 11 are made from copper that is plated with silver.

The low resistance plating on the conductor strands l l provides a reduction in high frequency resistance and thus a reduction m high frequency attenuation with better high frequency phase linearity and extended conduction to include higher frequencies.

The plating is of a conductivity and thickness to provide a low impedance path for the very high frequency harmonic and Founer components of signal transmitted through the conductor. In a preferred embodiment the plated surface matenahs Omicrons thick. In another preferred embodiment the plated surface material Is 1.06 times more conductive than the material constituting the inner part of the strands 11, 13 and 15.

The proportion of the amount of plated strands 11 relative to the non plated strands 13 and 15 Is selected to ensure a balance m the proportion of high frequency and lower frequency conducting media and to provided smooth transition of conduction of high frequencies flowing m the plated skin strand surfaces and the non-plated strand surfaces.

As Is Indicated in FIG. 1 less that 50% of the conductor strands are plated lo provide a low impedance skin effect path for the higher Fourier components and frequencies whilst simultaneous conduction can occur in the skin of the non-plated stucmds, thus causing a smooth and seamless transition of conduction between plated layer skin conduction and conduction m the skins of the non-plated strands and conduction in the bulk of the strands.

This arrangement electrically by passes any non conductive or other boundary effects that occurs at the Junction of the surface plated layer metal and the metal that constitutes the bulk of the strand. In a preferred embodiment a proportion of 47 % of' the conductor strands are plated to provide a smooth transition between conduction in the nonplated surfaces and in the plated surfaces and to by pass any effects caused by the Junction of the plating and the strand and thus ehminate any undesirable effects present In the zones where the plating bonds to the strand.

Refening to FIG. 1 the conductor Is Insulated with an extrusion 17 of a highly foamed expanded Insulation material of low dielectric constant. With Improvement of high frequency transmission and reduction in harmonic phase delay in a conductor the high frequency Fourier harmonic propagation delay and dissipation caused by the delectnc constant of the insulation becomes more significant. The insulation material 17 is of low dielectric constant in order to reduce propagation delay and dssipabon m the cable.

One of the lowest dielectric constant msulaton materials in common use for flexible cable Is foamed polyethylene that is foamed with aur. Referring to FIG. 1 the foamed dialectic layer 17 has a sohd insulation layer 19 extruded over it to provide rigidity and protection for the foamed polyethylene layer. This duet layer insulation system is a well known arrangement and Is often referred to as a 'dual insulation system' or a 'foam skin arrangement'.

In a preferred embodiment of the cable the Inner Insulation layer 17 is made from foamed polyethylene that is foamed to contam between 85% and 95% air. In a preferred embodiment of the cable the outer nsulabon layer 19 Is an extrusion made of the same polymer as the foamed layer so as cause the two insulation layers 17 and 19 to bond together during the extrusion process which aids the shipping of the cable m preparation for termmabon.

FIG 2 Illustrates an example of a preferred embodiment of the present Invention. Referring to FIG. 2 the cable conductor of the preferred embodiment described herem comprises three groups 11 of one hundred and fourteen 0.035mm radius circular strands of copper that are plated with 10 microns of silver and three groups 13 of one hundred and fourteen 0. 035mm radius circular strands of non-plated copper that are consecutively placed around a central group 15 of one hundred and fourteen 0.035mm radius circular strands of non-plated copper. Thus the conductor of the preferred embodiment described herein comprises a total of seven hundred and ninety eight strands of which approximately 43% are plated with silver.

Refernng to FIG. 2 the cable conductor of the preferred embodiment Is contained rhythm an extrusion of teamed polyethylene Insulation 17 which in this preferred embodiment Is foamed with approximately 85% air content. Referring to FIG. 2 the foamed Insulation layer 17 has a second insulation layer 19 extruded around it which In this preferred embodiment is made of solid polyethylene.

Referring to FIG 3 and FIG 4 a plurality of the present invention conductor and insulation arrangement can be laid up in a twisted or parallel fashion and sheathed with an overall jacket 21. In a preferred embodiment the sheath material 21 Is made of a dissimilar material to the solid insulation layer 19 such that the jacket 21 is prevented from bonding to the insulation 19. In a preferred embodiment the jacket material 21 is PVC and the msulabon layer 19 Is polyethylene.

Claims (1)

1. Claims I A conductor and msulaton system, which comprises an electrical

   conductor made up of a mmmum of a number of strands equal to the total cross sectional conducting area of the conductor measured m square mlhmelres multlphcd by two hundred, where a maximum of f t'ty percent of the strands are plated m a malcnal which has a relative conductivity ol'betwecn I 01 and 1 2 times higher than the conductor strand material that the plating Is apphed to, and a foamed skin Insulation system formed around the conductor, said foamed skin maculation system composing a first nsulatmg layer of a flexible dialectic material with a maximum dialectic constant of 3 which Is foamed with a minimum of 60% gas such as, but not Emoted to, air and a second sohd, flcxhle nsulabon layer that Is f'omcd around the said first msulatng layer 2 A cable compusmg a plurahly of conductor and msulalors systems according to claim I . eac. e a .. a'. a -