Question about Beyerdynamic DT 900 PRO X

Hello everyone, quick question: How should I imagine the open design? How loud are the headphones for outsiders? Can they understand every word or listen to a piece of music (exaggeratedly said like with normal music boxes)? I would only use them at home on my PC, but my partner is sometimes in the office and I don't want to disturb her unnecessarily with my sound.