This and That:
Three pairs of silicone tips, a microfibre cleaning cloth and a storage pouch are surprisingly good for the budget range.
Soft-touch plastic, which is something I find to look and feel cheap on most products.
Difficult to find side indicators.
Rear- but not front-vented shells.
Quite stiff cable that lacks a chin slider.
Too stiff accentuation points on the remote's buttons.
Stupid design that will unnecessarily limit comfort for several people is they try to wear the in-ears with the cables around the ears.
Strong driver flex that likely indicates weak magnets and membranes lacking stiffness.
Above-average isolation, although not completely at the level of completely closed in-ears.
Sound:
My mainly used source device was the HiFime 9018d.
I used the in-ear with the largest silicone tips that came included.
Tonality:
The sound is soft, smooth and balanced - until the bass kicks in...
Provided you get a good seal, the KingYou KM03 is a (sub-) bass monster.
Below about 600 Hz the bass begins to rise evenly and without hump, and then slowly rises towards low bass. Compared to an in-ear like the Etymotic ER-4S/SR that is diffuse-field-neutral in the bass range, the KM03 has an increase of about 16 dB in the mid bass and about 20 dB in the true low bass (20 dB corresponds to four times the perceived volume). So there is definitely no low bass weakness in this in-ear. With an emphasis this strong, it is likely also one of the bass-heaviest in-ears on the market, trumping several other already clearly bass-heavy models in sub-bass levels.
Tracks without any noteworthy bass extension sound smooth and balanced, but as soon as the low bass starts, it clearly dominates the action and makes the presentation seem quite chaotic and inhomogeneous. Acoustic instruments also get too much body in the lower fundamentals and sound unnaturally bloated.
Due to the very powerful, even dominant sub- and midbass, the sound is also very boomy and the bass appears disconnected.
The midrange tends into the warm direction and is surprisingly well done without drowning in fullness and warmth. Yes, I would probably describe the midrange as the only highlight of the in-ear - in contrast to what one would often expect in this price range (especially some years ago), this (mid) range is relatively natural and harmoniously tuned and sounds pleasant.
In the lower treble there is a subtle boost as a successful balance to the warmth, above that the level rolls off evenly, although a little slower compared to my Shure SE215m+SPE, and blends well into the smooth and harmonious sound - well, if there weren't be the overly dominant mid- and subbass.
- - -
If it weren't for the boomy, undifferentiated and overly exaggerated sub- and midbass, the KM03 would have a pleasantly warm, natural and inoffensive tuning.
As is so often the case in the budget segment, the KM03 ultimately also fails because of the bass (both in terms of quantity and quality).
Resolution:
As you can already guess from the overdone bass boost, the KingYou In-ear has a quite soft and diffuse sounding bass that is pretty typical for the price range.
If pieces with mainly upper bass still sound relatively pleasant, mid- and sub-bass-heavy titles are reproduced unpleasantly and clearly too blurry and the bass doesn't seem to be integrated but separated from the rest.
Despite having a more or less equally accentuated bass range, the wireless Anker SoundBuds Curve in-ears sound much better controlled in comparison.
The detail level as well as speech intelligibility in the midrange is, on the other hand, very good for the price range and you don't miss too much.
The high frequencies of the in-ear sound, however, also not really untypical for the low price, somewhat blurry.
Because of the bass, the in-ear unfortunately already collapses with only moderately complicated titles and just lacks control.
Soundstage:
The in-ear sounds quite open with an elliptical presentation, which exceeds the base between my ears a little bit in width, but separates instruments only moderately cleanly and collapses somewhat with more complex and densely populated tracks.
Conclusion:
Decent midrange and treble, but way over-bloated sub- and midbass that appear disconnected. Bad technical performance overall (very soft and clearly lacking control). Most more or less similarly priced Knowledge Zenith or Xiaomi products offer audibly superior technical performance for the price and a relatively more balanced tuning - even though not all are as natural in the midrange as the KM03, but that's probably the only area where this in-ear doesn't suck.