The device works at a distance, because it uses a directional mic for recording and a directional speaker for delayed playback. That allows one to limit output to a single individual. Quoting “WATCH: Video of the Japanese ‘Speech-Jammer’ gun in action” by David Ferguson for The Raw Story:
The sampled-and-returned speech is audible only to the targeted individual and the resulting effect is said to be like “hearing a recording of one’s own voice echoing inside one’s skull,” which creates a kind of induced stutter.The device works better in some contexts than in others. Quoting the SpeechJammer’s creators’ paper “SpeechJammer: A System Utilizing Artificial Speech Disturbance with Delayed Auditory Feedback”:
… we dealt with “reading news aloud” and “spontaneous monologue” as the speech contexts. From the results, we observed a tendency for speech jamming to occur more frequently in the “reading news aloud” context than in the “spontaneous monologue” context. Further, it is obvious that speech jamming never occurs when meaningless sound sequences such as "Ahhh" are uttered over a long time period.The paper also explains that the speech-jamming technique is called Delayed Audio Feedback and can help with stuttering:
It is thought that when we make utterances we not only generate sound as output, but also we utilize the sound actually heard by our ears (called “auditory feedback”) in our brains. Our natural utterances are jammed when the auditory feedback is artificially delayed. It is thought that this delay affects some cognitive processes in our brain. This phenomenon is known as speech disturbance by Delayed Auditory Feedback (DAF).There is a YouTube video online that shows SpeechJammer in action. Clearly, the video’s creators don’t suffer chatterboxes and boring presenters lightly.
DAF has a close relationship with stuttering. DAF leads physically unimpaired people to stutter; i.e., speech jamming. On the other hand, it is known that DAF can improve stuttering, and medical DAF devices are available.