Audio Jammer theory, application & circuit design help

[thanhhavdt]

Hi, I want to do an audio jammer as my final year project. Its objective is to prevent outsider record private conversation in the meeting. But, I dont know how to evaluate it through the experiment. How to jam a recording device using waveform generator. what is the setting of frequency , power , etc need to be set?

Thanks for help.

 

[Audioguru]

In an open office floor plan, we installed speakers that played continuous pink noise. People in the office did not notice it because it was simply background sounds.
People could not hear what a neighbour was talking about.

Since the idea is old, is very simple and has been used for many years it might not be suitable for a final year project.

 

[chuckey]

One interesting experimennt could be to have two ultrasonic devices radiating a high power at say 30 and 31 KHZ. Their effect would (should) not be noticeable to people, but if there was some recording apparatus, any cross modulation or non linearity in the microphone or amplifier circuitry would result in a 1KHZ beat note that might drown out any normal conversation picked up.
Frank

 

[Audioguru]

One interesting experiment could be to have two ultrasonic devices radiating a high power at say 30 and 31 KHZ. Their effect would (should) not be noticeable to people, but if there was some recording apparatus, any cross modulation or non linearity in the microphone or amplifier circuitry would result in a 1KHZ beat note that might drown out any normal conversation picked up.

A 1kHz beat note will not drown out a conversation. It will simply be a continuous beep.
That is why sound masking uses pink noise that contains all audible frequencies at random.

 

[chuckey]

Alright then, FM one ultrasonic carrier with pink noise.
Frank

 

[Audioguru]

Alright then, FM one ultrasonic carrier with pink noise.

Your new idea might work if a non-linear recording is made. But usually audio jamming needs to block people (not machines) from hearing a nearby conversation.
People cannot hear ultrasonic beat sounds.

Actually the opposite is used in museums. They blast an ultrasonic carrier and a specially modulated different ultrasonic carrier at an object. It seems that the object produces the modulation sounds.
In an audience they blast different ultrasonically modulated languages at people and the person beside you hears a different language that you hear.

 

[Darkcobra]

I've heard a high-speed turbine produce phantom tones in digital recordings, by producing ultrasonic frequencies over the recorder's digital Nyquist limit, of sufficient volume to overwhelm its analog low-pass filter.

But I don't think there is anything that will interfere with audio recording enough to reliably prevent it. At least short of operating a pulse magnetron in the area strong enough to disrupt all electronics (including pacemakers). Confidentially is best secured by eliminating the possibility of recording devices. Pursue this project only if well-documented failure is an acceptable conclusion.

 

[Audioguru]

Simply feed pink noise into the area. People there will think it is air conditioning noise. Neighbours talking will not be heard and will not be recorded.
It is old technology.