You know how fabric is often used to absorb sound? Think of the acoustic draperies in theaters, or when you pull the covers over your head. Now that we’re all wearing masks, it’s worth applying this understanding to our faces, and realizing that, yes, putting two or three layers of fabric in front of our mouths muffles the heck out of our speech. This is the conclusion of a new acoustics study that was presented this week at the annual meeting of the Acoustical Society of America.
Researcher Pasquale Bottalico, assistant professor of speech and hearing science at the University of Illinois at Urbana-Champaign, evaluated teachers in classrooms as they wore fabric masks (three layers), surgical masks, or N95 masks. He found that the fabric masks were the worst option for student listening comprehension, and strongly suggests that teachers use surgical or N95 masks. “The use of surgical and N95 masks can minimize the negative effects on speech intelligibility and students’ listening efforts,” he said in a statement.
His recommendations dovetail with indoor safety guidelines released by German aerosol experts just this week, which also strongly push N95s indoors to curb the spread of COVID-19.
If you’d like to understand why, just know that fabric is porous, and porous materials “absorb sound energy as it dampens the oscillation of the air particles through friction,” says Bottalico. Unfortunately, the frequencies most muffled by fabric are the ones used in speech.