Hard material in back of DCSB cab impeding sub box install

I'm trying to install a sub box and am having issues with fitment. There is some hard material pasted on the bottom of my cab behind the back seats and I think it is causing the issue as it is raising up the height of the box.

What is this stuff and can I remove it? It is almost cement like. Hard and has some cracks in it.

 

no clue.. second gens dont have this... so that helps narrow it down to only third gens. Thus, help you figure it out if yours is a one off or if all have them

 

I believe its factory sound deadening. It does come off. Had it on my old accord. Took a small chisel and hammer and just chipped away at it. It's pretty much glued on

 

The floor in that location isnt the thickest so try not to gouge too much

 

Yeah. Hit it softly at an angle. And do small chips at a time. Took me a while, but it all came off with no damage

 

the sound deadining is easy to take off, getr some dry ice, break it down on the deadening, the dry ice will freeze it so you can chip away at it easily, it will come off in big chunks and fast.... i use to do this in race cars all the time

 

I used an oscillating saw with a scraper blade. Fast and clean.

 

Well log story short.. I removed it. It chunked away quite easily with a hammer and chisel. Not hard enough to be hitting the cab but enough I crack up and dislodge the material.

Lowered the height of the sub box so it was sitting against the bottom of the can instead of the material. Geometrically then it made more space backwards for the back of the seat as the hypotenuse of the box was lower down (if you can picture what I mean). Pick a fixed position next to the slope of a triangle and lower the triangle --> the point of contact moves back.

Gave me maybe 1/4" or so more clearance which is critical for giving space between the face of the speaker and the back of the chair