But I can invert a transfer function only if the result is stable. With a ported speaker the delayed output of the resonator is higher than the output of the cone driving it so it would not be stable.
Or where do you differ from this work: http://www.speech.kth.se/prod/publications/files/qpsr/1966/1966_7_3_007-022.pdf, for example?
Fig. III-A-2 shows the effect of damping.