1) In your case, series from the amp and coils in parallel would be better. Wiring the coils in series would raise the Qts slightly (there is a formula for how much on Isaac MCN's page), and you'll want to keep the Qts below .5, since this will allow the driver to work well in a wider variety of enclosure sizes (important since you don't know the exact volume of your enclosure.)
2) I can't help you much with the enclosure, other than to say that you might consider putting a layer of Dynamat Xtreme in between the metal and the fiberglass. Using Dynamat (oe any soft sound deadening material for that matter) between two rigid surfaces will improve its performance, leaving you with a very dead wall. This will probably be more effective at stopping vibration than attaching extra metal to your trunk.
3) If you tune your subs by ear, use these guidelines:
- If the bass sounds muddy with a delayed or smeared attack, or the sub seems to bottom out on low notes prematurely, the box is too big (add bracing)
- If the bass sounds boomy with a long decay, and thin on very low notes, the box is too small (add stuffing)
Note that these guidelines should only be used after your woofers are well broken in. It would still be best to measure and calculate the volume of the finished box, so you know what to expect performance-wise, and use your ear for the final tuning.
Ben
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