A rendering of the Equal Loudness Contours as generated by Robinson and Dadson in the late ‘50s, expressed in 1/3 octave increments. Just so you know, I’ve extended the curves (using interpolation) on the bottom and on the top ends. Robinson and Dadson only went to 16 kHz. on the top, and as far as I can tell, didn’t take any measurements above 130 dB SPL (which seems like a reasonable and prudent course to me).