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Engineers Invent Acoustic Equivalent of One-Way Glass

Soulskill posted about 9 months ago | from the sound-waves-aren't-welcome-here dept.

Technology 114

Hugh Pickens DOT Com writes: "Up until now, acoustic waves traveling between two points in space always exhibited a basic symmetry summed up with the phrase, 'if you can hear, you can also be heard.' Not anymore; Tia Ghose reports at Live Science that a team at UT Austin has created a 'nonreciprocal acoustic circulator,' the first step that could lead to the sound equivalent of a one-way mirror. All waves — whether visible light, sound, radio or otherwise — have a physical property known as time reversal symmetry — a wave sent one way can always be sent back. For radio waves, researchers figured out how to break this rule using magnetic materials that set electrons spinning in one direction. The resulting radio waves detect the difference in the material in one direction versus the other, preventing reverse transmission. To accomplish the feat with sound waves, the team created a cavity loaded with tiny CPU fans that spin the air with a specific velocity. The air is spinning in one direction, so the flow of air 'feels' different to the wave in one direction versus the other, preventing backward transmission. As a result, sound waves can go in, but they can't go the other way. The result is one-directional sound. With such a device, people can hear someone talking, but they themselves cannot be heard. The findings will likely lead to many useful applications, says Sebastien Guenneau. 'I would be surprised if sound industries do not pick up this idea. This could have great applications in sound insulation of motorways, music studios, submarines and airplanes.'"

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Links (0)

Anonymous Coward | about 9 months ago | (#46121663)

We need more links on TFS...

I can hear my CPU fan... (0)

Anonymous Coward | about 9 months ago | (#46121703)

but apparently it can't hear me.

This doesn't make any sense (4, Interesting)

goombah99 (560566) | about 9 months ago | (#46122353)

I don't see how this explanation is breaking the symmetry. Accoustic waves don'e have circular polarication and are axially symmetric.

Your example sort of proves the point, one should be able to make a silent CPU fan where the sounds go in but don't come out if this is true.

Here's my guess about what is REALLY going on here. if you phase delay two separated fans such that the sound that went through the open part of the first fan, reaches the the second fan just as the open part of it is inline with the dound direction it passes through. It would not work in the backwards direction. then layer on that the fact that air column is moving in one direction.

But I' don't see the symmetry breaking for a compression or rarefraction wave happening like it does in the E&M case.

Re:This doesn't make any sense (1)

nashv (1479253) | about 9 months ago | (#46125309)

RTFA. You are assuming transmission occurs longitudinally through the tube of CPU fans. Actually, they are sending the sounds waves transverse to the tube. This means the air is spinning either along or against the direction of compression/rarefaction. Along works, against doesn't. Hence , one way transmission.

No such thing as one-way glass* (1)

Immerman (2627577) | about 9 months ago | (#46122355)

So, "Engineers invent acoustic equivalent to something that doesn't exist". Does that mean they didn't actually invent anything at all?

* one-way glass is a misnomer for semi-silvered glass. It only seems "one way" if one side is much more brightly illuminated than the other, so that the 50% of light reflected back to the bright side drowns out the 50% of light that makes it through from the dark side.

Re:No such thing as one-way glass* (1)

goombah99 (560566) | about 9 months ago | (#46122421)

So, "Engineers invent acoustic equivalent to something that doesn't exist". Does that mean they didn't actually invent anything at all?

* one-way glass is a misnomer for semi-silvered glass. It only seems "one way" if one side is much more brightly illuminated than the other, so that the 50% of light reflected back to the bright side drowns out the 50% of light that makes it through from the dark side.

wrong. google circulator. its a one way optical waveguide device. it doesn't violate any laws

Re:No such thing as one-way glass* (1)

Deadstick (535032) | about 9 months ago | (#46122951)

Methinks you could have parsed that sentence a bit better.

Re:No such thing as one-way glass* (1)

Tuidjy (321055) | about 9 months ago | (#46123541)

You're wrong on so many levels.

