Circuit diagram?

Audio Spotlight

Direct your sound to your audience with amazing precision.

Using sound with vision improves retention rates by up to 60%, but how do you get round the issue of noise pollution to the surrounding area? By using Audio spotlight - which concentrates the sound just as a spotlight does, so only those in the "beam" can hear your message. Use it outside your shop window, or under your billboard. People can hear, but can't always know where the sound is coming from. Creative opportunities
How it works:The directivity (narrowness) of any wave producing source depends on the size of the source, compared to the wavelengths it generates. Audible sound has wavelengths ranging from a few inches to several feet, and because these wavelengths are comparable to the size of most loudspeakers, sound generally propagates omnidirectionally. Only by creating a sound source much larger than the wavelengths it's producing can a narrow beam be created.
Clearly, having loudspeakers twenty meters wide is not very useful.
therefore ...
to make a narrow beam of sound from a small acoustic source, we instead generate only ultrasound.
The ultrasound, whose wavelengths are only a few millimeters long, are much smaller than the source, and consequently travel in an extremely narrow beam.
Of course, the ultrasound, which contains frequencies far outside our range of hearing, is completely inaudible. But as the ultrasonic beam travels through the air, the inherent properties of the air cause the ultrasound to distort (change shape) in a predictable way. This distortion gives rise to frequency components in the audible bandwidth, which can be accurately predicted, and therefore precisely controlled. By generating the correct ultrasonic signal, we can create, within the air itself, essentially any sound desired.
Note that the source of sound is not the physical device you see, but the invisible beam of ultrasound, which can be many meters long. This new sound source, while invisible, is very large compared to the audio wavelengths it's generating. So the resulting audio is now extremely directional, just like a beam of light.
If you're offering a special offer to customers and they might miss looking at your window, why not tell them to look in an easy non-obtrusive way, by talking to them as they pass. Even better, why not combine this with rear projection film on the shop window and ensure everyone looks and listens to your message.
By combining an IR sensor with your spotlight, you can trigger audio to individual people as they approach your building or advertisement. Target them with specific messages or contact their mobile phones via Bluetooth technology to allow audio or video downloads of your product.
In areas where headsets have previously been needed, such as museums or exhibitions, why not use multiple audio spotlights, so that customers can hear naturally about the piece without disturbing others around them.
The possibilities are endless! See more in the Audio Spotlight pdf.

http://www.google.co.uk/search?q=directional+sound+weapon&sourceid=ie7&rls=com.microsoft:en-gb:IE-SearchBox&ie=&oe=&rlz=1I7GZEU_en&redir_esc=&ei=lL2HTM6oMMbd4Abqm_3RBA

http://science.howstuffworks.com/lrad1.htm

Hi i saw this on future weapons

How LRAD Works

by Tracy V. Wilson

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Cite This! Close Please copy/paste the following text to properly cite this HowStuffWorks article:

Wilson, Tracy V.. "How LRAD Works" 03 March 2006. HowStuffWorks.com. <http://science.howstuffworks.com/lrad.htm> 08 September 2010. Inside this Article

1. Introduction to How LRAD Works
2. How the LRAD Unit Works
3. Pros & Cons of LRAD

1. Lots More Information
2. See all Acoustics articles

Acoustic Videos

• More Science Videos »

How the LRAD Unit Works

The LRAD's job is to make sound - lots of sound. It produces very loud sound that is audible over relatively long distances. But it's not limited to producing painful noise for use as a weapon. It can also amplify voices or recordings to a level that is loud and clear but not painful or debilitating.

Instead of using one big, moving device to make all this sound, the LRAD uses lots of little ones. A speaker usually uses one rapidly moving diaphragm to make sound. The LRAD uses has an array of piezoelectric transducers. A transducer is simply a device that changes one kind of energy into another kind of energy. In this case, it changes electrical impulses into sound.

Applying a charge to a piezoelectric material causes it to change shape.

A piezoelectric material is a substance that is permanently electrically polarized -- it has a positively charged side and a negatively charged side. If you apply pressure to a piezoelectric material, it creates an electrical impulse. On the other hand, if you apply an electrical charge to it, its molecules move and it changes shape. Using electrical current from a battery, generator or other source, the LRAD applies electrical charge to lots of piezoelectric transducers. The transducers rapidly change their shape and create sound waves.

The LRAD has lots of transducers in a staggered arrangement.

All of these transducers are attached to a mounting surface. They're staggered to allow more of them to fit into a smaller space. This helps the LRAD create very loud sounds -- identical waves emerge from the transducers, and their amplitudes combine to create louder sounds.

Photo courtesy American Technology Corp The back of the LRAD has handles so people can direct the majority of the sound it creates.

So that's how the LRAD creates lots of volume. But the sound coming from the LRAD is also relatively directional. It doesn't disperse as much as sounds from typical speakers. Fifteen degrees outside the beam, the volume drops about 20 dB. People behind or next to the device still hear the sound, it isn't as loud. Even outside the beam, the sound can still be loud, so operators and nearby personnel often wear ear protection.

The LRAD uses the phase of the sound waves, the size of the device and the properties of air to create more directional sound:

• The outer transducers are not completely in phase with the inner transducers. The sound waves interact with one another, canceling out some of the outermost waves and making the sound less audible outside of the "beam."
• The device's diameter is larger than most of the wavelengths it produces. This allows the device to create a wave front that's more flat than rounded, keeping the sound from dispersing.
• Air interferes with sound waves as they pass through it. As the LRAD's sound waves interact with the air, they create additional frequencies within the wave. Such waves are referred to as parametrically generated, and many speakers try to prevent them. The LRAD uses them to create a greater range of pitches and to add volume.

The result is essentially a loudspeaker that can receive input from a microphone, a recording device or a Phraselator translation device. It can then amplify that input, allowing law enforcement, security and military personnel to give instructions and warnings or to clear buildings and disperse crowds. If those verbal instructions don't produce a result, the LRAD can produce a loud warning tone that approaches or passes the threshold of pain.

When used to cause pain or disorientation, the LRAD is a non-lethal weapon. Next, we'll look at the pros and cons of using LRAD in this manner.

VIDEO: Check out amazing videos of UFOs and 22 interesting

OK,

Just call me Mr. Negative.

This can only work outside. Seems like rain or sand would attenuate the noise sooner, too.

Sound decays 6dB as the distance doubles_{(I think that's right)}, so the range is limited.

Maybe that's good.

In the hands of idiots(read young/drunken/stoned/vindictive/) it could render you totally deaf.

I've lost my train of thought. _{Maybe it's just de-railed.}

Another method involves two transducer arrays that are eparated by some distance and both aimed at the desired point. one sends out an unmodulated ultrasonic carrier frequency, the other sends out the same frequency 180 degrees out of phase and freqency modulated with the audio signal. where the two beams intersect, the carrier frequency interacts with the out of phase signal and they cancel each other out, leaving the modulating signal by itself. It can ONLY be heard where the two beams intersect.