Listen To This Noise

Your daily dose of amazing acoustics.

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Snap a chopstick in your hands, and you might just be holding a little earthquake. Researchers at National Tsing Hua University have recently proposed a new theory for why earthquakes work the way they do, and they’ve demonstrated their theory by snapping a single bamboo chopstick. It has long been known that the energy of earthquakes follows a power law known as the “Gutenberg-Richter law,” which says that there are more low energy earthquakes than high energy ones. Many explanations for this pattern have been proposed (including self-organizing criticality and fractals), but this new explanation is intriguingly simple. Just like how a bamboo stick is made up of a lot of individual fibers that break in clumps, the ground is made up of a lot of sedimentary layers, than crack in much the same way. Rather than complex math, it becomes a matter of simple geometry: earthquakes work like they do because the ground has layers. (Article credit: Phys.org. Photo credit: Yamashita Yohei.)

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Back in 2008, researchers at UNSW developed a clarinet playing robot that took first place in an international robotic music competition. As anyone who’s tried to pick up the instrument would know, clarinets are complicated, with unusual fingerings, difficult mouth control, and several quirks that take practice to overcome. But considering that even the best robotic clarinetist is far from a true virtuoso, are they really good for anything? Yes, actually, if the research team’s website is any indication! Because the robot’s actions are so consistent, scientists can study the exact effect of things like blowing pressure, lip force, lip position, and more! Robots like these are great tools for any musical acoustician, and I look forward to seeing how far these robotic musicians can take us. (Video credit: UNSW)

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Bats are an important, but often invisible, member of many ecosystems. They are pollinators, eaters of insects, and more. And yet, their populations are often hard to monitor because there are so many species to keep track of. But it turns out that sound can help make this task a little easier. Researchers from the University of Cambridge and Zoological Society of London have constructed a massive library of bat sounds for Mexican bats, which can now be used (in conjunction with some machine learning algorithms) to identify and count bats just by the sounds they make. This isn’t the first time bats sounds have been used in this way (there’s a similar database covering European species), but this is the biggest library of its type, and it covers a region where many species of bat are threatened. Hopefully, thanks to unobtrusive monitoring with sound, we will be able to spot falling populations before any more go extinct! (Photo credit: AlphaLu. Article credit: Phys.org)

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Golden moles are amazing animals, with a unique sense of hearing. Completely blind, these animals rely largely on their other senses to navigate and find prey (tiny ants), and yet they have no outer ears to speak of. That’s because, rather than listening to sound moving through the air, these tiny animals use the vibrations in the ground to see the world around them. Peter Narins, an expert on animal hearing, has published some interesting theories regarding the unique adaptations of the golden mole. Among the most interesting, he has shown that their middle ears have a unique shape, perfectly adapted to capturing sound in the air and in the ground. Even more interesting, where humans (and other animals adapted for airborne sound) have middle ear bones that lie parallel to each other, golden moles have perpendicular bones, allowing them to sense the direction of vibrations just like seismometers used for detecting earthquakes. All of this adds up to golden moles being easily one of my favorite acoustic animals. (Photo credit Galen Rathbun)

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How did this car seemingly sink into solid ground? The answer is a little known effect called “Liquefaction.” This unusual phenomena causes soil and sand to act like liquids, sometimes even flowing into the streets like a flood. In the above picture, the vibrations of an earthquake caused the road to turn to quicksand and rapidly swallow the car. You can even make your own model of liquefaction at home! Of course, there are much less catastrophic examples of liquefaction. In industry, shakers are sometimes used to sort small objects, because smaller and denser objects tend to “sink” when the mixture is jostled. And you may even have experienced liquefaction at home, as smaller chips and crumbs tend to sink to the bottom of a bag. (Photo credit: Mark Lincoln)

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Can sound help make your bread better? European researchers seem to think so. By using ultrasonic humidifiers, industrial bakers are now able to precisely control the humidity of bread during fermentation without introducing unwanted heat, as with traditional methods using steam. While the use of ultrasound may seem particularly high tech, this technology has been on the market for years in consumer humidifiers and misting fountains. For less than $100, the process could be emulated quite well by any home cook! (Photo credit: Rachel Hathaway, Article credit: Euronews.com)

