Car Stereos: Choosing an AMP, dual voice coil, watts rms

Question
Hello sir,

I have a 10" Type R SWR-1042D and I am having a hard time choosing an AMP.  The sub is a 4ohm and 500 watt RMS.  Every AMP I find with 500RMS is a 2ohm's.  I am looking at mono amps and the settings allow 4ohms but it cuts the RMS wattage in half.  Its confusing.  What AMP would you recommend for me?  Is 2ohms ok on a 4 ohm speaker?  

Thank you for your time,

Steve

Answer
Hi Steve,

As it happens, your Alpine subwoofer is a 4-ohm dual voice coil design.  As far as the wiring and impedance goes, a dual voice coil (DVC) sub is similar to a pair of 4-ohm single voice coil subs.  That means your single Type R sub can be wired for 8 ohms (with the voice coils in series) or for 2 ohms (with the coils in parallel) but not for 4 ohms.

This works out perfectly for you, because your sub can be matched with any of the amplifiers, rated for 500 watts RMS at 2 ohms, that you've already looked at.  I think the Alpine MRP-M500 amplifier is a good value for a single Type R, but there are plenty of other amps that will work as well.

Here's a wiring diagram showing how you'd get a 2-ohm load with your sub:

http://mobile.jlaudio.com/graphics/Support/Tutorials/wiring_images/DVC_Parallel_...

Just for reference: you'll find 2-ohm and 4-ohm power ratings on most amplifiers, because the majority of amplifiers can produce more power with lower load impedances (up to a point).  In general, though, if an amplifier is capable of driving 2-ohm loads, there's nothing at all wrong with using it with a 4-ohm (or even higher) impedance.  It's true that the power output will typically be cut substantially; but the amplifier will also run cooler, and may have a longer lifespan as a result.  It's certainly not harmful for the amplifier or the subwoofer.  If the 4-ohm rating is enough power for your needs, then don't be concerned about matching the amp with a 4-ohm sub. What you have, though, is really a 2-ohm sub.

Hope this helps!

Brian