I've been searching casually for this information for some time. The .pdf referenced by jbartos is the *first time I've even found numbers. What's so frustrating about the search, though, is that it should be so simple. y = ax^2 + bx + c. Differential theta summation -or whatever- just shouldn't be in it.
I have to assume the name is a dirty, dirty lie, as there's just not a website telling us the three missing variables. Gotta figure distance of the microphone from formost edge of the disk is one. Counter-intuitive as it is with a 3d object, I don't believe there's a Z. (X = distance from disk's radial center, Y = depth from rim.) So what remaining variables there are is a mystery.
Ah, well. If you get anywhere, Yan, I hope you'll let me know.
*=Actually, I got a formula from an e-mail group I was on. Naturally this evil datum let smoke out of that PC within a day or two, so I didn't get a chance to write it down, back it up or test it. Dunno if it was even valid. I tell myself, of course, that it wasn't.