The Speech Box can talk! It utilizes a text-to-speech system called MaryTTS to synthesize speech from any given message. Simply give it a sentence or phrase to say and, after a bit of intense processing, it will do so. You should consider using proper punctuation since doing so usually improves the quality of the spoken phrase.
Due to the system's size, this box does nothing by default; MaryTTS has to be installed in the game instance's directory separately for this to work. Installation instructions are detailed on the wiki.
If an audio cable is connected to the box, it will send the audio signal generated through the cable while active instead of playing sound itself.