  We present initial results from measurements of exhaled droplets by two
singers during singing, speaking, laughing, and recitation of poetry. We also
conducted measurements with a flute, a clarinet, a tuba, and only the tuba's
mouthpiece. To be able to image and track droplets, we have developed and built
a portable measurement set-up. We have detected droplets with diameters of
approximately 50 micrometre and above. We found that for a single subject, the
largest amount of droplets are produced during singing, but that laughing can
produce a comparable number of droplets. Speaking and recitation of poetry do
not produce as many droplets. We repeated exercises at varying distances and
found that the number of detected droplets decreased rapidly with increasing
distance. Most droplets we detected follow a ballistic trajectory, and hit the
ground after a distance of approximately 1 m. In case of the musical
instruments, we did not detect droplets exiting a tuba and only few single
droplets from a flute and a clarinet. A clarinet usually points downwards, such
that droplets follow a downward trajectory and hit the ground after a short
distance. The situation was different when the tubist used only the mouthpiece
(that is, detached from the tuba) during warm-up while partially blocking the
opening with a finger: in this case, many droplets were ejected from the
mouthpiece. These followed ballistic trajectories at different speeds, with
some droplets exiting the measurement volume. Two important limitations of this
study are that (i) the sample size is very small, such that a statistical
analysis is beyond our scope; and (ii) that we cannot draw conclusions about a
possible risk of infection with COVID-19 when performing any of the said
activities.
