INNOVATION

Why Navy Scientists Want to Mimic Cicadas

No, it’s not about learning to live underground for 17 years. It’s all about the noise.

June 4, 2013

I am cicada, hear me roar. Photo courtesy of Flickr user Roger Smith

Yes, the big red eyes are creepy.

Not to mention the bizarre 17-years-in-the-ground, six-weeks-in-the-trees, mad-trysting-and-death cycle. And the sheer volume–billions of them are expected to before the current invasion ends. (Last weekend, I stood under a copse of trees they had taken over and, though the wind was still, every treetop was moving.)

But really what fascinates U.S. Navy scientists about the brood of cicadas now infesting large pockets of the East Coast is their mind-boggling sound–a din that can climb over 90 decibels. That’s louder than a garbage disposal, food blender or a truck 50 feet away, and almost as loud as power mower or a 737 coming in for a landing.

A team of scientists at the Naval Undersea Warfare Center in Rhode Island has been studying cicada cacophony for several years now and this week they will present what they’ve learned at the International Congress on Acoustics in Montreal. Their goal is to see if humans can devise a way to replicate the sound.

Bring on the noise

I know what you’re thinking…why? Why try to mimic a noise that can turn a summer day into an aural beatdown?

But that’s what intrigues the Navy scientists. They’re trying to figure out how it’s possible to make a sound that loud without using much power. And they think that devices that sound like cicadas could be used for remote sensing underwater, ship-to-ship communications, maybe even rescue operations.

They know why male cicadas make the sound. It’s all about the sex. They’re vying for the attention of female cicadas. If a female makes a clicking sound with her wings, she’s interested. The researchers say that when a male gets closer to a female that has clicked her interest, the male softens his sound–the insect equivalent of going Barry White on her.

And they have a good idea of how the bugs make the sound. They’ve been able to use lasers to simultaneously measure the vibration of the insect’s “tymbals,” the ribbed membranes on both sides of a cicada’s torso. When a male seeks sex, it contorts its body and that buckling causes the membrane to click, then click again when it snaps back into place.

So why does the incessant noise sound more like a massive Star Trek phaser than a series of clicks? Because the male cicada repeats this cycle for its left and right sides about 300 to 400 times a second. That’s a lot of contorting, but it has the desired effect. And it’s loud, even with one cicada, because the creature has air sacs in its hollow abdominal cavity that amplifies the sound. It’s been compared to a hammer striking a gong.

So far, the scientists haven’t been able to replicate it. The problem is that it’s not just one moving part making the sound. The buckling of the cicada’s body isn’t uniform–its two tymbals aren’t in sync with each other. And apparently it’s the combination of those out-of-phase vibrations that creates such a deafening noise.

Ingenious…and this from a bug that spends 17 years in the ground.

Sound effects

Here are other revelations from this week’s acoustics conference:

Bringing harmony to families around the world: Researchers have devised a way to have your car speakers in the back play something different from what people are hearing in the front. This new system creates “independent listening zones” by using small, modified speakers to produce directional fields of sound, and has the ability to optimize the audio signals driving each of the speakers.
Puff up the volume: Danish jazz and rock drummer Niels Adelman-Larsen has invented a means of shape-shifting concert halls so they can provide the best reverberation for whatever kind of music is played in them. His system is made of airtight plastic foil membranes attached to the walls that can be inflated or deflated with the flip of a switch. When the membranes are inflated, the foil vibrates and that lowers the reverberation time in the hall, which makes it more suitable for rock music. Deflate the membranes and you get the long reverberation times that enrich classical music.
Because when did a text ever steer you wrong: Soldiers in the field have to deal with auditory overload, including what info or orders might be coming in over their headphones. So Canadian researchers wanted to see if visual cues could help them focus on what they needed to know. And sure enough, the research showed that soldiers performed much better when they received text messages reinforcing what they were told over a loudspeaker.
But beware of a powerful attraction to singing male crickets: The unique directional hearing ability of a parasitic fly has inspired scientists to design a microphone that could make hearing aids much more effective. The females of this type of fly use their auditory skills to locate singing male crickets, upon which they deposit their larvae. And that never turns out well for the crickets.
That’s one small explanation frrr(uh) man: Researchers from Ohio State and Michigan State have come to the conclusion that Neil Armstrong’s Ohio accent may have been responsible for the confusion over what he said when he took his first steps on the moon. While just about everyone on Earth thought they heard Armstrong say, “That’s one small step for man, one giant leap for mankind,” he always insisted that he said “for a man,” which would have made more sense. But the latest study points out that people in central Ohio, where Armstrong grew up, tend to blend together words like “for” and “a,” resulting in a phrase that “sounded something like ‘frrr(uh).’”

Video bonus: Watch a cicada come to life after 17 years in the ground. If you want a taste of cicada din, skip to the four-minute mark.

Video bonus bonus: Okay, these are not the 17-year cicadas. They’re from the 13-year-brood. Still, it’s worth watching David Rothenberg try to play his sax as they swarm around him.

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