A placebo effect is an actual change in experience, yes, but it's a change in experience to a cause that's not there, thus it is also perceived change that is not there. In this case I'm treating the EQ change as an experimental condition, thus the actual effect would be the different between Harman EQ to randomized EQ, and the placebo would be the perceive improvement in sound due to simply adjusting the EQ (the effect that I'm interested in). It is also confirmation bias in this case, as we have a bias to believe that EQ'ing to the target would improve our enjoyment.