Correct me if I'm wrong but aren't most avrs rated at 8ohm more than capable of driving 4ohm? I've heard if there's a switch to still keep it at 8. unless a draw at 3ohms or less is presented it'll be fine without going to standby. My opinion, 500 is more than enough to go used and def hopeful to be just fine without the newest codecs, bells/whistles, ect.
HD said "
Doesn't mean they can't drive 4 ohm loads but depends to what level "
Of course you are right, but so is HD.
Manufacturers created this circle of confusion by over simplifying specifications such as 100 W into 8 ohms at 0.05% THD+N, 20-20,000 Hz and then try to imply the device can also drive 4 ohm speakers but would also tell you to set the device impedance selector (via software or a physical switch/selector) to 4 ohms (or 6 ohms in some cases).
They should have simply provide two output rating under the same conditions except one for 8 ohm and the other for 4 ohm, such as 100 W into 8 ohms at 0.05% THD 20-20,000 Hz, and 100 W into 4 ohms at 0.1% THD 20-20,000 Hz. I have yet to see one single receiver that specifies their output this way. So a safe way to guess the 4 ohm rating would be to half the 8 ohm rating based on Ohm's law and the power formula, but that would not likely reflect reality for real world use.
Ideally, it is better to specify power amps in terms of voltage, current, duration (such as 20 ms, 10 minutes, continuous etc.) in terms of both average and peak ratings, then the consumer would have a better chance to answer such as the OP's. But of course manufacturers will never do such a thing unless they are regulated, and regulators aren't keen in using their resource to figure on what to do with audio power amps used for entertainment. They have more than enough to do on health and safety related issues. Some audio forums will get such kind of questions weekly if not daily, keeping some of us busy trying to help answer where we can..
