"What happened to the bass?" is my reaction to listening to the AD900s after experiencing the HD600! "No bass" is an off-the-cuff, flippant summary --- and it comes through with EQ or bass-boost features. Nothing scientific, or measured, but yes, I could, and did, enjoy music from Mahler to the Grateful Dead on those phones.
I enjoyed them, I suppose, for a couple of years. There is going to be big soft spot for them simply because they were/are my first pair of serious headphones.
The comfort is supreme. They look a bit frail, but I don't think they are. Well, no, I would not throw them, unprotected, in a suitcase. They are so light and well supported on their wings, it is possible to wear them and hardly know they are there. Yes... I've walked away from the chair and been pulled up tight by the cable! The wings work so well that I've actually levitated once or twice (but only when listening to the Dead's more psychedelic stuff).
They are so light they feel as if they will fall off, but they don't. Maybe not for serious headbanging, but quite secure enough for anything else.
Acting on a forum friend's recommendation of the ATH-AD700, I auditioned that, the AD900, and a couple of other 'phones while on a visit to Singapore. I was not a 'phones man at all; in fact I had never really enjoyed the sensation, and even felt a little claustrophobic with closed phones. Comfort was a big deal for me. The Audio Technicas fitted. I had budgeted for the 700s, but could hear the difference (clarity, highs and "air") with the 900s and paid the difference.
I can't remember the reviewer, but I have read that the 900 was the sweet spot for quality/value in the range. The higher-priced models don't get rated so well at their prices. Hence, I jumped ship to Sennheiser and, even though I no longer get built-in levitation, I am very happy with the HD600s on my head.
Last time I looked, the range had moved on a generation, with an "X" added to model numbers. I don't know if anything that matters (ie sound) changed.
By the way: I'm currently listening to my HD600s out of KG's Geek Out 450. Very nice.
