Apple Power Macintosh 4400 - Manual (Page 41)

About your computer’s sound ports and features
The sound input port is marked with an icon of a microphone (≈). The sound
output port is marked with an icon of a speaker (-).
The computer’s sound input port (≈) accepts the 3.5-mm audio connectors
shown below. The sound output port (-) (where you might connect external
speakers) accepts only the stereo miniplug.
The stereo miniplug is found most often on stereo equipment (such as
externally powered speakers). The extended miniplug, which is slightly longer
and is found on voice quality microphones (such as the Apple PlainTalk
Microphone), works only in your computer’s sound input port (≈). (Even
though it will fit into the sound output port, it won’t work there.) If your
equipment has a different type of connector from those shown here, you can
purchase an adapter at an electronics supply store.
Extended miniplug Stereo miniplug
Sound input port Sound output port
41 Connecting Equipment and Expanding Your Computer