Hello and thanks for looking.

I'm in the process of shopping for a new AV receiver. I think I may have broken my ho-hum Panasonic SA-HE100K receiver (100 watts per channel x 2 (into 6 ohms, 40 Hz to 20 kHz, with less than 0.9 percent THD); 100 watts per channel x 6 (into 6 ohms, 40 Hz to 1kHz, with less than 0.9 percent THD)) by using it to power some Acoustic Research AR-3a speakers (4 ohm impedance). Now I'm looking into getting a new receiver and I don't want any problems down the road because I am asking it to do too much.

So my questions are:
-what is a basic explanation of what impedance is with regard to receivers/speakers?
-can I damage a receiver (say one that is "110 Watts x 7 (20Hz - 20 kHz, 8 ohms, .09% THD FTC)" like a Pioneer that I'm looking at) by hooking up the 4 ohm AR-3As to it?