First, you assume that 'one-way glass' means 'one-way mirror'. For all we know, they mean 'optical frequency circulators' which use ferrimagnetic crystals, and can definitely let visible spectrum light only way. Look it up.

Second, even for one-way mirrors, the term 'one-way' is appropriate enough. Few things in the real world are 100%. City streets, diodes, etc... we refer to them as one way, even when they really aren't 100% one way - the random car/particle gets through.

Third, we're Engineers. It's about getting results. We invent things that don't exist all the time. Although in this case, I doubt there are as many applications as the original article wishes they were. In a lot of the cases, you will get cheaper results with conventional soundproofing, and if you need the sound on one side, you can get it there with some good old microphones and speakers.

And even fourth. It's good to be looking for new stuff. You never know what's under the rock you turn over, just because it's there. You may be looking for a new way to turn lead into gold, and discover porcelain instead.

Re: No such thing as one-way glass* (0)

Anonymous Coward | about 9 months ago | (#46125337)

Meh. Wake me up when someone invents a noise cancelling window screen so that I can get some air without being kept awake by all the racket a city makes.

Re:No such thing as one-way glass* (1)

Immerman (2627577) | about 9 months ago | (#46125563)

Woosh on the headline-directed snarkiness.

"Yes, circulators exist - but I have never, ever, heard them referred to as one way glass, and from what I can tell they rarely incorporate any glass at all.

As for "one way mirrors" - try flipping the mirror around, if it were one way it'd now be see-through in the opposite direction, but it's not. There is *zero* directionality to the effect, it's 100% determined by the relative lighting levels. Light the two rooms equally and you will see a 50/50 blend of your reflection and whoever is standing on the other side. With dimmable lighting it can actually be a very cool effect, but it there is absolutely nothing "one way" about it.

Completely agree that it's good to be looking for new effects and inventing things that don't already exist. But we're engineers, calling something by a blatantly misleading name should be beneath us.

Re:No such thing as one-way glass* (1)

nashv (1479253) | about 9 months ago | (#46125321)

You sure know how to make a fool of yourself. Why do you have to go talking about what you don't know/understand?

Begin here : http://en.wikipedia.org/wiki/O... [wikipedia.org]
Then here:
http://arxiv.org/abs/1109.1148 [arxiv.org]
http://www.physics.utoronto.ca... [utoronto.ca]
http://www.opticsinfobase.org/... [opticsinfobase.org]

Re:No such thing as one-way glass* (1)

Immerman (2627577) | about 9 months ago | (#46125587)

Yes, unidirectional optical waveguides do exist, but in what sense are they glass? Everything I've seen appears to discuss micro-engineered crystalline structures, whereas:
"Glass is an amorphous (non-crystalline) solid material that exhibits a glass transition, which is the reversible transition in amorphous materials (or in amorphous ..."

Marketing department (3, Funny)

i kan reed (749298) | about 9 months ago | (#46121677)

Can we put one between us and marketing. We don't have to hear their bad ideas to tell them they won't work for practical reasons.

Re:Marketing department (0)

Anonymous Coward | about 9 months ago | (#46123179)

I have mixed feelings about this. On one hand you lose the opportunity to tell them that it won't work. On the other hand, it's not as if they listened to you anyways. So which is more frustrating? Telling someone that it won't work but they sell it anyways? Or being blind-sided by something that won't work with no mental preparation?

Finally! (3, Funny)

lord_mike (567148) | about 9 months ago | (#46121691)

When can I order my "Cone of Silence"? I can't wait to be finally able use my shoe phone in public knowing my conversation will be secure and private!

Re:Finally! (1)

sconeu (64226) | about 9 months ago | (#46121751)

The Cone of Silence never works, Max.

Re:Finally! (2)

ackthpt (218170) | about 9 months ago | (#46121797)

The Cone of Silence never works, Max.

But this one, unlike all the others, will!

Now we just need it compact.

Re:Finally! (0)

Anonymous Coward | about 9 months ago | (#46121831)

The Cone of Silence never works, Max.

I DEMAND A CONE OF SILENCE!

