Method & limits
What this is
Raw measured response on one Head Acoustics HMS II.3 — not diffuse-field compensated, L/R averaged, normalized at 1 kHz, smoothed 1/12 octave for legibility. One unit per model.
How much to trust a line
Re-seating moves it: ±0.37 dB from 200 Hz–1 kHz, ±3.87 dBby 12–20 kHz. Turn the band on. Don't read fine treble detail here.
Open headphones read bass-light
That's the fixture's seal leak, not the headphone. It cancels between headphones that seal alike, and doesn't between a sealed one and an open one.