Sennheiser Set 820 Instruction Manual page 35

Additional information
The audio transmission technology used with this unit is basically that of a
radio. According to today's scientific knowledge, the radio waves
emitted by this unit are not harmful to humans or animals.
Varnish or furniture polish may degrade the rubber feet of the transmitter.
Place the transmitter on a nonslip pad to avoid potential staining of
furniture.
Delivery includes a pair of replacement ear pads. If necessary, remove the
old ear pads and slide on the new ones.
Use a soft cloth for cleaning the units. Do not use abrasive cleaners.
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