Woodbury, New York, May 14, 1997
What improvements should concert-hall designers introduce to make bass instruments easier to hear during musical performances? How do adults and children differ in the way they produce tongue twisters? Why can certain industrial chemicals cause hearing damage to workers?
These and other questions will be addressed at the 133rd Meeting of the Acoustical Society of America (ASA), to be held June 16-20, 1997 at the Penn State Conference Center in State College, PA. At the meeting over 800 papers will be delivered. With nearly 7000 members, the ASA is the largest scientific organization in the United States devoted to acoustics. Pennsylvania State University, the site of the meeting, is one of the world's major centers of acoustic research, with a large graduate program devoted exclusively to acoustics.
Elephant Talk Why Some Students Can't Hear in Class Tongue Twisters Ototoxins in the Workplace Frozen Wings Vibrational Hazards of Power Tools Turn Up the Bass Quantum Acoustics of Helium Superfluids Hot Topics in Acoustics Time-Reversal Mirrors Go Undersea Directional Tone Color Sonoluminescence Pops
African and Asian elephants make powerful "infrasonic calls," low-pitched sounds that are below 20 Hertz, the lowest frequency that is typically audible to humans. Since elephants make few visible gestures during these calls, researchers only began to realize about a decade ago that they serve as the primary form of vocal communication between these large mammals. Katharine Payne of Cornell University will describe how infrasonic calls serve to coordinate movements between elephants separated by miles. (Paper 4pAB1)
Many classrooms suffer from large amounts of reverberation and background noise, making it difficult for even the most attentive students to perceive speech. At session 2pAAa, speakers from the U.S. and Canada will address these problems and offer possible solutions. Carl Crandall of the University of Florida and his colleagues will describe studies suggesting that children do not gain an adult's ability to discern speech in noisy or echo-filled rooms until they are about 15 years of age. (2pAAa4) Tao Jiang of the Nova Scotia Hearing and Speech Clinic will describe a case study linking the high noise levels in a school gymnasium to hearing loss in a physical education teacher. (2pAAa7) And in the United States, there are currently no mandatory government standards for classroom acoustics. David Lubman, a California-based acoustical consultant, argues that a popular commercial guideline for designing classrooms known as NC-40 is "suboptimum for serious learning situations, even for general populations of children and adults." (2pAAa1)
In efforts to understand how children differ from adults in the way in which they organize and plan their speech, Patricia Schwartz and colleagues at St. John's University are studying the production of tongue twisters in adults and children. In general, studies have shown that children 10 years of age and older are closer to adults in how they produce their tongue twisters than younger children. In this study, the researchers describe how a group of 8-year old children vocalizes their tongue twisters and compare their data to those reported for adults. (3aED5)
For industrial workers, exposure to noise is the prevalent cause of hearing loss, but it is not the only cause. Those exposed to ototoxins, substances that can cause damage to the human hearing system, face additional risks. Examples of ototoxins include organic solvents such as trichloroethylene and styrene and metals such as mercury and lead. When these substances enter the bloodstream, they can either attack the auditory nervous system or cause physical damage to the hair cells in the inner ear. Thais C. Morata of the NationalInstitute for Occupational Safety and Health will present results from three studies aiming to determine the effects of ototoxins on hearing, either alone or in combination with noise. (3aNSa1) Donald Henderson of SUNY-Buffalo and colleagues will present evidence from animal studies suggesting that an increased presence of antioxidant enzymes may help protect the ear from harmful effects of noise. (3aNSa4)
Detecting ice formation on the wings of aircraft is absolutely crucial to ensuring safe flights during sub-freezing weather conditions. Xiao-Qi Bao of Penn State will present experimental results on an ice-formation sensor system which uses a novel design and materials. Each sensor in the system uses a pair of lead zirconate titanate rods attached to an aluminum plate. Stresses on these rods caused by ice formation are converted to electric current which can then be detected electronically. The researchers believe that this design can be used as the basis of a reliable, inexpensive sensor system for detecting ice formation before and during flight. (1pEA15)
