Pros: Very comfortable, non-harsh vocals, fun, soundstage, almost grain-free, excellent bass extension, value, build quality,
Cons: Needs a tube amp, slightly dipped mid range, very bright, cringeworthy treble before burn in, slightly thin upper bass (bottom heavy)
I bought the DT990s for use with bass music such as hip-hop, drum and bass and electronic dance music to compliment my AKG K702 65th Anniversies, which I have since sold.
Build and comfort: the build on the DT990s is excellent like most Beyers, and is made in Heilbronn, Germany. It is made from high impact plastic for the cups and spring steel for the headband and bales (yolks), with replaceable velour ear pads and a replaceable vinyl headband pad. The headphones are very grippy and tight, so that may be an issue for you guys who are sensitive to caliper pressure. It is not an issue after about 5 minutes of wearing. The pads have plenty of space for your ears. I have a badly (seemly) disproportionate left ear, so the back of the left pad slightly touches the back of my left ear, so sometimes it is a little irritating if I pay attention to it. Otherwise I don't have a problem. The yolks are metal and the headband is made from spring steel, so don't feel afraid to bend the yolks and headband out slightly to loosen the grip. This will keep the ear pads from collapsing and causing the drivers to touch the ears. Headband comfort is not an issue whatsoever. Keep in mind that these have a non-field serviceable hard wired 3 meter coiled cable terminated to a 3.5 mm plug with a screw-on 6.3 mm adapter, which is a must to use since these need a desktop amplifier.
Treble: Bright? Yes. Grainy or overly metallic? No. The treble on the 990 Pros is strong and very present, yes. I would call it more revealing than colored overly bright. But at the same time it isn't what I would call overly harsh. It is only harsh when a song is sibilant or badly mastered, and that is noticeable in the 8-10,000 Hz range. Thankfully, the 990s are very responsive to EQing, so all you have to do is turn the treble on the 8 kHz range down a decibel or two below flat, and that will take the bite off the treble nicely. But what I like most about the treble is that it isn't crunchy, metallic or grainy. Grain is the number one cause of ear pain for me, and it is why I hated the way the Audio-Technica ATH-M50 and the Beyerdynamic DT880s sounded in the treble region. I would say that the DT990 Pros have even less grain than the so-called laid back Sony MDR-MA900s.
Mids: The midrange is much smoother and has a warmer, dynamic sound without being harsh. These are not the most mid centric headphone for the price, though (the AKG K612 Pros for 199 US dollars are better for mid centric music), as there is a u-shape to the sound signature. Mids are still natural sounding though.
Bass: One word: Authoritative. The bass on the 990s hits hard, but it is not overly boomy so it doesn't give me an earache like on the DT770 Pro 80s. This is a great headphone for drum and bass, electronic dance music and hip-hop. The only downside I have is that the upper bass is a little thin, so bass signature is more of a rumbly, mid to sub-bass-centric sound. Unlike the AKG K240s or Sennheiser HD25s, which have more upper and mid bass than sub bass, and as a result, have a more punchy, visceral, warmer bass which is a little more suited for rock, some dance and jazz.
Source and burn in: When I first plugged them into my Maverick Audio A1 amplifier, I immediately had tinnitus from the ringing, overly splashy treble and boomy bass. After giving them about 20 hours of burn in, they settled down nicely and that harsh bite to the treble and overwhelming bass were taken off. These headphones still remain bright whether they are on a solid state or tube amplifier, but they are MUCH more dynamic on a tube amp. On a solid state, they will sound harsh and mechanical. Tube amps I recommend are the Maverick Audio Tubemagic A1, Little Dot amps, and the Woo Audio WA6 and WA7 are both supposed to be excellent matches for the 990 Pro.
I think that for the price, these headphones are a steal considering what you get for your money. Just keep in mind that you need to get a desktop amplifier for these to sound their best, preferably tubes. You can get a Maverick Audio A1 or Little Dot MKII for around 200 dollars. So you can have a serious listening rig for under 400 dollars. Highly recommended.