Parametric Interaction

[hubble]

Hi,
        Can somebody help me with the circuit to produce directional sound. I read somewhere that ultrasound of certain frequency acts as a carrier wave and the information is the modulating wave. But I couldn't find the schematic. Is it much like the same as producing AM or FM? 

[audioguru]

You did not desribe the details of what you are talking about.

A few years ago a company developed a very powerful array of ultrasonic transmitters because an array is very directional. They also developed an algorithm that modifies the AM modulation to make it more efficient and to reduce distortion.

The result is that when the ultrasonic beam stikes an object then the modulation is heard to be coming from the object. If the ultrasonic beam strikes your head then the modulation is heard only by you.
The displays "talk". You can hear one language and the person next to you hears another language.

It needs very high power ultrasonic transducers that are not available unless you buy them from that company.

[Hero999]

The details of how to do it are probably a trade secret so I doubt you'll be able to find a schematic anywhere.

[hubble]

You did not desribe the details of what you are talking about.

        I want the device to transmit within 7m. Basically I want to get rid of
        earphones. I don't want it to be so much powerful. I just want to use it at
        home for entertainment purpose. I don't want to disturb my neighbors when I
        am on loud music.


        I actually saw this system working in a disco where sound was 'embedded' in
        beams of light. I assume this works on the same principle.

[Hero999]

How about posting a link so we know what you're talking about?

I've done a quick Google and couldn't find it. I'm not doubting that it exists, I've seen it before, I'm just not going to click on ever link on every page of results to find it.

[hubble]

How about posting a link so we know what you're talking about?

I've done a quick Google and couldn't find it. I'm not doubting that it exists, I've seen it before, I'm just not going to click on ever link on every page of results to find it.

  I myself couldn't find enough relevant information. But I did find a link.

  http://www.explainthatstuff.com/directional-loudspeakers.html 

  See if that can help.

  Thank you.

[audioguru]

I think he is talking about common wireless headphones that use modulated IR or modulated ultrasonic waves.

Here is an IR transmitter and receiver that uses FM modulation:

An ultrasonic circuit would be similar.

[Hero999]

An ultrasonic circuit would be similar.

I don't think it's practical to use ultrasonics unless it's narrow bandwidth i.e. voice only or  you use digital compression. How many ultrasonic transducers can you buy that have a the 20kHz bandwidth required for single side-band AM?  Most transducers have a sharp resonant peak.

That's a point: a wide bandwidth ultrasonic transducer it required to build the device described by the original poster.

[hubble]

I think he is talking about common wireless headphones that use modulated IR or modulated ultrasonic waves.

    In my initial post I said I want to get rid of wireless headphones. My goal is to aim
    a sound signal at a particular point without anybody in the area hearing it.

[audioguru]

Yes.
Then you will need many custom-made 200kHz ultrasonic transducers, a circuit and an algorithm program.