Researcher Ryan Corey recently heard from a friend who teaches in a school where some students have hearing loss. The friend wanted to know if he had any ideas that would help her communicate with these students while wearing a mask to slow down the release of COVID-19. Corey, who also has hearing loss, did not know what to tell her. So he went to the Illinois Extended Hearing Lab to find solutions.
Corey, a postdoctoral researcher in electrical and computer engineering under Professor Andrew Singer at the University of Illinois at Urbana-Champaign, will lead a team that will study audio signal processing, specifically for hearing aids such as hearing aids. The results of the team’s new study assessing the acoustic effects of face masks on speech are published in Journal of the American Acoustical Society.
“Previous research on this topic has focused on medical masks worn in health care settings,” Corey said, “But no one has looked at the acoustic effects that is caused by different types of masks, so that’s where I focused on our study. “
The team tested medical masks, surgical masks, masks with clear plastic windows around the mouth, and homemade and masked clothing masks made with different types of clothing and numbers of layers.
The researchers used a special loudspeaker, a practice built by industrial and enterprise engineering graduate Uriah Jones and shaped like a human head so that sound radiates as if it were coming from a human mouth.
“We put the different masks on the headphone jack and played the same sound for every test,” said Corey. “We also put the speaker on a turntable to add a directional part. our data. “
The team collected data from a human-faced human speaker, too.
“Using a real person makes the sounds so repetitive because we can’t say the same thing the same way every time. However, it allows us to describe the true shape of the head and real movements. lips, “said Corey. “Even though those two datasets are slightly different, they both show which masks have the highest sound frequencies and which masks have the strongest effects.”
Their data showed that all the masks move around the silent, high-frequency sound that is created when a person utters consonants. “These sounds are already a challenge for those with hearing loss, with or without masks, and even a challenge for those without hearing loss when you throw a mask into the mix.”
Masks also prevent visual arrests such as facial expression and lip movement, so speech reading is no longer an option when wearing most masks. Almost everyone uses speech reading to some degree, with or without hearing loss, Corey said.
“That’s why we tested the popular window masks that are so popular,” he said. “Unfortunately, the trade-off is what you see through, but they block the best sound of the masks we’ve tested.”
The study found that disposable surgical masks offer the best acoustic performance among all tests, Corey said. Loose-fitting 100% cotton masks also perform well but, as seen in a study by other researchers in Illinois, may not be as effective as surgical masks at preventing respiratory droplets . That study showed that tight-knit cotton and blended fabrics could block more droplets, but Corey’s team found that they also block more noise. Based on the droplet study, Corey suggested that multilayer masks made of loose woven cotton could provide a reasonable compromise between droplet prevention effectiveness and acoustic performance.
The good news is that most masks don’t completely block out sound, they just let it out of the mouth. This detail means that simple masking speech extension devices can make them more accessible to everyone. In particular, the lapel microphones already in use in many classrooms and speech halls have little effect on face masks. Many aid kits support remote microphone utilities that are also worn near the lapel.
“Most people don’t walk around with lapel pads and extension systems while wearing a mask, but it can help in situations where it makes sense, such as classes and meetings,” said Corey.
Source:
University of Illinois at Urbana-Champaign