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Nature continues to surprise us. Researchers have long wondered how dolphin echolocation can outperform comparable manmade systems, but may have learned one of the dolphin’s sonar secrets: they don’t look directly at their prey! When dolphins echolocate, they generate multiple ultrasonic beams at different frequencies, each with a different width. Until recently, it was believed that they would point these beams directly at their target, but new research shows they actually aim about 7º off. By doing this, they take advantage of the difference between the beam widths, placing the edge of whatever they are looking at on the border between their narrowest beam and the second narrowest. Not only is this trick extremely effective, but calculations show that it’s mathematically optimal! Just another example of nature teaching us something new. (Image and article credit Laura Kloepper, et al)

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As you’ve probably heard by now, gravitational waves have been detected for the first time by the Laser Interferometer Gravitational-Wave Observatory (LIGO). This is a momentous occasion for physics, as it experimentally confirms a result of Einstein’s Theory of Relativity that was considered almost impossible to verify. And while gravitational waves may not be sound, there’s still a strong connection to acoustics. LIGO itself has been described as a “Gravity Microphone” measuring the motion of spacetime, and the way the observatory works is not too far off from a Laser Doppler Vibrometer, using the change in travel time of a laser to measure passing waves. And LIGO’s executive director, David Reitze, said at a press conference for this announcement that “...Up until now we’ve been deaf to gravitational waves, but today we’re able to hear them.” What’s more, you can even hear an auralization of the measurement, shifted away from it’s original frequency range of 35 to 250 Hz. After listening to that recording I would say that our first measurement of gravitational waves sounds like a drop falling into a pond, appropriate for something sending ripples through science! (Image credit National Science Foundation Article. Article credit LIGO)

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What does hearing loss sound like? For those of us lucky enough to still have good hearing, we might imagine that it’s like turning down the volume knob on a radio. But in actuality, hearing loss can take many forms and is difficult to appreciate without experiencing it first hand. Luckily, an article on NPR will let you get that experience without actually harming your ears. Of the types of hearing loss described in that article, high frequency hearing loss is by far the most common. Often this manifests itself in the inability to hear certain consonant sounds, like th, f, and s sounds. As hearing loss gets worse, more consonants are lost, making it increasingly difficult to make out what others are saying. The difficulty communicating may be part of why hearing loss is linked to depression, and should serve as a reminder to always protect your hearing around noise! (Photo credit mike krzeszak. Article credit NPR)

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Can a laptop be considered a musical instrument? Absolutely, when you are part of a Laptop Orchestra! The idea is simple, build an ensemble using computers as the primary instrument, with omni-directional speakers for each performer to root their performances in space. The two most well known groups are probably the Princeton Laptop Orchestra (PLOrk) and the Stanford Laptop Orchestra (SLOrk). SLOrk’s director, Ge Wang, developed one of the key pieces of software these groups use, an open source audio programming language called Chuck. In Wang’s TED Talk, he shows how Chuck is used to create the unique electronic instruments that make up this new age orchestra. Be sure to check out SLOrk’s performance of a song called Twilight, using the instruments shown in Wang’s talk! (Photo credit Princeton Laptop Orchestra)

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If you enjoy my posts about acoustics here on ListenToThisNoise, you’ll love my article series over at AcousticsToday.org. “The World Through Sound” covers fundamental acoustic concepts, and shows how learning about sound can teach us about the world at large. My most recent article on Resonance talks about how sound and vibrations can shake some things apart, but why you don’t have to worry about everything getting destroyed by a carefully chosen frequency. If you’re at all interested in sound, and even if you don’t consider yourself a scientist, please check the series out! (Photo credit Acoustics Today)

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This shouldn’t come as a surprise to anyone, but songbirds prefer quiet environments. A recent experiment carried out in Idaho has shown this preference, by placing speakers playing noise in open areas. By monitoring the bird populations it was found that birds not only avoid these noisy areas, but the ones that stay near the noise are decidedly worse off. Two major reasons lead to this. First, birds near noise are significantly more stressed because the higher noise levels force them to be more vigilant for dangers that they must see instead of hear. Second, songbirds are songbirds for a reason, and high noise levels interfere with their calls. This is consistent with other research that has shown that the “dawn chorus” of singing birds has not only gotten louder and changed pitch, but has also started earlier to avoid interference with manmade noise. Of course, birds near cities and roads aren’t the only animals at risk. Nearly every animal relies on sound in some way, and even noise in the ocean is a major concern for the animals there. (Photo credit dmtaucher)

