What's the difference between fs and fsa?

Fs-Fsa

Yes the measurements are diffrent. I suggest you take a look at chapter 8 of Dickason's book if possible. Fs is driver free air resonance and Fsa is the driver resonance with mass (usually clay) attached. The later is used to get the mass of the driver's cone assembly. You can call manufacturer and ask for the later which is simpliest. See pages 155-60 of the Loudspeaker Design Cookbook. Vance Dickason's book is the best $39.95 you can spend of speakers.

Good luck.