Re:Finally! (1)

Anonymous Coward | about 9 months ago | (#46121835)

What did you say, sir?

Re:Finally! (0)

Anonymous Coward | about 9 months ago | (#46123385)

The cone did work. It worked far too well. All communication was impossible in the cone of silence.

I've had this for years (1)

Anonymous Coward | about 9 months ago | (#46121711)

(sticks fingers in ears and yells 'I can't hear you')

Microphone and Speaker (3, Informative)

ZombieBraintrust (1685608) | about 9 months ago | (#46121715)

You can create the same effect with a microphone and a speaker behind a sound proof wall. Still pretty cool.

Re:Microphone and Speaker (2)

Anubis IV (1279820) | about 9 months ago | (#46122489)

That was my first thought, but if this really can be used as the equivalent of soundproofing on freeways or whatnot, like the summary suggested, then it would mean that it provides something much more interesting than simply a wall, speaker, and mic combo.

Applications? (4, Insightful)

badboy_tw2002 (524611) | about 9 months ago | (#46121739)

Music studios yes, but why would airplanes want to transmit sound from inside to outside, or vice-versa? Same with motorways. You definitely want to block traffic noise from adjacent buildings, but why would you care that folks in the cars can hear whats coming from the buildings? Just block it all.

Re:Applications? (0)

Anonymous Coward | about 9 months ago | (#46121829)

So my neighbor can hear his dog barking at 2:00 AM and I cannot.

Re:Applications? (1)

Lumpy (12016) | about 9 months ago | (#46123261)

That is called calling the cops. do it enough and the cops will actually come out to tase your neighbor for being a moron and having the dog out that late. Doggie can make it from 10pm to 6am without going outside. Mine was fine from 9pm to 7am. Only scumbag dog owners let the dog out and then let it bark and bark and bark.

Re:Applications? (1)

Kkloe (2751395) | about 9 months ago | (#46121983)

well for motorways because its probably cheaper to block it one way than both, say it costs 1000 to set up a concrete wall for blocking sound from both sides, but it costs 650 with this new type of wall, but doing it both sides would cost 1200, so its cheaper one way than two airplanes, did it even say where?, no, it could be around the engines or from the outside to the inside, was it that hard to understand?

Re:Applications? (2)

Garble Snarky (715674) | about 9 months ago | (#46122125)

Except this device is active, and a concrete wall is passive. Hard to believe the energy costs over, say, 20 years, would not more than make up the difference.

Re:Applications? (1)

Lumpy (12016) | about 9 months ago | (#46123269)

Or the fact that the concrete wall will last 20+ years without another penny spent on it, while the wall of fans will need constant repair and maintaince and end up costing $100,000 a year to keep working until they abandon it 3 years later.

Re:Applications? (1)

Dahamma (304068) | about 9 months ago | (#46122469)

Wait, so building a concrete wall is more expensive than building a wall filled with thousands (or millions?) of tiny fans? Not only is that not EVER likely to be true, but the latter will always require significant maintenance and electricity costs...

Re:Applications? (1)

badboy_tw2002 (524611) | about 9 months ago | (#46123107)

No I understand it I assure you. Again, why would you want to block the airplane sound coming in but not going out? Is there a specific reason you'd need to not hear the engines but hear what's going on outside form within the engine? Or from outside the cockpit but not vice versa? Neither of those are a good reason. And there's no way a sound damper wall or insulating material is more expensive than something filled with tiny fans.

Re:Applications? (1)

Lumpy (12016) | about 9 months ago | (#46123277)

So the man on the plane's wing cant hear that we are talking about him.

Re:Applications? (1)

Ksevio (865461) | about 9 months ago | (#46122243)

All the applications listed want to absorb and get rid of the sound. Even in a music studio, the recording engineer wants the sound to be picked up by the microphones, he doesn't need or want to hear it directly. I can think of very few practical uses for this.

Re:Applications? (1)

CanHasDIY (1672858) | about 9 months ago | (#46122411)

All the applications listed want to absorb and get rid of the sound. Even in a music studio, the recording engineer wants the sound to be picked up by the microphones, he doesn't need or want to hear it directly. I can think of very few practical uses for this.

