An electrodynamic loudspeaker is known to be a non-linear device due to many physical phenomena resulting in position and current dependent loudspeaker parameters. The most common position-dependent non-linear sources are the force factor Bl(x) and stiffness Kms(x). These non-linear effects have many consequences, the most commonly used in measurements being harmonic distortion and intermodulation distortion. Another consequence is the compression effect of the dynamics. Due to a lower Bl(x) and a higher Kms(x) for larger displacements, one would expect a compression behavior, i. e. a decreasing ratio of X/U or X/I with increasing excitation level (X, I, and U are the displacement, current, and voltage, respectively). Nevertheless, measurements in the low frequencies of many loudspeakers show an expansion behavior, i.e., an increase in the X/U and X/I ratio with increasing excitation level. This non-intuitive behavior, which runs counter to the fundamental theory of simple models of Bl(x) and Kms(x), is studied and discussed in this paper.