With the onset of the COVID-19 pandemic in March 2020, choral singing worldwide abruptly stopped. In several much-publicized cases, people fell ill, with some even dying following choir rehearsals and choral performances. Theaters and opera companies were silenced, and millions of performers, creative team members, and support staff were suddenly out of a job. Countless others, both volunteer performers and audience members, were deprived of music. While it was unclear at first why so many people contracted COVID-19 following these so-called "super-spreader events," we now know that the primary vector for the spread of SARS-CoV-2 virus is sprayed droplets from the infected individual being inhaled by a healthy individual. Anything that forcefully propels droplets presents a risk, including coughing, sneezing, yelling, and singing. In addition, we now understand that asymptomatic people can spread enough of the virus to make others ill. Without knowing who was carrying the virus, there was no safe way for people to sing together.[1, 2] The National Collaborating Centre for Environmental Health published an article with a list of outbreaks related to singing rehearsals or performances.[3]
Aerosols are microscopic particles (0.01 µm to 100 µm in size) suspended in the air.[4] Ninety-nine percent of aerosols produced by humans, regardless of age, sex, weight, and height, are less than 10 µm in size.[4] This is a major concern since smaller aerosols take longer to settle and greatly increase the probability that other individuals will breathe them in before the virus is detected.[5] In a turbulent atmosphere, aerosols of 100 µm take just 5.8 seconds to settle, while those of 0.5 µm take as long as 41 hours. If aerosols contain viable pathogens, they are a threat even after settling, as they can continue to be sources of contamination.[5] The SARS-CoV-2 virus can be viable on a surface for up to 2 days [6] and can be spread through aerosol particles ranging from 0.2 µm to 10 µm in size.[7, 8] Because of this, aerosols released by infected individuals during a choir rehearsal or performance may remain in the air or on surfaces for hours, posing a great risk to those who have not contracted the virus.
This became a major problem because of the large number of people participating in various types of choruses at churches, schools, in their community, and as professionals. A Chorus America study released in 2009 estimated that nearly 23% of households in the US have at least one member who sings in a choir, while in the US alone, 32.5 million adults and 10.1 million children, or 18.9% of the US population at that time, have sung in choruses.[9]
Together with other recommendations and guidelines, it was shown that wearing a mask reduced the risk of spreading the virus through aerosols significantly. However, wearing a mask while singing presented several difficulties. While many people find masks annoying and uncomfortable, they are especially so when breathing heavily (as for singing): they rest against the nose and mouth, are inhaled when breathing through the mouth, and trap vapor from the breath. Even more problematic is that they interfere with sound to some extent, muffling the noise, especially the words. Most problematic, however, is that these masks obscure the lower part of the face, robbing singers of an important tool of communication and expression. Singers would find a clear mask that prevents the release of microdroplets and aerosols much more useful.
Shortly after the Coronavirus pandemic took hold in the United States, companies began marketing "singers' masks." [10] [11] These masks were bulky and almost obscured the face, making it impossible for any facial expressions to be understood. The reasons for the above outcome are: 1- Voice teachers and choral conductors watch singers' facial expressions to understand how they use the vocal mechanism. 2- Singers similarly rely on visual cues to start and stop together, to mirror effects, and to communicate which part is in the lead. 3- Finally, the audience relies on seeing the performer's full face to understand the words clearly and to sense the music's emotional content.
Even more concerning was the lack of proven safety in singers' masks. Previous publications suggest that surgical masks while preventing the release of aerosols when the wearer is speaking, allow significant aerosols to pass through them when the wearer sings.[12] Therefore, there was a need to demonstrate that any singing mask prevents aerosols' release. [8] In anticipation of safeguarding public health during potential surges in airborne transmitted diseases, we introduce an innovative Aerosol Barrier System designed specifically for singing events. We designed this system to meet four requirements we have termed "the 4 S Challenges":
SAFETY: To meet this challenge, reliable data must demonstrate that the system's materials and design reduce the release of aerosols while singing to acceptable levels- ideally, to the baseline of particles in the empty room.
SINGING COMFORTABLY: The system must allow the user to breathe comfortably and inhale sufficient oxygen without accumulating moisture or carbon dioxide while remaining secure as the singer moves. Both breathing and movement are important during singing, and the system must account for this. The jaw, throat, and neck muscles operate at high levels of engagement during singing and must be released before singing and able to move freely during singing. Therefore, this barrier must create no physical constraints or tension in these body parts.[13]
SOUND QUALITY: To meet this challenge, the system must not interfere with the wearer and listener's sound, an issue commonly seen with N95 masks.[14–17] For example, a transparent face shield (such as welders wear) reflects so much sound back to the singer's ears that it would be unbearable to wear. In addition, the system must not muffle or mute the sound for the listener. Sound propagates through the air like a mechanical longitudinal wave, with regions of compressed and decompressed air particles. The higher the difference between the compressions and decompressions of the sound wave, the higher the intensity of the sound.[18] The speed of sound is the distance traveled per unit of time by a sound wave as it propagates through the air elastic medium. At 20°C (68°F), the speed of sound in air is about 343 meters per second. Solid or liquid media interfere with the quality of the sound, causing reflection, diffraction, and/or refraction.[19] Therefore, sound waves must be carefully handled to avoid disturbances and alteration from the original source (in this case, the singer). Preventing aerosol spread without disrupting the sound creates an additional challenge. As mentioned, current masks present a solid barrier that can alter sound waves. In addition, condensation from the singer's breath accumulates on the mask over time. The additional liquid component further alters the sound as the mask becomes damp from this condensation.
SIGHT: Finally, the entire system must permit others to see the wearer's face while meeting the other challenges. There are multiple masks on the market that allow the wearer's face to be seen, but they have obvious shortcomings: leakage from around the edges of the mask allows significant release of aerosols, and the mask itself muffles sound, making it inappropriate for singing applications. On many levels, the visual element enhances the listener's emotional experience. Both the audience and the singers consistently report that seeing singers live is more engaging than listening to a recording.[20] However, a choir wearing masks gives the audience an emotionless visual experience. Obscuring the singers' faces limits the audience's enjoyment of a live event because viewers respond positively to singers' facial expressions and gestures. Choral singers rely in part upon seeing one another's faces to coordinate teamwork as they sing. Teachers of singing and choir conductors rely heavily on observing how the singers use the muscles of the face, mouth, tongue, and neck (in addition to the muscles involved with breathing and body alignment) to diagnose and solve musical and vocal problems.[21] The mask should be made with transparent materials so that the wearer's mouth, face, and upper neck anatomy are fully visible.
This work presents a system that attempts to mitigate the dispersion of microdroplets and aerosols. The system is designed to be safe and comfortable for singers/speakers with no disruption to sound, all while allowing the wearer's face to be seen.