anyway here are several types of distortion to avoid:

Many factors can contribute to distortion in the driver: cone behaviour,coil-end windings passing out of the main magnetic field at maximum excursion,uneven magnetic field distibution and non-linear
compliance of the cone suspension.

Other types such as doppler distortion,harmonic distortion,noise,
transient responce,clipping,intermodulation distortion.

Also what is the benefit of having a tweeter mounted inside the bass [co-axial]