It is my understanding that a boost in the mid bass tends to "cloud" the midrange up a little. I think many have spoken up about the W4 lower mid boost doing this very thing. But the W3 has a significant mid bass hump but has exceptional clarity across the entire spectrum. I wondered with such a large mid-bass boost why the W3 wasn't cloudy sounding as well so I asked Westone this exact question and asked my inquiry be directed to an engineer type person.
As far as the W3 and W4 goes, keep in mind that doing A-B comparisons are subjective, how you perceive one may be different than how someone else perceives it. Neither one has a mid- bass hump built into the configuration. Both are designed to be as neutral as possible, the W4 being the most neutral universal headphone we offer.
I LOVE my W3....but "neutral as possible"?? Did they miss?? LOL!