Yamaha R-S202 Receiver Review

[Sure Not]

I'd like to hook up two pairs of Polk Audio XT15s (8 ohm speakers) - one to the "a" set and one the "b" set, to be used at the same time. My understanding is this parallel setup will drop the impedence from 8 to 4 ohms. The owner's manual states the receiver needs 8 ohms, but in the specs and in this review, it is clearly capable of 4 ohms. Is the only disadvantage that there is more distortion at high volume levels? Would wiring the speakers in series to increase the load to 16 ohms be of any value? Thanks.

According to the impedance graph on Erin's audio corner, these speakers drop down to 4 ohms. I would not run A and B together in parallel. You can hook them up in series, which will get you an 8 ohm load, but you'll only be getting 2 channels worth of power to the 4 speakers. So each speaker will be essentially running at half power. Most AVRs don't have the current to run 4 channels at full power anyway.

 

[Bob101]

I'd like to hook up two pairs of Polk Audio XT15s (8 ohm speakers) - one to the "a" set and one the "b" set, to be used at the same time. My understanding is this parallel setup will drop the impedence from 8 to 4 ohms. The owner's manual states the receiver needs 8 ohms, but in the specs and in this review, it is clearly capable of 4 ohms. Is the only disadvantage that there is more distortion at high volume levels? Would wiring the speakers in series to increase the load to 16 ohms be of any value? Thanks.

Simple answer: connecting identical speakers in series will double the total impedance instead of halving it when connected in parallel (what your amp does). You will have less distortion, but (to keep it simple) half the power, divided over four (rated 86dB/W not really sensitive) speakers. Plus you lose the capability to switch pairs on and off on the amp itself.
Do keep in mind that speakers rated 8 Ohm are rarely 'real' 8 Ohm speakers these days. These Polks drop to 4 Ohm at several frequencies, notably between 200 and 400 Hz. So in parallel two pairs of these would drop the load for your amp to 2 Ohm, in a frequency region where generally most of the power is needed. For low volumes: not really a problem. At high volume your amp should go in protection mode (in practice: shut down) before anything breaks, but long after very audible distortion kicks in.