Do Not completely deminish the 250-500Hz range. That is the frequency range in which we hear vowel sounds. If anything, that segment should be made the loudest it can.
Take this two pages for reference:
http://www.proav.de/index.html?http&...ech-level.html
http://hyperphysics.phy-astr.gsu.edu...sic/vowel.html
I suggest actively listening to the radio while making changes to the EQ.