I don't really go for these Japanese headunits with all kinds of buttons and lights, so I chose a Becker Mexico Radio/CD with a Becker Silverstone 6CD-changer in the boot. It's a high-end unit which blends in very well with the Miata's interior.
The amplifier is an Audison LR3041 which delivers 2x40Wrms/1x120Wrms into a 4 ohm load. It runs both the front set and the Legacy open air subs in the rear shelf. The subs are wired in series and bridged over the front speakers. This way the amp sees a total load of 2.67 ohm. I'm not to pleased with their quality, so I'm looking out for something better. With 8' subs one can't expect to get breathtaking bass, but they do give a nice punch in the back. Driving open is no problem at all. There's plenty of power.
I mounted the amp in the left tunnel, next to the gas tank. I didn't want to drill holes in the car to mount it, so I screwed it on a piece of MDF. I then glued that into the tunnel with silicone. It sits rock solid that way, and yet it's easy to get it out again if needed.
It is possible to mount 2 8' subs in the rear shelf, but it requires cutting the metal. Since I wanted to do as little damage to the car as possible I removed the metal panel and made a replacement out of 8mm MDF (Medium Density Fiberboard). MDF actually is wood. It's made out of sawdust, mixed with glue. So it has no structure, is completely dead (thus no vibrations) and extremely easy to work with. You can buy it at any DIY-store. It's very cheap and comes in different thickness. Most common is 12mm and 18mm, but it also exists in 8mm (what I used) and 30mm and more! Very heavy stuff!
I bended it
by cutting grooves about every 3-5mm in the MDF. They have to go almost through
(7.5mm deep)! This way the MDF can be
easily bended. Of course the strength is all gone now, so it'll
be necessary to reinforce it with some polyester mats. Worked like a
What you could
also do is to soak it in water for a while (begin with half a day and see what
happens, it can take a few days). After a while it'll get soft and you
will be able to bend it without having to cut it. Bend it over a pipe or
over the original metal plate and let it dry. Didn't try this myself, but
I see no reason why it shouldn't work. Keep in mind
that all this will only work with MDF, with ordinary wood/plywood will crack.
What you could also do is to soak it in water for a while (begin with half a day and see what happens, it can take a few days). After a while it'll get soft and you will be able to bend it without having to cut it. Bend it over a pipe or over the original metal plate and let it dry. Didn't try this myself, but I see no reason why it shouldn't work.
Keep in mind that all this will only work with MDF, with ordinary wood/plywood will crack.
The speakers can be fitted invisible, under the carpet. There's no need to cut a hole in the carpet as the bass goes straight through it. I didn't, but if you really want to protect the subs, you could put some grilles under the carpet.
Check out some other interesting Miata subwoofer solutions.
I replaced the headunit with an oem Mercedes Comand 2.0 Navigation Unit. The Comand fits nicely in the center console. Looks perfectly stock :)