Sennheiser PXC550 Instructions Manual page 43

Listening to music
Announcement volume limit er
When in-flight mode, the volume limiter feature of the headphones protects you
from sudden volume jumps when the in-flight entertainment (IFE) system is
interrupted by the PA announcement. Typically, the PA announcement is much
louder than the volume of the IFE.
After the announcement is made, the volume of the headphones remains low
and can be increased only by adjusting the volume from the IFE.
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