NORFOLK PROGRAM HIGHLIGHTS

Unusual Acoustics in the U.S. Civil War
Ancient Recording from the Mayans?
The Hazards of Air Bag Noise
Painless Sound Waves for Gum Disease Diagnosis
Designing Good Acoustics for Organs
Are Blue-Eyed People More Susceptible to Hearing Loss?
Sonic Band Gaps
Ultrasound Hearing in Insects
Sonic Booms
Thermoacoustic Dehumidifier
The Noisiest Creatures in Shallow Waters

Unusual Acoustics in the U.S. Civil War

Historical accounts of major U.S. Civil War battles sometimes describe unusual acoustical conditions. Analyzing wartime diaries, anecdotal weather records, and battlefield terrain, Chuck Ross of Longwood College in Virginia ( cross@longwood.lwc.edu, 804-395-2577) will explain how unusual acoustics apparently played a significant role in Gettysburg and many other Civil War battles. For example, in the battle of Seven Pines, near Richmond, Virginia, Confederate commander Joseph Johnston could not hear the sounds of Union soldiers even though they were two miles away, although Richmond residents 10 miles away could hear them loud and clear. As a result, Johnston failed to send in reinforcements, turning what should have been an easy Confederate victory into a draw. Ross will identify the unusual acoustics and their causes, such as sound absorption by ground surfaces, nonuniformities in temperature across battlefields, and differences in wind speed across terrain. (Paper 2aPAa1)

Ancient Recording from the Mayans?

Clap your hands inside the Mayan pyramid at Chichen Itza, located in Mexico's northern Yucatan, and you will hear intriguing pulselike echoes emanating from any of the building's limestone staircases, even those in partial ruins. Archaeologists have typically dismissed these "chirped" echoes as an unintended design defect. Performing an analysis of the acoustical physics responsible for this effect, acoustical consultant David Lubman ( dlubman@ix.netcom.com) attributes these echoes to a "picket fence effect" resulting from the reflections of sound from the stairs. As Lubman points out, the chirped echoes seem to resemble the primary call of the Mayan sacred bird, the resplendent quetzal. Lubman will present recorded sound samples which show close similarities between the echoes and the bird sounds. Lubman argues that the simple engineering required to intentionally design this feature falls well within the capabilities of the stone-age Mayan culture."If the hypothesis of intentional design is true," Lubman says, "the chirped echo may be the world's oldest known sound recording!" (2pAAa1)

The Hazards of Air Bag Noise

Although they have saved thousands of lives and prevented serious injury in countless others, airbags in automobiles have a number of serious hazards associated with them. Much media attention has centered on the fact that their high speed of inflation poses a risk to adults and children who are too close to the air bags. At the ASA meeting, researchers will discuss another serious problem associated with airbags: their powerful, short bursts of sound can potentially cause hearing damage. James Saunders of the University of Oklahoma Health Sciences Center ( James.R.Saunders-1@ou.edu) and his colleagues will discuss reports of hearing loss, tinnitus (ringing in the ears), and other problems in six of their patients (2pNS3). Kathleen Yaremchuk of the Henry Ford Hospital in Detroit will discuss a survey reporting hearing problems in 29 patients after airbag deployment (2pNS4). G. Richard Price of the US Army Research Lab ( dprice@ARL.MIL) will describe an epidemiological study, just underway, that aims to track hearing abilities of Department of Defense workers before and after airbag noise exposure (2pNS2).

Painless Sound Waves for Gum Disease Diagnosis

Approximately three-quarters of all adults above 35 have some form of gum disease, a tissue infection which in some cases can lead to tooth loss. Typically, the process of diagnosing gum disease involves x-rays and painful probing of the gums. In what the researchers call "the first noninvasive measure of peridontal disease activity," Mark Hinders and his colleagues at the College of William and Mary in Virginia ( mkhind@facstaff.wm.edu) have developed an ultrasound probe for monitoring gum disease without the need for x-rays or manual probing of the gums. Although the technique has thus far been tested on nonliving objects, the researchers plan to develop the system for clinical use. (4pBB7)

Designing Good Acoustics for Organs

"Organs, perhaps more than any other instrument, rely on their surroundings for their ultimate success or failure," points out David C. Pike ( cfisk@cove.com), one of 18 acousticians, pipe-organ builders and scientists from around the world who will share their experiences at a day-long ASA symposium on the acoustics of organ performance spaces (Sessions 4aAA and 4pAA). Dan Clayton ( DanClayton@compuserve.com") will trace the history of organs from their appearance in Greece several centuries before Christ, to their exclusive ownership by the Church throughout the Middle Ages, to their outbreak in royal salons and concert halls in the 18th and 19th century, and the advent of highly specialized "organ rooms" in the 20th century (4aAA1). Fritz Noack ( noackorgan@aol.com) will present an acoustical study of the pipe organ isolated from its architectural surroundings (4aAA8), and Mendel Kleiner of Chalmers Institute of Technology ( mk@ta.chalmers.se) will describe Sweden's Goteborg Organ Art Center, an international research center for organ history, building, teaching, and practice (4pAA1).

