Stock head unit & sub - where's the low end?
 

I have a 2007 Honda Accord EX-L. I have a line out convert hooked up to my stock head unit (no nav). The LOC is connected to a Rockford Fosgate 1200D amp, and attached to that is a 12" B2 IS12 subwoofer. The sub box is tuned to 32 Hz, and I know for a fact that the subwoofer itself can push 30 Hz notes.

Here's the issue:

Everything below ~32-33Hz seems to drop off hard. For example, playing Jeezy's "Put On", the final note in the main bassline almost disappears. I know that note is 30 Hz. I've tried with different subwoofers, and recently purchased an LC2i to fix the issue. I haven't tuned the LC2i, but whatever the shop set it at, I'm still missing the really low notes.

Does anybody here with a factory head unit 2007 Honda Accord have trouble with low notes? I need to know if it's the factory head unit that is stripping my music of sub-33Hz range, or if something else in my setup is messed up.

With a 32Hz tuned port, you won't get output below that without damaging the sub (this is because the sub becomes unloaded below tuning frequency and will experience excessive mechanical movement) besides getting cancellation. Additionally, the subsonic filter should be set around 30Hz to protect the sub. With that box tune, you don't want sub 30Hz bass.

The head unit won't drop off at 30Hz.

No Bass
 

The other issue might be that your LOC and Lc2i are installed after the factory amp, and if that is the issue then you need to have the Lc2i installed before the amp. The reason for this is that the factory head unit is pre-tuned my the manufacturer so unless you attenuate those frequencies prior to the amp, then you can't get the proper flat signal your looking for.

I don't think the 2007 had a subsonic filter in the factory amp. A sharp roll-off would require a 30Hz 24dB/oct subsonic filter, which I haven't seen in Honda factory systems. I've seen roll-off, but not that sharp or that low. We do know that aftermarket sub amps have that feature built-in and we also know subs become unloaded below tuning frequency.