A couple questions.... (sub related)

Aight ill get right to it..
I have 2 15" Fisher subs (was in a set of three, (sub, mid, high), for the house. I Put the whole box in my trunk, and it gives your so much bass..... Now for comparisons... I had 2 lightening audio (12 inch) (AWFUL) subs, smoking off of a Xplode amp. I hook these up to the same Xplode amp, They dont crack, distort or do anything there not suppost to. Why's that? and would it be a better idead to build a box for them or leave them in the stock tower?

And I've heard something passing around, about a resistor you buy from radio shack thats suppost to double the bass, with half as much thump? If thats true, what would i be looking for?

And for a final question....... What difference does the ohms make? i always thought the higher the ohm, the better the speakers will sound......
Thanks,
Bill