Tony,
hm, that’s difficult: I would say it’s an incremental improvement, but a very significant one :-) The DT 990/600 Ω already offers great detail resolution and juicy, sparkling sound with a fat, enjoyable bass (at least when powered by an OTL valve amp). I wear eyeglasses, so please allow me this metaphor: The T1 offers you a bright and clear view on familar landscapes (the Beyer house sound), but it feels as if the glasses have been cleaned, polished, and extra high resolution details and color saturation have been added – without any exaggeration, it just sounds absolutely convincing, effortless and naturally flowing.
And at the latest in this moment you realize: you’re in serious trouble, because there’s simply no way back for you to ever enjoy headphones of lesser quality again :-) I guess every male remembers very well that special, private moment in this life when experiencing for the first time the difference between women and girls. To stay on this topic and use female icons of the 1960s: the DT 990 might be Twiggy with just a little bit too much make-up in the face, while the T1 would be Sophia Loren in full bloom.
Yes, the headphones cost a little bit more than average, but the headphone amplifier and the DAC (£ 223.– each box, VAT not included) in my opinion are inexpensive, although they don’t sound and of course don’t look and feel cheap – quite the reverse! I’m sure much better headphone amplifiers and DACs are existing, but for the moment I’m perfectly happy with the Schiit boxes. The finish of the T1 appears valuable, high-grade and sturdy, the cable is thick; some persons may feel that the weight of the cable is too heavy. Although both share the same industrial design principles, the T1 certainly looks better and more precious than the DT 990, but it is more expensive.
Gosh, even in my native language this would be very difficult for me, not to mention attempting doing this in English! There are a lot of great Beyerdynamic T1 reviews to be found on the web, written by competent native speakers.
That's true, and with headphones one can enjoy music at real high volume late at night without causing troubles for partners, cats or neighbours. But the spatial experience when listening to speakers from the “sweet spot” still isn’t available with headphones. The “in-head location” with the T1 isn’t that strong or even claustrophobic as with other headphones, because unlike most other headphones (well-known exception: Sennheiser HD 800) the drivers are placed a little in front and more sideways of the auditory canals. And another quality still is missing with headphones: the physical sense of perceiving and feeling deep bass notes with the skin and the body.
Werner.