QED Reference XT25 BiWire Speaker Cable
XT25 Bi-Wire with X-Tube™ Technology
XT25 Bi-Wire was designed as the natural complement to XT25, the 5-star-award winning*, entry-level X-Tube™ cable from QED. It incorporates four separate conductor bundles into a single, convenient X-Quad™ type geometry and is intended to present a much more enjoyable rendition of the musical performance when used in a bi-wire or bi-amped configuration.
In common with all our cables, XT25 Bi-Wire’s design was informed by the lessons learned during our exhaustive research into loudspeaker cable design, which was begun in 1995 and detailed in the recently updated Genesis Report. This report sets out the design principles to which we have adhered ever since and which resulted in the development of QED Supremus speaker cable – the ultimate expression of
sound through science without compromise.
Each QED cable in the range is based on this unique concept and although their designs may be variously influenced by price, size or ease of use, each retains the basic original features of the flagship model. This gives even the base-model cables a sonic advantage over their similarly priced competitors. XT25 Bi-Wire, for example, is essentially a scaled down version of
the top-of-the-range Genesis Bi-Wire cable sharing many of its geometrical features but having a smaller cross-sectional area and using 99.999% oxygen-free copper conductors in place of the more expensive silver-plated variety.
Very Low DC Resistance
At QED we recognise 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 by the amplifier’s negative feedback loop.
Very Low Inductance
Cable inductance is a prime cause of high-frequency attenuation and phase shift in loudspeaker cables. High inductance causes cable impedance to rise with frequency, reducing output in the very upper frequency range, sometimes preceded by response peaking.
It is not generally appreciated that electrical signals, moving at or near the speed of light in a circuit, do so via the medium of electromagnetic (EM) waveforms, which exist not only within the copper conductors themselves but also within the dielectric which insulates one from another. The movement of electrons around the circuit merely facilitates generation of the EM waveform, as their drift velocity, measuring only a few centimetres per second, is much slower than the speed of light.
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 mm 2 cross-sectional area, not all of that area is available for an analogue music signal to use.
|Outside diameter ||13.1 mm |
|Conductor area ||5.0 mm2 |
|Conductor chemistry ||99.999% oxygen-free copper |
|Dielectric properties ||Air Gap (εr = 1.69) |
|Loop resistance ||7.0 mΩ/m |
|Parallel capacitance ||69 pF/m |
|Dissipation factor @ 10 kHz ||0.0001 |
|Self-inductance ||0.36 μH/m |