[sanso]

hmm... why is it exactly two EQ's You're asking for?

You might as well ask how deep one can go without equalizing (and then do the math from there on, if required). Calculated in units of pressure (bar), the answer will essentially give You the ratio of how much peoples' airspaces are compressible (without pain, etc..). E.g. for an answer of 5m, that would give You 1:1,5 (== 2/3)

That will leave less room for variation, because the answer to Your question as is depends on where people equalize the first and second time, which may vary.

Ah, and I think the major parts are a. and c. It's possible that b. is a factor, but You'll have to find that one out yourself.