Dayton Audio PS180-8 6-1 - Manual (Page 5)

The inductance components Le (x) and Bl(i) of most drivers have a strong asymmetric characteristic. If the voice coil
moves towards the back plate the inductance usually increases since the magnetic field generated by the current in the voice
coil has a lower magnetic resistance due to the shorter air path.
The nonlinear inductance Le(x) has two nonlinear effects. First the variation of the electrical impedance with voice coil
displacement x affects the input current of the driver. Here the nonlinear source of distortion is the multiplication of
displacement and current. The second effect is the generation of a reluctance force which may be interpreted as an
electromagnetic motor force proportional to the squared input current.
The flux modulation Bl(i) has two effects too. On the electrical side the back EMF Bl(i)*v produces nonlinear distortion due to
the multiplication of current i and velocity v. On the mechanical side the driving force F = Bl(i)*i comprises a nonlinear term due
to the squared current i. This force produces similar effects as the variable term Le(x).
Nonlinear Parameters