A team of researchers conducted a study on the acoustic effects of face masks on speech. For this, the team tested medical masks, disposable surgical masks, masks with clear plastic windows around the mouth, and homemade and store-bought cloth masks made of different fabric types and numbers of layers.

Lead author Corey, an electrical and computer engineering pos-tdoctoral researcher at the University of Illinois Urbana-Champaign said: "Previous research performed on this subject has focused on medical masks worn in healthcare settings."

"But no one has looked at the acoustic effects caused by different kinds of fabric masks, so that's where I focused our study," he said.

The researchers used a special loudspeaker, custom built by School of Art and Design graduate Uriah Jones and shaped like a human head so that sound radiates as it would coming from a human mouth. The team further gathered data from a mask-wearing human speaker as well.

"We put the different masks onto the head-shaped loudspeaker and played the same sound for every test," Corey said. "We also placed the speaker onto a turntable to add a directional component to our data."

"Using a real person makes the sounds less repeatable because we can't say the same thing the same way every time. However, it does let us account for the real shape of the head and real movements of lips," the lead author said.

"Even though these two data sets are a bit different, they both show which sound frequencies are most affected by mask-wearing and which masks have the strongest effects," he added.

Acoustic performance

The findings of the experiment showed that all masks muffle the quiet, high-frequency sound generated when a person pronounces consonants.

Corey said in the study: "Those sounds are already a challenge for those with hearing loss, with or without masks, and even become a challenge for those without hearing loss when you throw a mask into the mix."

The study revealed that disposable surgical masks offer the best acoustic performance among all tested. They found that loosely woven cotton masks also perform well but they may not be as effective as surgical masks at blocking respiratory droplets.

That study showed that tightly woven cotton and blended fabrics may block more droplets, but Corey's team found that they also block more sound.

As far as the droplet study is concerned, Corey suggested that multilayer masks made of loosely woven cotton may offer a reasonable compromise between droplet-blocking efficiency and acoustic performance.

"Most people do not walk around with lapel mics and amplification systems while wearing a mask, but it can help in settings where it does make sense, like classrooms and meetings," Corey said.

The study was published in the Journal of the Acoustical Society of America.

 

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