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Re: making a cable snake

Posted by Haldor (A) on March 28, 2002 at 19:35:52

In Reply to: Re: making a cable snake posted by Roland on March 27, 2002 at 14:54:13:

Hi Roland,

Point by point responses.

>Digital cables are normally designed for 110 Ohm impedance so are
>not suitable for mic leads, thats why manufacturers make both.

The characteristic impedance of a cable is only important for high frequency (RF) signals. At audio frequencies your cable length needs to get into the kilometers before you will notice any bad effects due to this. You are correct that digital audio cable needs to be 110 ohm since the edges of digital audio signals have a very high frequency component, but analog signals don't nor do they particularly care about the cables impedance. This means that very good digital cable can also be very good analog cable.

>Any high quality mic cable should not exhibit any significant HF
>roll-off under a distance of well over 300 metres!!

The roll off frequency is determined by your source impedance and the cable capacitance. Lower capacitance is better.

>PA companies regulary pass line and mic level signals up and down
>the same multicore without frying there systems.

PA companies also regularly recone smoked speakers and repair damaged amps. I don't know how ofter this is caused by ultrasonic feedback rather than just normal abuse, but I have seen this particular problem myself. Since then I have done research on this subject and discovered that this is not that uncommon a problem. In addition it is a very difficult problem to detect during a performance since nothing obviously sounds wrong, except your amps lack drive power and overheat too easily.

>Who would dream of sending amplifier outputs down multicore mic
>cables?

Just about every snake manufacturer I know of carries a line of "Powered" snakes that combines speaker cables with mic cables. I agree this is a very dumb idea. I didn't want this poster to copy their mistake thinking it's ok since Whirlwind, Rapco, etc do it.

The reason why this particular Belden cable is so much better than the competition (including Starquad) is a combination of very low capacitance, very superior shielding (two thick layers of braided shields), very consistant construction and very good handling properties. The only think the 1800F is lacking in my opinion is a plenum rated version.

Phil

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