Q. How long can my speaker cables be?
Generally speaking, you should not use speaker cable with a loop
resistance more than 5% of the nominal speaker impedance. This means
that, as an example, the limit for Silver Anniversary XT is 18m/59 feet for an 8 ohm
speaker and at this length, you will just begin to hear a indisputable
change in speaker frequency response due to the cable. A sensible hi-fi limit would be half this length, so at 30 feet you should be okay, as this is well within the limit.