Does anyone have any experience or suggestions on how to position subs in the trunk (facing front or facing back) for the best sound? About to start designing a new custom box and was just looking for some input. Thanks.

In the rear corners fireing towards the middle line of the car.

under the girl friends seat

i would have them in the trunk pushed up against the back of the car facing out. thats supposed to be the hardest hitting. if you had a car that had folding rear seats, then you would benefit from pushing them up against the backseat facing them towards the seats as well. just my 02 cents

It depends on what your crossover settings are. If staying under 70-80 hz the wave is not as directional and it doesn't matter as much where you position them. If you are letting higher frequencies in then positioning matters more.

right now i have my setup facing out. be warned, the mark viii is a rattle trap. i am working on a box that will fire through the back deck to help clean up the sound a little bit

Facing the sub to the rear of the car let's the wave develope futher and sound better in the car. The size of the box will set the stage. In general ..... Depending on the sub a small box will hit tight at a higher freq (like rock music)
a larger box will be boomy and hit a much lower freq.
If you don't want it to sound like a bunch of tin cans in a bag.. Rattle trap then you could go through the rear deck. Sealed or ported box, my advice would be bandpass (5th order) through the rear deck.
For tuning I would go 65-70hz and below on a sealed or ported if you go bandpass I'd go 30-100 and set the sub xover somewhere between 65-80.
If you had say a s10 pickup the natural resonance freq of the cab is around 68hz and that where it hits the hardest. The cabin in a mark should be around 59hz and have a 3db down second peak around 35-40hz.
Hope that helps, more than you asked for but food for thought.

in my Taurus I got the best sound from putting it in the far corner closest to the passengers tail light pointing towards the drivers side.

just mess around with them and put them where they sound best for your car and setup

this gets pretty technical but the wave drawings half way down will give you an idea
http://www.installer.com/tech/aiming.html

The electronic compass module is on the the driver's side, and will malfunction if your sub is too close to it.

The electronic compass module is on the the driver's side, and will malfunction if your sub is too close to it.
on a gen 1

The electronic compass module is on the the driver's side, and will malfunction if your sub is too close to it.

wait, the compass actually works for some people?

mine is backwards no matter what calibrating I go through

OK, I have been doing this for over 15 years and have done 6-7 Marks with full on systems and prolly 50 Taurus and Sables. The trunk acoustics in all three cars are the same and has much cancelation between 50-90 hz for sealed systems and 30-70hz for ported systems. Can you make it sound good with rear fireing subs? Yes you can but it will sound MUCH better if you corner load the subs in the rear of the trunk by the bumper and angle then to the centerline of the car or have them fire directly across the car. I have installed almost any combo of sub/box you can think of in them and it was always the same. It just sounded better mounting them like I said.
My friend has two 12" subs in a ported box fireing backwards and I have a single ten firing to the middle. My bass is tighter and deeper and almost as loud. Thats just a downside of our trunk shape.

Now if you get fancy and run the port through the rear deck or run a bandpass box then you can get about the same sound mounting them under the shelf and fireing backwards into the tail of the car but I dont know how much work you wanted to do there.

I have 2 polk 12's in a sealed box facing the rear of the car, in the trunk with a 1400 watt amp.

Sounds pretty damn good. Not sound competition worthy...but sounds pretty damn good..