Are Blue-Eyed People More Susceptible to Hearing Loss?

Intriguing research suggests that eye color may partially dictate a person's susceptibility to both temporary and permanent hearing problems. Pigmentation in the eye is related to the concentration of melanin in the inner ear, and recently researchers have proposed some physiological explanations for how the presence of melanin could affect resistance to hearing damage. Julia Royster of Environmental Noise Consultants Inc. ( EFFECTIVE_HCPS@compuserve.com") and Larry Royster of North Carolina State University will review the studies done on this subject, and describe new data from a study of employees at a large industrial site (2aNSb1). At session 2aNSb, other speakers will describe how people's risk of hearing loss may be affected by such factors as ear canal shape, eardrum stiffness, and musculature in the middle ear.

Sonic Band Gaps

Water waves have the ability to overlap with one another and produce beautiful rippling patterns. Under the right conditions they can even cancel each other out, in a wave phenomenon known as "destructive interference." Light behaves the same way, and researchers in the 1990s devised "photonic crystals," materials with geometrical arrangements that exploit destructive interference and create "optical band gaps" that block light waves over a certain range of frequencies. (In turn, these are analogous to the electronic band gaps which help give semiconductors their useful properties by forbidding electrons with a certain range of energies from existing in the material.) Taking inspiration from photonic crystals, and a beautiful sculpture in outdoor Madrid, Francisco Meseguer of the Institute of Material Science in Madrid ( fmese@fis.upv.es) and his colleagues have devised materials with "sonic band gaps" that block certain ranges of sound frequencies from passing through. Made of metal bars arranged in specially designed geometrical patterns, such materials may lead to a fundamental new approach to soundproofing. (1pPA3, 1pPA4)

Ultrasound Hearing in Insects

Although bats are blind, evolution has given them a highly sophisticated, ultrasound-based sonar system that helps them to navigate their surroundings and find prey, such as insects. True to form, evolution has armed insects with a countermeasure: a keen ability to hear ultrasound, which helps them to evade insect-eating bats. Hamilton Farris of Cornell ( hef1@cornell.edu) will describe how researchers can use ultrasound to learn more about the evasive behaviors and hearing capabilities of certain insects, such as crickets and beetles. (3aED1)

Sonic Booms

When an aircraft moves faster than the speed of sound (about 750 miles/hr in the sky), it pushes aside air at such a high rate that an enormous amount of pressure accrues around it, culminating in a powerful shock wave that generates a loud popping noise known as a "sonic boom" that can be heard tens of miles away. People find sonic booms so disruptive--even if they occur only occasionally--that overland flights of commercial supersonic jets are unlikely anytime soon. Still, researchers are exploring whether supersonic jets flying primarily over the ocean have adverse environmental effects. Acoustician Robert Young will describe studies of 13 sonic booms of space shuttles approaching Edwards Air Force Base, from 1988-1993 (4pPA1). Victor Sparrow of Penn State University ( sparrow@helmholtz.psu.edu) will review research on the penetration of sonic boom noise into the ocean (4aPA9). In an encouraging finding, Elizabeth Perry of the National Zoo in Washington, DC and her colleagues have concluded that overhead Concorde flights did not affect the mating habits of seals in Sable Island, Canada (5aPA4).

Thermoacoustic Dehumidifier

In recent years, scientists have built "thermoacoustic refrigerators," devices that chill objects by using sound waves in place of chemical refrigerants and mechanical compressors with seals and bearings that generally fail over time. In this scheme, researchers broadcast sound waves through an inert gas; regions of expansion and compression in the gas produce hotter and colder regions, the latter of which can be used to remove heat from objects. Now, Robert A. Hiller of Los Alamos ( hiller@lanl.gov) will discuss an extension of the concept to "thermoacoustic dehumidification" in which sound waves in a flowing humid air stream cool the stream to its dew point and remove its water. Hiller will discuss an experimental prototype of this device, and its potential applications. (2pPA10)

The Noisiest Creatures in Shallow Waters

In the past few years, acoustical scientists have been working to make sure that man-made noise from underwater acoustics experiments does not disrupt creatures in the underwater environment. Well, the reverse situation is a concern for them too. In shallow waters, snapping shrimp are among the noisiest creatures, creating loud sounds over a wide range of frequencies which can disrupt underwater acoustics experiments. As Whitlow Au of the Hawaii Institute of Marine Biology ( au@lono.nosc.mil) explains, collections of shrimp can produce sounds as high as 189 decibels in the water, and over a wide frequency range. What's worse, the shrimp are always present despite changes in seasons or the times of day. Dolphins also make lots of noise, in the form of whistles, burst pulses, and ultrasound clicks, but luckily they often leave an area after a short amount of time. On the other hand, "snapping shrimps are forever," Au states. (4aAB1)