Especially considering that the fans in the device are going to generate both audible and electrical noise themselves.

I was doing some recordings in my home studio a while back, and kept getting this buzzing sound in all my tracks. After an hour or so of sticking my ear against various surfaces in the room, I finally figured out that the noise was being generated by a device plugged into the same circuit as my recording gear, and was transmitting to the microphone through the wires.

Re:Applications? (1)

Ksevio (865461) | about 9 months ago | (#46122939)

Need a ground lift plug

Re:Applications? (1)

CanHasDIY (1672858) | about 9 months ago | (#46123091)

Need a ground lift plug

Yea, or don't put a compressor motor on the same circuit leg as your DAW...

Re:Applications? (2)

sunderland56 (621843) | about 9 months ago | (#46124313)

So that you can hear noise from your kids bedrooms, but they can't hear the (ahem) noises from yours? Although, seriously, soundproof your walls and get a baby monitor.

This sounds more to me like "let's invent this and see what we can do with it", than an invention with a current application.

Re:Applications? (1)

Aighearach (97333) | about 9 months ago | (#46124671)

I know what to do with it!

Carnival tricks!

Already (0)

Anonymous Coward | about 9 months ago | (#46121747)

We already have one-way sound and sound-cancelling devices, they're called amplifiers and sound-cancelling algorithms.

Re:Already (1)

ZombieBraintrust (1685608) | about 9 months ago | (#46121837)

I suppose it is the difference between a 1 way mirror and a tellivision connnected to a camera. In one case the input travels through the medium in the other the input is digitized sent through a wire and replicated on the other side. The only benifit I see is that no data is lost/distorted based on microphone placement. Not sure who needs that though.

Speak but not hear? (0)

Anonymous Coward | about 9 months ago | (#46121765)

Congress has prior art.

Re:Speak but not hear? (1)

ackthpt (218170) | about 9 months ago | (#46121817)

Congress has prior art.

Oh, they hear alright, they just don't listen.

Re:Speak but not hear? (1)

knarfling (735361) | about 9 months ago | (#46122299)

Congress has prior art.

Oh, they hear alright, they just don't listen.

To quote Homer Simpson: "Just because I don't care, doesn't mean I'm not listening."

What? (-1)

Anonymous Coward | about 9 months ago | (#46121779)

What?

Re:What? (-1)

Anonymous Coward | about 9 months ago | (#46122271)

Wut

Re:What? (-1)

Anonymous Coward | about 9 months ago | (#46123109)

Wat?

Audio equivalent of a roach motel (1)

cruff (171569) | about 9 months ago | (#46121791)

Remember the old commercials for the roach motels? The roaches check in but they can't check out.

party on (0)

Anonymous Coward | about 9 months ago | (#46121793)

Now I can party on the whole Night withouth annoying the neighbors

Re:party on (1)

ackthpt (218170) | about 9 months ago | (#46121809)

Now I can party on the whole Night withouth annoying the neighbors

You'e going to party in your car?

Interrogation rooms (1)

rsborg (111459) | about 9 months ago | (#46121803)

...might become much easier to design.

On the other hand, not sure how this will help with airplanes, where the entire cabin is simply "rumbling" including whatever one-way surface

Re:Interrogation rooms (1)

femtobyte (710429) | about 9 months ago | (#46124557)

Interrogation rooms ...might become much easier to design.

Because sticking a microphone in a corner is obviously a gigantic difficulty in design, that has baffled engineers since the dawn of the electronic age.

Except for the fact that... (2, Informative)

Vihai (668734) | about 9 months ago | (#46121815)

...true one-way mirrors do not and can not exist: http://en.wikipedia.org/wiki/O... [wikipedia.org]

Re:Except for the fact that... (1)

jmv (93421) | about 9 months ago | (#46121931)

More generally, any device that lets energy (light, sound, heat, ...) only flow in one direction has to spend energy to avoid violating the laws of thermodynamics. That's true of this device just like for a heat pump. You could probably also create a real one-way mirror, but again it could not be a passive device and would require energy to operate.

