not sure if this was stated before but after trying a multitude of different ear tips, this is what i found:
the sony hybridss a small bump up the mid bass , the subbass a tad, makes it more punchy and exciting. Better for subway or public transit commuting.
i somehow fit the klipsch oval tips on it. it provided better isolation imo, but i can see why the s4is have a huge midbass bump, its the small silcone , made the sound too congested and ruined the magic that is the re400 and makes it mid bass mess, still nice mids, but there is bass bleed into the mids but ruins the treble (gets out of control), fantastic for subway commuting but it ruins the sound signature imo
the stock tips i think has the least bump in mid bass and bass, keeping magic but i think this set up would be better at home or in a moderately loud area, maybe just walking on the streets in a mildly populated neigbourhood. ---> not enough for subway commuting i would think (haven't tried this yet compared to the two above! ( the hybrids i felt was a bit bass light in the subway, if this is less, then i would imagine it feels bass deficent)
Lesson learned: bass affects isolation more than i thought especially in loud environments! i guess why a lot of people like the s4s, velodyne signature for the average listener