VoiceChannel

Events here are to be used when in a voice channel. Discord emits all events in all voice channels within the server, however.

Assuming:

client.joinVoiceChannel(channelID, function(error, events) {});

speaking

Indicates that someone's speaking presence has just changed. The event contains their User ID, SSRC (identifier, not really required unless you know what you're doing) and a boolean indicating whether they're now speaking (true), or have stopped speaking (false).

events.on('speaking', function(userID, SSRC, speakingBool) {});