Jay Menon wrote:I just read up about starquad cable...two internal cores that cancel each other's interference - like a humbucker?
I think we know what you mean... but for the uninitiated there are four cores in starquad cable -- the clue in in the 'quad' part of the name ;) -- plus an overall screen.
The four cores are very tightly twisted with each other and rotate over a relatively short length. If you image the four cores arranged at the ends of the two arms that form a plus sign, then the two cores on the vertical arm are wired together in parallel to form one side of a balanced line, and the two cores on the ends of the horizontal arm are wired together in parallel to form the other side of the balanced line.
Obviously, with four wires in the cable, the core-core and core-screen capacitance will be much higher than a more conventional two-core cable, and that's the down side. it means there will be greater HF loss in long cable runs. Not a problem with 10 metres, or even 50, but a hundred metres or more will start to exhibit audible HF loss.
The upside is better rejection of very close source electromagnetically induced interference -- the kind of interference that might come from laying a mic cable alongside something that radiates strong and nasty interference -- like some kinds of mains dimmer cables, for instance.
If you consider a standard two-core mic cable lying for a short length alonsgide a nasty interference source, then some of that interference will break into both cores. To be rejected by the balanced input of whatever it is connected to, it MUST break into both cores equally.
However, the inverse square law dictates that there will be more energy transferred into the closer core and less into the further core -- and since the two cores twist around each other in a lazy spiral down the mic cable -- there's a good chance that one core will pick up slightly more interference from that close source than the other core. The result is audible interference because the imbalance means it won't all get rejected.
Starquad overcomes this problem because the cores are wired in opposite pairs. So replacing the standard mic cable above with starquad, one pair of wires will be effectively either end of that vertical bar of the plus sign, and will therefore pick up equal amounts of interference because they are the same distance from the nasty cable lying alongside. The other pair areon the horizontal arms, which means one core is slightly closer to the interfering cable than the vertical pair, but the other is slightly further away -- by equal and oppiste amounts. So the net average interference in the two cores will be exactly the same as that of the two vertical cores. Hey presto -- much better balance of interference and therefore better rejection. The much tighter cable twist helps too.
Starquad was invented for use in telephone cables back in the 1930s, and was adopted in the TV world in the 60s an 70s -- I think. It is widely used, particularly where there is a liklihood of having to lay mic cables alongside strong sources of interference.
would you guys use starquad cable in preference to ordinary balanced cable? I'm thinking in terms of microphone cables of 10 metres length...and its for use at home...
No, not particularly. With that short a cable run, and in a domestic situation, interference isn't likely to be an issue at all. No reason not to buy starquad if you can get a good deal -- but I wouldn't seek it out specially. You're very unlikely to gain an significant benefit.
I'd look for a decent two-core cable from a reputable supplier. I particularly like double-screened cables (reussen screen) which are also widely used in broadcasting.