Notch Filter to damp resonance.

I am designing a crossover for a friend. The midrange is of the dome variety with the following specs.

Resonance: 543Hz

The crossover points are 1200Hz and 6000Hz.

I have read that if the crossover HP point is within 2 octaves of the resonance it maybe worth while to add a series notch filter across the driver terminals to maximize electrical damping and minimize excursion at Fs. Clearly this is nearly with in an octave. The crossover has been designed in CALSOD and renders a 2nd order electrical slope and 4th order LKR acoustic slope.

Can anyone tell me how effective a notch filter is?