Sennheiser IS 150 Notice D'emploi page 19

Front
Free line of sight
Infra-red light from the TI 150 / TI 300 transmitter is transmitted in the
same way as the light from a light bulb. Do not obstruct the path of the light
between the transmitter and the receiver, and stay in the room where the
transmission is taking place! Make sure that you wear the stethoset receiver
the right way round, with the „Sennheiser" logo at the front.
There is a simple rule:
If you can see the transmitter from where you are,
transmission can take place without any interference.
Volume up? – No!
When people use headphones, they tend to choose a higher volume than
with loudspeakers. Listening at high volume levels for long periods can lead
to permanent hearing defects. Please protect your hearing, Sennheiser
headphones have an excellent sound quality even at low volumes.
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