I've been using my DT770 Pros (80 ohm) for years. I love their neutrality and clarity. My only complaints have their quietness and, more importantly, their lack of bass. I've been at this awhile so I know being quiet and lacking low-end is to be expected in studio monitoring headphones but I mix a lot of hiphop so I have to rely completely on my MR5s monitors and LSR310S subwoofer to get a good mix.

Anyway, I've just finished a big studio overhaul and am now looking at the smaller details. I need to retire my old Audio-Technica ATH-M45 headphones I'd assigned to the vocal booth. The pleather headband is just getting too old and frayed to hand to an artist standing in front of a Neumann U87 they paid me $200 to record them on for the night.
I was thinking about replacing the ear pads then retiring the Beyerdynamic DT770 Pros to the vocal booth and retiring the ATH-M45s to just being an extra set of headphones for groups and entourages to listen in on.
If I do that, I'm gonna need a new set of headphones for the sound engineer (me).

So, to get to the point:
Should I go with DT1770 Pro or DT1990 Pro? (250ohm)
Is there any difference besides open/closed back?
Would you recommend open or closed for mixing?
Will I reap much benefit over another set 770s or 990s?
Which do you think is best for mixing and mastering?
Is there anything you'd recommend over the 1770/1990s?

I read a few reviews where some had praised the 1770s and 1990s on their bass response. Do they, in fact, allow you to monitor lows well?

I havent tried the 1990 but i have the 1770 for 3 years now and they are my main headphones for checking my mixes and mastering... I love their sonic balance and built quality

Wait your 80 ohms DT770 lack bass?

Mine are almost wobbly in the bass, much more so than my 600 Ohm pair.

I have the DT770's here and had the DT1990's here for a couple of weeks.

Firstly I wouldn't say the DT770's are neutral at all! I find them to be quite scooped.
The DT1990's are definitely more neutral than the DT770's but I still wasn't a huge fan and sent them back.
I personally prefer the Beyer DT880pro's for mixing as I find these to be the most neutral

Yeah, I work mostly in hiphop and R&B so the music I mix often requires a lot of attention in the low-end and subs. Its not that the bass is practically absent (like my K240s), they're much better than my M45s in every way, but I have to keep in mind that any mix that sounds full in the DT770s will blow the speakers in your car apart. In order to properly balance a song, I have to let it be thin in the headphones. I've recently started leaving the subwoofer on when I'm in in the cans to literally get a feel for where I'm at.

On a plus side, the 80Hz spike over the rest of the pretty close to neutral mix (according to Waves Analyzer), that results from not hearing the full weight of the lows, has unintentionally become sort of a signature of mine. Fortunately, I get more "I like the bass when I play it in my car" than "its too bassy" but I'd still prefer to hear what I'm doing in the first place.

I don't. I'd say they're pretty neutral (other than 80Hz drop)... then again I'd also call them really "clear", which would seem to indicate a dip in the mid, so you might be right.
You didn't say how the 1990s and 880s compare to the 770s on lows.

I've used the DT 880 Pro's (my main headphones for 10 years), as well as the DT 770 Pro 80 Ohms (for a few months) and DT 1770 (my current main headphones).

If you don't need the noise isolation, open backs are generally preferred for their long-term comfort and more open sound stage. The DT 1770 have more bass than the 1990's, but that's mostly due to the bass reflections from the closed ear cups. So you get a bit more of a "thump" from the bass, but the 1990's go just as low from what I understand. I'm surprised you find the 770's lacing in bass, though. If anything, I think the DT 1770's have less bass, but higher quality (you can make out individual notes of a sub bass, where as on the 770's it's more of an indistinct rumble).

The DT 1770's feel surprisingly open and "wide" for closed backs. The ear cups are deeper than on the 770's. With the velour pads, they sound fairly similar to my DT 880 Pro's, clear, bright and detailed, but more intimate and with more bass. If you do need a lot of bass, they're probably a nice upgrade from the 770's. Otherwise I'd just go with the 880's, but if you need a lot of bass, forget about them...

