Epson 73c - Manual (Page 85)

Appendix A: Connecting to Additional Equipment 79
Connecting the Audio Cable
If your presentation includes sound and you want to use the
projector’s built-in speaker, you can use a computer audio cable. The
required cable (3.5-mm stereo miniplug cable) is available from
computer or electronics dealers.
1. Connect one end of the audio cable to the Audio1 port on the
projector.
2. Connect the other end of the audio cable to the speaker or
audio out port on the computer’s sound card.