Lenovo ThinkPad T420i - Manual (Page 14)

Using headphones or earphones
If your computer has both a headphone connector and an audio line-out
connector, always use the headphone connector for headphones (also called a
headset) or earphones.
CAUTION:
Excessive sound pressure from earphones and headphones can cause
hearing loss. Adjustment of the equalizer to maximum increases the
earphones and headphones output voltage and therefore the sound pressure
level.
Excessive use of headphones or earphones for a long period of time at high
volume can be dangerous if the output of the headphone or earphone connectors
do not comply with specifications of EN 50332-2. The headphone output
connector of your computer complies with EN 50332-2 Sub clause 7. This
specification limits the computer’s maximum wide band true RMS output voltage
to 150 mV. To help protect against hearing loss, ensure that the headphones or
earphones you use also comply with EN 50332-2 (Clause 7 Limits) for a wide band
characteristic voltage of 75 mV. Using headphones that do not comply with EN
50332-2 can be dangerous due to excessive sound pressure levels.
If your Lenovo computer came with headphones or earphones in the package,
as a set, the combination of the headphones or earphones and the computer
already complies with the specifications of EN 50332-1. If different headphones
or earphones are used, ensure that they comply with EN 50332-1 (Clause 6.5
Limitation Values). Using headphones that do not comply with EN 50332-1 can be
dangerous due to excessive sound pressure levels.
Data safety
Do not delete unknown files or change the name of files or directories that were
not created by you; otherwise, your computer software might fail to work.
Be aware that accessing network resources can leave your computer vulnerable
to computer viruses, hackers, spyware, and other malicious activities that might
damage your computer, software, or data. It is your responsibility to ensure that
you have adequate protection in the form of firewalls, antivirus software, and
anti-spyware software and keep this software up to date.
Additional safety information
DANGER
Plastic bags can be dangerous. Keep plastic bags away from babies and
children to avoid danger of suffocation.
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Safety and Warranty Guide