Re:Except for the fact that... (1)

Anonymous Coward | about 9 months ago | (#46122385)

You could probably also create a real one-way mirror, but again it could not be a passive device and would require energy to operate.

You mean like a TV?

Re:Except for the fact that... (1)

goombah99 (560566) | about 9 months ago | (#46122519)

More generally, any device that lets energy (light, sound, heat, ...) only flow in one direction has to spend energy to avoid violating the laws of thermodynamics. That's true of this device just like for a heat pump. You could probably also create a real one-way mirror, but again it could not be a passive device and would require energy to operate.

Wrong. Circulators are able to perform this function without any input energy.

http://en.wikipedia.org/wiki/C... [wikipedia.org]

Re:Except for the fact that... (1)

AdamHaun (43173) | about 9 months ago | (#46122829)

Wrong. Circulators are able to perform this function without any input energy.

Technically, some of the energy from the transmitted signal is lost.

Also, you're not going to be making glass out of these [oemarket.com] .

Re:Except for the fact that... (1)

johndoe42 (179131) | about 9 months ago | (#46122659)

This is incorrect. You can't build a passive device that is 100% transmissive from one side and 100% reflective on the other side.

You can, however (in theory), build a device that with these properties:

  1. Light from side A is transmitted and comes out side B
  2. Light from side B is absorbed and turns into heat
  3. Absorbed heat is re-radiated, mostly from side A

This thing will be non-reciprocal [wikipedia.org] . I've never heard of anyone building one that looks like a sheet of glass, but they're common for microwaves -- they're called circulators [wikipedia.org] . There's a reason that this new contraption is called an acoustic circulator. The only misleading part is that one-way glass is reciprocal -- this new thing is much more impressive than one-way glass.

Re:Except for the fact that... (0)

Anonymous Coward | about 9 months ago | (#46121963)

What?!? How will I build my panopticon?

Re:Except for the fact that... (1)

MozeeToby (1163751) | about 9 months ago | (#46121985)

With semi-silvered glass, bright lights on the prisoners and very dim lights on the watchers. Which is how "one way glass" works in the real world today.

Re:Except for the fact that... (1)

iggymanz (596061) | about 9 months ago | (#46121971)

that depends only on definition. while a conventional silvered glass can't act as true one-way glass, powered devices certainly can. Some cameras, a computer with wares that left-right reverse image, a large screen, and presto a " true one way glass". or at least we'll have marketing tell people that.

Re:Except for the fact that... (1)

Dahamma (304068) | about 9 months ago | (#46122537)

Just polarize a window between two rooms and then make everyone in one room wear complementary polarized glasses :)

Re:Except for the fact that... (1)

iggymanz (596061) | about 9 months ago | (#46123721)

but they'll lean their heads when you're not looking!

Re:Except for the fact that... (1)

Dahamma (304068) | about 9 months ago | (#46124245)

Aha! Then make sure it's circularly polarized! (and I suppose, tape the glasses to their heads and tie their hands behind their backs)

And since it's an absurd amount of effort and expense just to create a simple one-way window, the US DHS is sure to demand its large scale implementation right away. Time to patent it and make billions! And as a bonus, with everyone wearing these shades Guantanamo will be the new height of style in secret detention centers...

Re:Except for the fact that... (1)

Macman408 (1308925) | about 9 months ago | (#46122021)

Yeah, this. The real "acoustic equivalent of one-way glass" would be to play some loud noise near the people who shouldn't be able to hear you - they have to yell really loudly to hear each other, which everybody else (including you) can hear over the noise. But they can't distinguish sounds you make from the noise because the noise is much closer and louder than you.

Re:Except for the fact that... (1)

Dahamma (304068) | about 9 months ago | (#46122589)

Actually, this was the first thing I thought of when I read "'if you can hear, you can also be heard" in the summary.

