HP PL Class 450/500/550/600/650/700/750 User Manual page 22

Setting Up and Using Your HP Visualize Linux Workstation
Connecting Audio Accessories
WARNING To avoid discomfort from unexpected noise, always turn down
the volume before connecting headphones or speakers. Listening
to loud sounds for prolonged periods may permanently damage
your hearing.
Before putting on headphones, place them around your neck and
turn down the volume. When you put on the headphones, slowly
increase the volume until you find a comfortable listening level,
then leave the volume control in that position.
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