Pics of my custom subbox
 

It fits nice and hits decent not carpeted yet

Cardommain

What size sub are you using?

Is your box sealed or ported?

Could you post the measurements of your box?

10" Dual Voice coil 4ohm powerbass usa PBX 10vd2
250watt RMS 5.75" mounting depth sealed
I figure my empty volume is .76 and about .67 with the sub.

I am making a new box. This one has some issue, especially with the big sub and small volume. I heard my buddies brand new box in a new tacoma 4 8" kickers with 400watt kicker sub. It was tight and load not much boom but much louder and cleaner then anything my sub would do.

I started playing with my box and noticed
the sub was actually hitting the floor and extreme bass.
I have about 3/8" off the floor.
the miter joints are clean cuts but still not air tight. I need to make the angles different. I routed the sides and they are tight. I assembled the whole box during test it could stay completely together with no glue or nails.

I still think the volume is too small or maybe my amp is blown?

and the 1/2" vibrates too.

I have 3/4" MDF. I am going to make a simple rectangular box with all routed pressed fit square joints. It wil be tight and probably 1.2cuft.

If that works I know it is a volume thing. I will then build a cleaner fit box. All of the off the shelf units are only 0.65-0.70 cu ft for a similiar setup and they have no vilume and only sound good at 58-70hz