Recently in Acoustics Category

Science: A mere 475 right whales summer in the western North Atlantic Ocean, and they have much lower reproduction rates than right whales that summer near Antarctica. One reason for that may be noise-induced stress. Rosalind Rolland of the New England Aquarium in Boston and colleagues report in the Proceedings of the Royal Society B that reduced ship traffic in the Bay of Fundy in the aftermath of the September 11, 2001, terrorist attacks resulted in a 6-decibel decrease in underwater noise, specifically low-frequency noise. Baleen whales, including right whales, use low-frequency sounds to communicate, and prior studies have shown that they change their behavior and vocalizations when noise increases. Rolland found that the Bay of Fundy's period of quiet was associated with a significant reduction in stress-related fecal hormone metabolites excreted by the whales.

Science: Katydids, crickets, and other arthropods produce their characteristic chirps by stridulation, a process in which they scrape one rough body part against another, writes Sid Perkins for Science. Until now, it was not known whether ancient insects chirped at a single frequency or across a variety of frequencies. A recent analysis of 165-million-year-old katydid wing fragments shows that katydids sang at a single frequency of about 6.4 kilohertz, or about 6400 cycles per second. That tone is about half the frequency created by today's katydids but within the range of tones generated by living species of crickets. The chirps, which lasted about 16 milliseconds, probably helped the katydids distinguish the calls of their species in a forest filled with the sounds other insects.

Daily Mail: Neuroscientists at the University of California, Berkeley, have been developing a computer program that can decode brain activity and put it into words, writes Tamara Cohen for the Daily Mail. To monitor information from the temporal lobe, where sounds are processed, the scientists inserted electrodes into the brains of 15 patients whose skulls had been cut open for an epilepsy treatment. As the patients listened to a person speaking, the computer analyzed how the brain processed the words they heard. It was able to translate the spoken words into patterns of electrical activity and then translate them back into the original sounds, or something very similar. Brian Pasley, coauthor of a paper published in PLoS Biology, said that with more work, brain recordings could allow scientists to "synthesize the actual sound a person is thinking." Such technology could benefit people whose speech has been affected by stroke or degenerative disease.

Science: The terrorizing wail of the Stuka dive bomber came from wing-mounted sirens called Jericho Trumpets. The male Anna's hummingbird (Calypte anna) also makes a characteristic noise when it dives, but the squeaky sound is meant to woo, not frighten, females. Three years ago Christopher Clark discovered that the hummingbird's diving sound originates in its tail feathers. Now, as Science's Daniel Strain reports, Clark has identified the underlying mechanism. By putting tail feathers in a wind tunnel, Clark, who is now at Yale University, and his colleagues found that the feathers begin to flutter with sound-generating rhythm when the wind speed matches the bird's diving speed of 7–20 m/s. Clark's paper describing his research also appears in Science.

BBC: Researchers have developed a mathematical model to describe the acoustics and fluid dynamics of water in ceremonial Tibetan singing bowls. According to John Bush of MIT and Denis Terwagne of Belgium’s University of Liege, who yesterday published a paper in the journal Nonlinearity, “rubbing a fluid-filled bowl excites wall vibrations, and concomitant waves at the fluid surface” much like what occurs when a wine glass is rubbed by a moist finger. However, the waves in Tibetan singing bowls—called edge-induced Faraday waves—exhibited behavior that is “odd by any standards, even to specialists in fluid dynamics,” said Bush. At a certain point the waves become chaotic, causing water droplets to break free and bounce on the water’s surface. Bush and Terwagne found that the relatively low vibration frequency of the bowls makes them a more efficient generator of edge-induced Faraday waves and droplet generation via surface fracture. Their research could shed light on other fluid processes, such as fuel injection.