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Owls are amazing silent fliers and are giving the aerospace industry a master course in aeroacoustics. Owls rely on stealth to catch their prey, and evolution has specially equipped them to fly more quietly than hawks of falcons. Three special features help to make owls so quiet. First, a comb-like fringe on the leading edge of their feathers breaks up the still air as it reaches their wing. Next, a downy covering helps to reduce noise and break up air flow. Finally, the trailing edge of the flight feathers has a rough fringe, which reduces turbulence off the back of the wing. Since turbulence is the main cause of aeroacoustic noise, the result is near silent flight! This adaptation is unique to owls, as this PBS Deep Look video shows. Of course, engineers are always happy to learn from nature, and soon these tricks could find their way into fans, wind turbines, and airplanes. (Photo credits Ian-S and Kersti)

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Sometimes the sounds we don’t notice are the most influential. Without even realizing it, consumers choices are influenced by the sounds they hear, and that means there’s money in making even the most mundane sounds perfect. Car door sounds are notorious for this. It’s a little known fact that the sound that a closing car door makes influences a buyer’s opinion of the car. Deeper, heavier sounds suggest a well-made vehicle, while high-pitched rattling suggests a lemon. Of course, while these subjective assessments may have some grounding in fact, car designers have taken this  to heart, and can now make even the most flimsy car seem sturdy and reliable through the magic of sound. Of course, cars aren’t the only industry that use sound to their advantage. A recent study has shown that soda can manufacturers can improve the acoustics of the pop top, which might translate to better sales. Just another example of how sound shows up in the most unexpected places.

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Sometimes, a single room isn’t quiet enough, and you need to go deeper. “Room within a room” construction is the gold-standard for soundproofing, and is regularly used by those who are serious about reducing noise. Not only do these rooms need heavy walls and insulated glass to block noise in the air, they also need to be isolated from any noise that might be moving through the walls or the ground. This noise (sometimes called structure-borne sound) carries extremely well, and bypasses any absorbing insulation that might be present in the walls. To avoid this, sound isolation booths, anechoic chambers, and other room-within-a-room constructions use “floating floors,” floors suspended entirely on springs or rubber. When done correctly, sound has no easy path in or out, greatly reducing both the noise within the booth and the sounds that escape it. (Photo credit MetalWorks Studios)

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Acoustics may open the door for 3-D printing of living tissue. Researchers at MIT, Carnegie Mellon, and Penn State have developed a new design for acoustic tweezers that use sound to manipulate individual cells in three dimensions, without harming their viability. The method uses a form of acoustic levitation, where objects are held in place using the pressure nodes of standing waves. Using a finely controlled algorithm and a two dimensional acoustic plate, this device can not only suspend the cells in the air, but slowly move and reposition them. While acoustic levitation itself is nothing new, the scale and precision of this device is what sets it apart. Manipulating individual cells allows for the construction of complex tissues and structures, the first step in printing organs for implant. (Photo and article credit MIT)

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Can you imagine life on dial-up? That’s the reality for wireless networks in the ocean. Electromagnetic waves, like the ones used for radio communications, don’t travel very well in the ocean. That’s why sound has become the preferred mode of underwater communication for humans and animals alike. Or course, the ocean is a difficult environment, and the “underwater internet” has a lot of limitations. There’s doppler shift (changes in frequency caused by motion), multipath (signals bouncing off the ocean surface and seafloor), path loss, and an ever increasing background of noise, not to mention that sound just travels slower than radio waves. All of this adds up to a problem that engineers are always working hard to solve. One notable group working on this problem can be found at the University at Buffalo. They’ve deployed underwater modems using TCP/IP, the protocol that’s the backbone of the internet, and have recently adapted smart radio, a method used for adaptively changing frequency bands, to help improve data transmission rates for underwater communication. And just like how broadband communication has revolutionized technology on land, these steps could help realize a new future in underwater exploration and technology. (Photo credit University at Buffalo)