Is the mouth shutter machine effective?

In our

podcast 

, Laure Beaudonnet, journalist specializing in technological developments and innovations at

,

returns to an innovation of the American Navy, a machine "to shut the mouths". The idea is attractive as the end of year family meals approach, when the one you can't stand is in front of you ... Silence your brother or your aunt, simply by pressing a button. button, may no longer be fiction. The US Navy has created a device capable of preventing people from speaking, the US website

reported in September

. This portable acoustic call and disturbance system (AHAD) was developed by engineers from the Naval Surface Warfare research and development center. The patent, reports the science magazine

, was issued in 2019. But it was not revealed until this year.

What does this technology consist of?

It is inspired a bit by a childish game, which consists of repeating the words spoken by a person, in a staggered way. "If you force a speaker to hear his own speech in a quirky way, you send it to the wall," notes Xavier Lurton, retired researcher from Ifremer, and consultant in underwater acoustics. "Almost nobody is able at the same time to state something, to hear this something in real time, and to hear it shifted with a small delay", he underlines. The person who hears his speech with a delay, disturbed by these sounds, will eventually shut up. The technique is not new, and was the subject of publications in the 1950s. “The electronics of the time made it possible to produce simple machines which made it possible to implement this process.We have been able to show that this very quickly and very strongly disrupted the speech of the targeted person, ”continues the scientist.

What is the difference with current technology?

What is different about this patent is the technological implementation.

The idea is to use a microphone towards a person, at a distance, to pick up their voice, delay the voice signal, and send it back to them through speakers.

These are somewhat specific loudspeakers: they can make it possible to obtain directivity, that is to say a very important capacity of the transmitters to exercise their function in different directions.

What could this machine be used for?

This machine could be useful for flushing out people pretending to be hard of hearing, argues the former researcher.

Faking deafness to avoid military service, or claiming disability allowance with this machine would become extremely complicated.

Because if you are not hard of hearing and someone makes you read a text while wearing headphones, you will be very disturbed by the sound of your voice out of sync.

What are the limits of this technology?

Two limitations are noted by the consultant. First of all, about the directivity of a loudspeaker, this ability to make it emit in as narrow a beam as desired. As directive as the speakers are, the sound cannot be entirely "trapped", notes Xavier Lurton. There will always be imperfections. Second limitation: this machine for silencing is not very realistic. For very directional sound beams, you need very large speaker systems. This is based on a principle of wave propagation, for optics, radar. To obtain fine beams, you will need very large antennas. A huge machine for silencing potential protesters would then lack discretion!"It is hard to imagine a police car showing up at a meeting where we want to silence the speaker," resumes Xavier Lurton. There must be other, easier ways to silence someone… ”.

Then, this technology can work on people located a few tens of meters away. But hardly beyond: "100 meters would be miraculous, one kilometer, we do not even talk about it", notes the acoustician. It would therefore be useless for military operations, and very complicated to implement for law enforcement operations ...

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