Tri Mode Setup

With a properly designed crossover network, a 4Ohm bridged load along with a 2Ohm stereo load will be fine.  With a properly designed crossover network, at any given frequency, the amp will see only the bridged woofer or the mid/tweeter combination. 

ledmodman, easy there....

...you started out saying that tri-mode could be effective in getting the most out of the amp, and even provided an excellent link that goes on to explain the concept visually, but you're lost with your "basic math".  The reason the crossover caps and coil are used is so that the amplifier is not effectively loaded by the full musical range at any one time, so  you do not use ohm's law equations to find load on the amp as you are describing.

For a motorcycle, with the excessive noise inherent and the too-little room to work with, I can see how using a setup like tri-mode can work out okay.  But, nordo, for a vehicle that has plenty of room for another cheap amplifier, the disadvantages of tri-mode outweigh any perceived benefit of going that route.  Nowadays, power in car audio is cheaper than its ever been.  Keep the value of sound as high as you can relative to the quality of each of your speaker sources, and use the advice I printed above.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

As I said, I do not have room for another amp. It's a regular cab mini truck. I have a power inverter under the ds seat and I keep my laptop under my ps seat. The amp is mounted behind the ps seat on the back wall. When I'm done building the enclosure for the sub, it will take up the rest of the room behind the seats. I would like to go this route for now. I can always upgrade to a single 4 ch amp in the future when the budget allows. I'm sure it will sound better than my previous setup. I had a cheap 35watt bazooka bass tube and that sounded like crap. I had it for 4 years and it finally died last week. I already have the JL sub lying around and have plenty of 3/4" MDF so I figured I'd build a box and run the sub off the same amp for now until I decide to upgrade. I figure coils and capacitors would be relatively cheap compared to a another amp. I could buy several sets for different frequencies like 80, 90, 100, 110, 120Hz etc. and see which ones worked best. I also figure I will be able to regulate the bass pretty well with the equalizer on my head unit.

Have you thought about getting the Bazooka amp repaired?

JL and Alpine both make a 4 channel amp that is smaller in size than the amp you have.  Though pricey, a much better solution.

With the money you'd spend on the appropriate inductors and capacitors, you're better off buying a dedicated sub amp or as mentioned above, a 4channel amp.2013 Kia Rio -90a alternator

DDX470HD GTO14001 GTO1014D (x3)

Big3 in 1/0G

1/0G to GTO14001

Or, (also agreeing with jmelton86) for good kwality inductors and caps, you might be in the 100 dollar range or above... The Alpine PDX-5 is a five channel, 600WRMS, Class D amp that'll do everything you need it to. Check it out.

Well guys. It looks like I'm going to be going with a 4 ch amp after all. I found a nice used one. I decided to do this after receiving my new kenwood kdc x994. When I looked in the audio configuration I found some great crossover capabilities. The unit lets you set the high pass for the pairs of front and rear speakers as low as 40Hz. The unit lets you set the sub-woofer low pass all the way up to 250Hz. In addition to this, it lets you set the slopes from 6db all the way to 24db. so (6, 12, 18, 24) after seeing this feature, I decided that it was the best way to go. I would have stuck with Tri-mode on a cheaper head unit that didn't offer these cababilities. I'm going to use 2 ch to power the front speakers and I'm going to bridge 2 ch to power the sub. I'll use the head unit to power the rear speakers. Thanks for all the advice guys.