[Lincoln30]

Originally Posted by M4TW

What is flat sound and how is it achieved with EQ settings? I'm interested in the subject and am trying to learn something.

Flat sound means that using a real time analyzer and pink noise (sounds like static) you set the EQ to make all the RTA bands as flat as possible (each frequency band outputting the same decibel level at the measurement microphone). Microphone placement is important and I use ear level, drivers seat and tune the system to my seat...if you like you passengers more then I do you can use an ear level position in between the seats. Now an audio system really can't be set to perfectly flat for a multitude of reasons but this method and some others will result in an "as good as you can make it" scenario. For those of us that probably won't upgrade the OE system this is about the best you can do for making the system sound it's best. Set it as flat as possible and then make some personal adjustments from that reference point. I usually leave mine flat.

Since you are getting an M4, my measurements in the M3 won't be totally invalid but it will be better if your reference settings come from measurements taken in an M4. If you want to get really picky the reference settings in an M4 with full leather would likely be slightly different in a car with just extended leather or cloth. There may not be enough fine adjustment on the EQ to compensate for these small difference but I'll bet it would measurable if you had all 3 cars with the various major interior surface differences measured using the same equipment and mic positions.

You can buy an app called audiotunes and it has the RTA. It's not great but it works. You can buy a good mic for the phone, which is better then using the phone mic (I borrow a co-workers). I use an IASCA judging CD with a pick noise track.