When I sourced the subs for the Alpine system in my truck, I bought Alpine SWS1043D DVC subs because they were 4 ohm and in the right RMS range for bridged mode on a Alpine PDX-F4 amp.
I bought two of the PDX-F4's because I wanted the same amp for the door speakers and the subs, in bridged mode (200WX2@4ohms). I realize there are better choices for a sub amp, that is another discussion though.
The mistake I made when I bought the subs was not knowing that a 200W RMS DVC sub advertised as 4 ohm is actually two 4 ohm voice coils that run in series or parallel. Meaning the load to the amp is actually 2 or 8 ohms. I didn't realize this until 4 months after buying them when I was ready to start the first phase of the install. So, I decided to use them in 8 ohm mode (actually, they measure 6.8 ohms on my meter in series).
So, last weekend I finished the main install and powered up, set levels, EQ, etc. -- they sound pretty good. But, predictably, don't hit hard enough. I am more interested in SQ than massive thump but I think the kick drum and picked bass guitar needs to punch through with a little more authority. It's not bad, just could be better.
So, what I am thinking about doing is un-bridging the PDX-F4 amp and running each voice coil on a discrete channel for each side. That is:
* Left channel, two pairs of outputs, one for each voice coil on the Left sub.
* Right channel, two pairs of outputs, one for each voice coil on the Right sub.
That way, my amp sees a 4 ohm load on all channels which is what it is designed for in non-bridged mode and the subs are getting the FULL 200W (as opposed to around 140W now because of the higher impedance, lower current, E=IR, etc.). It is the exact same signal to each coil on each sub so no, it isn't going to cause thrashing between the coils.
I think they are going to sound a lot better. But, wanted to post about this in case anybody has done this in a similar arrangement and has comments, suggestions, observations, etc.