The optimum insulation material would be one with absolutely no response to an electric field and a complete resistance to the flow of an electric charge. Unfortunately though, there is no perfect insulator! On the other hand, there are many materials with very effective insulation properties that can easily outweigh the requirements of many electrical applications, such as the protection of cable conductors. After a thorough research on the electrical and physical properties of many insulation materials, we concluded that the optimum solution for cable conductors would be a combination of such materials. However, before we present the materials we use and the techniques we follow, it would be useful to consider the multiple uses of insulation and how it can affect some major cables characteristics.
The basic function of insulation is to protect conductors from being exposed or coming into contact with external factors or other electrical conductors in a way to prevent current from passing through them.
A very important role of insulation is to help controlling and maintaining capacitance at the lowest possible levels, so as to keep the unwanted attenuations away from the audible frequency range. This can be achieved by reducing the values of relative permittivity. Theoretically, relative permittivity is a ratio of the amount of electrical energy stored in an insulating material by the voltage that passes through the insulated conductor, in relation to the voltage stored in a vacuum, which is the reference standard insulation. In practice, the values of relative permittivity can be controlled by the type of material (or the combination of materials) that will be used and by their thickness.
Another important use of insulation is to help reducing energy losses that are dissipated as heat. The most accurate indication for these losses can be given by the values of Dissipation Factor. In physics, a Dissipation Factor (DF) is the measurement of the loss-rate of energy of a mode of oscillation (mechanical, electrical, or electromechanical) in a dissipative system. In cable making, the values of a Dissipation Factor can provide a clear view of the dielectric losses in the conductors’ insulation. A low dissipation factor indicates low dielectric losses and this can also be controlled by the proper selection of insulation materials.
At very low frequencies, cables primarily appear inductive and at higher frequencies become capacitive. The Quality Factor is a measurement of how abruptly the change from inductance to capacitance occurs. At the point of transition, the cable is in resonance and so it appears like a pure resistance. But again, with the proper mix of insulation materials, the correct thickness and the overall internal cable design, we can achieve a very high quality factor that practically controls and moves the point of resonance to the right frequencies, helping cables resistance to be ideal and phase response to be more linear. In sound, this is translated into a more natural-sized soundstage, a better clarity and a balanced response across the full frequency range.
The insulation techniques of Signal Projects
In order to achieve the maximum protection for our conductors, to keep relative permittivity and dissipation factor at the lowest possible levels, to score the highest possible values of quality factor and in the same time to provide a quite satisfactory flexibility, we have developed specific insulation techniques for each type of cable that we produce, based on multi-layer designs. The materials we use are presented on the board below:
The order of usage and the thickness of these materials varies between different cable types and it is worth to mention that for some demanding applications that require even higher dielectric strength (e.g. interconnects and digital cables from our top ranges), we also use air as an insulation layer by leaving symmetrical spaces between the other two layers of the conductor. The results of our insulation techniques speak for themselves through the language of measurements, with the very low capacitance levels that are ranging between 25pF to 10pF per feet in almost all our cable designs, with the equally low levels of inductance that are moving below 0,7 μH per feet, with the natural dynamics due to the very low dissipation factor and with the impressively flat response across the audible frequency range due to the extremely high quality factor.