how well wil a regular box built for 2 X 12" work if i cut two holes in the back and add two more 12" subs facing in wards ?/?

 

try it and let us know.

 

You just halved your air space.

 

air volume was considered, the idea is of it to work like an isobaric or isobarik loudspeaker construction.

 

you can`t do just by cutting two holes.You may want to look at how they are set up as space between the subs is just enough for them not to bang in to one another.

If you do what you suggest its still a regular box.

If you go iso then use spacer rings big enough and mount one to the face of the other(cone to cone) with as little space between them.You need to change up the wire job as well.

If you want better help let us know the subs and your box specs and we can give you a better idea