Originally Posted by Technic
The iDrive outputs 25W x 4 (@2 ohms), not flat (OEM pre-EQ) signal, full range in the front outputs and high pass at around 100Hz in the rear outputs.
Therefore this signal is quite cumbersome to work with if you do not plan to use any summing and de-EQ processor before an aftermarket amp. You could, but as you can see you will have a couple of sound quality issues if you use the OEM outputs thru just a line level converter into an amplifier without any processing. In other words, you will be just amplifying whatever the OEM EQ curve is -which is mostly designed to match OEM speaker characteristics and not sound quality itself, after all there are no tweeters in your system. That should tell you something about this signal EQ.
There are some devices that can help you to "fix" this signal and even set your own EQ/time delay processing, all depends of your budget and plans.
Now that is kind of ugly. I bet that EQ is set in the software in the system. It wouldn't be cost effective for them to put those EQ settings into a chip when they already have an onboard computer that is programmable. I wonder if it can be modified by special request to BMW (doubtfull).
Eventually, I'll be taking that hard-drive out to make an image (dd) of it so I can see what I can do software-wise. Just got to be mindfull of that warranty!
Maybe someday, when there is time, I can put linux on it and really get control of the thing - I may have to write some of my own "drivers", though, but that is way down the road (no puns intended).