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i have 2 rockford fosgate P2 12 inch subwoofers. they are 200 watts RMS each at 4 ohms single voice coil. im looking for an amp that will match these well. i have heard that if you bridge subs the rms stays the same so if i have 2 subs at 400 total rms then i would need a amp that has 200 rms if i bridge it but im not sure how many ohm amp etc and if this is even true? also someone told me that you cant bridge single voice coil subs? im looking into the alpine MRP-M350 mono amp 350 rms at 4 ohms. im wondering if its a good match and if it will work for my setup? thank you.
Answer -
Ok, well first let me try to clear up a few of the confusing misconceptions you've heard.
1. the term "bridging" only applies to amplifiers, not speakers. if an amplifier has 2 channels (left and right) you can "bridge" them into a mono channel. Bridging the amp will provide aprox. the combined power of both the left and right chanels into 1 so if the amp is rated for 200 watts PER channel (and it has 2 channels) then bridged it should provide 400 watts into 1 channel. The minimum ohms of each channel add together as well when bridged so if each channel can support a minimum of 4 ohms in stereo, when you bridge the 2 channels together the amp will only take an 8 ohm load.
As for the speakers you can wire the coils in series or parallel. look these up or ask me again if you need help on how to wire series or parallel.
All you do to figure it out the ohms is you divide the ohms of one coil by the number of coils when the coils are in parallel. and you multiply the ohms of one coil by the number of coils if they are in series.
2 coils 4 ohms each in parallel is 2 ohms
2 coils 4 ohms each in series is 8 ohms
4 coils 4 ohms each in parallel is 1 ohm
4 coils 4 ohms each in series is 16 ohms
and you can do combinations in series and parallel if you have enough coils:
If you have 4 single voice coil subs or 2 dual voice coil subs then:
4 coils 4 ohms each, wire 2 of them in series and the other 2 in series forming 2 8 ohm loads. now you have:
2 loads 8 ohms each. wire them in parallel and you have 1 4 ohm load.
so your subs are what they are. they are 4 ohms each so your only options are:
2 coils 4 ohms each in parallel is 2 ohms
2 coils 4 ohms each in series is 8 ohms
I always opt for parallel over series so you are looking for an amp that runs a mono 2 ohm load. finding a stereo amp that's bridgable to 2 ohms is a rare find and would be more exensive so we will look for a single channel mono amp. the amp you found is pretty good. it's a mono amp and is 2 ohms stable. it's also a class D amp so it's more efficient and will put very little strain on your car's electrical system. A pretty good match
What type of box are these going to be in? If ported, what size and tuning, if sealed what size? If the box is bigger than the subs are rated for then this amp is probably a great match since its less wattage than recomended. If the box is exaclty to spec or a little smaller then recomended I would get the MRP-M450.
well they are in a sealed .88cu. ft. box and they call for .8 so i should maybe get the m350. the other question i have heard was if it was true when you bridge the amp the watts on one of the sub stays the same. so you have 2 subs 400 watts total then you would need an amp that is 200 watts bridged?
AnswerI'm sorry I don't get what you're saying here. you have 2 subs that are rated to take 200 watts each. so you need 400 watts to power the both of them. that's it. 400 watts. the m350 puts out 350 at 2 ohms which is the load that 2 x 4 ohm coils in parallel will give it, so that's great.
You're sure they are in .88 cubic feet each? you have to subtract for wall thickness, bracing if any, and driver displacment. let me know the external meausurements of your box and the thickness of the material on all walls if you are unsure. Even if it is .88 I would go with the 450 amp not the 350. you are more likely to blow the speakers with a smaller amp. I know this sounds stupid but trust me espeically in a sealed box. i can explain if you want me too but the bigger amp will serve you better.
