Wanting to put 4 15"s or 4 12"s in the back by putting a lid over the entire cargo area like the pull out protector thing does.

I don't know the exact name of the type of setup.

Basically I would take a sheet of plywood and put it level with the top of the seats and make it snug with the hatch so it's sealed when the hatch closes.

Then put the subs in that piece of plywood.

When the hatch closes, it would make a box, but there is really just one piece.

Any one know what I am talking about?

Also looking for suggestions on wattage.

If I get 4x 4 ohm single coil subs, would a 1 ohm amp work?

I'm not looking to shake the block, just have more feelable bass at lower volumes.

Am I correct to think that more cone area would do this and that I won't need 10,000 watts to achieve this?

 

You're talking about an IB setup. An IB (Infinite Baffle) setup requires that a driver be mounted to a baffle with "infinite" space behind it. It always requires that the back wave (sound waves from the back of the driver) be COMPLETELY isolated from the front wave (sound waves from the front of the driver). Now the infinite space is pretty negotiable, anything nearing several times the drivers Vas (a theile-small parameter that measures the driver's equivalent acoustic compliance) is acceptable for use as IB. The biggest problem and hardest to deal with, especially in vehicles, is sealing the back wave from the front wave so there's no cancellations. While doing what you described would be a fairly easy way to start out on an IB setup, it will be VERY difficult to prevent wave interaction which ruins the response of the setup. Another problem is that an IB setup is basically running a driver in Free Air, or in other words, without the trapped air in an enclosure to help control cone movement. Due to that fact it can be VERY easy to drive a speaker into mechanical destruction with VERY little power. Some subwoofers are better suited to use in IB than others as well.

This is something you can do, but be prepared to put in a lot more work than you were figuring and don't be expecting a great deal of output either. IB designs aren't typically used for high output purposes, they're mainly aimed toward SQ setups in typical uses.

You are correct to think that more cone area and no where near 10,000 watts of power are needed to get the lower bass you're wanting. Though I believe you should be looking at a well designed ported setup that's tuned low for very good low frequency extension. Although typically the lower you tune, the better your front stage will need to be in order to make up for the lost upper bass frequencies. With ANY design there are trade-offs, the best way to design your system is to decide exactly what you're wanting it to do and what the trade-offs are that you can deal with and build it accordingly.

 

My goal was SQ (having more feel-able bass at low volumes)

I was going to get 4-6 10"s or 12"s that would use the EXACT amount of space so the box would be perfect.

I was thinking 125-250w rms per sub.

But I also thought how subs with higher RMS rating sound louder even when lower wattage is supplied...

 

I believe what you're thinking is right on target with the goal you seem to have in mind. Though if at any time you saw a higher power sub get louder than a lower powered sub on the same low power it was likely due mostly to the setup as a whole (box, vehicle, driver's sensitivity rating, etc.). Ultimately the power rating of a driver has only to do with how much heat the motor can discipate. The biggest reason high powered drivers can get louder than lower powered ones is that they have the ability to withstand the heat induced by the high power and the result is very strong and plentiful cone movement which moves more air with more force and therefore creates higher SPL levels.

Anyway, I like what you're thinking, I just hope you understand how difficult it's going to be to seal the seams and keep the waves from interacting and causing cancellations and distortions. Otherwise I think you'll like what it can/will do.