Posts Tagged ‘demonstrations’

Sight of sound

Your eardrum converts the motion of the air into something you can hear, but what if everything around you could work the same way? In a recent TED Talk, MIT researcher Abe Davis demonstrates cutting edge research into extracting audio from silent video of everyday objects exposed to sound. Using high-speed video equipment and even a consumer-level camera, he extracts intelligible music and speech just by watching a nearby houseplant or a snack bag—the proverbial “fly on the wall”. Acknowledging the surveillance possibilities (which were already feasible using lasers), the research pushes beyond audio to expose the natural modal movement of an object by simply ensonifying it and recording what happens, allowing one to push, pull, and shake something virtually without ever touching it.

This sound is on fire

Many aspects of a firefighter’s work are not quite like the movies, and locating each other is one of them, according to a recent story from KUT News in Texas.  Visibility is poor or nonexistent in a real fire, so firefighters often have to rely on sound rather than vision.  A Personal Alert Safety System (PASS) is a device that emits a loud audible alarm if the wearer stops moving for more than a few seconds, allowing colleagues to come to the rescue.  Researchers at the University of Texas at Austin are working on ways to improve this system, which despite saving many lives doesn’t always work as well as it could.

For starters, an active fireground is a loud, noisy place, from things like sirens, power tools, engines, and the fire itself.  But beyond that, heat can do funny things to sound—hotter and colder parts of a room make sound travel faster or slower, and these changes in the speed of sound can actually bend sound waves that would otherwise travel in a straight line.  (Similar effects occur outdoors when the air temperature varies with height, such as being able to hear campers far away across a lake that cools the air.)  This heat refraction can wreak havoc with audibility and locating the source of a PASS beacon.  The current UT research will provide valuable insight into the sensory environment within a fire scene, and how compensation might be made for some of these acoustic challenges.


A new record

Putting a new spin on the long-playing vinyl record, an editor at Instructables has devised a new method for producing LP records using a rapid prototyping “3D printer”.  Working directly from a digital audio file, Amanda Ghassaei uses the waveform profile to create a 3D computer model of the familiar LP groove, which is then built up in physical form by a UV-cured resin printer.

Despite the cutting-edge 16-micron resolution of the printer, the end result is rather crude, with a frequency response and audio quality as yet far beneath a typical analog vinyl record.  The all-digital noise introduced by the discrete print (in time, aliasing, and in amplitude, quantization) is also harsh compared with the traditional “warm” analog distortion sought after by vinyl enthusiasts and audiophiles.  Even so, one could foresee a niche market for one-off, just-in-time pressing of records to keep alive long out-of-print material (or new material that might be in limited demand).  Even though this can be accomplished with .mp3 files or CD-R discs, sometimes there’s simply nothing like setting needle to vinyl!

[via Wired]

Drop-less droplets

In a setup that’s equal parts science and Harry Potter, scientists at Argonne National Laboratory acoustically levitate liquids in midair to further critical pharmaceutical reasearch. Using a technology originally developed by NASA to simulate microgravity conditions, the pharmaceutical droplets are suspended in midair using standing waves of inaudible ultrasound generated by small speakers above and below.

By suspending a drug this way—free from any container or other physical contact—scientists can study its various forms and the ways it might be absorbed by the body. Not to mention putting on a pretty cool show in the process!

Things that go thump in the night…

Maybe you are familiar with images of the northern lights or perhaps have been lucky enough to see them yourself, but did you know that apparently they also make a sound?  According to, acoustic researchers at Alto University in Finland have identified a clapping sound associated with the aurora borealis that occurs 230 ft above the ground!  Just as is true with most mystery noises, they are brief and faint, require very careful listening as well as very low background noise in order to be heard.   There is an audio recording on here if you want to listen…

aurora borealis

[via, photo: shawn malone]

Frozen spring

One of the things one learns studying acoustics (and many other physics topics) is that the behavior of a complicated physical system can often be simplified into an analogy of masses and springs.  The gobs of air that surround us have elasticity and they have mass, and these are the properties that allow waves to travel through the air as sound.

Perhaps a more intuitive example of a spring-mass system can be found in any toy store: the classic Slinky.  The familiar coil toy can be used to demonstrate lots of different wave phenomena (longitudinal waves, transverse waves, standing waves), and when that gets boring, it is more commonly used to demonstrate walking down stairs.

We recently came across this high-speed video of the very interesting spring-mass behavior of an extended Slinky at rest, dropped from height, in which the bottom end of the Slinky seems frozen in mid-air.  There are excellent technical explanations of what is going on out there (and probably on a tricky physics midterm or two), but suffice it to say that it all goes back to the interplay between mass and elasticity as the Slinky simultaneously contracts and falls.

[Via, @jenvalentino]