The invention relates to an electric conducting cable with one or more cores, in particular for signal transfer, in which the conductors are embedded in a sheath cxπprising synthetic material.

For the transmission of electric signals, according to the usual prior art, cables with conductors of an electrically good ∞nducting metal, are generally used.

In general, such conductors are considered as a homogeneous transfer medium and the flow of electrons therein is considered as the flow of a liquid. It is known, that the quality of music reproduced by apparatus of high quality will be affected to a considerable extent or win reduce in the long term due to the type of cable which connects the various parts of the music reproducing apparatus. In particular, it is known, that chemical attacks from the env_i__ronment may seriously harm the quality of the cable as a signal transferring medium. A proven remedy against such attacks is electrolytically coating the conductor with a protection layer consisting of for exaπple tin or silver.

Up to new, as criterium for expressing the differences between various conductors of electrical cables the specific resistance (ohm.cm) , therefore the electrical attenuation, is generally used as a measure. Nevertheless, in practice, differences in sound effect are experienced with cables in sound reproducing apparatus, which diffe¬ rences cannot be explained by differences in the conductor material used or by differences in electrical attenuation. Ihe aim of the invention is to provide an iπprσvement of the usual conductors in transmission cables and in particular to improve the transfer properties at the lower signal levels.

Ihe underlying insight in aiming this improvement, is that the usual metal conductor cannot be considered at all as a homogeneous medium and that much more significance should be given to the circum¬ stance that in a metal conductor it is in fact a natter of a not reproducible grouping of metal crystals substantially established along mechanical way, with ∞πtaminance and boundary areas there¬ between, which form barriers for an optimal transfer at low signal levels. Even protecting layers consisting of for exaπple tin or silver cannot avoid that the iirpurity of the conductor (at the long term) increases by for example absorption of gas and oxidation and also the

barriers against an cptimum signal transfer will increase, so that the quality of the conductor reduces cxiπtiπuously.

It should be noted, that the usual way of fabricating (by pulling) the kncwn metal conductors is beneficial to the occurrence of dislocations with a similar barrier effect. During the electrolytical coating process as well as during normal use, in which the conductor is subject to distortions such as bending, such dislocations and an associated deterioration of the signal transmission may occur.

Tests and measurements on metal conductors at lower signal levels, at which the number of higher harmonics in the output signal showed a significant increase, support this insight. Against the background of this insight, the observed deterioration of the transfer of the lower signal levels with the known metal conductors might be described as being the result of a phenomenon, which could be indi- cated with "cross-crystal distortion", that could be σoπpared with the kncwn phenomenon "cross-over distortion" in amplifiers of lower quality.

The iπprσvemeπt according to the invention is achieved in that the conductor of at least one core comprises a carbon filament obtained by dehydrogenating a cyclic hydrocarbon C _χ H .

It should be noted, that manufacturing a carbon filament by extrusion of a carbon black obtained by dehydrogenating a hydrocarbon is on itself kncwn in general. However, these carbon filaments are generally used as reinforcement in synthetic material. Furthermore, it is kncwn that the carbon fiber is very flexible, chemically inert, strong and has a good electric conductivity. Hcwever, the electric α_aιductivity depends to a great extent on the degree of order of the carbon atoms. However, this degree of order of carbon atoms forms a very uncertain factor in the carbon black (obtained by dehydrogenating of a hydrocarbon) as basic material for the carbon fiber.

Ihe invention has surprisingly shewn that, when using a carbon black obtained by dehydrogenating a cyclic hydrocarbon as basic material in the fabrication of carbon fibers, the cyclic molecular structure has evidently a strong arranging effect on the reorien¬ tation of the carbon atoms taking place during the extrusion or spinning process of the fiber.

It may be assumed, that in the thus obtained carbon fiber the original cyclic structure is maintained and that in the fiber it is a

matter of a linear structure of partially overlapping "loops" of double bonds and the purity of the carbon fiber guarantees an unob¬ structed transfer of electrons in the longitudinal direction. In particular it was surprisingly, that measurement of the impedance on a large number of individual carbon fibers, having a thickness of 7 micron, by kncwn fiber extrusion or spinning techniques from a carbon black obtained by dehydrogenating benzene as well as a large number of conductors according to the invention with a diameter of 1 mm and composed of about 12000 carbon filaments having a thickness of 7 micron, resulted in surprisingly low and hardly fluctuating values of approximately 400 Knhm.m and 35 ohm.m, respectively.

