need sub box help plz

[straghtclownin]

got a 98 gmc jimmy 4door got a fi fully loaded btl need help with box size sub up port back or what not whats the best way to do it right now i got 2 fi 15s in there but miss my 18 so im goin back to it it was in my car but got the suv so need box tips plz

[cubs_fan0718]

Sub up port back, around 7cubes after displacement, and tuned @ 32 is my suggestion.

[straghtclownin]

Sub up port back, around 7cubes after displacement, and tuned @ 32 is my suggestion.

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...ok cuz im just kickin some stuff around i took the box apart it was for my towncar sub up port up and i started with 1 fi 15 in my suv hittin 145.6 db not bad but want louder my bosses truck hit 156db sealed his shop is on meades page but ya i want it loud and i have heard sub up port back alot so thanks