Thursday, July 19, 2012

Behold the magic powers of awesome bass

DARPA (you know, those guys who actually did invent the internet) has a piece on using "acoustic fields" (ie, killer bass) to snuff out flames. Looks like magic to me!

It's totally not clear to me, from the video, what the sound spectrum being used is, or (perhaps more importantly?) what sound pressure levels are required. All I hear is a buzz. It's not so loud that there can't be a person standing next to it (perhaps wearing ear protection), but it seems to require two huge speakers on either side of the flame, attached to ginormous tubes. Also, after the flame is out, the sound switches off, accompanied by a loud click, as if a huge relay is required to maintain the "acoustic field". Here's what they say about it:
Performers also evaluated the use of acoustic fields to suppress flames. In the video below, a flame is extinguished by an acoustic field generated by speakers on either side of the pool of fuel. Two dynamics are at play in this approach. First, the acoustic field increases the air velocity. As the velocity goes up, the flame boundary layer, where combustion occurs, thins, making it easier to disrupt the flame. Second, by disturbing the pool surface, the acoustic field leads to higher fuel vaporization, which widens the flame, but also drops the overall flame temperature. Combustion is disrupted as the same amount of heat is spread over a larger area. Essentially, in this demonstration the performers used speakers to blast sound at specific frequencies that extinguish the flame.
My reaction: yeah, I know lots of those words. It's still magic.

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