Hey, to those with the ZS3. I found a new mod tonight.
It has been previously posted by a few people that removing the red screen on the very end of the nozzle affects the sound. Removing it reduces the bass quantity slightly (while simultaneously removing the muddiness), and also improves the midrange.
Well, I found a different mod that makes further improvements.
BEHIND the red screen is a small piece of black acoustic foam. It's stuffed in the very tip of the plastic tube (the color of the plastic tube might be red or blue). It's exactly like the piece of foam stuffed inside of the shiny gold ED9 filter. Anyways, you REMOVE this piece of foam by just grabbing it with the tip of a sewing needle. You'll need a flashlight to assist seeing down inside of the nozzle to where the foam is. Carefully set aside the foam - they're extremely small and easy to lose. You can store the foam pieces in a small ziplock baggie like the one that many silicone eartips come in.
The change is a very noticeable improvement - the boominess that the ZS3 had is now gone, upper mids are less recessed, and the treble is sparkly and clear. They kind of remind me of an improved ATR, but I need to A/B them with the ATR to verify. Synthesizers, pianos, & guitars sound great.
It's tuned much more towards neutral with the mods, but there's still plenty of bass when called upon. It just isn't boomy and muddy like it was stock. Don't get me wrong, I think the ZS3 is a pretty good in-ear (especially for bassheads). I just know a lot of people are turned off by its overpowering bass that dominates the whole listening experience. This mod corrects that.
It's up to you if you remove the foam yet put the red screen back, or remove both the foam and the red screen. It's easy enough to try it both ways and see which you like better. I settled on removing both after trying it both ways. Just keep an eye on ear wax buildup inside the nozzle if you run with no red screen (remove ear tip every once in a while and carefully clean out any funk).
The mod is very easy, takes less than 30 seconds total, and is totally reversible.
The following interior diagram will show you everything that you need to know (you don't actually open the shell for the foam mod - the interior diagram is just to illustrate where the foam is located):
UPDATE: I found a camera lens and settings that would allow me to get a good shot of the foam. It's impossible to gauge the depth in this photo, but that foam is located about 1/4" down inside the nozzle: