The always informative Roger Russell site suggests that for runs under ~30 feet, it simply won't matter.

If you WANT to do the math, there's this:

Quote:
A wire resistance of less than 5% of the nominal speaker impedance is chosen to work well with almost all speaker systems and can be considered conservative. Even a resistance of less than 10% of the nominal value could be used with some speakers and would not be audible. A further explanation can be found in a later section.


bibere usque ad hilaritatem