Does anyone know what kind of specs a regular box that is being used for equipment as an example has?
I'm really interested to hear what frequencies will a sealed box filled with rigid fiberglass affect.
I have many peaces of mineral wool left over & want to pack them up in something to use as more bass traps in the room instead of trashing it, but don't want to suck up any more of higher frequencies, any ideas for cheap?

You could build a slat resonator tuned to your room modes. Do a Google search for Helmholtz resonators, and check out John Sayers' site, here, look under "Wall Units.", and the forum here.

There's a calculator somewhere on that forum that will tell you what your room modes are, and one that will tell you what specs to build your units to.

Hope that helps.