I got quite a shock when I first played this new Monitor 'FX' headphone and the treble was essentially missing. It did come back for the most part after removing two different screens and using some EQ:
http://www.hifiheadphones.co.uk/for...shall-monitor-fx-stereo-headphone-review.html
http://www.hifiheadphones.co.uk/for...shall-monitor-fx-stereo-headphone-review.html