posted this in the sub forum and got little response so I figured I would give it a try here.
I just bought an Eclipse SW 8122 a few weeks back and built my first box for it. Based on some suggestions that I received here as well as from Eclipse I went with a sealed box around 1.25 ft^3. The amp that I am using is a PPI PC2150 giving the sub 600 watts.
I am still working out the kinks in the setup the main one being the to adjust the level between my sub and my interior speakers(waiting for my amp to get fixed). I will start off by saying that at this point I am still running the garbage factory speakers that came in my car so the solution to my problem may come when I replace the front speakers with some nice comps and my rear with a pair of good mid bass drivers but here is my problem. When running a 0-100 Hz frequency sweep I notice that the sub output is at its loudest between roughly 35-65 hz and then it starts to drop off.
If I were interested in gaining more output above 60/70 hz would a new box design help? Like I mentioned I have a feeling that upgrading my speakers all around might be the key but I figured I would check to see if a new box would help also. I have toyed with the idea of building a ported box for the sub but was not sure how to handle port for a sloped box(I want to make sure the box is angled so it fits up against the rear seat).
thanks for the help and or suggestions.