Hey guys,
I have an F90BT and I listen to a lot of rock and metal music. I usually have it on POWERFUL but I was curious if any of you guys have manually changed your equalizer to make it sound much better than the factory setting. Please include pics if you have any of what you have done. Thanks! 
yes i have custom settings, however since every car is different, along with every sound system being different, not even taking into consideration that everyone's personal preference is different, what sounds good to me might not sound good to you, or might not sound good with you speakers, amps...
bottom line, just play with the settings making small adjustments here and there, and taking time to listen to many different songs until it sounds best to you.
The purpose of the EQ is to correct imbalances in the frequency response of your speakers due to the properties of your speakers, the enclosures they're in, and your car's cabin. There is no universally correct EQ settings, but if you find someone with the same speakers as you they might be able to help you out. In general, most people prefer a "smile" EQ for rock music. This means that the midrange is turned down a bit and the bass and treble are turned up a bit.
My usual technique for adjusting the EQ:
1)Set everything to 0 (flat)
2)Go to each frequency and turn it all the way down, then all the way up, to see how that frequency affects the overall sound (so I know what part of the sound I'm adjusting)
3)Adjust this frequency to the point where I think it sounds the best.
Another tip I found is that if you have a subwoofer, set the crossover frequency lower than you might normally. For my home theatre, I set the crossover at 60Hz, but for the car I found that 50Hz sounds better. For the front speakers I have the Highpass set at 80Hz ideally, although for songs with a lot of bass I have to change it to 100Hz. This make vocals sound thinner but my speakers rattle from the bass if I leave it at 80Hz cutoff.
SpaceyWilly's pretty spot on with that description. I'm a Sound Engineer & Producer in the UK and use EQ extensively in the studio. The car is pretty much the same setup, just an awful lot cheaper!!!LOL!!
Here's a couple of things that if the whole concept of EQ is rather illusive, might help explain it a bit easier 
The above chart shows how different instruments have different frequencies associated to them - you can see the different instrument groups and how they tie into the frequency range (from 20HZ - 20kHz) - think about Bass guitar/Kick drum being Low Frequency, and Cymbal.HiHats etc being High Frequency.
This next picture shows how a graphic EQ like the one in the AVIC can be used - bearing in mind that you're not setting up individual instruments, but fully mixed music - almost impossible to get right across the board because all music gets mixed by different people!!LOL! But you get the idea
But as stated in previous posts, whilst it is a device used to not necessarily correct how crap your speakers are (I would twist it around and actually say that it's to maximize the efficiency of your installation 
) but to tweak the sound in the car to YOUR preference.
FWIW, I've got different EQ setups for the different types of music I'm listening to
Hope this helps,
Scoob/Dan
Here is a starting point for you. This is what my brother, an installer usually sets them for then you can start adjusting from there. As already stated, each car environment is different and each person's taste are different so get it to your liking. It will probably take several tweaks before you get it where you feel it is just right.
