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Directed Sound
yawningyellowyak writes "Technology Review has an interesting article on directed sound. Ultrasonic 'sound' is sent out from a 'speaker' and the distortion encountered on hitting the air produces hearable sound, but only in certain spots. You could be standing right next to someone and they would hear nothing.
One step closer to the cone of silence!"
I don't see how this is anything new. I saw a show on TechTV about a year ago where some guy had perfected what most other companies had given up on (he is an inventor and has come up with a lot of other tech things). What he perfected was a speaker which could be totally directional and was completely flat. Some of the applications he considered were having them installed in a vending machine. For example, you could hear the sound of coke being poured into a glass - fizzing, glub glub glubbing, ice clanking as the soda fills the glass - that would only be audible if you were directly in front of the vending machine but step aside and you would not be able to hear anything at all.
"We are focused on achieving high volume applications featuring the unique benefits of HSS directed sound. --"To the Shareholders of American Technology Corp." Business Wire, March 25, 2002
from here and here.
i'm sure this'll come around again in the next few months...
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Previous story is here
Not difficult to find from July 2002.
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I don't know what the official definition of vapourware is, but I have seen this in use from rooftops at MIT (it's fun to see the reaction of people as they try and figure out if anyone else heard that voice), and am helping in the development of a line of products that use these speakers as a key component.
I think the reason you probably haven't seen it yet is that there aren't many finished products made yet, and part of that might have to do with the fact that lots of local bylaws seem concerned with this kind of thing (they liken it to talking on cell phones while driving).
It won't be long before this is everywhere. I think the tech is just slightly outpacing the market right now.
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Based on this it seemed to be pretty far advanced (and that was two years ago). Granted I've yet to see it being used commercially.
Tab books published instructions how to build a device that does exactly this decades ago... TAB!
Yeah, I know the cover looks ridiculous... I bought it when I was a teen and still have it - neat projects inside and better written than the cover would indicate.
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"The fine folks at the MIT Sound Media Lab have come up with a cheap and practical way to focus sound: "A beam of light can be controlled in many ways - it can be aimed at one person in a crowd, spread to fill a room, or projected to create rich, distant imagery. We can now do these very same things with sound. The Audio Spotlight can be used in two major ways: As directed audio, sound is directed at a specific listener or area, to provide a private or area specific listening space. As projected audio, sound is projected against a distant object, creating an audio image. This audio image is literally a projected loudspeaker - sound appears to come directly from the projection, just like light." While still under development, they are testing applications of the device in collaboration with several of their media lab sponsors in preparation for eventual commercial release."
I also recall another story someplace where a guy was messing with a portable version of this in a mall, spooking people out. Apparently the sound appears in the persons head, but you do know exactly which direction it is coming from.
I can see the potential to harrass politicians and other public speakers right now. It is definitely an acquired skill to be able to speak without stumbling despite that kind of distraction.
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I thought the basic principle of this was creating a beat frequency matching the original sound effect you want people to hear?
Beat frequencies are usually demonstrated by tapping two tuning forks. The difference between their frequencies is audible as a third "beat" frequency.
I could be wrong on this, but when I heard this effect during a science awards show at Epcot 5-6 years ago, that's how I assumed it was done =)
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You've missed what happens completely. Two different ultra-sonic sounds combine at the focal point, join together linearly, and the beat frequency they create is sonic. Plain old normal sound. The signals themselves are ultra sonic (ie. S1 and S2), but the diff is sonic (S1-S2, or the beat subtracted from S1+S2)
For pure bamboozlement, the effect of an ultrasonic parametric array (the things that produce these "directed sound beams") can't be beaten -- I experienced a demonstration of one two years ago at the Physical Acoustics Summer School in California. It's pretty amazing to have the demonstrator up front with a little antenna looking thing, playing music through it... but you can't hear it! However, just one or two people in the audience have this awestruck look on their faces. Then, when he swings the thing about, a line of people will suddenly perk up, as the cone of sound sweeps by. So although the "ultrasound method," as you call it, may not be as practically useful as time-reversal acoustics, it's really going to capture the public's attention.
Also, time-reversal acoustics is nothing new. The concepts have been around for a long, long time. It's just now, though, that digital amplifiers and computers are fast enough to quickly reverse tone bursts -- because sound travels so "slowly", it's difficult to get the "reversed" sound back to its source before conditions really change a lot. With light, though, this has been going on for a long time, because the danged stuff travels so fast (see any nonlinear optics book).
So, you're right: Time-reversal acoustics is "new" in the sense that the technology has almost caught up to the science. Still, practical difficulties exist, and there are a LOT of environments in which it won't be able to be applied. Just like there are a lot of environments in which nonlinear parametric arrays will do you no good because the intrinsic nonlinearity of the medium isn't high enough.
You could be standing right next to someone and they would hear nothing.
That's the idea, but in reality it works a tad different. Wherever the beam hits sort of becomes the apparent source of the sound. So if you aim it at someone, they'll hear it quite clearly - more so than everyone else - but the sound will now appear to be coming from them. Quieter, but still apparent.
I've got 2 of the HSS units right here, and though they're super-cool for messing with people, (See other posts) they've got some drawbacks.
1) There's no bass, treble only.
2) The units we have come with a rather noisy cooling fan.
3) They clip quite easily - you have to watch your volume levels.
4) They're not terribly reliable. I've seen them in a few labs I've worked in or with, and we all seem to have the same issues.
Overall a cool product, especially for the gee-whiz factory, but certainly not ready for practical use just yet.
You can do that, with a vortex cannon.
I have read the article, and what this particular article doesn't tell you (but has been in previous articles also posted on slashdot on the same tech), is that two ultrasound beams in parallel come out of the same emitter, and when they hit some object, they reflect in all sorts of directions, which causes them to interact, which cause the beat frequencies to be heard.
I find it interesting that after all these years the Cone of Silence, the useless security divice from the spy spoof Get Smart, still needs no introduction.
It's doubly funny since the term actually predates Get Smart - and refers to something else entirely.
The "Cone of Silence" is the area directly over a vertically-polarized radio antenna (i.e. off the end of the dipole) where there is little or no signal.
In WW II, aircraft did a lot of navigation using radio beacons. The easy way to do this is to fly to, and over, a beacon, perhaps setting a course that went from beacon to beacon, rather than navigating by obtaining bearings from multiple beacons (although the latter was also done).
As you approach a beacon the signal strength increases. But as you fly over it, through the "cone of silence", it suddenaly drops out - then reappears behind you. Then you know that you just went right over it - and thus exactly where you are - and that it's time to set your course for the next waypoint.
With so many bomber crews (and stories about them) the term "cone of silence" became publically known. But with few people other than navigators and radiomen familiar enough with it to know exactly what was meant, it became a buzzword with the implication of having something to do with wartime and security.
Which gave the writers of Get Smart an opportunity to use a rotten pun for a couple air minutes of slapstick by redefining it. B-)
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If marketers had any interest whatsoever in this type of advertising, there would be bullhorns in public places already constantly exhorting everyone to Drink Coke or Join The Army or whatever. As it stands, only political candidates and ice cream trucks are willing to do this.
Depends on where you are, in Tokyo it's extremely common to see people paid to hand out tissues advertising a shop/resteraunt, or just stand out front and yell (well, yell's not the right word, but close enough) at passerby's to advertise the shop. This tech combined with some sensors to track moving objects (aka people) could cut out the need to pay a person to do that, and make sure you hit even more people going by with your message.