• Original Reporting
  • On the Ground
  • Sources Cited
  • Subject Specialist
Original Reporting This article contains new, firsthand information uncovered by its reporter(s). This includes directly interviewing sources and research / analysis of primary source documents.
On the Ground Indicates that a Newsmaker/Newsmakers was/were physically present to report the article from some/all of the location(s) it concerns.
Sources Cited As a news piece, this article cites verifiable, third-party sources which have all been thoroughly fact-checked and deemed credible by the Newsroom in accordance with the Civil Constitution.
Subject Specialist This Newsmaker has been deemed by this Newsroom as having a specialized knowledge of the subject covered in this article.
CU Boulder environmental engineering Ph.D. student Tehya Stockman displays her clarinet and its handmade surgical-mask bell cover. She is one of several researchers exploring the ways in which wind-instrument musicians’ performances generate aerosol particles that may transmit COVID-19. (Andy Colwell, Special to The Colorado Sun)

Fabric mask dangling around her neck, Tehya Stockman guides her fingers through a series of arpeggios from muscle memory – her wrists buried in the distinct yellow armholes of a sturdy canvas bag.

“Any clarinet player would despise it,” she said. “My fingers kept getting snagged by it.”

A simple white shoelace cinches the bag closed around her instrument’s upper joint, leaving only the barrel and mouthpiece free from the canvas. Soft ripples emerge on a mirror next to her, cascading along the glass with far less fervor than those in previous video footage – when Stockman played similar sequences on her entirely unclothed wooden clarinet. 

The music, some of it familiar, is part of a major research project trying to figure out how much aerosol – the tiny particles emitted when we exhale – flows from wind instruments and how to make performance safe in the COVID era.

Aiming to determine the safest possible ways for performing arts activities to occur without worsening the coronavirus pandemic, the inter-university Performing Arts Aerosol Study is exploring the pathways and the size of particles and their concentration released from wind instruments and singing.

The research is one of two projects in Colorado focused on reducing risk associated with music performance. The other is at Colorado State University in Fort Collins.


The latest from the coronavirus outbreak in Colorado:

  • MAP: Cases and deaths in Colorado.
  • TESTINGHere’s where to find a community testing site. The state is now encouraging anyone with symptoms to get tested.
  • VACCINE HOTLINE: Get up-to-date information.


Preliminary recommendations from the Performing Arts Aerosol Study – released prior to peer review – provide guidance to educators as to how they might best position their musicians and keep the virus at bay as they head into an unprecedented school year. 

“It’s very atypical and it makes me very uncomfortable,” said Shelly Miller, a CU Boulder mechanical engineering professor, who is leading the study with Jelena Srebic at the University of Maryland. “We are doing this to try to help you to reduce transmission, so it’s for the greater good.”

The study’s initial results are coming at a particularly significant moment for schools and universities nationwide plotting a safe return to the classroom. Locally, Denver Public Schools recently announced that “singing and wind instruments would be prohibited in music class” when in-person instruction resumes this year, according to a draft planning document obtained by Chalkbeat. 

Miller agreed to co-pilot the research at the request of the study’s chairs, James Weaver, the director of performing arts and sports at the National Federation of State High School Associations, and Mark Spede, president of the College Band Directors National Association and director of bands at Clemson University. 

The study was commissioned by the National Federation of State High School Associations, the College Band Directors National Association and more than 125 performing arts organizations.

The researchers started out by conducting flow visualization tests with two different equipment setups. By locating the main places from which air exits each instrument, they have been able to identify exactly where to make quantitative measurements, said Jean Hertzberg, an associate professor of mechanical engineering at CU. 

The first arrangement involves a process called “fog visualization,” during which the researchers fill the room with stage fog – typically vaporized water combined with glycerin – and instruct the participants to play their instruments in this cloudy setting. When the performers breathe in the mix, the warmth of their bodies causes the fog to evaporate, making any exhalation now free of fog, Hertzberg explained. The scientists then use a laser beam to visualize the exhalation, which appears dark due to the fog evaporation. 

“It shows us a very clear delineation between where the flow is and where the flow isn’t,” Hertzberg said. 

