Car audio: Speakers with dual voice coils?

Factual Questions
1

[crotchety voice]
Back in my day, our subwoofers only had one voice coil, AND WE LIKED IT!
[/crotchety voice]

I have a 4/3/2 bridgeable 4-ohm amplifier. My (formerly) trusty old subwoofer I’ve had for about 12 years is shot. One speaker I’m looking at is a Pioneer TS-W256DVC and it has dual 4-ohm voice coils, and hence dual inputs. Dual voice coils is pretty new to me, but I think I understand the concept, and I just want to make sure I have this right before I order this speaker. I’m going to go over my understanding of it - please correct or expound where needed.

If I put the amp in 3-channel mode using one channel for the single speaker subwoofer, I would have to wire the speaker in series using the dual inputs. Positive from the amp to positive on one set of inputs, negative from the amp to negative on the other set of inputs. Then a wire connecting the unused negative on one input to the unused positive on the other input.
Now the speaker is actually running at 8-ohms, right? Is this a bad thing, since my amp is 4-ohm? If my thinking is right, this would put less strain on the amp and speaker, but they wouldn’t be cranking at their full potential.

The other way I’m thinking of doing it is running the amp in 2-channel mode and using both channels on both inputs of the single (dual 4-ohm voice coil) speaker. Would this work? Would it be one channel from the amp to one voice coil input, and the second channel from the amp to the second voice coil input? Or would the speaker be running out of phase that way? Should the positive and negative from each channel go to different voice coil inputs? What would the ohms be at using this setup?

Thanks in advance for any help!

2

I swear, this is only an incidental bump!

Same setup as above: What would happen if you wired up to only one of the inputs on a dual voice coil subwoofer?

3

Here’s one arrangement.

4

I have been told by a car stereo expert this is ‘bad’, but he worked in tweeter so take it for what it’s worth.

The amplifier I had would only ‘see’ half the load on it when bridged (I think most automotive amps are like this), so if the amp was bridged and connected to a four ohm speaker then the amp would act as if it where driving 2 ohms. If your amp is the same way then the the three channel setup you describe would let the amp see 4 ohms, nice and safe but not getting all you can out of your amp. (Sub wired in series = 8 ohms, briged amp only sees half the load). If you used the three channel setup and a parallel connection like the one in David Simons link your amp would act as if it where driving one ohm (Sub wired in prallel = 2 ohms, amp sees half the load). If your amp can handle a one ohm load this would be a good way to get maximum power from it (assuming you are already using the other two channels) but it may run hotter this way.

If you ran the amp in two channel mode then each channel would be hooked up to a 4 ohm voice coil but act as if it where running a two ohm speaker. This would be the best setup in my opinion.

This is assuming the speaker has two 4 ohm voice coils.