Wired: Birds, amphibians, and mammals often use hard-to-discern sounds to add an extra layer of vocal information, but until now such sounds had not been detected in fish, writes Dave Mosher for Wired. In a new study published in Proceedings of the Royal Society B, Aaron Rice, a biologist at Cornell University, and coworkers analyzed the vocalizations of the three-spined toadfish. Swim bladders, air-filled sacs that allow the toadfish to alter its buoyancy, also serve as sonic instruments when the fish vibrates the muscles in the sacs. The researchers found that the sound produced contains surprisingly complex information, including subtle harmonics and dissonances.

Science: Research has indicated that sonar and other anthropogenic sounds can damage a wide spectrum of ocean fauna, but the effect of such sound on cephalopods was unknown. Now Michel André of the Technical University of Catalonia in Spain and colleagues have been studying the effect of high-decibel, low-frequency sound on wild cephalopods held in laboratory aquariums, and discovered that all of the animals exposed to the noise suffered severe damage to their statocysts (sound-detecting structures behind the cephalopod eye). Damage ranged from crumpled or displaced sensory cells to large lesions. More damage appeared to develop as post-exposure times increased. Peter Madsen at Aarhus University in Denmark expresses some skepticism about the results, partly because the control animals used by the researchers were not housed in an aquarium as the experimental animals were, which leaves open the possibility that captivity caused or contributed to the sensory damage in the latter group. T. Aran Mooney at Woods Hole Oceanographic Institution in Massachusetts questions how André and his team measured the animals' exposure to noise, but also says their research is "a good first step" in determining whether anthropogenic noise harms cephalopods.

New Scientist: A company based in Australia has been working on a cochlear implant for the hearing impaired. Unlike a traditional hearing aid, which acoustically amplifies sound, the bionic device translates sound into electrical signals that are used to electrically stimulate the cochlea—a spiral-shaped part of the inner ear attached to the auditory nerve, writes Duncan Graham-Rowe for New Scientist. Because of its small size, the new device can be fully implanted in a patient's ear—unlike current devices, which require an external unit containing the power supply, processors, and microphone. The fully implantable system, would, however, require replacement every 10 years when its batteries run out.

Nature: An "acoustic rectifier" has been developed by a group of researchers at Nanjing University in China, who published their results yesterday in Nature Materials. According to Nature's Daniel Cressey, the device allows sound to travel in only one direction, in the same way that electronic diodes allow current to move in only one direction. When sound waves hit a layer of ultrasound gel, it converts some of the energy of the acoustic wave into a wave of double the frequency, and then a lattice of alternating layers of water and glass screens out all frequencies except the second, higher frequency. The device could be useful for medical ultrasound applications.

New Scientist: The meter-long plastic trumpet known as the vuvuzela has famously—or infamously, depending on your point of view—become the instrument of choice of 2010 World Cup fans. It was introduced a year ago at a previous soccer tournament held in South Africa, the Confederations Cup. Since then, the vuvuzela has spread among fans like a virus. When hundreds of vuvuzelas are blown simultaneously by football fans, the racket can be deafening. Trevor Cox, president of the UK Institute of Acoustics, explains the science behind the noise.

Wired UK: This wreck image attached is not computer generated. It's the sonar image of Russian nuclear submarine B-159 (called K-159 before decommissioning), which has been lying 248 meters down in the Barents Sea, between Norway and Russia, since 2003. The Russian Federation hired Adus, a Scottish company that specializes in high-resolution sonar surveying, to evaluate if it would be possible to recover the wreck.

NPR: In Antarctica, you'll find 90 percent of the world's glacial ice, but new research from the US Geological Survey shows that every ice front in the southern part of the Antarctic Peninsula is retreating.

Jane Ferrigno US Geological Survey is the lead author of that new report. She tells NPR that scientists have known for a while that some of the peninsula's ice shelves are breaking up.

Sciencebase: Back in the 1970s LP's were the common medium of choice for Hi-fi enthusiasts. When the compact disc emerged on to the market with its claims of superior quality and scratch resistance, the hi-fi enthusiasts split into two camps: those who clung to vinyl and those who went digital.

But, was concentrating on audio quality all for nothing? Within another generation the notion of digital audio had changed with compressed formats such as MP3's becoming popular.

