
Have you heard the Audio Spotlight? - robg
http://www.boston.com/business/technology/innoeco/2010/05/have_you_heard_the_audio_spotl.html
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Anechoic
I've heard the Audio Spotlight at a demo that Pompei gave at a meeting of
Boston-area acoustical consultants (of which I am one, hence the username).

It's a great device, (as Joe Pompei told us) there are some misconceptions
people have when they read about the device:

1\. The audio spotlight does direct most of the audio sound at a point, but
sound does spill over to off-axis listeners, so even if it's not pointed
directly at you, you'll hear the audio (but at a greatly reduced level). You
couldn't really use this to direct a beam sound to one person in a crown and
expect no one else to hear it. But in a kiosk setting (for example) the
spillover would be acceptable.

2\. The video isn't quite right, but the technology doesn't work by using
constructive interference or beat frequencies. It takes advantage of the non-
linearities of ultrasound propagating through air to convert the ultrasound
into audible sound. One side effect of this process is that the sound has to
propagate through enough distance for the non-linearilities to have an effect
(I think the minimum distance for it to work is around 6-10 ft, but it
actually works best at large distances of 20ft or more). This isn't something
you could put on your desktop and have it work. You can read Pompei's thesis
about the technology here: <http://dspace.mit.edu/handle/1721.1/7987>

3\. By no means does it produce high-fidelity audio, it's maybe FM quality at
best. Similarly because of the wavelengths involved, the Audio Spotlight can
only produce upper mid-range and treble, no bass, so it won't be replacing
normal loudspeaker in applications where audio quality it key. But again, it
works perfectly fine for any number of other applications.

Overall, it's a nifty product and actually quite affordable. It's worth taking
a look at if if you have an application that can benefit from having directed
audio.

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ryandvm
Fascinating, but the explanation they gave in the video seems bogus.
Mathematically predicting how air currents will convert ultrasound into human
range? Bullshit.

If it's really beaming ultrasound then I suspect it relies on constructive
interference to produce audible sound.

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zxc
You're right, the video's explanation is totally wrong.

The proper information is here:

<http://holosonics.com/technology.html>

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cryptnoob
Woody Norris did this 10 years ago using the same technology. I actually have
one sitting beside me at my desk that I got back in 2001.

<http://en.wikipedia.org/wiki/American_Technology_Corporation>

It's fun for practical jokes or making the neighbors think their house is
haunted. I'm not sure how this guy is getting credit for this.

~~~
Anechoic
The Audio Spotlight was introduced around the same time as HSS (~2000-2001
IIRC). The LRAD was introduced earlier, but that uses a different tech (it's
just a large two-dimensional array).

