Once rebooted, follow along with the instructions below: Set Up a Universal Audio Equalizer for Mac OS X
We'll show you how to do both by creating your own universal EQ using two free tools, follow along: Requirements Ever wish you had a system wide equalizer to adjust all audio output in Mac OS X and not just in iTunes? Maybe you want to adjust the way all audio output sounds or maybe you just want to boost the output volume of the built-in Mac speakers.