Nokia MD-3 Manual page 4

ENGLISH
Use the speakers
To connect the speakers to the phone or audio device, plug the speaker
cable into the connector on the device. If the phone or audio device has a
Pop-Port connector or a 2.5-mm connector, connect the AD-15 or AD-50
adapter (respectively) to the device. Then connect the speaker cable to the
adapter.
To switch the speakers on or off, press the power key located at the top
of the speakers. When the speakers are switched on, the green indicator
light is on.
To set the volume, use the slider at the top of the speakers. If the sound
level of the speakers becomes too low when using battery power, change
the batteries.