Passive radiator specification measurment

Hi, I have an old pair of Celestion Ditton 15 cabinets with ABRs in. I would like to realign then with a new pair of drive units however I can't find any specificatiosn for the ABR.

Does anyone know how to measure these specifications.

The real problem measurements are;



I can calculate Sd easly

I can estimate Xmax

I can even get an estimate of Fs by firing a sinewave signal at the ABR and searching for max displacement.

I just don't know how to even start on the other two measurements.