Typically, when there is music playing in a room but you aren't inside to hear it directly, the only instruments you can hear from outside are the bass and drums. It is fair to say that sound waves of lower frequencies travel through solids easily, so is it also fair to say that Morino, who plays bass, has dirtier eyes than Sakashita, who plays drums?
Low notes can have wavelengths of up to 9.5 meters. Usually it will depend on the thickness of the wall, because if the wavelengths are less than or equal to the thickness of the wall they will be partially reflected. So we can take the thickness of a wall separating a room and call that the "standard of perversion." Because both the drums and bass can be heard from outside the wall, or in another words both Morino and Sakashita surpass the "standard of perversion" already, from a typical person's perspective it appears that they are on the same level.
Exactly wrong. The average bass guitar frequency range is 30Hz-164Hz, while the drums has a range of about 80Hz-600Hz, even with the kick. Therefore, the bass can travel through a wall easier and this carries on to Morino who surpasses the "standard of perversion" more so than Sakashita claims to. This can also mean that Morino's dick is part vibrator, so Sakashita will experience 10x more pleasure. One might think that this will mean Sakashita is more perverted for enjoying it, but then again this can only happen if Morino is aroused.
Conclusion: Morino is thinking of dirtier things than senpai.