The current DT-48E sounds much different than the DT-48 of the mid-1970's, which had the same oval circumaural cushions. The difference in the lower midrange and bass I attribute to the thicker cushions on the current model, and the fact that the cushions are sealed onto the driver units. With the 1970's model, the cushions could be rotated 360 degrees, and were easy to remove, and I suspect that the low frequencies leaked accordingly. In fact, I can make the current model sound much like the 1970's model just by yawning, and thus compromising the seal between the cushions and my head. The difference in the high frequencies is more difficult to account for, and my best guess there (aside from whatever contribution the better seal might make) is that Beyer may now have superior manufacturing technology for the DT-48 diaphragms.
I've read many posts and articles now about the DT-48 series, and much of that is speculation or people's experiences with modifications to the headphone itself. So in this review I'd like to list what facts I've gathered in my own experience.
I first heard of the DT-48 series via Stereophile Magazine's Recommended Components section circa 1972, in which they listed the "DT-48S with round cushions" as a Class B headphone (i.e. second-tier, or next to the best), having "Extremely tight and well-defined bass".
The first DT-48 I bought was the DT-48 (no letter following the '48'), which was black and came with oval circumaural cushions. My first reaction was "Where is the sound?", since they sounded to me like a pocket-size radio played through its own speaker - perhaps a little better than that, but not a lot better. After listening at some length and letting the cushions seal better, the sound seemed to improve slightly, but next to headphones like the Koss ESP9 or Pro4AA's, they sounded extremely shy in the low and high end.
Going back to Stereophile's Recommended Components (and not having an Internet or BBS to research these issues), I noted that it specified round cushions and a DT-48S model, which I then ordered from my dealer. When the DT-48S arrived, with a beautiful carrycase made of something called "Skai", I was shocked to discover that what little bass I had with the DT-48 was entirely absent from the DT-48S. So, with great patience I ordered a set of oval cushions from Beyer, and after removing the round supraaural cushions and placing the oval circumaural cushions on the DT-48S, the sound became essentially the same as the DT-48. At this time I had a Soundcraftsmen equalizer and could equalize the DT-48 to sound exactly like the Koss ESP9 on a given song, within one decibel of accuracy. I did not detect any difference between the DT-48 and the DT-48S using the same type of cushions.
Apparently there was a special version of the DT-48 in the 1970's and before then, which used the same round cushions that came with the DT-48S. That version of the DT-48 came with different cable terminations, most commonly open-ended from what I surmised. But since Stereophile didn't refer to it, and given my experience with the DT-48S's round cushions, I avoided looking into that model.
Fast forward to 2011 and my new DT-48E with oval cushions, which looks more or less the same as the DT-48 of the 1970's, except that the DT-48E has a single-sided cable configuration, whereas the old DT-48 connected directly to each driver unit from the 'Y' split in the main cable.
I've described the differences in sound between the current DT-48E and the DT-48's of the 1970's in the first paragraph, and now I'll describe how the current model compares to conventional modern headphones like the Sennheiser HD-800. To begin with, I was surprised to find the new DT-48E comfortable to wear for hours at a time, although I take one-minute breaks every 30 to 60 minutes to remove sweat from the earcups, exactly like I did with the 1970's models. I could certainly argue that the HD-800 is more comfortable since the head pressure is much lighter, but due to the thicker cushions on the DT-48 compared to the 1970's versions, I don't feel any specific discomforts like I did with the old models, which pressed on the outer ear parts and could even be painful.
After listening to the DT-48E for about three hours, I put the Sennheiser 800's on in the middle of a track, and my immediate impression was that of a shift to a lower register, tonal-wise. I don't have a good explanation for that, since both headphones reproduce the same music at the same pitch, albeit with different emphases in different octaves. I didn't have any other strong impressions of differences, and no negatives. So for me, the significant difference between the DT-48 and the HD-800 was as if I could take just the midrange between, say, 130 hz and one to two octaves above that and tilt it to the right for the HD-800 (warmer or more distant), or to the left for the DT-48 (cooler or closer).
The bass with the DT-48E is not as strong as the Sennheiser 800, even though the HD-800 does not have a pronounced bass, or "bassiness". I was inclined to think that the DT-48's bass rolled off below 100 hz, and was probably near-nonexistent at 30 hz or thereabouts. But such is not the case. The bass is lower in level than the HD-800's below 100 hz, but does not fall off that much, so depending on how good of a seal you get with the oval cushions, what you hear could vary from "tight and well-defined" to very weak if the seal is inadequate.
The midrange of the DT-48E is marvelous, to put it very simply. Compared to the Sennheiser 800, the DT-48's midrange is more forward or pronounced, but has none of the "nasal" or "honky" effect I've experienced with other headphones. It simply sounds "there" and very clean, with one possible undesirable effect for some applications: Playing "Day In The Life" from Sgt. Pepper - the acid-trip "Ahhhhhhh...." following "Somebody spoke and I went into a dream", the DT-48 makes the soundstage narrower than some other headphones, which was a little disappointing. In exchange for that, you get that fabulous, clear midrange that's rare even with headphones costing twice as much as the DT-48.
The high end of the DT-48E is difficult for me to judge. My hearing seems to be flat to about 10 khz, with about a 3-4 db dropoff at 12 khz and perhaps 8 db at 14 khz. Generally, the high end sounds fine, but if you have source material that has sibilants or other such things that are borderline irritating on other headphones like the Sennheiser 800, they may cross that borderline and be irritating on the DT-48. Based on my experience of a few days and a few hundred music tracks of many genres, I don't experience that problem with good source material at substantial volumes, only with a few bad recordings played fairly loud.
If I could rate the overall qualities of the DT-48E on a scale of 1 to 10 (10 being the best), they would be: Sound = 9, sensitivity (25 ohm) = 7, comfort = 7, durability = 10, looks and styling = 9. I've seen comments to the effect that the DT-48E needs a good amp to achieve the best sound, and while that's true insofar as the better amps do sound better than an iPod or other pocket media player, those pocket players will drive the DT-48 to very loud levels with most source material, and with comparable balance of bass and highs.
There is one other feature of the DT-48E that I alluded to in the first paragraph with the "yawning" comment: The sound, particularly in the lower midrange and bass, will change significantly if you yawn, turn your head far to either side, or otherwise move around in a way that compromises the seal between the ear cushions and your head. For me, this tends to force me to sit still and actually listen to the music, rather than do other things such as typing this review. And for me that's good, but your experience may vary.