CU Boulder environmental engineering Ph.D. student Tehya Stockman enters a laboratory testing room with her clarinet. Stockman is one of several researchers exploring the ways in which wind-instrument musicians’ performances generate aerosol particles that may transmit COVID-19. (Andy Colwell, Special to The Colorado Sun)

The second visualization setup involves a “schlieren test,” which allows researchers to understand where airflow is warm, according to Hertzberg. The musician stands close to a large spherical mirror with a long “focal length,” or a strong capability of focusing a light source. An optical imaging device – in this case, a video camera – stands outside the door. 

Through the camera, the viewer can see ripples rising as Stockman plays her clarinet. Those ripples, Hertzberg said, are actually “temperature gradients,” or regions where the air varies in temperature. Light rays, which pass through this air, change direction based on the temperature.  A razor blade cuts off the light that went through the edges of the warm areas – creating a visualization in which these edges appear darker than the rest of the image.

“Whatever she blows into the bag has to come out of the bag,” Hertzberg said. 

The temperature gradients appear to be much steeper when Stockman plays the clarinet uncovered, Hertzberg said. The bag, on the other hand, spreads the airflow over a wider distance, making the gradients far less steep and much harder to see, as they are not bending the light significantly.  

After visualizing the airflow and aerosol release pathways, the researchers are also measuring particle size and concentration close to the release sites, using two technologies: a condensation particle counter and an aerodynamic particle sizer spectrometer.

While in the room, the musicians play a variety of pieces to demonstrate their range. Chromatic scales. Arpeggios. An arrangement of Gustav Holst’s First Suite in E-flat – one of the most famous compositions for military band. 

 “We have the participant play so that we can probe around where we see the airflow coming out,” Miller said. 

The researchers have so far tested about six or seven woodwind and brass instruments, as well as one singer, and will be evaluating a bassoon or a saxophone soon, Miller said. Their next step will involve looking at the effects of theater performance by analyzing the aerosol pathways generated by a monologue piece. 

After evaluating every participant once, Miller said the scientists plan to repeat the tests and refine their techniques, in order to improve their quantitative understanding of emission rates.  

The Maryland team is following a similar course of inquiry, but is also conducting computational fluid dynamics modeling for the project. This added piece will help the team predict certain physical manifestations of indoor performance, as well as the impact of heavier breathing or more ventilation in such settings, she explained. 

Inhaling matters, too

Although the study focuses on the aerosol release that occurs during exhalation, Miller also acknowledged that the increased air intake of wind musicians should also be a serious consideration in adhering to protective measures. 

“Breathing is a very important factor in your potential exposure to virus particles,” she said. “Everyone has this little personal cloud of potential aerosol around them.”  

While a canvas bag around the instrument might help to diminish such a cloud, Stockman worries it’s not a good solution for beginners, who need to see their fingers. The bag also is uncomfortable, she said.

“My hands got really sweaty quite quickly,” added Stockman, 23, the clarinetist. She is a doctoral candidate in engineering at CU and also a researcher in the aerosol study. “All that moisture from the instrument is just in the bag.” 

The clarinet is fairly unique among woodwinds – saxophones, oboes, bassoons and flutes generally all have keys that at least partially cover their finger holes, but clarinets do not. Stockman said the research team has sent out a call to musicians who might conjure a better solution than the canvas bag. 

Handmade clarinet bell covers sit on a music stand as Tehya Stockman monitors equipment used in an aerosol-generation study. The bell cover is one method being explored for its ability to cut down on particle transmission, but because no commercially produced options are available, Stockman sewed these herself using fabric and half over-the-counter surgical masks. (Andy Colwell, Special to The Colorado Sun)

In the meantime, the scientists are testing a number of different materials that could potentially work as bell covers for all of the woodwind and brass instruments – including the slightly more problematic clarinet. One such material they are exploring is a two-layer nylon material similar to pantyhose. Stockman said she also has tried making a cover for her clarinet bell from surgical masks.

“Materials are really important,” she said. “You can’t just flap anything over it and just expect it to work. We don’t want people to feel a false sense of security.” 

Brian Sugrue, a 28-year-old doctoral candidate at CU Boulder’s College of Music, participated in the study with both his tuba and euphonium – both of which he hopes to teach on the collegiate level in the future. While he has not yet received bell covers big enough for his instruments, he tried out wearing a mask with a slit for his mouthpieces. 

“It restricts jaw movement a little bit, but it wasn’t so bad,” Sugrue said, noting how accustomed he has become to wearing a mask all day. “Having the slit is kind of liberating.”

