Sennheiser ACCENTUM Over-Ear Wireless Headphones (Black) - Manual (Page 22)

Using the headphones
22 | ACCENTUM
Depending on the length of the button press, you adjust the volume
in smaller increments (short button press) or larger increments (long
button press).
When switching the headphones off, very high volume levels are
automatically reset to a moderate level to protect your hearing when
you switch the headphones on again.
You can also adjust the volume using the connected Bluetooth
device.
If you have activated the voice assistant (> 30) and then change
the volume of the headphones, the volume of the voice assis-
tant is adjusted accordingly and saved permanently.
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