At what distance are balanced XLR cables needed?

Atmasphere, whose opinion carries a lot of weight, has suggested that fancy wire is of little value in balanced interconnects.

There is a little more to that statement than meets the eye. For example, Ralph indicates that the balanced cable used between his preamps and amps need not be anything more than Mogami cable. The reason being his designs support the 600 ohm standard, something used in pro audio, and thereby controls the interconnect and makes the capacitive, inductive, resistive and other aspects of the cable negligible. Not all components are designed to this standard.

To further clarify, according to Ralph who posted this in another thread I'm a participant in, a low output impedance will mean that the preamp can drive a load of less than 1000 ohms without loss of bandwidth, voltage or increase in distortion. IOW if you can hear differences in the cable between the line section and the power amp, then the cable is not being controlled.

I was about to compose a post saying essentially the same things as in Clio's post above, but he saved me the trouble :-)

Ralph has particularly emphasized the part about "not all components are designed to this standard," meaning that it is common for balanced interfaces to have inadequately low output impedance, or to be otherwise poorly designed. That would seem likely to be the major reason for differences being reported between balanced cables.

Kijanki 1-19-11: You can spend arm and a leg for a balanced IC as well. They're also made of fancy materials - both metals and insulation. There is no reason why it should be different IMHO. Purity of metal still applies since impurity reside between crystals while insulation material directly affects capacitance and dielectric absorption.

This assumes that differences in impurities between crystals and differences in dielectric absorption are sonically significant, neither assumption having been proven based on widely recognized science, as far as I am aware. Although neither assumption has been disproven either, as far as I am aware.

Low capacitance, of course, is easily obtainable in low priced as well as high priced cables, and is only significant if output impedance is high and run length is long.

Regards,
-- Al

Al - I'm not sure if metal purity or dielectric absorption or capacitance play role in any particular setup either, but if they do - I can't see any reason why it would be different for balanced vs unbalanced cable.

Balanced versions are always slightly more expensive. If noise is the only concern balanced cable can be more effective for less money. Shield on single ended cable protects from capacitive coupling and high frequency EMI, but might be less then perfect in lower range of the radio frequencies where it works still as an antenna (poor one) while skin effect (that causes induced EMI to run on the outside - shield)is not strong yet. Balanced configuration suppresses common mode signals in this range of frequencies, while twisted conductors provide further noise rejection (cancellation thru even exposure).

IME, more than 15ft.

Kijanki -- I agree 100% with your post just above.

I would additionally mention the fact that balanced interfaces will be much less susceptible to ground loop issues than unbalanced interfaces. That susceptibility can be length-dependent, because it is sensitive to the resistance of the inter-chassis connection path. But the length-dependency will be system-dependent and unpredictable.

Best regards,
-- Al