Researchers from the NIH and the University of Pennsylvania have put up a preprint titled Could SARS-CoV-2 be transmitted via speech droplets?

They write

Considering that reports of asymptomatic transmission account for 50-80% of COVID-19 cases, droplet emission while speaking could be a significant factor driving transmission.

They point to the high upper respiratory viral loads that have been documented elsewhere to support this idea.

Using laser light-scattering, they recorded the number of expelled droplets detected when volunteers said ‘stay healthy’ 3 times in a row. Image below shows the number of droplets visible per 16.6 ms frame in the video capture.

Furthermore, a mask greatly reduced droplet emission

A damp homemade cloth face mask dramatically reduced droplet excretion, with none of the spoken words causing a droplet rise above the background

Video of droplets without mask and with a damp homemade mask

These droplets are much smaller than the kinds you’d get from coughing or sneezing, invisible to the naked eye. However, the authors point to studies that find speaking generates more droplets than coughing or sneezing.

They conclude by recommending further exploration.