With two dual 2-ohm VC subwoofers, you could do a few things:
- Wire each sub in series for two 4 ohm subs, wiring them together in parallel for a single resulting 2 ohm load
- Wire each sub in series for two 4 ohm subs, wiring each 4 ohm sub to one channel of the amp (two 4 ohm loads)
- Wire each sub in series for two 4 ohm subs, wiring them together in series for a single resulting 8 ohm load
If you had a single channel class D amp, you would not have a problem as most class D mono amps are 2 ohm stable - making max power into 2 ohms.
Unfortunately, you have a 2 channel amp, which is likely 2 ohm stable.
It's 2 ohm stability means also that it's only 4 ohm stable when bridged (because internally the amp rail voltage doubles when you bridge the amp).
With a 2 channel, 2 ohm stable amp, maximum output power is given at either 2 ohms stereo, or 4 ohms bridged.
Unfortunately, you can only wire to 4 ohms stereo (where the amp will be making approximately half the power it is capable of), or 2 ohms mono (where the amp is not stable, could overheat, go into protection, or worse).
Alternatively, you could wire for the third option, bridging the amp and running it at 8 ohms mono - but again, the amp is only making half the power that you paid for.
![2 x Rockford amps and capacitor? -- posted image.](https://www.the12volt.com/installbay/smileys/smiley2.gif)
If you haven't gotten the sub amp yet - I would reconsider your options, because this option will cost you nearly two times the $$$ to get the same power you could otherwise supply to your subs.
The most cost-effective route would be to purchase a 2 ohm stable mono amp - and additional benefits would be significant electrical efficiency.
If the amp line you are shopping in doesn't offer one, I'd explore the possibility of purchasing a 4 channel amp that provides the power you are desiring when bridged from 4 channels to 2 - you have two 4 ohm loads, after all - this would also yield maximum power to your subs, at a lower price point.
![2 x Rockford amps and capacitor? -- posted image.](https://www.the12volt.com/installbay/smileys/smiley16.gif)
The only downsides to the 4 channel amp approach is that it would be a class A/B amp, which generally is a more expensive topology than class D amps, and they are inherently less efficient, electrically speaking.
If you already have the amps and subs, you could explore the future possibility of upgrading the amp...
Or else upgrading the subs to a single, larger cone dual 2 ohm voice coil unit, or to two dual 4 ohm voice coil subs, which would allow you to present the full power of your amplifier to them.
If you don't want to upgrade either, you still have options -
After all, it takes a 4x increase in power to effect a 2x increase in output (6dB)... dramatic power increases for less dramatic output increases... not to mention it's not even that good, there are other inefficiencies at play ... but anyway...
Following Hoffman's Iron Law, you could build the enclosure larger and/or port it to a higher tuning frequency to get much higher efficiency out of the subwoofer
system. It's very possible to reach the mechanical and acoustical output limits of a subwoofer driver with wattage that is far below the driver's thermal powerhandling ratings.
Good luck!