Workers who operate low-vibration power tools are at risk of developing long-term loss of motor function in their hands and arms. Studying a group of 18 chain-saw operators, Anthony J. Brammer of the National Research Council of Canada and his colleagues have detected progressive deterioration in tactile acuity (how keenly they could experience tactile sensation) in 12 of the 36 hands of the workers. The researchers predict that many others will develop tactile problems should they continue to work in the same fashion for an additional 5 years. The workers predicted to be most severely affected already exhibit reduced hand grip, and reduced hand and arm strength. Brammer will discuss this study at his ASA talk. (5aBV3)
High-pitched instruments such as violins are relatively easy to hear at concerts but low-pitched instruments like the bass are often more difficult to pick out. Conventional wisdom states that the reverberation times of low-frequency sounds play a big role in determining how well bass is perceived. But new studies by John Bradley of the National Research Council in Canada and colleagues suggest that this factor is unimportant. Instead, the researchers' experiments show that the sound levels of early- and late-arriving low-frequency sounds played the most significant role in determining how well experimental subjects perceived the bass. These findings may hold importance for future designs of music halls. (4aAA6)
Physicists at the University of California in Berkeley recently announced that they had built a device for measuring the Earth's rotation using superfluids, ultracold liquids that have zero resistance to flow. Similar to superconductors, which exhibit zero resistance to electrical current, superfluids are governed by the peculiar laws of quantum mechanics. Now, the Berkeley research group has opened possibilities for using superfluids to define an international pressure standard based on the highly precisely known constants of quantum mechanics. In their experimental setup, the researchers put a helium-4 superfluid in a vessel and insert a square barrier containing a tiny hole. By creating a pressure difference between the two sides of the barrier, they cause the fluid to move back and forth across the hole at a frequency determined by quantum theory. When the helium crosses the hole, it creates sound waves which can be detected and could therefore serve as a way for relating pressure to quantum-mechanical constants. (1aPA1)
Session 3pID will cover the latest advances in several areas of acoustics. Richard Campbell of Worcester Polytechnic Institute will discuss the emerging field of "auralization," which makes it possible to hear realistic simulations of the acoustical environment in a "virtual auditorium." Michael Buckingham of the Scripps Institute will discuss the latest advances in acoustical oceanography, including explorations into using time-reversal acoustical mirrors (discussed below) in the ocean environment. J. Brian Fowlkes of the University of Michigan will describe advances in "ultrasound contrast agents," which are designed to improve the images in ultrasound examinations. Such contrast agents, which include small, stable gas bubbles that are injected into the bloodstream, may have therapeutic applications as well.
One of the neatest new inventions in physics is the acoustic time-reversal mirror (TRM), which takes an incoming sound wave and reflects a reversed version of the wave right back to the source. These devices have many potentially useful applications, including pinpointing mechanical defects in airplanes. William Kuperman of the Scripps Institute of Oceanography and colleagues will describe an experimental demonstration of a TRM in the ocean (2pUW3), which can potentially be used to detect objects buried in the seabed (2pUW14). Mathias Fink, one of the pioneers of TRM, will give an overview of time-reversed ultrasound, which has potential medical applications such as breaking up kidney stones. (2pUW2)
Violins and other instruments possess a special property known as "directional tone color." For a person listeningto violins in a concert, this means that every note, or component of each note, seems to come from a different direction. This produces the effect of filling the concert hall more completely with sound. Gabriel Weinreich,a University of Michigan scientist and a pioneer in violin acoustics, has now developed a new loudspeaker design which takes this effect into account. (2pEA4)
Scientists continue their efforts to understand the mysterious process known as sonoluminescence, in which sound waves aimed at a water tank collapse air bubbles to create ultrashort light flashes representing a trillionfold focusing of the initial sound energy. Tom Matula of the University of Washington and colleagues will present the latest measurements of the acoustical "pop" accompanying each sonoluminescence flash. The scientists are scrutinizing this data in order to test the various hypotheses for the still-unresolved mechanism that causes sonoluminescence. (2aPA9) William Moss of Livermore and coworkers will discuss models supporting the idea that a sonoluminescing air bubble probably contains only argon and not other atmospheric gases like nitrogen. (2aPA10)
For more information during the meeting contact Elaine Moran (elaine@aip.org) at the ASA registration desk, 814-863-5000. For information before the meeting, contact Ben Stein, bstein@aip.acp.org, or 301-209-3091.
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