Not happy w/ the car audio at all so far. Not sure if it is the amp or what. The tweeters sound terrible. They have distortion even with the crossover set very high on the amp. And the passenger side door midrange is substantially louder than the driver side. This is w/o the DSP connected so that isn't the issue.
I bought some other used gear today. Will swap out my old amps for the Hertz 5-channel. Will ditch the rear mid-bass speakers. Swap out the front door speakers for some better ones i got today. And decided to throw in a small sub.
So tonight I hooked up the sub to the Dayton Audio DATS V3 test system to get parameters in order to design a proper enclosure.
Then I enter this info in to WinISD, an app that show the performance of a enclosure for the speaker. Thinking on a 0.9 c.ft ported enclosure as I want it small as possible. Then a 18Hz high-pass filter @ 18Hz to prevent over-excursion when playing 20-30Hz. And a low-pass filter @ 100Hz so its only playing sub-bass. Estimated frequency response curve. Black is the ported enclosure. Blue is a sealed enclosure of the same size.
Graph showing the excursion of the subs in the enclosure w/ a 380W going to it. The limit on the sub is 15mm, so this will be safe.
And the group delay, which is is the delay between when the audio input and output. I have 20ms @ 40Hz, which I believe is pretty decent. You can see this is where a sealed enclosure actually benefits over a vented. Which is why people say sealed enclosures are quicker / punchy. But that should only really be an issue w/ prefabricated boxes which are not tuned @ all for the specific driver.
Now on to designing something up in Fusion 360.