I messed around with the tone controls and equalizers on my computer. When I had the equalizer on and didn't realize it (in iTunes). I was saying to my self, "Wow, these speakers are starting to sound awful. The high end is really harsh." Then, I flipped off the equalizer. Huge difference. Any equalizing you do should be done in very small increments, if at all. However, it is up to you how you like your music. Keep in mind that hi-fi speakers are designed to not need an equalizer. An equalizer is only really necessary on the dinky computer speakers or cheaper headphones unless your room is really making the sound sound bad.
