While you have the sub out it should say on the magnet if its dual 2 or 4 ohm.

 

hmmm as godzilla pointed out (his impedance breakdown was correct) I am guessing you have a dual 2 ohm voice coil in parallel giving your amp a 1ohm load (which is unfortunate if you own 2 ohm stable amps ... and you do the Kicker is 2 ohm stable and the only specs I can find on clarion amps have them 2 ohm stable)

The alpine is also only 2 ohm stable.... hmmmm (it is a more efficient amp and has less heat loss... (the alpine may be better than ratings but the kicker should be too)

so you know how to measure voltage with a DMM... how about resistance from the speaker? disconnect the speaker from the amp and measure the resistance across the positive and negative to the sub

it could also be a thermal overload, is your amp mounted correctly and not covered with stuff or in the sun.. can the air get to it?

also turn the gain down turn on the amp, turn the bass boost off, turn the loudness off and see if that helps.... you should be just as loud just with the **** on the HU turned up more

If the sub is 4 ohms... well that makes it even more odd as it doesn't make much sense at all... is any of this used or abused equipment?

 

ok, info:

amp is actually a Kicker KX1200.1 (thought it was smaller for some reason), i have the clarion but its not wired in as i thought it was the one with the problem and left the kicker in when it was no better.
sub is a DVC 4 ohm.
it was not wired correctly also. it was wired parallel but coil #1 had the main positive and negative. coil 2 was the "bridged"/ "daisy chained" coil. (not sure if it would cause an issue but was wired wrong. (not me that wired it that time)

it is currently setup in parallel (makes it a 2 ohm load?)

i tried in on series (8 ohm load?) and was clearly not good as there was no difference in the amp cutting out.

but with the 2 ohm load parallel wired correctly it is much better. i have the gain at 10 (goes to 11) and it is hitting hard. now the volts will drop to 13.7 before it kicks out and is definately hitting more DB's as i could feel my ear drums compressing (couldn't b4)

would it be a good idea to upgrade the power wire from the alternator? factory its about 8ga (maybe bigger but not a normal size bigger like 7ga, its Toyota so who knows what they have in Japan) and what is the best option for a cap? 1 1farad, 2 1 farads as is, or the 5 farad?
also, would it be better to run the clarion or the kicker amp?

what ever the case i have another car that will get the other cap/s as i also have a pair of MTX thunder 8000's with 2 900Watt fosgates.

thanks again for all the help

 

I'm ready to bet it's power issues. Also what is the resistance of the sub, "eith 2 or 4 ohm" doesn't make sense. Take a multimeter and stick the leads to one terminal and set it to read resistance, then we will know what the resitance of the sub is.