Yeah, it might be one of the reasons why Harman found the preferred bass for in-ears to be higher than for headphones, because the stapedius reflex mostly reduces transmission at lower frequencies, so listeners may have compensated for this by turning up the bass control. The paper linked above does also say though:
(Maybe this is a contributor to the flattening of the equal loudness contours in the midrange with increasing SPL?)
Also of note is the prevalence of the reflex was actually found to only be ~75% in
this study, but more common at ~85% for younger listeners ages 18-30. This may (partly) explain the variation in preferred bass Harman found with in-ears:
View attachment 235368
And also the higher preferred bass by younger listeners in their over-ear tests (which may still have triggered the stapedius reflex for some, as people's trigger SPL threshold ranges from ~70-100 dB, and Harman's listening level is within this range):
Interestingly, the paper
@xnor linked also mentions infrasound (which I've
previously posited could be contributing to perceptions of bass impact):
This boosted infrasound would more readily trigger the stapedius reflex. Initially you'd think this would mean less perceived bass impact, but it might be more complicated than that. The reflex has a letency of ~10 milliseconds, but maximum tension of the intra-aural muscles involved
may not be reached for 100 milliseconds or more, too late for sudden, intense sounds (e.g. percussive sounds like a kick-drum). Also, this tension reduces by about 50% after a few seconds. This could result in repeated initiation of the stapedius reflex when listening to music, with the sound during periods after sudden loud (e.g. percussive) parts sounding quieter, but not those sudden loud parts themselves, due to the latency of the reflex, and its relaxation. This could then be an explanation for an increased perception of percussive bass impact, and could even explain
@Resolve 's (and others') perception that some headphones (which it seems mostly have well-sealed front volumes) have greater 'macrocontrast/macrodynamics' than others with a similar response above 20 Hz - because the stapedius reflex literally changes the dynamic range of the ear:
Unless sub-20 Hz responses of such headphones are measured, we won't be able to investigate this potential influence of infrasound and static pressure on perceived sound further.