In my previous post I shared my impressions on the ED16. I regard them as the best all-round KZ IEM I have heard to date (ZST, ZSR, ZS5v2, ZS6).
Though the ED16 ended my quest for a good sounding IEM with which I can comfortably sport with, I still pulled the trigger on an ES4 since many people here praised it and I kind of dig the cyan color. Was I wise to join the hype train?
My conclusion in short: The ES4 has a fun-tuned, likeable sound-signature and does very little wrong for those looking for some colored IEM's with an enhanced bass or for those who are particulary sensitive to sibilance. However, those seeking more detail, better staging and an overal more neutral and coherent sound signature should choose the ED16 for just 5 bucks more.
The ES4 has a fun sound signature with a boosted bass and succesfully dodges many typical KZ problems such as recessed mids and sibilance. In fact, the ES4 has the least sibilance of any KZ I tried thusfar (equalling my IT01 in this respect). However, the ES4 clearly achieves this through recessed upper-mids & lower-treble. And this has it's side effects. E.g. acoustic guitars quickly loose their spark and sound dull since the higher-pitched crispy sounds when the strings are picked seem absent (Listen e.g. to the intros of "Seven Days in Sunny June" by Jamiroquai or "Landslide" by Fleetwood Mac.)
Vocals are placed prominently up front with the ES4, more so then the ED16 or IT01. However in music where vocals are accompanied by deep bass, some bass bleed is noticable. The ES4 has a prominent bass boost which gives it a boomy character in the low-end (unlike the ZSR which has a more punch like character). Check for example "Limit To Your Love" by James Blake. It is a song with a relatively simple composition but has a bass that goes unusually deep and kicks in for the first time around the 0:55 mark. The ED16 and IT01 show better detail, seperation and imaging over the ES4 in the parts where this deep bass is present.
Though the ES4 is bass heavy, it does not go as deep as the IT01. At the 3:40 mark of "Limit to Your Love", for example, the bass on the IT01 sounds a bit like a distant nightclub playing loud-music such that you feel the rumble of the deep bass through the vibrations of the ground. However, I can't help but picturing myself one of these heavily bass boosted car-stereos when I'm listening to the same part through the ES4. The ED16 on the other hand might be lacking some bass here and is not as submersive as the other 2.