Human ear - freq log scale
So Robert Wannamaker did a real bang-up job parameterizing the 0 dB curve and came up with, what he called F-weighting.  It's in this AES paper from the 90s:



you can see that this can be turned into an $H(s)$, and with the bilinear transform, into an $H(z)$.

here is the curve on a dB vs. log/linear freq scale.  the log frequency plot is the upside-down version of your 0 dB curve above but is more updated from Fletcher-Munson to the ISO standard which cam from i dunno where.



here's a table of poles and zeros: