If musical instruments were people, trumpets would be super spreaders. When a trumpeter blows into the mouthpiece, tiny respiratory droplets, known as aerosols, travel out of the musician’s mouth, whiz through the brass tubing and spray into the air.
During a deadly pandemic, when a musician might unwittingly be exhaling an infectious virus, that poses a potential problem for orchestras. And the trumpet is not the only musical health hazard.
“Wind instruments are like machines to aerosolize respiratory droplets,” said Tony Saad, a chemical engineer and expert in computational fluid dynamics at the University of Utah.
A simple but radical change — rearranging the musicians — could significantly reduce the aerosol buildup on stage, Dr. Saad and his colleagues reported in a new study, which was published in Science Advances on Wednesday.
The work began last summer, when the Utah Symphony began to wonder whether, and how, they could return to performing safely.
“They were looking for people that could provide insight into mitigation strategies that people would have some faith in,” said James Sutherland, a chemical engineer at the University of Utah and a co-author of the study.
The researchers created a detailed computer model of the symphony’s concert hall, noting the location of every air vent and the rate of air flow through the HVAC system.
Then they mapped the typical position of each musician. The Utah Symphony, like most modern orchestras, positioned its musicians in a standard pattern, with the string instruments at the front of the stage, followed by several rows of woodwinds and brass instruments — the flutes and oboes, then the bassoons and clarinets, and then the trumpets and French horns. The trombones and the percussion section were positioned at the very back of the stage.
To model the spread of aerosols during a concert, they incorporated recent research led by Jiarong Hong, a mechanical engineer at the University of Minnesota. Working with the Minnesota Orchestra, Dr. Hong and his colleagues had measured the concentration and size of aerosol particles emitted by a variety of different wind instruments. (Among their findings: The trumpet, bass trombone and oboe posed the highest risk.)
With these parameters in place, Dr. Saad and Dr. Sutherland used what are known as computational fluid dynamics simulations to model how the air, and aerosols, would flow through the Utah concert hall when all the musicians were playing.
The simulation revealed complex patterns of airflow. In general, the air flowed down from the air supply vents in the ceiling to the air return vents in the floor at the back of the stage. But two distinct vortices, at the front and the back of the stage, also formed, they found. “You see these large regions that are recirculating like a big tornado,” Dr. Saad said.
Aerosols can get caught in these vortices, swirling around and around the stage and building up over time.
The trumpets, which emitted large, concentrated aerosol clouds, posed a particular problem. As the instruments’ aerosol plumes traveled toward the air vents at the back of the stage, they passed directly through the percussionists’ breathing zone.
“We saw this and said, ‘OK, this is a big problem, we’ve got to solve this,’” Dr. Sutherland said. “And given the insight we had into how the flow was moving, we said, ‘Well, let’s move some of these instruments around.’”
They knew the idea might be controversial; orchestras have generally been arranged the same way for decades, for reasons that include both acoustics and tradition. “We asked them when we started the project, ‘What constraints do we have to work with? Can we move people?” Dr. Sutherland said. “And they said, ‘You do whatever you think you can to mitigate risk.’”
They moved the trumpets to the very back of the stage, right next to the air-return vents. Then they shifted the other wind instruments from the middle of the stage, moving them either closer to the back air vents or to the stage doors, which they suggested opening.
These moves, the team hoped, would allow the aerosols to flow directly out of the concert hall, without passing through the breathing zones of other musicians or getting caught in an onstage vortex. “You want the smoker to sit close to the window,” Dr. Saad said. “That’s exactly what we did here.”
Finally, they moved the instruments that do not generate aerosols at all — the piano and the percussion section — to the center of the stage. Together, these tweaks reduced the average aerosol concentration in the musicians’ breathing zones a hundredfold, the researchers calculated.
Although the precise air flow patterns will be different in every venue, the general principles should hold everywhere, the team said. Orchestras can reduce the risk of aerosol spread by positioning the highest risk instruments near open doors and air return vents. (Orchestras that cannot do their own computer modeling could put a fog machine onstage and track how the fog flows, the researchers suggested.)
Dr. Hong, who was not involved in the Utah study, praised the modeling work. “Simulating the flow inside an orchestra hall is not easy,” he said. “They did beautiful work in terms of characterizing flow.”
But he questioned whether moving musicians was really a practical solution. “We work with musicians closely, and they don’t like to be rearranged,” he said. (He did note, however, that “for a student band, I think it’s perfectly fine.”)
Instead, he proposed a different, albeit equally unconventional, solution: Masks, for the instruments. In a recent study, he found that covering the bell of a trumpet with a single layer of acoustic fabric could reduce particle emissions by about 60 percent without compromising sound quality.
The Utah Symphony, for its part, proved open to rethinking the seating. And when it took the stage last fall, it did so with the stage doors open and the wind instruments at the rear.
“That was a huge challenge for the musicians,” said Steven Brosvik, the president and chief executive of the Utah Symphony and Utah Opera. “But they all dove into it, and said, ‘Let’s go, let’s give it a try.’”
It took a few weeks for the musicians to get comfortable with the new arrangement, and they plan to return to their traditional seating configuration this fall, Mr. Brosvik said. But the simulations gave the musicians peace of mind and allowed them to get back onstage, he said: “For us, it was life changing.”
The researchers were pleased with how willing the musicians were to embrace an unusual solution, although their findings may have hit some instrumentalists harder than others. As Dr. Sutherland said, “We had to apologize to the trumpets in advance.”