Illustration of the importance of source position with respect to nodes and antinodes of the eigenfunction associated to a mode to explain its asymmetry. The blue and red lines show the radial profile of the oscillation for two angular frequencies very close to one another (ω_red <  ω_blue). The bold vertical dashed lines show two source positions generating opposite mode asymmetries: positive for r₁, negative for r₂. The third vertical dashed line marks the edge of the acoustic cavity r = a.