Technology / Home Audio / Fletcher-Munson Curves: Fletcher and Munson were pioneering researchers who provided the basis of High Fidelity in the '30s. They accurately measured and published a set of plots showing the human's ear's sensitivity to loudness verses frequency. They conclusively demonstrated that human hearing acuity is essentially dependent upon loudness. The curves show the ear most sensitive to sounds in the 3 khz to 4 khz area. This means sounds above and below 3-4 khz must be louder in order to be heard just as loud. For this reason, the Fletcher-Munson curves are referred to as 'equal loudness contours.' They represent a range of sensitivity from 'barely heard,' (0 db SPL) all the way to 'painfully loud' (120 db SPL), usually plotted in 10 db increments.