Maybe I've been to hard in my criticism of them. The DT770 Pros have bass. I can get the mix to sound good in them. The problem is that, when I get it sounding perfect then mixdown and check it in my car (Cadillac with premium sound upgrade) the bass is overpowering; causing me to have to reduce bass on the stereo settings from where I normally keep it.
I know there's always gonna be a difference between how mixes sound in the studio and car/club/home-stereo/consumer-headphones but I'd like to get a better representation for how the 808s are gonna hit in the Cadillac's subwoofer BEFORE I mixdown. I know aim asking a lot from a pair of headphones though because the JBL LSR310S sub I added to try to solve the issue won't pump strong enough to show me how much bass I'll hear in the car or the club either.

What's the impedance on your DT770 set again?

I recommend you use sonarworks reference 4.. they have a correction curve for most headphones including the 1770

I have and love the Beyerdynamic 1990 Pro headphones. I tried the Sonarworks Reference 4 software and it made them sound terrible, so I wouldn't recommend using it. Sonarworks do allow you to demo the Reference 4 headphone version, so try the software yourself.

The use of the expression "correction curve" is inaccurate. That would imply that manufacturers are making headphones that are incorrect. There aren't any headphones that are flat, so why is that? The Sonarworks marketing is nonsense in my opinion. People will still be playing back music on so many different devices, so one can't create the "perfect" mix that will sound great to everyone on all devices. It is so much more complex.

I like to put my attention on accurate reproduction, and not "flat" response curves. This is best done by listening to acoustic instruments in my opinion, which requires that one has developed their hearing so they can hear all the very delicate harmonic qualities.

So much of the music being made today is highly compressed and lacks dynamic range. I find it annoying and frankly boring. It is like eating low quality highly seasoned food in a large quantity, and pretending it is great. I like to be able to hear each sound in the mix clearly, so that they compliment each other, instead of crowding into the same space covering each other up.

I have two 1770 pro's. Havent tried the 1990's but compared to the 770's they sound much better. Much clearer, bigger and tight/defined. Also have the HD800 and K271. Whatever headphones I use I can struggle a bit with the lowend. I need to do both the card test and check on monitors with sub to get the lowend good enough.

But for tracking vocals the 1770 pro are great. Very clear and detailed compared to 770 (wich sound a bit wooly in comparison).

For me, I enjoy the sound of more accurate headphones, like you have described. If the bass is accentuated then ones ability to hear other frequencies is diminished. Balance is the key for me. I used food in my last post trying to use that as an expression of my experience. If one has really strong spicy food (lots of bass and high volumes) then ones ability to taste subtleties in wonderful delicate foods is diminished. You can try by eating a bite of the spicy food, and then eating a bite of the delicate food separately, but even that doesn't work great unless enough time is given between the experiences, or one drinks some water in-between. Sometimes what we want is the problem!

I like the Grandeur piano that Native Instruments has, and will be buying the Noire, which is included in the new Komplete 13. The lowest frequency on a piano is 27.5 Hz, which is almost at the start of the human hearing range. The low notes on the Grandeur sound great on my Beyerdynamic 1990 Pro headphones, with lots of bass.

How do these compare to the T1?

From memory the T1 sounded agressively bright. I much prefer the 1770 pro. 1770 pro is better sounding imo.

DT 1770 is greatly admired here. Accurate sound and seals out distractions.
Totally hot, totally pro.

I would greatly recommend using Sonarworks Reference to correct the DT 1990 Pro. Hearing the DT 1990's intrinsic EQ profile and then hearing it again with Reference simply takes getting used to - but I've used Reference for about 3 years with Sennheiser HD25-1, AKG 712 Pro and more recently the DT 1990 and in contrast to the other opinion expressed here, I say Reference definitely gives you a more honest and neutral profile to mix with.

I totally disagree. I spent a lot of time in communications with people at Sonarworks dealing with the problems in the DT 1990 Pro version of the software for the analytical pads, and it doesn't work well at all. Your use of the word "correct" is actually not correct! It is just different. If Beyerdynamic were to make a pair of headphones that sounded like the DT 1990 Pro with the Sonarworks software, I doubt it would sell well or receive good reviews. I think people are getting caught up in the sales concept of Sonarworks. I can definitely see it being of help with speakers in a room.

Open back headphones offer less fatigue vs closed back. I much prefer open back for that reason. Closed back are best for vocalist and whne you don't want the music to bleed into a nearby mic. Therefore for me the 1990's are the better option