The ActivPanel is not designed to be a standalone amplifier. Sound will be played provided there is a device connected, either to one of the video sources, or the audio-in port.  
 

If there is no sound from an external device/source or OPS: 

If there is a source input (i.e. HDMI 1) but no sound, please try a different source or OPS device, or a different cable. Make sure the device is connected directly to the ActivPanel, bypassing any extenders or wall connection boxes.  

• Is the ActivPanel listed as a sound device in the audio settings of your external device?  
• Is the volume turned up and unmuted? 

If there are sound abnormalities (crackling, buzzing or static noise from the speakers)

Test the ActivPanel with a different, known working device. Does the issue persist?  
Alternatively, test with a different cable, bypassing any extensions or wall connection boxes.  

If the ActivPanel was working fine previously, but has now suddenly developed feedback or buzzing, check that there is no electrical device near the ActivPanel that is causing the feedback. Unplug nearby devices and chargers as a test.

https://support.prometheanworld.com/s/article/2417?language=en_US