Usually when someone says they’re going to silence you with a gun, you should start worrying about bullet holes. Japan’s SpeechJammer gun, however, can keep you quiet without aerating your shirt. This prototype device uses a directional mic to listen to someone talking up to 34 meters away. The gun then plays those sounds back to the talker delayed by just a few tenths of a second. Speakers hearing their own delayed voice suddenly stop talking. Why isn’t exactly well known, but it’s suspected that the brain becomes confused when trying to synchronize what it’s saying to what it’s hearing. While its creators are still figuring out the science behind this phenomenon, that hasn’t stopped them from trying out the SpeechJammer gun on colleagues and friends, often with stunning effect (see the video below). A finished version of this device could be used to quiet annoying speakers in public places, manage arguments, or even silence protestors. Not only that, but the underlying technology of the gun is simple enough that someone could develop it commercially very soon.

The enjoyment of the SpeechJammer creators is almost palpable in this slightly zany demonstration of the device.



Some technologies appear so silly, strange, or downright sinister that they almost have to be a hoax. Yet Japan’s SpeechJammer was created by real researchers, is discussed in a real journal article, and based on some very interesting science. Developed by Kazutaka Kurihara of the National Institute of Advanced Industrial Science and Technology (AIST) and Koji Tsukada of the Japan Science and Technology Agency (JST), the prototype silencer relies on delayed auditory feedback (DAF). DAF has been shown to help treat stuttering. The sound of a stutterer’s voice, delayed by a fraction of a second and played back to the speaker, can be used to train some stutterer’s to overcome the ailment. In other research DAF has also been shown to induce mental stress in normal speakers. Influenced by previous DAF devices, Kurikara and Tsukada set out to build a prototype that could selectively inflict DAF on targets at range. The result was the Speech Jamming Gun.

Really, the device is pretty simple. A directional microphone picks up sounds while a range finder determines the distance between the speaker and the device. A large directional speaker then “fires” the sound, delayed a hundred milliseconds or so, back at the person talking. Add in a trigger to turn it off and on, and a laser pointer to help aim and you’ve got the Speech Jamming Gun. It all runs on just 8 AA batteries, too.

The only really difficult bit of engineering here seems to be in calculating the appropriate delay for the distance between target and gun using an onboard microchip. That delay has to be adjusted quickly so that the repeated sound arrives at the speaker with the correct delay. If too little time passes (a few milliseconds) the gun doesn’t work, and the opposite is likely also true, though the researchers comment in their paper that delays of even greater than one second produce a silencing effect. Clearly the optimal delay has yet to be determined.

In fact, the main thrust of Kurihara and Tsukada’s paper seems to be that there’s a lot to be learned with the Speech Jamming Gun. They played with volume, delay time, varying the delay time dynamically (with a sine wave), and even the context of speech and found that all those factors affected the gun’s influence on a speaker. Louder is better, so is a fluctuating delay, a relatively longer delay (hundreds of milliseconds), and more complicated speech. Simple feedback (just “oohs” and “ahhs”) didn’t work as well as real words.

There’s little doubt then, that Kurihara and Tsukada have a long way to go before they can perfect the Speech Jamming Gun for optimal use…but that doesn’t mean we won’t see something similar arrive much sooner. DAF devices have been around for years, and they aren’t hard to build. Most of the components are off the shelf, including the parametric (directional) speaker which is available as a kit. The real innovation here was making it all portable and using onboard processing to handle calculating the delay – that could be repeated by others very easily. I’m not saying I could hack one of these together in my garage…but I bet I know some people who could.

Now that the speech jamming cat is out of the bag, it’s only a matter of time before others start building these things, maybe even creating commercial versions. What happens then? Well, there’s three main applications here. Kurihara and Tsukada discuss the possibilities of managing conversations – everyone speaks into a mic and a directional speaker silences someone when it’s not their turn to speak. Clearly, however, that sort of consensual use is just the tip of the iceberg. Speech jamming could be used to enforce noise policies in public places (I’m sure there are librarians who are already salivating over this thing). The same technology might also be used to quiet agitators in mobs, or just silence protestors in general. Its effective range, about 34 meters, is set by the speed of sound in air and the small delay times used, but if longer (or variable) delay times prove to work then the gun could theoretically be applied over much greater distances.

The Speech Jamming Gun is just the latest in a suite of devices that could drastically change the way humanity speaks in public. Singularity Hub has already discussed elaborate microphone arrays that can pick out individual voices from a crowd of thousands. There’s also software that can sift through thousands of hours of recorded audio and determine how people feel about key words or phrases (sentimental analysis). Now, those with the right technology will not only be able to listen, they’ll be able to selectively silence those who say something undesirable. A sobering possibility for sure, but probably not the closest application. A commercial version of a portable speech jamming gun is going to be novelty at first, and maybe a crowd control device once the engineering is optimized. It seems like such a fun and harmless device. Let’s hope it stays that way.

[image and video credits: Kazutaka Kurihara (AIST) and Koji Tsukada (JST)]

[source: Kazutaka Kurihara, Koji Tsukada, “SpeechJammer: A System Utilizing Artificial Speech Disturbance with Delayed Auditory Feedback” (2012 via arXiv)]