On the 400s it was just like... it was THERE, and I could HEAR it, but it didn't really fill up the ear cups. The LCD2s felt like there was some actual sound pressure from the bass, although it wasn't exactly powerful.
To me, bass heavy means in busy music the low frequencies are prominent, not just apparent. Yes, on the open headphones I could hear the bass, but to call that sound "balanced" is just weird to me. The cymbals were shimmery and right up front, but the bass tones were more like background noise. Yes, the HE-400s and LCD2s can go VERY deep. They can hit frequencies all the way down. They're just not very loud, and if they're in the midst of other music you won't really be conscious of them.
It's a weird double standard to me. A headphone like the Grado RS1i is considered top-notch and apparently worth nearly a grand and people will rave about how it's just like sitting in a "jazz club" (to quote a head-fi review). It's "proper" and "audiophile-level" to ooh and ahh over EXTREMELY prominent treble or mids, but if you like bass you can feel you're just a trend-kiddie who got caught up in the Beats sound.
Let me tell you, by the way. I've been to a lot of rock and metal concerts, and those open headphones do NOT sound like being the audience of one. The power of the bass and the impact of the kick drum is so heavy you can feel it in your CHEST. The more "consumer grade" headphones are more accurate from that end.