I've built a few boxes in the past but don't have much experience using the t/s parameters. I usually go a little bigger than the sub manufacturers volume and go around 30-35 hz for tuning as well staying in the "port area range" on Torres. Some things I have noticed with my 2001 Malibu...
With port back sub up it rattles everything but you don't really get much spl.
With port and sub facing trunk, the further away from the trunk the box/port are the louder it gets.
What I'm really trying to get out of this is to be able to use the t/s parameters of the sub to try to build a box that is going to help see the full potential of the sub. I'm not trying to win comps or even get scores but I would like to make something that gets loud and sounds good. I will be making this for a dual 2 12" HCCA silver cone model. I guess I'm not really looking for help actually designing the box but for tips and pointers on what parameters I need to use and how to use them. Also does staying in a different port area help with SQ/SPL. For example: would 9"^3 per cu ft be more for sq where 13"^3 per cu ft may be more for spl?
The box would be for daily use. I listen to everything.. Rap, rock, country but would obviously be looking for it to get loud with rap and "bass songs".