I took some real speakers characteristics, then randomly distorted them to avoid copying. As a result it does not emulate anything from real world, still sounds like a guitar speaker. Add this effect after distortion plug-ins to reach real sounding.
Speaker characteristic is emulated with set of 2-st order band-pass filters, which have appropriate frequencies, coefficients and narrow bandwidths to make the characteristic more rough. You can see this at the pictures like peaks grid.
Guitarist/vocalist/another live artist (while recording and working at PC), sound engeneer.