@That_4.0_ranger ,
Without additional info, I presume that the 91 is a standard cab. Three sub setups come to mind for a standard cab:
• a pair of 8" driver's in boxes behind the seat. With my seat nearly pinned to the back wall, I was able to install a 1.87cu.ft. enclosure which is easily more volume than two high throw 8" driver require.
• my favorite, a single 10" driver. My favorites are Nakamichi, MB Quart and Alpine S line but I have no issue using a healthy Punch, Kenwood, Sound Stream or Orion 10's.
• to save on space and maintain full seat adjustability, look into Bass Shakers. They aren't speakers/driver's, they do not move air but they send a pulse into the seat structure which feels like a sound wave. It simulates the low frequency air pulse and does feel similar.
In regards to an amp, there are many that will easily perform the duty. A great deal is an older Alpine V12 series, 2 or 4 channel set up. They usually include an active crossover with both input/output gain sensitivity adjustments.
I have a simple formula that I use to determine how much power I need for my subs on a given system. Whatever RMS watt level the front mains are working on, I use that number X3 to get proper balance since the larger drivers require much more power to equal the sound output level of the mains.
EXAMPLE:
- if the mains are running 50wrms, then I use 150 wrms on the sub(s).
- if the mains are running 12.5 wrms, then I run the subs at 30-50 wrms and dial it on with the gain controls.
There are a few good new amplifier companies and a bunch of good older companies, my favorites are:
Nakamichi, Alpine, Phenix Gold but I have no issue using a solid Rockford Fosgate, Punch, Orion, Sound Stream or Kenwood.
When purchasing a used amplifier my price formula is $0.50 or less a wrms; if I am looking at a solid looking, known working two channel, 30 wrms/ch, I'm willing to pay $30.00 for a mint condition or less if not mint condition.
IF you have any questions, feel free to ask. There are a ton of ways to do things right or wrong, in the end, what we hear is the story of which route was taken.