It's also my explanation to my girlfriend as to why I can't hear her when she tries to talk to me through the bathroom door while I'm in the shower, but she can hear me ;)

Re:Except for the fact that... (1)

goombah99 (560566) | about 9 months ago | (#46122371)

Except that they do exist and are made all the time for waveguides. they are called circulators. Wikipedia is 100% wrong on that.

Re:Except for the fact that... (1)

ljw1004 (764174) | about 9 months ago | (#46122623)

...true one-way mirrors do not and can not exist: http://en.wikipedia.org/wiki/O... [wikipedia.org]

Citation needed. The wikipedia page contains your assertion ("true one-way mirrors do not and can not exist") but it backs it up with a now-dead link that, when it was active, never said anything of the kind...

Two-Way Mirrors, copyright 1999, Jim Loy

A two-way mirror is often called a "one-way mirror" by members of the general public. The misconception is that such a mirror acts as a mirror from one side, and acts as a window (letting light through) from the other side. Actually, the two-way mirror is letting about half of the light through, and reflecting the other half of the light, from both sides. it is also called a half-silvered surface, as just enough reflecting metal film (usually aluminum as far as I can determine) is deposited on the glass, so that about half of the light is reflected.

So, why does a two-way mirror seem to behave like the two sides are different? It behaves this way when one side is in the dark. Then almost no light goes from the dark side to the light side, and almost no light is reflected back from the dark side to the dark side. Most of the light comes from the bright side. Plenty of light travels through the mirror, and plenty of light is reflected back. To people on both sides of the mirror, the light from the bright side overwhelms the light from the dark side. So, people on the bright side see a mirror, and people on the dark side see a window. See the above diagram.

Robin Williams told a joke about policemen in the South having mirrors on the inside of their glasses. Good joke, but such glasses are two-way mirrors, and are shaped so that your eyes are always in the dark.

Bah (4, Funny)

Jeremi (14640) | about 9 months ago | (#46121821)

My cell phone has been doing this for years.

YcUO FAIL IT (-1)

Anonymous Coward | about 9 months ago | (#46121867)

Emergency Vehicles? (0)

Anonymous Coward | about 9 months ago | (#46121879)

I understand they have lights designed to get your attention, but sound I would assume is also a key factor.

I wonder if this will bring more attention to the emergency vehicle warning technologies that are in their infancy right now.

Granted this is all built on the assumption this proposed one-way sound technology bears any fruit.

Re:Emergency Vehicles? (0)

Anonymous Coward | about 9 months ago | (#46122077)

You mean the flashing stobes ontop of school buses use constantly that is yet another distraction?

We need self-driving cars, not more garbage that causes distractions on the roads and more wrecks because some muckety-muck thought adding strobes on vehicles is a good idea.

Re:Emergency Vehicles? (1)

Lumpy (12016) | about 9 months ago | (#46123351)

No we don't. we need a drivers license to be a lot harder to get and keep. Take the blonde bimbo's drivers license and car when she causes an accident and was texting for 5 years. yes 5 YEARS of no driving and losing your car for being a dumb ass. also allow the victim to SUE the person causing the accident, she will learn if she has to give up 20% of her paycheck every week until she pays for the other guys costs and medical bills.

There are no consequences for being idiots anymore, we need to bring them back.

Re:Emergency Vehicles? (0)

Anonymous Coward | about 9 months ago | (#46124793)

Just remember your own penalties when you fuck up.

LOL (0)

Anonymous Coward | about 9 months ago | (#46121885)

"With such a device, people can hear someone talking, but they themselves cannot be heard."

Pretty sure I accidentally invented this for my wife.

1 way sound transmission medium (1)

rossdee (243626) | about 9 months ago | (#46121941)

We have that in the midwest already
its called the wind
also useful for generating power

Cone of Silence? (0)

Anonymous Coward | about 9 months ago | (#46121961)

Imagine that -- an actual working Cone of Silence, like the one from the Get Smart TV series.

Re:Cone of Silence? (1)

Overzeetop (214511) | about 9 months ago | (#46123997)

I can't tell you how disappointed I am that it took this long for the CoS to be posted.

