(a) A number of plastic kitchen funnels of different
sizes, a tube of a bicycle klaxon, a
medical phonendoscope and other tubes of
truncated cone geometry (figure 3).
(b) A mini sound level meter. Using it one should
be aware of the possible innaccuracy of the
obtained results due to the manual measurement
and background noise.
(c) A small loudspeaker connected to a computer.
The area of the loudspeaker should be
of the same order of magnitude as the funnels’
lower edges.