According to a further characteristic of the invention it has been found, that the arranging effect of the original cyclic structure can be enhanced fay applying an electric field in the extrusion and spinning process of the fibers and that as a result the above mentioned values and the fluctuations may be further lowered.

By applying an alternating magnetic field perpendicular to the production direction (and therefore also perpendicular to the electric field) a still stronger arranging effect can be obtained. In terms of analogy this could be conpared with the premagnetising process through a bias signal in magnetising of tape as is kncwn from the recording technique. By a correct tuning of the direct current field in the production direction with the alternating magnetic field perpendicular thereto, an additional arranging effect results, which reveals itself in a further decreasing resistance of the final product.

As a result of the small thickness (in the order of 10 micron) of the (individual) carbon fibers distorsions such as effected by bending in using, will not result in dislocations, in contrast to the known metal conductors, which would lead to a deterioration of the signal transmission at lower levels, whereas as a result of the purity of the carbon fiber and the chemical inertness thereof the life span in all respects is nearly unlimited.

In a practical application, the conductor according to the invention will consist of a bundle of carbon filaments described above. As is the case with a cable comprising metal conductors, this bundle of carbon filaments will be embedded in a sheath of synthetic material, for which in case of the invention, the synthetic materials polyethylene, polypropylene and polytetrafluorethylene are specifi¬ cally suitable.

To obtain an optimal, advantage of the high chemical stability and purity of the carbon fiber, in this case it is advisable to provide each fiber with an insulating layer (e.g. by immersion) in the course of the fabrication process, so that the transport of electrons may only take place in the longitudinal direction of the conductor and therefore no undesirable "cross traffic" may occur.

Thereby, it is practical to choose a protection layer or lacquer layer, that is soluble in a solvent such as aαetαn. This offers the possibility to remove fcy immersion in aceton a certain length of the insulating layers from the bundle of conductors insulated from each other by the insulating layers, which conductors need to be finished with a connecting element (connector) thereby resulting in a desired effective contact in cross direction between the individual carbon fibers at the conductor end, which is necessary for diverting the electron flews of all fibers to a connecting sleeve or sleeve forming part of the connector, which has to be attached to the thus "inter¬ nally stripped" conductor end through mechanical way.

The invention also relates to a method of manufacturing a carbon fiber adapted to be used as conductor in an electrical conductive cable by extruding or spinning a carbon black obtained by dehydroge¬ nating a hydrocarbon C__Hγ. A first characteristic of the method accor¬ ding to the invention consists therein, that during the extrusion and spinning process an electric field is applied to the extrusion and spinning area respectively, while preferably a cyclic hydrocarbon is used as hydrocarbon. As mentioned above, the application of an electric field in manufacturing the carbon fiber has an arranging effect on the arrangement of atoms during the creation phase of the carbon fiber, whereas the cyclic molecule structure of the cyclic hydrocarbon has also an arranging effect en the arrangement of atoms in the developing carbon fiber.

Furthermore, a particular aspect of the invention relates to processing a residu of cables and unusable cables.

At present, unusable cables with metal conductors are generally processed fay burning. As is kncwn, such way of processing is conside- red to be extremely damaging to the environment and an increasing opposition against this way of processing exists.

In this respect a transmission cable according to the invention, of which all the conductors consist of carbon fibers, offers other possibilities of processing, which does not damage the environment.

A preferable way of processing the (residu of) cables according to the invention consists in that the cables and the residu of the cables are chopped up into small pieces, which are then melted together by heating to produce a coating mass suitable to be reused as a conductive shield for electrical conductors. This coating mass is a synthetic material homogeneously mixed with carbon and is therefore electrically conductive, of which coating mass the basis mass is formed by the insulating sheath of the (carbon) conductors in the cable. Ihe invention is applicable to all types of cables with one or more cores, including so called coax cables, in which a central conductor consisting of carbon fibers according to the invention, is surrounded or shielded by an outer conductor consisting of a web of carbon fibers. Briefly, the invention provides the possibility to maximize the electrically conducting properties of carbon fibers in a reproducable way and therefore make the carbon fibers suitable for utilization as electrical conductor in transmission cables, of which especially the signal transmission on the lower levels is of great significance. When used with music reproducin apparatus of high quality, a transmission cable according to the invention cxaitributes to music, which d___stinguishes itself to ejφerts fay a remarkable "three- dimensionality", just because of the excellent transmission properties on the lower levels.