Jerald Hughes of University of Texas Pan American in Edinburg writing in the International Journal Services and Standards has a nice table showing the technical specification of the human ear and comparing it to the various analogue formats. It turns out that if you want the best quality, LP's are not the way to go, an older format reel-to-reel better matches to the audio range of the human ear.

Related Link
Int. J. Services and Standards, 5 (4), 333-353

NYTimes.com: Specialists say such safeguards, such as ear muffs at loud stadiums, are critical for young ears in a deafening world. Hearing loss from exposure to loud noises is cumulative and irreversible; if such exposure starts in infancy, children can live “half their lives with hearing loss,” said Brian Fligor, director of diagnostic audiology at Children’s Hospital Boston.

The Economist: Thanks to advances in manufacturing techniques, which allow miniature mechanical components to be built into electronic chips, it is now possible to add better noise-canceling features to phones, and also to other products, such as the small “earbuds” used to listen to music players.

Wired.com: The long-distance scientific recordings of the blast wave from the first hydrogen bomb test have been rediscovered in a formerly classified safe at Columbia University.

On 1 November 1952, the US created a 10-megaton blast that set off a low-frequency sound wave, which was recorded halfway around the world at special listening stations designed by the Lamont Geological Observatory in Palisades, New York.

It was the first time a nuclear explosion had been detected from such a long distance and it marked the beginning of international test monitoring, a key element of nuclear nonproliferation plans.

Related Link
Build your own microbarograph

NPR: One of the more dramatic changes we've heard in music over the last 10 years is that it seems to have gotten louder.

The reason is compression, the dynamic compression that's used a lot in popular music. The idea is to make a song jump out of your iPod compared with the song that preceded it.

However, the technique can make listening to music fatiguing as well as distort the sound of the instruments.

This issue came to a head last year with the release of Metallica's album Death Magnetic.

That record is so loud that the International Telecommunication Union has set standardization measurements for long-term loudness, says Bob Ludwig, a record mastering engineer. "And that Metallica record is one of the loudest records ever produced."

Nature: An array of air bubbles in a rubber-like material can be made to block the transmission of sound. This finding might help in the design of soundproof walls for music rooms and urban apartments.

NYTimes.com: The ceremonial pipe organ of the 18th century was a masterpiece of human ingenuity, so elegant in its outward appearance that a casual observer could only guess at the complexity that lay within.

The builders were precision craftsmen celebrated for their skill in hand-making thousands of moving parts and in shaping and tuning metal and wooden pipes to mimic the sounds of each instrument in an orchestra.

The effect was breathtaking. "Each instrument speaks to you in a different way," said Hans Davidsson, a concert organist, sitting before the console of the organ at the cavernous Christ Church, Episcopal, in Rochester.

The organ, the Craighead-Saunders, is a unique instrument, not only because of its lovely sound, but also because it is a nearly exact copy of a late Baroque organ built by Adam Gottlob Casparini of East Prussia in 1776. The original stands in the Holy Ghost Church in Vilnius, Lithuania.

The Daily Telegraph: UK academics are calling on members of the public to use their mobile phones to record their local soundscape and send them the results.
 
It is hoped that the clips will then make up a detailed acoustic map of the noise environment around the country and help offset the growing menace of noise pollution.

The project—which will make the raw acoustic data available on the web—aims to get a better idea of why some sounds add to the atmosphere of a place and others detract and cause annoyance.

The Guardian: An orchestra of ancient instruments, many of which exist only in paintings and yellowing manuscripts, will perform its first concert at the end of the year.

Many of the instruments have not been heard since the times of Socrates in the fifth century BC, though some of the instruments date back even further, to the bronze age a thousand years earlier.

Scientists are reconstructing the sounds of the instruments, including the earliest predecessors of the bass guitar, harp, and oboe, by building mathematical models of them on computers and using descriptions in ancient texts and paintings on artifacts recovered from archaeological sites in Greece.