Sub set up. Not pretty but sounds great!
 

I've had big high power set ups in the trunk you could hear a mile away but for the Miata I'm willing to sacrifice a little boom if I can keep it out of the trunk. Also I ride in the car enough the foot well idea is out too. So I decided the deck and the doors are all I have to work with for speakers.

I started with a simple down firing sub cab I could set on the deck.
https://www.miataforumz.com/attachme...ine=1418705914

The sub I am using is an infinity 8" speaker.
https://www.miataforumz.com/attachme...ine=1418705914

https://www.miataforumz.com/attachme...ine=1418705914

https://www.miataforumz.com/attachme...ine=1418705914

https://www.miataforumz.com/attachme...ine=1418705914

https://www.miataforumz.com/attachme...ine=1418705914

I changed out the 6.5 rounds to 6x9s at the same time. Mounted in the sheet metal like this they did not sound very good.
https://www.miataforumz.com/attachme...ine=1418706658

I decided it would be wise not to bury the panel to access the fuel pump so I trimmed my speaker mounts so the panel could come out with out taking the speakers out.
https://www.miataforumz.com/attachme...ine=1418706658

I had to do a little beating to get the 6x9s in, especially on the passenger side. I probably pushed it down far enough to hit the tank but I just used a tap hammer to not push the tank in at all. Hopefully I did not pinch any fuel lines either!
https://www.miataforumz.com/attachme...ine=1418706658

They are not symmetrical because 1, I don't care, 2, no need to beat on the drivers side if they are not and 3, no way am I moving the fire extinguisher again! (This is the 3rd mount)
https://www.miataforumz.com/attachme...ine=1418706658

https://www.miataforumz.com/attachme...ine=1418706658

I can't decide if I should put the carpet back on the deck under the sub or not...
https://www.miataforumz.com/attachme...ine=1418706658

It really doesn't show much from the back. Not that I would care if it did... it's all about the bass!
https://www.miataforumz.com/attachme...ine=1418706658

I painted it all with left over car paint.
https://www.miataforumz.com/attachme...ine=1418706658

The amp is behind the passenger side seat and the sub cab comes right out for racing or what not. The cab would have to mount differently for a glass back window but it could be done.