I used Noico mats... they're a Dynamat knock-off, but highly rated and worked wonders. They tightened up the sound significantly, and I didn't even cover the doors completely - maybe 30-40% coverage. It was less expensive than Dynamat and from what I've read, easier to install. It was a breeze to lay down. I upgraded the doors to Polk DB6502s as well. Very happy with the results.

 

Another plus on the Dynamat. It goes a long way to keep sound inside the car.

So without going into it too deep, you are experiencing frequency dissipation. The reason your car audio sounds good in your garage is because your garage is acting like a sound box and keeping all the music inside (its more sound proof than your car). Our cars do not come very well sound proof (because racer) and so when you play music, it all just dissipates through the cracks and holes and seams of the car. It also doesnt help that the car being so bare actually creates a lot of "dead noise" in the center. Effectively whats happening is that sound coming from the speakers hits each other and almost cancels each other out. Which is why you feel the need to increase the volume at a significant level the faster you go.

The Sub you have is actually fine for the application at hand. You just need to direct the sound towards you rather than away. Dynamat helps with that. It should also help against drone from your exhaust. I'd recommend lining your trunk and doors first. If you really want to go all out, do under your seats and it should help with tire and road noise.

 

Thank you. Come spring i'll line the trunk and doors with sound deadening... The idq is definitely not enough for the s2000. Maybe if it were ported or inside the cabin. But i'll do the sound deadening and see what that does but will most likely upgrade the subwoofer.