What's that Box BEFORE the Air-filter?

Just purchased a 2001 Civic LX. Looking through the engine bay, and identified where all the important things were that I can lightly service. I noticed that the cold-air inlet horn between the batttery & fuse box goes into a HUGE box, which, in turn, feeds the air-filter box. What IS that big ol' box? It's not described in the owners manual, as the air-filter location is. Are there any 'user serviceable' parts in there, or should one leave it alone? I've not been tempted to crack it open, yet, but I'm feeling the urge... :naughty:

take pix?

I've found out that it's called a 'resonator.' It's purpose is to lower the sound that the intake makes, or so I've been told.

Has anyone tried throwing a straight 3" dia aluminum pipe on it? Like run it from the air box, slight bend and have it go to where th battery is or so. Even throw on a cone filter and take the stock one out of the air box. I ask because it sounds feasible. There aren't any sensors along the way, and would think you would get much better airflow, and it would sound pretty mean. Just don't know if it would mess with the PCM's job at all. If anyone has, please let me know. I really wanna put an intake on the hx. I know the model is intended to economical, but it'll still be better then a truck

I've put a CAI onto my Civic before...I haven't though of putting a pipe onto that resonator and doing it that way. If you do that, you're really losing the benefit of a cold air intake, since it still has to go through the resonator, and has to be filtered again. You might even hamper the engine with double-filtering. So, if all you're looking for is a neat sound, go ahead. Just keep in mind you aren't going to be getting as much air to the motor, which might drop your throttle response and MPG.