Wow finally a thread that is based in science...

OK so you want to measure the cars response...

You will need a microphone, a well recorded track of uncorrelated pink noise, and a device or computer based RTA.

Now, the question is ...

What resolution is appropriate to measure at 1/3 octave, 1/12, or 1/24?

How are you going to generate the microphone calibration file for the computer or send it out with the RTA to be calibrated (otherwise your readings won't be accurate).

Once you see what is going on, how do you correct the issues? Identify what the issues are, and which ones can't you fix?

Ok, so here are a few tips...

1. Do a search for True RTA and you can download their RTA software (depending on what you want you can go from 1 octave to 1/24th of an octave).

2. Look under microphone calibration and there are some preset files so all you need to do is find one of them at a place like guitar center or other source.

3. Set up the system, (calibrate your sound card ect) and off you go.

4. Only use a CD for the pink noise as a wav file since mp3 sacrifices too much at the top and bottom of the audio range.

5. If using the factory amp set the volume between 20 and 25 that will get you out of the factory volume dependant loudness eq (you are not moving so the speed dependant stuff is not functional) and keep you away form triggering the limiters which begin to come online at 26.

6. Know what you are looking at! Low frequency below 100hz is VERY position dependant and this is where Parametric EQ filtering can be very useful when applied properly, remember you cant fix dips only address the peaks.

7. Above 100hz this issues begin to form around the design of the speaker, destructive interference from surrounding materials, and the interior materials reflective properties. EQ applied higher int he range can generally destroy the quality of the sound so be careful.

8. What is the curve you are trying to get to? There has been years of research to determine the curve that is the best sounding to people, and then there is ruler flat, be sure you know what you want because you will surprise yourself when you get to flat and you seem to have no bass and the top end is too shrill.

9. How are you going to address spatial characteristics? You cant unless you do measurements at multiple points and angles. So since you cant do this with these basic tools don't try, but be wary of the changes you make to the system and the effect it has on the location of sounds across the dash.

10. Never loose sight of the fact that this is your system and you have to be happy with the way it sounds. That means ALWAYS make your product choices based on application, brand does have some influence in performance look for the ones that are still run by their original company (that is very few these days with many going belly up and then bought up for the name). Look for some serious engineering at work on the woofer, is it cosmetic or not... rubber covers, embossed plastics, and chrome do nothing for the sound. If you are looking for SPL one note wonder woofers that don't expect them to be musical. Generally you should stay with the same amp and speaker company as they are now taking a systems approach and thus will make specific recommendation for paring subs and amps based on the application. For example on the Infinity 10" you would look for a Ref 1300 or 1600.