Generally, you can read a lot of generalizations about this subject : )
Balanced lines are less susceptible to running into problems with long line lengths. They are still subject to degrading / losing signal via dielectric absorption and the impedances that they bring with them into the system.
Single ended interconnects ( RCA's ) are more susceptible to signal degradation due to their design and are also more susceptible to picking up RFI / EMI interference. They too are subject to degrading / losing signal via dielectric absorption and altering system response / loading characteristics due to their impedances and component matching.
Having said that, all interconnects deal with a signal that is sometimes measured in millivolts and of extremely low current levels. Once a signal is lost / distorted prior to high level amplification, that signal is then passed on in lesser, more distorted form for further amplification. The effects of this signal loss / distortion are compounded as they go through each link in the signal amplification chain.
Speaker cables typically deal with higher level signals i.e. increased voltage and current levels. All of the above criteria regarding interconnects applies here too ( dielectric absorption, impedances altering loading characteristics, etc... ), but since we are already dealing with a higher level signal that can no longer be amplified, losing / distorting the signal is not as impactful on system performance.
To put things in English using money as compared to signal, if you had a dime's worth of signal going through an interconnect and lost a penny, that 10% distortion would probably be quite noticeable. This is because the signal distortion ( loss is a form of distortion ) was noticeable AND the effects of that signal distortion are further compounded as the signal is amplified as it passes through each gain stage.
On the other hand, if you had a dollars worth of signal ( fully amplified with no further amplification taking place ), losing that same penny would result in a 1% distortion figure. While we are still at the same amount of loss ( one penny's worth ), those losses are no longer compounded through further amplification. Since we have more signal to "play with" and there is no further chance for errors to be further amplified, it makes the most sense to "take your chances" with longer speaker cables than with longer interconnects.
Obviously, if one has a mild load in terms of speaker impedances and levels of reactance, you will always be better off regardless of what path you take. If one has a highly reactive load and / or a load that has erratic impedances presented to the amp, speaker cable length and impedance can play very important roles in what you hear.
While most will say that shorter cables allow the amp to get a better "grip" on a highly reactive speaker, the reverse is also true. Since there is less "buffer zone" provided by the impedance that a longer length of speaker cable would provide, high levels of reactance from the speaker can more easily "modulate" or influence the amplifier's output stage, power supply and other devices ( like the preamp ) further up in the signal change. It is in these types of situations that using what one might consider "less than optimum" cables can result in actual improvements to the system. In some cases, changing cables can make the difference between normal operation via buffering the load that the amp sees and sending the amp into protection mode due to being completely revealing of a radical speaker load.
Given all of the above, common sense would dictate that the weakest signals are the most delicate and any distortion introduced into the system at that point will only further compound those distortions as they are amplified. As such, one should "take the most care" of the signals prior to final amplification. This is not to say that speaker cables / lengths are "less important", as a system is only as strong as its' weakest link. Obviously, there is enough variance from system to system, components used and personal preference that you may like / prefer something different than what i like, so use what works best in your system. As usual, this means trial and error, which can be as cheap or expensive as you care to make it. Sean
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