Oscillations
and Waves > Instruments > Air Columns
DCS#
3D30.21
DISPLACEMENT NODES
AND ANTINODES IN CONICAL RESONATORS
APPARATUS
brass phonograph horn
202-07-C
HP audio generator
202-08-G
speaker on a tube
202-06-D
DESCRIPTION
Move a
speaker on a
long tube
along the axis of the cone.
Set the function
generator at some high harmonic
(2
kHz) of the fundamental (200 Hz) of the resonator. Then there
will
be many wavelengths inside the cone. As the speaker is pushed
further
into cone you will hear frequent alternations of high and low intensity
sound, according to whether the speaker is near an antinode or a node
of
displacement.
I.e., you can only excite a mode near one of its antinodes.
Alternately,
you can view it as an interference phenomenon, which is what standing
waves
are.