Car Stereos: Maximum RMS differential btwn sub and amp, rockford fosgate punch, dual voice coil

Question
Hello Brian,

I've searched through your answers, and I've found one that pretty much explains it -that you need to have an amp's RMS at 50-100% of the subs RMS.. but if the RMS is the usual maximum, would it be ok to have an amp RMS that is 50 bigger than my subs RMS? and the peak of the sub, would also match the larger RMS. idunno, totally confused right now, here are the specs:


I currently have:

a SINGLE(1) - Rockford Fosgate Punch XLC - 12" Subwoofer
(200RMS / 400 peak / 4 ohm Impedance Dual Coil)
link->
http://www.epinions.com/pr-Rockford_Fosgate_RFP2412_Car-Subwoofer/display_~full_...


with one Rockford Fosgate Punch 150a2 amp (150alpha2 ?)
(37.5x2 @ 4 ohms  OR 75x2 @ 2 ohms). (sorry couldnt find link)

and I'm thinking of upgrading to 400 watt monoblock
(CEA RMS Power: 1x250W @ 4 Ohm or  CEA RMS Power: 1x400W @ 2 Ohm) http://www.bbg.eu.com/Coustic_C400.html


My question is: would this new amp be too powerful and blow my sub because the RMS on the new amp would be 250/400W and the sub itself has a lower RMS of 200?

This is the text on the description that confuses me: "Optimised for 2Ohm load (Two 4Ohm subs in parallel for example)"

Since my sub says 4 ohm on it, does that mean the new amp would only run at the 1x400W @ 2 Ohm setting?





please write back soon, as the auction for the amp ends in two days.

Answer
Hi Daniel,

The first thing you need to understand about your subwoofer is this:  because it's a dual voice coil sub, it can't be wired for a 4-ohm load.  As far as the wiring goes, a 4-ohm DVC sub is similar to a pair of 4-ohm single voice coil subs:  if you combine them on a mono amplifier, then you'll end up with a 2-ohm load (if the voice coils are wired in parallel) or an 8-ohm load (if they're wired in series).  That means with your particular subwoofer, you can't match it with that amplifier in a way that gives you the 250-watt power rating.  

Your options would be to wire the sub for 2 ohms, and get the 400-watt output; or wire it for 8 ohms, and get an output that's probably around 125-150 watts.  The 8-ohm option probably would work out fairly well.  There aren't many amps that would be a perfect match for a single sub like yours; the ideal amp would be a mono amplifier rated at around 200 watts at 2 ohms, but lately it's rare to see a mono amplifier with a power rating that low.

Another possibility would be a 2-channel amplifier, rated around 100 watts per channel at 4 ohms, and between 300-400 at 4 ohms bridged.  An amplifier with that rating should produce about 200 watts bridged into an 8-ohm load.

I think the Coustic amplifier would be an acceptable match for your subwoofer if it's wired properly, and should outperform the Rockford amp; but there are probably amps out there that will be a little better match if you decide to keep looking.  If, later on, you decide to upgrade to a pair of 4-ohm, single voice coil subwoofers, the Coustic would probably be perfect.

Hope this helps!

Brian