No sound on iMac using the video library

When I play the loop example from the video library and use a video with sound then I can hear the sound playing on my macbook pro.

When I play the same script with the same video on an iMac (late 2015, 10.11.6) then I hear no sound. The sound is on! If I play in quicktime or vlc then I do hear sound. I tried processing 3.3 and 3.3.4.

I even tried more then one iMac, all the same.

I really have no clue what to do. This is for the exam of a student that I help. So if someone can help me that would be great.