What?
References :

If you cant Increase your trunk,the next thing to do is to decrease your box size.

there's three ways of doing that.

first threes this thing called "isobaric",that's when you have two speakers and you have a small single box,you take and put one of the speakers in the box and then take the other speaker and put it face-to-face on the other speaker <[>] like so,now you've just increased your sound by x2(or your box sounds bigger)

then there's this thing called "DVC or dual voice coil",that's when you have a speaker with two voice coils,and then you put that speaker in that same small box and get the same effect(well not really,but they are engineered to give the same effect)[there is no sound like isobaric,but we try]

there is also "pro subs",you take a pro sub and put it into that same small box,you get the same effect(which sounds better than DVC but costs more than DVC)

these all take alot of power*pro subs taking the most power but sounds better from the second and third option*(when you decrease your box you have to increase your power)get a bigger amp

I would prefer you take the "pro sub" in a small box option

Shelly…you silly girl
References :
5 years of box building,and common sense.