Looking again at the curve, the slope would seem to be more like 20 dB per half octave. (1 octave is 1 decade of frequency, correct?)
However, I do not trust my laptop at all for high frequencies, since I hear a weird echo on multiple headphones from time to time. I don't want to show a plot until I repeat this on my desktop.
Bass lens - I can try this. Is this what Sony do with their MDR (F1 etc) line?