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Speak Softly and Spread Fewer Coronavirus Particles, Say UC Davis Researchers

TOKYO (Reuters) – Lowering speaking volume can reduce the transmissibility of the coronavirus, researchers said, a finding that could have implications for the management of high-risk indoor spaces such as hospitals and restaurants.

A 6-decibel reduction in average vocalization intensity can have the same effect in curbing contagion risks as doubling the ventilation rate in a room, scientists from the University of California Davis said in a study posted on Wednesday on the arXiv preprint server (

“The results suggest that public health authorities should consider implementing ‘quiet zones’ in high-risk indoor environments, such as hospital waiting rooms or dining facilities,” the researchers wrote.

The World Health Organisation changed its guidance in July to acknowledge the possibility of aerosol transmission, such as during choir practice, in restaurants or in fitness classes.

Vocalization ejects micron-scale droplets which evaporate to leave behind aerosol particles large enough to carry viable virus, according to the paper. A loudness increase of about 35 decibels, the difference between whispering and shouting, boosts the particle emission rate by 50 times.

Normal conversation is over the 10 decibel range, while ambient noise in restaurants is around 70.

“Not all indoor environments are equal in terms of aerosol transmission risk,” said lead researcher William Ristenpart. “A crowded but quiet classroom is much less dangerous than an uncrowded karaoke bar where patrons are socially distanced but talking and singing over loud music.”


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