Written for Synergy 3 (v3.7.2) and Synergy 1 (v1.21.4), checked 3 October 2026.
To hear two computers through one set of speakers or headphones, use hardware: an audio cable between the computers, or an audio switch or mixer. Synergy 1 and Synergy 3 don't support sharing audio between computers; they share your keyboard, mouse and clipboard, but not sound. Hardware alternatives generally perform better than sending sound over the network anyway.
Connect the audio output of one computer to the audio input (line in) of the other. Where both computers have optical ports, an optical audio cable (S/PDIF or TOSLINK) gives you a cleaner, digital signal, which is less likely to suffer from interference. Then, on the computer the speakers are connected to, turn on Listen to this device for that input, which mixes in the audio from the other computer, and use that computer's sound as the primary output.
On Windows, Listen to this device is in the Sound control panel: on the Recording tab, open Properties for the input the cable is plugged into, then select the Listen tab.