One of the new offerings by KZ are the ED16, and those are suspecially similar to ZSR, both in frequency response and overall sound quality. Main differences include subtler bass response, better-tuned mids and a smaller form factor.
If you want a more balanced listening experience, and not a fan of the massive bass response delivered by the ZSR, or just in need for a good sounding pair of earphones for relatively smaller ears, then the ED16 are an excellent choice.
It saddens me that they didn't include one of their braided cables instead of this rubbery one, which is identical to the one you get with ZSR.
While not exactly as ergonomic as the ZSR, I found the ED16 to be very easy to wear and they are nowhere as bulky as the ZSR. Those with smaller ears will be delighted to wear them, and the rest are not likely to complain.
Lows / Bass
The bass is deep with hints of sub-bass rumble in the background. It's not as prominent as ZSR's bass, but I actually find to be an upgrade, as the bass is in better balance with the mids and highs, but I would understand those who might feel the lower frequencies appearing to be colder. Mid-bass "hum" is very mild here, in comparison. Quality-wise, the bass isn't that different than previous hybrid earphones by KZ. It's all familiar by now.
Mids / Vocals
Very similar to ZSR overall, but seem to be more defined, more upfront and the timbre seems to be more precise. While both earphones seem to have identical hardware, the ED16 seem to be tuned closer to being natural and true-to-life, while ZSR seem to focus on bass and sharper treble. The mids on the ED16 are excellent, even if a bit intimate at times.
Highs / Treble
The highs sound almost identical to ZSR, but seem to be in a better balance with lower frequencies. While some pierce is still a possibility, it's not as often as many of KZ'z previous products. Possibly one of the best-balanced earphones released by KZ to date.