Question on Impedance (Ohms)

[pozesterizer]

I assume this question has been asked a million times over, but I'm having a hard time wrapping my head around this. I have a Marantz MR 235 and has an A and B channel. I have 2 8 ohm speakers.

If I plug one speaker into the left terminal and one into the right (nothing fancy just - to - and + to +), that's using them in parallel? Or is it only in parallel if I use the A+B setting for 4 speakers? (Channel A 2 speakers still = 8ohms or does it actually mean it's parallel and turns to 4ohms)

I'm mostly curious because a Yamaha R-S202BL I'm looking at says A+B channel minimum impedance is 16 ohms. So I'm wondering how you'd even get 16 ohms this way. Channel A in series separate from channel B also in series? This way you're running 2 series channels in parallel?
I guess what I'm truly wondering is, does each terminal support an 8 ohm speaker? Therefore it's fine to plug 4 8 ohm speakers into a receiver with 2 channels? And through some sort of wizardry the A+B channel with 4 8 ohm speakers plugged in = a total of 16ohms?

I probably sound so stupid. Series and parallel makes sense to me on just traditional drivers, but doesn't really make sense with a normal speaker to receiver setup.

Thanks in advance!

 

[americanaudiophile]

Left and right channels are never connected to each other in a receiver.
Some receivers with speakers A+B connect them in parallel and some in series.
If the are connected in parallel the amp needs to be able to handle the combined lower impedance of the speakers. This requires a more expensive to make amp. The power should increase at the lower impedance.
If they hook them in series then the impedance doubles which is safe but reduces the available power by 1/2 and changes the damping factor so bass isn't going to be a tight.
You can always tell if the speakers are in series because if you don't have any speakers connected to the B terminals and select A+B you get no sound.

 

[pozesterizer]

So basically I just have to figure out if the receiver plays A+B channels in series or parallel to figure out if it's safe to play both channels at once, with your simple method? Thanks a ton!