A nonaxial mode in which the amplitude is 180° out of phase (i.e., exactly opposite in phase) at symmetric locations on the same resonator. Since the amplitudes are 180° out of phase, there must be at least one node between the two locations. Thus, an asymmetric resonance cannot be an axial resonance.
Example: a bar horn has a resonance where the instantaneous amplitude at one end of the horn face is +100 microns, while at the same instant the amplitude at the other end of the horn face is -90 microns. Note that the amplitudes at either end of the horn face are opposite in phase (sign), which indicates an asymmetric mode, even though the magnitude of the amplitudes is not necessarily equal (100 microns versus 90 microns).