QED has announced that its new XT25 loudspeaker cable would be available from QED stockists in the UK by the end of the November. Retailers around the world should receive stock in December.

XT25 was developed as a first upgrade cable for all speaker types whether they be floor-standing, bookshelf stereo or home theatre and therefore was deliberately designed to be small and flexible enough for use in this demanding and price sensitive environment.

In common with all QED’s cables, XT25’s design is informed by the results of their research into loudspeaker cable design which began in 1995 and is detailed in the recently updated The Science of Sound Report. This report sets out the design principles to which QED have adhered ever since and which along with many hours of listening and iteration resulted in the development of their flagship Supremus speaker cable, on which all their designs are based.

Calculation can accurately predict the maximum skin depth at a given frequency for a particular conducting material making it possible to keep the diameter of the cables below the critical size determined by the maximum frequency expected. QED cables above 1.5 mm2 cross-sectional area utilise air core technology to obviate the skin effect by bundling several smaller cores together to make up a larger CSA. As frequency increases electrons flow more and more towards the periphery of a conductor so that if the frequency is high enough only a very thin layer (or skin) on the outside of the conductor is used. This skin depth varies for different materials at a fixed frequency and in copper it means that if a conductor has larger than 0.66 mm2 cross-sectional area not all of that area is available for an analogue music signal to use. In previous QED cables the skin effect problem was effectively eliminated by the use of X-Tube™ Technology which works by placing all of the conducting material around a central hollow insulating rod. However, for ac signals, changing magnetic fields generated by the flow of current set up eddy currents in nearby conductors which force current to flow only in areas furthest away from conductors carrying current in the same direction and vice versa. This proximity effect has a detrimental influence on current distribution in a speaker cable even if it utilises X-Tube™ Technology. By forming the conductors into a tube-like shape with hollow centre, current densities at different frequencies are maintained because the electric field which contributes towards the skin effect acts towards the centre of the conductor from where the conductive material has been removed. At the same time the ring of conductors is formed into separate bundles with only a loose electrical association which are then twisted into a 90 mm lay so that no single conductor bundle remains on the inside or outside of the cable (and therefore prey to the proximity effect) for long enough for it to become an audible problem.

QED say that they have long recognised that low DC resistance of the loudspeaker cable is of paramount importance for high fidelity signal transfer. This is because the speaker presents a frequency dependent load to the amplifier of which the cable forms a variable proportion. If resistance is allowed to be too large, then audible changes to the frequency response characteristics of the loudspeaker will be introduced which cannot be corrected for by the amplifier’s negative feedback loop. In order to improve upon previous budget cables, QED’s first target was to increase the CSA without increasing the overall size of the cable substantially. To that end, combined with QED’s exclusive use of 99.999% oxygen-free copper, the CSA has been increased from 1.5 mm2 to 2.5 mm2 which instantly gives the new cable a considerably lower dc resistance.

It is not generally appreciated that the electrical signals moving at or near the speed of light in a wire do so via the medium of electromagnetic (EM) waveforms which exist within the dielectric which surrounds the conductors as well as within the conductors themselves. The movement of electrons along the conductor merely facilitates generation of the EM waveform as their drift velocity is much slower – being only a few centimetres per second. It is therefore important to ensure that the dielectric material used to insulate and protect the central conductors of the speaker cable is of a type which ‘permits’ the establishment of EM waveforms without appreciable loss. Dielectric losses are directly proportional to the permittivity of the material used and as this a measure of each material relative to that in a vacuum it should be as close to unity as possible. Like its predecessors, XT25 uses a specially formulated low-density polyethylene (LDPE) dielectric which at 1.69 has the lowest relative permittivity practically available. QED say that their research has shown that low capacitance cables are generally preferred in listening tests over high capacitance counterparts and this is usually because low loss dielectrics have been utilised. The use of LDPE and careful control of conductor spacing results in a cable with a very low capacitance per meter and a dissipation factor (loss tangent) of 0.0001 at 10 kHz.

Speaker cables have to carry a lot of current. If the electrical resistance of the cable is too large, part of the music signal will be lost, causing a detrimental effect on the fidelity of the sound you hear. To stop this from happening QED makes the resistance of their speaker cables as small as possible. This is done by using the largest practical cross-sectional area of copper within the size constraints of each cable. In order to squeeze the last drop of performance from the conductors QED make sure that there are no impurities in the copper which would defeat the object of making them so large. That’s why they use 99.999% oxygen free copper exclusively.

XT25 will cost approximately £6 (€7.50) per linear metre unterminated.

Cold-welded termination with QED’s Airloc 4mm plugs or spades would normally cost around £5 (€6)per plug. This makes a 3m pair of terminated cables around £70 (€85).

QED offer an unlimited lifetime guarantee which means that if a QED cable ever fails to deliver to its full potential during its lifetime QED will replace it free of charge.