Already Implemented (0)

Anonymous Coward | about 9 months ago | (#46121973)

By Google Support

heyyyyyyyy ooooh

Headline-induced dream dashed by the summary (2)

MiniMike (234881) | about 9 months ago | (#46122065)

the team created a cavity loaded with tiny CPU fans

And I was hoping I could use this to reduce fan noise in my computer.

Re:Headline-induced dream dashed by the summary (0)

Anonymous Coward | about 9 months ago | (#46123293)

Because it's important that the inside of your computer can hear you?

Mechanical notch filter? (3, Interesting)

Sertis (2789687) | about 9 months ago | (#46122121)

seems like it only affects sound or wave functions in a specific frequency as determined by the speed of the air movement or electron migration rates or whatnot. Might not be very effective for general sound insulation unless it's fixed frequency, o (or else you'd hear the generated harmonics). Not too different than active noise cancellation.

Sound insulation of motorways? (3, Insightful)

Gordo_1 (256312) | about 9 months ago | (#46122223)

> "This could have great applications in sound insulation of motorways"

Last I checked, the screams of children within neighborhoods protected by motorway sound barriers were not a major nuisance or safety hazard for motorists.

Or are we just brainstorming ideas without any thought behind them?

A one way sound barrier makes sense if you have an application where you actually need sound to go through in one direction. If you don't, then a wall is a better and almost certainly cheaper solution.

Re:Sound insulation of motorways? (1)

Gravis Zero (934156) | about 9 months ago | (#46124393)

> "This could have great applications in sound insulation of motorways"

Last I checked, the screams of children within neighborhoods protected by motorway sound barriers were not a major nuisance or safety hazard for motorists.

but the children can barely hear the loud roaring traffic as it goes by. think of the children!

Time Reversal Violation (4, Informative)

Roger W Moore (538166) | about 9 months ago | (#46122363)

All waves — whether visible light, sound, radio or otherwise — have a physical property known as time reversal symmetry — a wave sent one way can always be sent back.

No, not all waves. Kaon and B-meson waves violate time reversal symmetry. We have known about this for almost 20 years since the first CPLEAR paper on the evidence of this and the more recent papers from Babar have confirmed it beyond any reasonable doubt. I'm always amazed how such a fundamental result as the laws of physics defining a direction of time (even when you take account of phase space/entropy effects) seems to be forgotten by many physicists.

There are other ways to do it (5, Informative)

Solandri (704621) | about 9 months ago | (#46122391)

The gizmo they're describing is for acoustic transmission along a single axis. i.e. you have a pipe between points A and B, and A can hear B but B can't hear A.

You can do the same with impedance changes if A and B are in different mediums. The impedance difference due to the density change causes asymmetrical transmission to reflection ratios [psu.edu] (bottom two animations). Consequently, if you're underwater in a swimming pool, you can hear all the noise from people talking in the air. But if you're outside the water, you can't hear sound originating in the water. (You can hear it a little, but nowhere near as well as sound from the air transmitted into the water.)

You can also do it with refraction changes if sound is allowed to propagate along two or more axes. The ocean creates a natural acoustic waveguide [wikipedia.org] this way. If you're in the middle of the waveguide, you can easily hear things at the edge of the waveguide. Sound from the thing at the edge of the waveguide spreads radially, and consequently about half of it captured by the waveguide. Whereas sound from the middle of the waveguide reaches that point at the edge only at a very specific angle. Consequently the listener inside the waveguide gets greater amplification. (A conceptually easier example is a megaphone if you use it to try to communicate with someone standing far away. If you speak through it, all your acoustic energy is directed in one direction, before it reaches the end of the megaphone and is allowed to spread radially. Most of it continues in the direction you pointed the megaphone. If you listen through it though, the acoustic energy from the other person spreads radially first, then the tiny bit captured by the broad end of the megaphone is concentrated. Consequently the megaphone is much more effective as a speaking amplifier than it is as a listening amplifier.)

