Out of curiosity, what weighting did you use when you measured the SPL of the fans?
what is SPL? I am not familiar with this term.
Sound pressure level. It's the dBs you got.
Why was this question asked? [The thread never got continued]. Short or long weighting should come out near identical, one just takes longer to get to the reading.
There is a lot more than just averaging going on between A weighting and C weighting. C is much flatter and extends significantly farther into the low part of the spectrum. Many people have noted the higher pitch of the S5's stock fan running full out.