How does this ultrasonic parametric speaker produce sound?

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
57
The link to the project is here:

How is it able to produce audible sound? I thought humans can only hear till 20KHz and as they age it decreases to 16KHz or even less. The person says the ultrasonic sound is demodulated by ear, is that possible?
 

Audioguru again

Joined Oct 21, 2019
3,540
The guy shows no details of his circuit. The sounds it made in the video were only faint shhh, shhh, shhh sounds of cymbals and normal sounds of traffic in the background. I heard no speech or music.

Professionals use the ultrasonic system to make statues talk in a museum, paintings talk in an art gallery and different languages are spoken to a few people in a large conference.

I think an ultrasonic carrier is aimed at a person or object and ultrasonic sidebands modulated with audio are also aimed. The two ultrasonic beams have a very narrow angle and their interference with each other after bouncing off an object causes audio that sounds like it is produced by the object.

I am 75 and have normal for my age high frequency hearing loss. I cannot hear a smoke detector beeping or a telephone with a piezo beeper. People talking to me sound like they talk only in vowels that is not speech. My modern hearing aids boost high frequencies a lot so that everything sounds normal plus tricks like muting, extra sensitivity and noise reduction selected with a button.

When I was young I heard a burglar alarm's motion detector at a very high pitch and I asked why is it on in the daytime. They said it operated at 25kHz and they never turned it off because nobody could hear it. I did.

Acouspade is one of many. Look at it and hear it in Google.
 
Last edited:

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
57
The guy shows no details of his circuit. The sounds it made in the video were only faint shhh, shhh, shhh sounds of cymbals and normal sounds of traffic in the background. I heard no speech or music.

Professionals use the ultrasonic system to make statues talk in a museum, paintings talk in an art gallery and different languages are spoken to a few people in a large conference.

I think an ultrasonic carrier is aimed at a person or object and ultrasonic sidebands modulated with audio are also aimed. The two ultrasonic beams have a very narrow angle and their interference with each other after bouncing off an object causes audio that sounds like it is produced by the object.

I am 75 and have normal for my age high frequency hearing loss. I cannot hear a smoke detector beeping or a telephone with a piezo beeper. People talking to me sound like they talk only in vowels that is not speech. My modern hearing aids boost high frequencies a lot so that everything sounds normal plus tricks like muting, extra sensitivity and noise reduction selected with a button.

When I was young I heard a burglar alarm's motion detector at a very high pitch and I asked why is it on in the daytime. They said it operated at 25kHz and they never turned it off because nobody could hear it. I did.

Acouspade is one of many. Look at it and hear it in Google.
I think this link has schematic of the circuit: https://www.instructables.com/Ultrasonic-Sound-Gun-Parametric-Speaker/

What does the ultrasonic carrier have and what does the sidebands have? You mean to say the air particles velocity reduces to audible range after interference?
 

Audioguru again

Joined Oct 21, 2019
3,540
The Instructables circuit shows a 1k resistor to ground on the 555 pin 5 which causes audio from the capacitor to drive it positive and negative. But it should never go negative and is already biased. Then the 1k resistor should not be used and a higher value capacitor is needed to pass low audio frequencies.

The sidebands are produced with Pulse-Width-Modulation (PWM) by the audio on pin 5 of the 555. The PWM has its own carrier.
 
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