Possum,
I’m with mr_slacker: how about some break-in? My brand-new DT 770s improved noticeably within a week or two, I’d say. As I recall, they became faster and more dynamic and their soundstage opened up a bit. Some people say, any transducer will keep on improving and is probably most relaxed right before it breaks because of wear-out. But any changes after the two-week mark are probably too subtle and gradual to be easily noticed. I couldn’t say for sure, that the 770s kept on improving after this initial one or two week period.
Something that didn’t change too much during the first weeks has been their basic tonal balance. They will always sound darker than HD 600s (and slightly darker than the 990 Pros). But keep in mind: this darker tonal balance is in large part due to their considerable bass extension. They just have to sound darker because of it. Of course, whether all this body, heft and weight is more realistic or causes a simply bloated, less airy sound is for you to decide. I strongly feel , that the errors committed by the HD 600s are the far graver ones.
How bad can it be, if the bottom octave is missing, right? It’s just the area from 20 to 40 Hz, isn’t it? Well, if the top octave went missing, there wouldn’t be response from 10,000 to 20,000 Hz. Imagine this: response down by 10dB at 10,000 Hz – would anyone dare to call that hi-fi? We are so used to the absence of the bottom octaves or the feeling of impact that is conveyed through them, that it is more than mildly surprising if one hears this for the first time through a headphone. Having already owned the DT 990 Pros for some months, I got used to the DT 770 Pros almost instantaneously. To me, the DT 990 Pros are a tad brighter, which gives an impression of airiness, but at the same time they are less homogenous and therefore less transparent. I know this sounds strange and goes against the common belief that pronounced treble will give one more transparency, but I like the 770 Pros just a bit better than the 990 Pros because they are more transparent, they convey instruments as playing in unison, in tune and in rhythm regardless of their frequency bands, an regardless how loud the fortissimo. They let one hear through the mix or through complex harmonic and rhythmic structures. To me, it is just a bit easier to relax into the music and become emotionally involved into the performance with the 770s.
The DT 770 Pros have even more bass extension and impact than the DT 990 Pros. In direct comparison, the 990 Pros will show a slightly bloated upper bass and lower mids. In this sense, the 990 Pros even sound a little thicker. If one looks at the original frequency response measurements of HeadRoom, that are only available on the sites dedicated specifically to each headphone (without this misleading “normalisation” at the product measurements section, which is nothing but a comparative response curve with what HeadRoom thinks are ten of the best headphones), this actually seems to be supported by the graphs.
Finally, to my ears both the DT 770 and 990 Pros are more enjoyable, musical and have more extended bass response than the DT 250-80. In spite of the DT 250-80s' slightly boxy and closed sound, they are very good headphones, tough. It’s very likely that the DT 250-250 are even better. I don’t know it, but lini and Beyerdynamic say so.
Back to your original question, Possum: the Beyer headphones that most closely resemble the tonal balance of the HD 600s are probably the DT 531s, which are very fine headphones as well. However, finding a headphone that sports bass reproduction similar to the DT 770 Pros might prove to be impossible. They just might be the World Champions of “bass power”. Love 'em or hate 'em for it.
