Hi Alxx911, and John Hammer1. After reading John's reply - " You can plug something into it's headphone jack. though" . I thought i'd try out of curiosity. I plugged in some headphones. I didn't expect anything to happen and nothing happened. The audio jack is for the Dell soundbar which is optional.
Here's a direct copy and paste from the users manual: Section About Your Monitor.
Attaching the Soundbar AX510 / AX510PA (Optional) CAUTION: Do not use with any device other than the Dell Soundbar. NOTE: The Soundbar power connector (+12 V DC output) is for the optional Dell Soundbar AX510/AX510PAonly. To attach the Soundbar: 1. Working from the back of the monitor, attach the Soundbar by aligning the two slots with the two tabs along the bottom of the monitor. 2. Slide the Soundbar to the left until it snaps into place. 3. Connectthe Soundbar with the DC power connector. 4. Insert the mini stereo plug from the back of the Soundbar into the computerís audio output jack. For HDMI/DP, you can insert the mini stereo plug into the monitorís audio output port. If there is no sound, check your PC if the Audio output is configured to HDMI/DP output.
This monitor has no speakers. (Like John Hammer1 mentioned). The no speakers feature was one of the reasons I chose this monitor.
Good Luck !