I don't think any of these methods allow for a perfect "one-way mirror" though, where someone at A can hear B, but B cannot hear anything from A.. I can see the device in TFA getting close. It uses moving air to guide sound one way - move the air faster than the speed of sound and in theory it can't go backwards. But I have to think there will be some sound transmission back along the stationary frame used to contain the moving air (not to mention in their device the air is moving in a circle).

Re:There are other ways to do it (0)

Anonymous Coward | about 9 months ago | (#46122539)

The gizmo they're describing is for acoustic transmission along a single axis. i.e. you have a pipe between points A and B, and A can hear B but B can't hear A.

You can do the same with impedance changes if A and B are in different mediums. The impedance difference due to the density change causes asymmetrical transmission to reflection ratios [psu.edu] (bottom two animations). Consequently, if you're underwater in a swimming pool, you can hear all the noise from people talking in the air. But if you're outside the water, you can't hear sound originating in the water.

So you're suggesting that we need to flood room A full of water so room B can't hear them?

I like the idea in the TFA better.

That explains a lot about technical support.... (1)

David_Hart (1184661) | about 9 months ago | (#46122457)

How many times have you asked a user to do something, but they end up doing something completely different?

Obviously, they can't hear you because of the CPU fans...

I have the perfect use (1)

surfdaddy (930829) | about 9 months ago | (#46122527)

I need this for my wife. She can hear me, I can't hear her!

Soundproof Lair/Mancave.... (1)

rts008 (812749) | about 9 months ago | (#46122591)

This has the potential to save many marriages!

Oh, my bad...this is /.
What was I thinking? *scurries back to basement

Re:Soundproof Lair/Mancave.... (1)

KingOfBLASH (620432) | about 9 months ago | (#46122655)

Is that because the wife can hear you screaming for a beer but you can't hear her screaming at you?

Imod do3n (-1)

Anonymous Coward | about 9 months ago | (#46122635)

is Hdying and 1ts

Similar to electronics (0)

Anonymous Coward | about 9 months ago | (#46122651)

Kind of like an acoustic diode.
I'm not really sure what use it is other than some things that are are really esoteric, or done easier and cheaper by other means.
Still, who knows what somebody will eventually think to do with this, just look at what a couple of centuries has done with electricity.

Prior Art (1)

halexists (2587109) | about 9 months ago | (#46122923)

My bathroom fan already does this! If I'm standing in the bathroom talking, my wife can hear me from another room. If she talks, however, I can't hear her at all.

I guess they just built a higher resolution version of my bathroom?

Re:Prior Art (1)

nashv (1479253) | about 9 months ago | (#46125347)

Unless your bathroom fan is creating hurricane level winds in your home, it is unlikely that it is functional as an acoustic circulator. More likely , it's too noisy.

At last the Get Smart Cone of Silence (0)

Anonymous Coward | about 9 months ago | (#46123433)

NT

Spyware... (0)

Anonymous Coward | about 9 months ago | (#46123549)

Only a matter of time until they throw this on a drone so the spy/CI can talk to the people at home while they "spray" commands to him from the sky.

Frack... (0)

Anonymous Coward | about 9 months ago | (#46123841)

try and tell me that our species isn't neurotic...

False Flag Fuel (0)

Anonymous Coward | about 9 months ago | (#46124775)

This would be a great tool to get a schizophrenic to go out and pull a false flag for the CIA to push somebody's agenda.

Thanks Dr. Obvious (1)

Billy the Mountain (225541) | about 9 months ago | (#46126011)

Of course you can eliminate all sounds, duh. You just have to make sure the fans are blowing supersonic air. Sound can't travel upstream supersonically.

Reminds me of WWII Britain & the "battle of th (1)

johnpipe (304501) | about 9 months ago | (#46126039)

I've read Professor R.V. Jones "The Wizard War" (originally published in Britain as "Most Secret War"), and this reminds me very much of the story of the electronic warfare between England and Germany in WWII. This device reminds me very much of the cavity magnetron oscillator, sort of an "acoustic-frequency "magnetron"", not the best descriptor perhaps, but that's what immediately comes to my mind.

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