Pros: Timbre accuracy, transparency, detail, resolution, flat, imaging,
Cons: Bass impact and extension, comfort, long mental break in.
These headphones are not really meant for casual music enjoyment or pleasure. They are more of a tool for critical listening, or monitoring.
The DT48 sound like how water tastes. Very plain, clear, tasteless, boring but still technically correct and perfect. Sennheiser and Denon are like a tasty Coke or Pepsi by comparison. The soda tastes great on first sip. Water (DT48) is boring and can be gross depending on the container its held in.
The DT48 really takes time to mentally burn-in because they lack the toe tapping "party" factor that most headphones have. They don't attempt to help you enjoy the music, and it actually can be a challenge to listen to and interpret the music with them because of their lighting speed. They can seem claustrophobic sounding with background music. The DT48 require full concentration, high volume, and critical listening skills or else the musical groove gets lost. Your brain has to be in "monitor" mode.
The DT48 are extremely neutral and uncolored. They sound machine flat, not human ear flat, neutral instead of natural (but can sound extremely natural with good clean recordings). The sound is very normal and plain, with no glamour to the sound. They can sound very bad with certain recordings, and simply brilliant with others.
The sound is very refined and precisely tuned, like a headphone that's been in production for over 70 years. Beyerdynamic said in a nutshell: "The sound of the DT48 sets the reference for which other headphones can be judged". This does not mean they are the best sounding headphones in the world. Instead they are a standard headphone that is just a reference, so that other headphones can be interpreted. They are a great tool for when I'm doing headphone reviews. These headphones have taught me what the music should sound like.
They are used everywhere from studios, to audiologists, acoustic investigators, research facilities, sound labs, and now by audiophiles. They will never be available at Best Buy, your average consumer hates their sound.
Bass: Only goes to 55 or 60 Hz before rapidly dropping off. The bass is very precise in timing and never blurred or sloppy, never bloated. The attack is ultra fast, double bass kicks sound great on them. They have almost no decay in the bass, which is partly why they are bass light. There is no mid bass emphasis at all. You can hear the bass timbre decently and it comes through very clean and undistorted, ultra low harmonic distortion. No ear cup resonance, rattling sounds or air whistling. Just very pure tone. There is almost no slam to the bass. You can hear the bass but not feel it. Its a little 1 dimensional due to lack of ultra low sub bass. The bass is like listening to very very high end bookshelf speakers, but without a sub. Not much LFE, and not a lot of air/pressure being pushed by the drivers. You could say the bass takes a back seat to the rest of the sound, but it can be full and engaging with the right recording. In fact they are capable of going deep when the low end of the recording is emphasized to begin with. It will tell you if the recording is bass heavy or not.
Mids: The best part IMO. These headphones are tonality and timbre monsters. Voices, guitar, electronic sounds, piano, sax, everything sounds right. No matter the singers name, synthesizer effects, guitar amp used, mic, it all gets presented consistently fair and with correct tonality and timbre. By far the best mid range Ive ever heard. The "impact" and physical force of the sound waves is quite small. It has the loudness but not the intensity. Its like plugging in a usb cable straight to your brain and listening to the music like that. You can hear the start and stop of every detail, and the microphones clicking on and off, extremely subtle recording flaws. Basically, the mid range is absolutely effortless.
Treble: Unfatiguing yet present and not rolled off to my ears. Its in your face, very headphone like. It is not smooth sweet treble like speakers with a tweeter. There is tons of detail and speed. It is never harsh. I can listen to these headphones at high volumes with little fatigue. It extends further than my hearing does, which is good enough for me. And much like the mids, the cymbals sound very correct timbre-wise, and their is a lot of air and ambiance to the sound for a closed headphone. But again, there isn't much attack or authority to the highs and cymbals. This is probably why the highs are unfatuiging. It will reveal bad mp3's with ease. There is still a treble spike around 8khz that is very typical for almost any headphones.
Soundstage and imaging: The soundstage is somewhat small but is extremely precise and is capable of depth and space, again when the recording calls for it. I find other headphones stretching out the soundstage too much and trying to reproduce a soundstage similar to loudspeakers in a room.. The DT48 has a more traditional headphone soundstage that is very accurate. It feels like a small orb engulfing the outside of your head. Most other headphones make you feel like your in a permanent artificial concert hall or club. With the DT48, every instrument/sound has their own little space and shape to it, and imaging is pinpoint accurate and sensitive.
Other thoughts: It seems like the amount of detail is unlimited, almost too much sometimes. Its not the fake type of detail like treble happy Grado's, it does not force anything down your throat. The midrange is done right and the most critical frequencies are crystal clear. The sacrifice is in the bass response. The sound in general has little personality/musicality, and that's why they are so uncolored, so honest. They just display the recording as is. The sound is so "normal", but in a perfect crystal clear way.
A lot of people are put off by the lack of slam and impact in the bass, and the lack of musicality. The thing is, they lack personality and musicality without sounding cheap or colored (which is actually their charm). It just lets the recording display its own musicality (or lack thereof). As far as bass, you must remember they are headphones, not speakers. Headphone drivers are very small and cannot move much air to begin with, so cannot do bass like a real sub. In order to make headphone drivers sound like a subwoofer, you have to skew the frequency response and add purposeful reflections and resonances in the ear cups to make up for the loss of rumble. Most headphones do this to simulate a real sub woofer. The DT-48 does not attempt to reproduce a sub woofer or real kick drum. If you want to simulate the feeling of a sub, I recommend the DT770. If you EQ the bass up on DT48, it ruins the sound IMO. They are "bass light" for a reason.
If you want to be transported to the live event and feel like your physically "there" with the band, like your seeing them live, the DT48 is not for you.
The DT48 instead shows you what was recorded with the microphone. When you compare different recordings, sources, amps, the DT48 really shows you what is going on. It is chameleon like, and can be overly recording-dependent for many people. After all, they are studio monitors. One recording will sound completely different from the next with these. Very accurate.
Comfort on these is not so great, not unbearable but a little bit uncomfortable compared to most headphones because of their clamping force and weight. They take some time to get used to. If your concerned with comfort don't get these. If you never really cared about comfort with headphones (like me), they are just fine.
They are VERY picky about the fit and seal. If you wear a hat or eyeglasses while listening, or cover your ears with hair, wear your beanie, etc... you will be disappointed. They are IEM-like in regards to fit and seal. You gotta adjust them and wear them properly to actually get the right sound. Again, seal is critical with these. The pads will warm up over time and create a better seal the longer you wear them. With the DT48, its best to stay still, minimize movement, and just concentrate on the music instead of head banging. They require all the seal they can get.
Isolation is pretty decent. The data sheet says 12db noise reduction. Not quite the level of a good IEM. But it blocks enough important noises such as your AC, light traffic noises, distant TV's in other rooms, etc... When the music is on, disturbances are pretty minimal, and the other person usually has to yell (but not scream) to get your attention.
As far as amping, they are not hard to drive power wise. But they really respond to better gear. A portable will drive them fine but will not do them justice. Source is the same. Crap in, crap out applies to the DT48 very much so, in both the amp and DAC. This does not mean you must spend a fortune to make them sound good, it just means they are a window to the recording and gear used. By the way, amping them does not make them bass monsters or anything. It just makes them better at what they are already good at. Don't waste your money on upgrades if you dont like the general sonic signature of them.
The sound of these headphones is not for everyone. Many new audiophiles are told by others to look for uncolored and flat response to achieve the best sound. These new people need to take a closer look at their priorities and what they are trying to achieve. Neutral is not always natural.
If you want any and every song to sound amazing, do not buy these. They are tremendously honest.