Speech Jammer. Easy to make!.

Today, Kazutaka Kurihara at the National Institute of Advanced Industrial Science and Technology in Tskuba and Koji Tsukada at Ochanomizu University, both in Japan, present a radical solution: a speech-jamming device that forces recalcitrant speakers into submission.

The idea is simple. Psychologists have known for some years that it is almost impossible to speak when your words are replayed to you with a delay of a fraction of a second.

Kurihara and Tsukada have simply built a handheld device consisting of a microphone and a speaker that does just that: it records a person’s voice and replays it to them with a delay of about 0.2 seconds. The microphone and speaker are directional, so the device can be aimed at a speaker from a distance, like a gun.

https://www.technologyreview.com/2012/03/01/116437/how-to-build-a-speech-jamming-gun/

Thumb Nail Source from artical :
https://www.technologyreview.com/2012/03/01/116437/how-to-build-a-speech-jamming-gun/