Acoustical Society of America
Gold Medal Award - 1993

David T. Blackstock

DAVID THEOBALD BLACKSTOCK was born in Austin, Texas, on 13 February 1930. The site of his home during high school is now occupied by the Mechanical Engineering Department building at the University of Texas at Austin, where David currently holds the position of Professor. He received B.S. and M.A. degrees in Physics from the University of Texas, after which he served as an Air Force officer at Wright Field in Ohio under the supervision of Henning von Gierke. While in Ohio, David met and married Marjorie Goodson. He later joined Ted Hunt's acoustics group at Harvard University, where he developed his interest in nonlinear acoustics. He received the Ph.D. in 1960 with a dissertation written under the supervision of William Raney (and typed by Marjorie, who said "never again"). David and Marjorie's first two children, Silas and Susan, were born in Boston, and their second two, Stephen and Peter, were born in Rochester, New York, where the family moved after David's graduation from Harvard.

David began his truly independent research in acoustics at General Dynamics/Electronics in Rochester, and after three years he joined the Electrical Engineering Department at the University of Rochester, where he was able to indulge his academic interests. A leave of absence spent at the University of Texas in 196970 led to a return home to Austin, with a subsequent appointment as Faculty Research Scientist at the Applied Research Laboratories. After many years teaching part time in the Mechanical Engineering Department, he became Professor in 1987. For the last five summers, David has returned to the cooler environs of the University of Rochester, where he works with Ed Carstensen and other colleagues at the Center for Biomedical Ultrasound.

The two individuals who are most often cited for their work in the 1960s on the fundamental theory of nonlinear acoustics are D. T. Blackstock in the United States and the late R. V. Khokhlov in the (former) Soviet Union. Working independently, Blackstock and Khokhlov established the foundation for modern approaches to the theory of nonlinear acoustics. David's main contribution during this period was the development of a consistent framework for existing models of finite amplitude sound. His framework incorporated the pioneering work by the 19th century physicists Poisson, Stokes, and Earnshaw, the Burgers equation for acoustics developed by Mendousse, Lighthill, and Khokhlov, and the weak shock theory constructed by Friedrichs, Landau, and Whitham. David investigated the connection between these earlier theories and showed how their solutions could be combined. He referred to his framework was a "low-amplitude nonlinear theory of simple waves," and his articles on the subject are frequently the first to be cited by subsequent authors writing about fundamental problems in nonlinear acoustics. Perhaps the defining achievement of David's approach was his proof that two well-known (and seemingly unrelated) solutions that were derived in the 1930s, one by Fubini for finite amplitude waves in the preshock region and another by Fay for sawtooth shock waves, are limiting cases of a single, more general solution for the propagation of finite amplitude sound.

At the University of Texas, David's theoretical models were tested by experiments performed by his students. The data they obtained on acoustic saturation, high-intensity sound beams, finite amplitude noise, N waves, and suppression of sound by sound now are regarded as reference data with which newly developed theories should be compared. To complement these experiments, computer codes were developed for modeling finite amplitude sound (the Pestorius and Anderson algorithms), and these have since been used in other laboratories around the world. Colleagues who influenced the experimental work in David's laboratory include Tom Muir, Allan Pierce, Izzy Rudnick, and Wayne Wright.

David's papers are known for their phenomenological insight and historical perspective. The terminology he introduced has frequently become standard in the field of nonlinear acoustics. Perhaps the most famous symbol he introduced has an ironic origin, however. In his seminal 1964 paper on solutions of Burgers' equation (not "Burger's equation," which is one of David's pet peeves), he discussed the critical importance of a dimensionless ratio of parameters that had been identified in the 1950s by Russian physicist Z. A. Gol'dberg. David labeled this ratio G, but the reviewer of his paper felt that such a label gave too much recognition to Gol'dberg and requested that the symbol be changed. David obliged by using the symbol Γ. But Γ is the first letter in the name Gol'dberg when written with the Cyrillic alphabet, so the published symbol still was appreciated by the Russian acoustics community. The symbol Γ now is used internationally to characterize the relative effects of viscosity and nonlinearity in a finite amplitude wave. Other (now common) symbols introduced by David include β (for the coefficient of nonlinearity), \sigma (used to characterize the extent of nonlinear distortion), and EXDB (for extra attenuation caused by finite amplitude effects). David thus is a scientist of considerable stature (for which he was elected to the Natl. Academy of Engineering in 1992), but that is not all.

As everyone who has heard David give a technical presentation knows, he is a gifted teacher with an insatiable curiosity. It is not unusual for David to ask a probing question of every single speaker in a technical session at a Society meeting. Nor is it uncommon for him to jump to a speaker's defense, particularly when the speaker is a student presenting a paper for the first time. David is passionately concerned with students, and his graduate courses at the University of Texas constitute a rite of passage within the acoustics program. The daily homework problems he assigns are characterized by novelty and relevance. Among the sources of inspiration for his problems are papers he hears at Society meetings. The solution of one of David's more challenging early problems (on explosion waves), one he believed to be sufficiently well understood to be suitable for a homework assignment, was later published independently by another researcher. Also, David's students learn to their chagrin that their homework is corrected for grammar as well as science, and that unsolicited observations may cost them points if they are incorrect. The theses and dissertations David supervises are models of clarity as well as technical excellence (usually not at first, but they are rewritten until they become so).

One place where David's students look forward to meeting him on equal footing is on the soccer field during lunch time. Perhaps it was after David corrected one to many dangling participles in a thesis draft that he found himself with a broken rib on one occasion, and required stitches on another, as the results of soccer matches with his students. After a few minor repairs, however, David was soon back on the field.

Finally, David is a true gentleman, and he is one of the most respected individuals within both the national and the international acoustics communities. David's stature in large part is due to his integrity, ethics, and concern for others, as is understood by anyone who knows him. He has chaired five ASA standing committees, and he was held every elected position through President of the ASA. He also has been a long-time member of three major international committees: he currently is the Chairman and the only U.S. member of the International Commission on Acoustics (which oversees the International Congresses on Acoustics); he is on the Organizing Committee for the International Symposia on Nonlinear Acoustics, and he serves on the U.S. National Liaison Committee to the International Union of Pure and Applied Physics.

Both the international acoustics community and the Acoustical Society of America long have benefitted from David's interest, dedication, and ability. It therefore is fitting that he be honored with the Gold Medal of the Acoustical Society of America.

Mack A. Breazeale
Mark F. Hamilton
Wayne M. Wright