Hi
@Wertigo,
For somewhat useful information on the NDH 20, I suggest looking at the dedicated thread below, started by
@FullBright1, who can also give you a better rundown on both headphones.
https://www.head-fi.org/threads/neumann-ndh-20.898630/
Also, as a NDH 20 owner & someone heavy into Sound Monitoring, I may be slightly biased but while I only own the NDH 20, I have also heard the DT 1700 Pro separately & side by side.
Subjectively & personally, I prefer the NDH 20.
It is important to note the NDH 20 has a very even, balanced sound across the frequency range so if you're looking for elevated bass response, this may not be the headphone for you as this in more in line with a
more natural, accurate bass response as it is a Mastering/Mixing headphone, after all...however, saying that, depending on source & track recording quality, the NDH 20 does & will pick up any emphasis in the bass response
VERY ACCURATELY, eg, 6 db + though if any track has an average 8 db + in bass then NDH 20 may feel Bass Responsive but your mileage will vary.
In short, as long as your work has the bass response you're after then it should come across, especially since the isolation on NDH 20 is close to anechoic but in a good way.
For a slightly more bass elevated headphone, I would suggest looking into the Sony 1AM2 as it goes down to 5 hz so any bass emphasised tracks you have will definitely come across with a kick though isolation is average for these headphones.
Ultrasone Signature DXP might also work for you though subjectively sound is closer to slightly less refined version of NDH 20.
Hope this makes sense, feel free to ask more if you need.
Hope you have a great day !