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Cable mechanics

Description of the types of cable suitable for recording studio installation.


The mechanical properties of a cable are as important as the electrical properties. Ever had one of those cables that can tie itself into a knot without human intervention? We all have, and we know that it is something to avoid. The types of mic cables I described above are suitable for everyday use in the studio - cables that you would connect for a particular purpose then disconnect and coil up for storage. The two features that make them good for this application are flexibility and coilability. Flexibility comes from the fine stranded wire used, and also from the soft plastic insulation. Coilability - I don’t think it’s a scientifically measurable quantity - comes from the relationship between the flexibility of the cable and its diameter. There is a point where a cable can be too flexible and too small in diameter for its own good, and creates the knotty problem described above. Six or seven millimetres is a good diameter for a mic cable.

Cables of lesser diameter can be used for installation work. That is where the cable will be wired up and left undisturbed for evermore, so it doesn’t matter what its handling properties are like as long as it’s reasonably easy to hook up in the first place. You won’t touch it after that. There are two types of cable that I find very useful for installation. The first, I use basically because it’s cheap. There’s nothing wrong with that as long as it is electrically OK. It is a single conductor cable (therefore only suitable for unbalanced connections) with a 7/0.2mm signal conductor and a lapped screen. The overall diameter is 3mm and the cost is a mere 15p or so per metre. Its big advantage is that it is ideal for making into a loom. A loom, as you are probably aware, is a collection of twenty or thirty individual cables fastened together and all going to the same place. I’ll be explaining how to make one in the next chapter.

My other favourite installation cable is known as FST, standing for Foil Screen Twin (Fig. 5.1c). The brand I use is available with two 7/0.2mm conductors. But instead of having a copper wire screen, it has an aluminium foil screen. To connect the screen to earth there is a drain wire, which is an uninsulated 7/0.2mm wire in electrical contact with the screen throughout the length of the cable. It is actually a much better cable than the one I described above, having a lower capacitance, making it good for use in long runs. It is of course more expensive, around 30p per metre in 100m lengths. FST cable is fairly stiff, which makes it easier to install inside racks. The one thing you can’t do with FST cable is to use it as you would an ordinary mic cable. It tends to kink and would soon become difficult to work with.

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Equipping Your Home Recording Studio
By David Mellor Tuesday February 1, 2000