Choir singers help researchers design quieter airplanes

As the beautiful harmonies of the Century Singers echo through the hallway, dozens of microphones pick up the sound of their voices—while software tracks each note. This may not sound like a typical aerospace engineering experiment, but the results may improve commercial and military airplanes.

Led by Dr. Darren Hartl, an associate professor of aerospace engineering, and aerospace engineering Ph.D. student Kevin Lieb, the multidisciplinary experiment aims to further develop a unique instrument—built by Lieb, senior design students, and other graduate students—that can detect where a sound is coming from, allowing researchers to “see sound.”

Previous tests of the acoustic imaging instrument used an airplane wing in a wind tunnel to track single sounds and noises.

“The sounds from the previous tests could be boring, so we decided to test the instrument in a more right-brained way,” said Hartl.

Hartl and Lieb decided to call upon a small subset of The Century Singers, a 100-member concert choir of men and women and the second-oldest choral ensemble at Texas A&M University. The students sang in front of the instrument, allowing their voices to be ‘seen.’

“This experiment allowed us to explore more of the instrument’s capabilities, as opposed to answering a specific research question,” said Hartl.

The experiment compared the student-built instrument with an off-the-shelf acoustic imaging system. While the off-the-shelf model provides near-instant results, the student-built model uses more microphones to more accurately detect where sounds are coming from.

When put into practice, this acoustic imaging instrument will aim to make airplanes quieter. To control the noise coming from a plane, it is important to know where sounds are coming from, be it the moving parts of wings or landing gear bays.

“With techniques like this, we’re able to look at the plane and not just ask ‘is it loud?’, but ‘why is it loud?'” said Lieb. “We can address where a sound is coming from, and what we can do about it, which makes this a really cool diagnostic technique.”

Quieter airplanes are important for a variety of reasons, from passenger comfort to improved focus for pilots, and even in the aid of military operations. Additionally, as congestion creeps into many cities, more homes are built near airports, making it pressing to keep aircraft noise in check.

“If you’ve ever flown, you may notice that you take off and then all of a sudden it feels like the thrust falls off once you’re in the air. That’s a noise control regulation. Pilots have to cut back, so the planes don’t expose neighborhoods too loud of sound,” Lieb said. “Anything we can do to reduce aircraft noise is good.”

Hartl and Lieb have worked together since Lieb’s freshman year at Texas A&M.

“When I sent out an advertisement to the photography club for a student to take photographs of experiments, who would answer the call but a 4.0 aerospace engineering student, another cool right-brain connection,” said Hartl.

“Kevin is incredibly talented, and I’m very fortunate to get to work with him. He is a leading researcher in this country, and he’s setting himself up to be a national resource when he graduates.”

The experiment also provided a unique perspective to Hari Vasudevan, a freshman engineering student and singer. The experiment allowed him to think about the interplay between right- and left-brain thinking by combining singing with science.

“The experiment gives an insight into sound that we don’t usually think about,” said Vasudevan. “When we sing, we mostly listen to each other to make corrections. Looking at the science of sound using these sensors gives us additional insight about our voices and ways we can improve.”