After undergoing a variety of tests in the room, including the fog visualization and the particle measurements, Sugrue said he felt cautiously optimistic about the work the musicians and scientists are doing to resolve a problem they could have never anticipated.

“I think it’s really bringing out a lot of innovation in music in general,” he said. “To survive in that career, you have to be innovative and creative. It’s just adapting and adjusting to the times.” 

Researchers are fairly certain that singing and playing band instruments produce “particles of concern,” said John Volckens, a Colorado State University mechanical engineering professor who is a lead researcher on the similar Aerosols Emissions Study. 

The CSU project uses a “human exposure chamber” equipped with a computer control system to track data like temperature, pressure, relative humidity, particle concentrations and carbon dioxide emissions, as well as noise levels and sounds – which could help indicate whether variances like pitch and volume play a role in emissions. 

“We are trying to keep our studies separate but related,” Volckens said.

While the CU-Maryland project is focusing on a smaller sample size but performing many more repeated activities within that specific population, the CSU study has a pool about 10 times larger and contains a greater age range – including children 12 and up – but involves less individual repetition. Volckens said his research could be generalizable to a broader population, while the work by the CU team could reach more precise conclusions about certain activities.

Volckens said that he and his team also plan to release some preliminary results in early August, prior to peer review. 

“I think it’s important to release data that we think is informative,” he added. “But really it’s going to take months before we can get to the point where we’re going to have actionable information.”

Social distance during band practice

The CU-Maryland team has published some concrete recommendations based on their initial findings. 

First and foremost, they advised that all students and staff members wear masks in performance settings, even while playing an instrument, by wedging the mouthpiece through a slit in the fabric. Those musicians who are unable to play with a mask should keep one around their chin to wear during breaks, while teachers should reduce their vocal emissions by means of a portable amplifier. 

The scientists recommended that student musicians all sit facing the same direction with a 6-by-6 space around each player – 9-by-6 for trombonists –and stressed that under no circumstances should trumpeters empty their spit valves on the floor. While practicing outdoors is highly preferable, they stressed that all indoor HVAC units should be outfitted with HEPA filters.

The researchers also reiterated the importance of employing bell covers, made of a suitably protective material like multi-layered nylon, as an additional protective measure. 

Despite the decision of many school districts to prohibit wind and vocal performance entirely this year, the researchers did conclude marching band may still be a safe activity. 

“Outdoor rehearsals are considered best practice,” they wrote, also instructing educators to refer to the “Guidance for a Return to High School Marching Band,” published by the National Federation of State High School Associations.

At CU, the Golden Buffalo Marching Band plans to hold in-person activities, beginning Aug. 24, the first day of classes on the Boulder campus, a university spokeswoman confirmed in a written statement.

The band will be using Miller’s research to guide decision-making and is redesigning activities to mandate social distancing and masks, conduct outdoor meetings, redirect indoor traffic flow and position participants in one direction, with the wind on their backs. Musicians will also be practicing in smaller pods of 30 individuals for shorter periods of time, with enforced breaks to encourage aerosol dispersal, the written statement said.

Meanwhile back in the lab. And the practice room.

Miller’s research team is continuing to gather data and she said she hopes to complete the peer-review process by December.

Sugrue, the tuba and euphonium Ph.D. student, meanwhile, said his brass band is already planning to conduct master classes via Zoom. 

“To study music, you don’t need to be playing it,” he said. 

Such virtual listening activities, Sugrue said, will likely be more practical in the foreseeable future than assembling in person to play as an ensemble. 

“I would love to be optimistic but not until this whole thing is under control,” he said. “I don’t think you’re going to be able to turn a light switch and be back to normal.” 

Even if no sense of normalcy is on the horizon, Miller stressed that increasing awareness about how to effectively mitigate risk while performing could still prove invaluable – both to the growing scientific repertoire about aerosol generation and to professional musicians who may resume performing before students do so. 

“This is a lifestyle for many people,” she said. “We just all have to make smart choices.” 

Stockman echoed these sentiments, adding that such knowledge could also be valuable in a future pandemic or to other countries as they formulate their own music education plans. The results of the study could also help musicians make informed decisions about playing even at small social gatherings, as well as help remind musicians and their teachers that instruments are potentially a source of spreading viruses.

“The flu goes around all the time, and trumpet players emptying their spit valves directly onto the carpet was probably never OK,” Stockman said, “we just never thought about it.”

Email: Twitter: @sharonudasin