The basis for these speaker cables is common CAT-5 solid UTP network cable. It can be obtained in a reasonably good quality practically anywhere and is not expensive. Use the kind that has a non-PVC inner isolation, like poly-olefin or polypropylene. The chloride that's present in the PVC appears to erode the copper in the course of time.
The concept of multiple parallel connected, individually isolated conductors that's used here, is already being used by several manufacturers in the audio-world for a longer period of time, like Monster, Nordost and Supra (this manufacturer uses a layer of tin as an isolator instead of plastic).
Mostly stranded wire is used for speaker cables, in which one core consists of multiple conductors that are twisted together. Within this core the electrons can skip from one conductor to another, at which a small treshold voltage must be overcome. These treshold voltages appear to cause loss of micro-detail and resolution. In the case of very fine stranded cable, like the one that's often seen as 'OFC with 2048 or even more conductors', this effect is even stronger. This could explain why this type of cable often sounds a bit 'grainy'. By using individually isolated conductors, this effect is prevented. Beware to use solid UTP for fixed installations and not the stranded type, of which the flexible patchcables are made.
An UTP cable consists of eight cores, divided in four twisted pairs. The desired wire cross-section can be simply obtained by connecting multiple UTP cables in parallel and joining their cores. In this case six cables are used, with a total of 6 x 8 = 48 cores. Of each cable, the four fully coloured cores and the four with a white stripe are being paralleled. So all brown, orange, green and blue cores together make the first conductor (the 'plus'), and the brown/white, orange/white, green/white en blue/white cores make the other one (the 'minus'). That makes 24 cores per conductor. The diameter of each core is 24AWG, or approximately 0,2mm2. So, the final cross-section of this speaker cable will be 24 x 0,2 = 4,8mm2, or a little under 10AWG.
After cutting the cables to the desired lenght, they are temporary held together with ty-raps. Then, on one side of the cables, the outer jackets are removed so the colored and the striped cores can be sorted. Now the isolation of the cores can be stripped and they can be twisted together. This results in two cores, and when they are cut to an equal length, they can be soldered. In this case, 4mm banana-plugs are used, in which the 24 cores exactly fit. With an adequate amount of solder and lots of heat, this is very well feasible. The cores are finished with red and black heatshrink, and the plug's sleeves are fitted. The cable itself is finished with a black nylon sleeve over it's entire length, which is fixed in place by a piece of heatshrink on both sides. Before fitting the sleeve, all ty-raps are removed, except the first one. While sliding the sleeve over the cables, keep the cables apart so they end up next to each other and do not twist together. This way, all of them will end up nice and straight in the sleeve. When this is done, remove the tie-rap on the first side and finish it with heatshrink. Straighten the sleeve one last time, and fix it with a cable-tie on the other end. Now this side can be finished. When the cores are twisted together here also, the two connections can be checked for a short-circuit with a multimeter, just to make sure all 48 cores have been sorted correctly.