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.

I would also like to give a special thanks to Jeff Jent at sweet water for his help though out the many years. Let me tell you exactly the sound of these headphones, as when i first started listening hours ago, i recognized such a similarity with another set of headphones. However, if there's one other part that rivals the microphone in significance, it's the monitoring system. No self‑respecting studio can afford to skimp in this area either, and in 2005, Neumann's parent company Sennheiser acquired German loudspeaker manufacturers Klein+Hummel. Four years later, the studio monitor arm of K+H was folded into the Neumann stable, and since then, there have been numerous loudspeaker releases under the Neumann brand. These have built on K+H's already strong reputation to develop a very highly regarded product portfolio. Neumann don’t publish frequency response plots for either model, but quote upper and lower limits of 34kHz and 12Hz for the NDH 30s. Without any tolerances, these figures are of limited value, and I doubt anyone will notice the differences compared with the NDH 20s’ alleged 7Hz‑30kHz bandwidth. What may be more noticeable is that the NDH 30s improve significantly on the NDH 20s’ already impressive distortion figures, taking THD from below 0.1 percent for a 1kHz input at 100dB SPL, to less than 0.03 percent. Whatever they’ve done, it’s worked, because these headphones sound really, really good. Drawing A Line Ultrasone Signature DXP might also work for you though subjectively sound is closer to slightly less refined version of NDH 20.The removable headphone cable is light but has this spring action to it that was annoying. I literally had to put something on top of it on my desk to keep it from interfering with my mouse. The comfort is surprisingly bad. The headphones are very heavy and the headband is quite hard. After an hour you will feel like taking a break. The ear cups are big enough but I wish they were oval shape, rather than round. In my opinion, this headphone is exactly what its designed to be.........a studio monitor on your head, first and foremost, and an Audiophile tool for those who prefer flat and clear, vs sweet, or rich, or overly extended. The treble and upper-treble on the NDH 30 are detailed yet slightly uneven. There’s no severe peaking that imbues the sound signature with faux detail, just enough to make overtones sound strange if they hit the right regions. Not terrible, but also not too remarkable. Where to Buy

It’s not an understatement to call Neumann a legendary pro audio company. Their microphones have been used by all kinds of celebrities – starting from a certain controversial Austria-born politician in the 1930s all the way up to now with Billie Eilish and others looking to make their mark upon the world with sound.Neumann states that these headphones sound like their monitor speakers calibrated to flat in a treated control room. The NDH 30 can be folded flat for transportation, but there is no hard case.