hi glenn, it's the impedance of the instrument/mic cable, it won't blow anything up if you use them but you don't get your full juice from the amp..i have used them in emergencies only..if you do get speaker cable get the heaviest you can..what i have found is that 1.2 and above SWG electrical cable works really well with my P.A, which is around 3000 watts RMS, plus its cheap and pretty indestructible. the 6.3mm (1/4") jacks still wire up the same, tip hot sleeve cold..but be aware that if you use XLR connectors the 2 pin is not used..3 is hot(+) and 1 is cold (-)....hope that helps

dennis
peace, out