I'm trying to plan out my system for my new truck. I found some nice Infinity Kappas that handle 85 watts RMS at 2 ohms. I am planning on using an Alpine MRX-F30 amp for the speakers but I'm wondering how to set the system up for 2 ohms instead of 4? Is it changed on the amp or is there a way to wire it?

Thanks.

These are the speakers I was going to buy, if it makes a difference. Front Rear

 

Well technically these speakers are 2ohms. I think Infinity puts 4ohm on the box meaning if your amp will drive speakers at 4ohms it will drive these speakers at 2ohms. Realize the system impedance may be closer to 4 when you factor in wiring, speakers and connections. There isn't really anthing you can simply do to make sure these run at 2 ohms unless the speakers are tapped directly off the amp (no wire). So these will see anywhere from 50 - 75W RMS. Which personally, the amp might struggle to keep up, especially the rears which are rated 100W rms.

I would personally dump the rears, use the money for a better set of speakers for the front. Then bridge the amp and only drive the front speakers on two channels. You could keep the OEM rears in place and still drive them off the HU. Even cheaply replaced rears might help but OEM speakers are fairly efficient but low power handling.

For example, I'm driving my fronts (150W RMS) with a 300W per channel amplifier. 2x the headroom which ensures a good quality signal and the speakers really like the power. You'll find most speakers actually sound better when they are driven harder.

If you are really hung up on having front & rears just note that amps will provide better sq when they have headroom. Also, overdriving amplifiers can be damaged along with the speakers if the output is clipped.

Where you can control the impedance is when wiring speakers together (either in series or parallel) for subs or mids.