Which Z27 monitor do you have? I looked through the specifications for several models and none of them had built-in speakers. They do have a headphone jack and also support the HP S-100 series add on speakers but do not have speakers built-in. The headphone jack will show as the monitor being an audio output device.
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I have: HP Z27 - LED monitor - 27" (27" viewable) - 3840 x 2160 4K UHD (2160p) - IPS - 350 cd/m - 1300:1 - 8 ms - HDMI, DisplayPort, Mini DisplayPort, USB-C -
I just you are right, though it says built in speakers on my end It may just mean the audio jack.
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