Quote:
Originally posted by painttoad:

System impedance indicates whether the speaker presents a "hard" or "easy" load on the amplifier. True 8ohm speakers are less amplifier and cable sensitive, and partner well with a broader range of amplifiers, including tube designs.
Today's home theater amplifiers are nowhere as robust as the stereo amplifiers of 20 years ago - the presence of the "6 ohm" switch is a result of this. A good stereo amplifier of that period would have no problem whatsoever driving a 4 ohm load all day long. "Hard" and "Easy" are relative terms - 4 ohms is hard for most home thater amps, but easy for a more robust one, depending on how they're designed.