Skoop, except for these harsh-sounding headphones I recently acquired, I'd have agreed with you. I got a pair of cheaper studio monitor headphones that sound great except for one thing: the spoken letter "S". Without equalization, any whistling sound is piercing and literally painful to the ears when coming through these headphones. While this is probably great for music recording/post-processing, it's just plain unpleasant in personal music listening.
By turning down two bands on the 10-band equalizer, I was able to get rid of the whistle. Unfortunately, this also reduced all of the sound between those two bands. Turning down 2/10 bands (or something like 20% of the sound) on the default equalizer is a poor trade-off just to get rid of one piercing whistle - everything sounded pretty bad.
With the equalizer voon recommended, I was able to test very narrow bandwidths, find the offending whistle, and reduce a very specific range. Much better now!