Apple PowerBook (500 Series) - Manual (Page 46)

Connecting sound input and output devices
Your computer has a built-in microphone just below the display. For
information on using the microphone to record sounds, see the “Sound” topic
of Macintosh Guide, available in the Guide (h) menu.
Your PowerBook also has a stereo sound input port (marked with the icon √)
for connecting external sound input devices that provide line-level output.
You cannot use the internal microphone and an external sound input device at
the same time. For instructions on selecting a sound device in the Sound
control panel, see the “Sound” topic of Macintosh Guide, available in the
Guide (h) menu.
The PowerBook also has a stereo sound output port (marked with the icon -)
to which you can connect speakers, an amplifier, headphones, or other audio
output devices. The sound output port accepts a standard stereo miniplug,
like that used to attach headphones to a portable tape player.
WARNING Do not plug a sound output device (such as a pair of
headphones) into the sound input port. Doing so may damage your
audio equipment.
Microphone
39 Connecting Additional Equipment