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Engineering is Music to Her Ears

In Lily Wang’s life, mathematics and music go hand in hand. An accomplished musician, she started singing and playing piano at the age of four. In junior high school, she fell in love with mathematics.

“Math always seemed very beautiful and organized to me,” she said, “and music is also very structured. When I took an advanced placement music course as a sophomore, the textbook had a page on acoustical consulting. I read that and thought, this is the perfect career for me. I could couple math and science with my music background. I decided then, at the age of 15, that I was going to be an acoustical engineer.”

A Tennessee native, Wang enrolled at Princeton University, where she studied civil engineering and architecture. She received her Ph.D. in acoustics at the Pennsylvania State University.

Now an assistant professor of architectural engineering, Wang still is passionate about acoustics. Her research focus is on architectural acoustics, building upon her postdoctoral research program at the Technical University of Denmark. There she worked with ODEON, a room modeling program, and conducted tests on the perception of spatial impression in concert halls.

“Much of what I’m looking at deals with human perception and how to quantify this in acoustics.” she said. “When you go into a concert hall, there’s this quality of spatial impression that makes you feel surrounded by the music. But what gives you that impression?”

It could be the direction from which the sound comes or the signals that arrive at the left and right ear are slightly different—or that people perceive them as being different on a subconscious level, she said.
Wang has devised tests to measure the relationship between various objective and subjective measures in different sound fields. “Subjective testing is tricky,” she said. “You can have a person listen to sound through a set of headphones and imagine himself being in a room, but it’s not the same experience as him actually being there in the room.”

With a $377,000 Faculty Early Career Development grant from the National Science Foundation, Wang is using a simulation process to measure study time-variant source directivity. She is examining the extent to which changes in the directional patterns of sound over time affect the distribution of acoustic energy in a room as well as human perception of the sound field.

“This project starts with basic physics,” she said. “A source such as a violin radiates sound energy, sometimes more in some directions than in others. So there are directional patterns to the sound field. The acoustic radiated energy then interacts with the boundaries of a room in some way on its way to the listener—the sound gets reflected or diffracted, for example.

“But most acoustic sources change frequency and directional patterns over time, and this hasn’t really been considered in previous simulation studies. So our results will add to the scientific knowledge base of architectural acoustics.”

The modeling simulation procedure, called auralization, is designed to more accurately represent the listening experience in a particular space. An auralization system tries to fool your brain into thinking that you’re listening to a sound source in a space you’re not in. It takes the original sound source and alters the frequency spectrum through a process known as convolution according to how the room affects the wave and how your head/ears affect the wave.
The two signals (one for each ear) are then convolved and played back through a set of headphones, giving the feeling that what you’re listening to is what you would hear if you were in the room with the acoustical source.
Auralization technology can be applied in a number of ways: In 3D gaming as the audio counterpart to virtual reality; to help train the hearing- or sight-impaired; or to improve the design of acoustically sensitive spaces. But the technology has its limitations.

“For example, how well can I model a particular hall to account for every piece of furniture in it? I’m trying to get at the directional approximations—to increase the realism of these simulations.”

And what she accomplishes professionally likely will be satisfying on a personal level. She always has wanted to design her own acoustically perfect performance space. “I’ve seen a great deal of progress in this field over the last ten years,” she said, “and I want to push it to the next level.”

—Deb Derrick
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