KZ has a track record of delivering good products at very low prices. Alas their history with Bluetooth products has been less than stellar, with the KZ E10 being underwhelming and their other attempts at creating “true wireless” earphones not being great either. The KZ S2 are their latest attempt but, alas, they are not successful despite their attractive price.
Disclaimer: Linsoul provided this sample for free. The KZ S2 retail for $35 on Indiegogo.
|Very fatiguing treble
Super-invasive background hiss
No volume control
Connection issues: stutters and weird pitch fluctuations
Limited battery life
Update (30/05/20): I lowered the rating from 5 to 3 as I realised the former rating was far too generous for headphones with all these issues.
Packaging & Accessories
The KZ S2 come in a simple cardboard box which holds the earphones, the case, a USB-A to USB-C cable and two sets of identical eartips. Yes, KZ, I need larger eartips, thank you.
Design & Comfort
The design of the KZ S2 is identical to that of the E10, save for the absence of the ear hooks. This makes them certainly smaller and leaner-looking. They’re made of shiny black plastic, with a matte circle in the centre of the faceplate. The design is nothing new, as it looks like a generic IEM, but it’s nice.
Build quality appears to be decent, with the plastic used being seemingly durable and the pieces fitting together well. That applies to the dock as well. It’s not super-high-quality plastic and it shows, but it’s adequate for the price.
Comfort is quite good, especially if you use eartips other than those included in the box; the shells are large, but not so much that the size goes in the way of a comfortable fit. I could wear them for more than two hours without issues.
Isolation is sufficient to block faint noises, but the earphones don’t shield the listener from louder sounds. In these times of social distancing and #stayathome I could only test the S2 at my desk and realise how they could not block noise coming from my my mechanical keyboard (with black switches, so not obnoxiously noisy either).
The case-dock is small to the point you barely realise it’s there if you put it into your pocket. It’s matte black and it has a button on the back: if you press it, the LED inside the case lights up. The USB Type-C connector to charge the battery is on the bottom, for whatever reason: it’s certainly an original choice. Overall the case is well-assembled and well thought-out, save for the placement of the USB port, with a magnetic lid that ensures it stays closed at all times.
Extra Features & Battery Life
The KZ S2 use the Bluetooth 5.0 standard with the AAC codec on top of the standard SBC – no aptX. The company says it’s because of the absence of aptX on Apple devices, though on the other hand AAC is missing on many Android devices. There are also many headphones offering both. The true reason why they’re not offering aptX is because the Realtek 8763 chip used does not support aptX. Qualcomm/CSR alternatives offering aptX are more expensive and that’s an issue when you are selling a product with thin-razor margins for ~$25.
Now the Realtek 8763 chip seems to have some issues, at least with the way it’s been implemented by KZ. There are a very strong hiss (which I will discuss further in the next section) and constant stutters and other issues with music reproduction. Micro-stutters are normal and almost expected in this type of product, especially in the lower price brackets. In this case, though, stutters are constant and independent of the source or its position – they just happen, even if you are sitting still with the source on the desk some 50 cm away from you.
The worst issue, though, is the fact that on multiple occasions I have experienced an extremely weird alteration of the music: it’s as if the music was sped up and then slowed down, therefore sounding higher and lower in pitch. There were a few ups and downs before it actually set on the correct speed and pitch. In order to exclude issues with the source, I tried connecting the S2 to my HP EliteBook 745 G5 laptop. The result was even worse than with the Shanling M2X I used most of the time. I couldn’t get a single note played in the right way, even though I have been using the laptop to try most of the Bluetooth headphones in the past year – and none of them has had any issues until now. It’s not the source’s fault, though, it’s the S2 which are just genuinely bad.
There is a so-called “high performance mode” which improves the latency and that actually works quite well. It’s not as lag-free as wired earphones, but it’s a very good compromise.
Range is average, though that has little meaning given how music stutters even at close distance.
The earphones offer touch controls, which comes as both a good and a bad news. The good news is that there are no buttons, so you don’t have to press the earphones further in your ear canal causing discomfort; the bad news is that the touch surface is so sensitive you will often end up doing random stuff (including turning off the earphones) just by adjusting your hair and inadvertently touching the earphones. Among controls offered (play, pause, next track, previous track, voice assistant) there is no option to adjust the volume, which is unfortunate.
Battery life is decent for the price, but underwhelming compared to most recent offerings. The KZ S2 offer around 3.5 hours of playback, also depending on the volume (I listen to the lowest volume possible, so you might get even less battery life). By comparison, the $79 Sabbat E12 Ultra offer 6.5 hours. The 500 mAh case-dock offers three additional charges, for a total that’s barely over 10 hours.
Sound & Specs
I tested the KZ S2 with multiple sources including the aforementioned HP EliteBook 745 G5 laptop and Shanling M2X DAP. Both were loaded with FLAC files, most of which in 16 bit / 44.1 kHz resolution.
|Frequency response||10 – 20,000 Hz|
As in KZ’s tradition, they took a dynamic driver and a balanced armature and shoved them in the shell with little regard for tuning. This produces KZ’s famously V-shaped tuning, which in this case is dominated by piercing treble.
In order to keep costs at a minimum KZ seems to have stinted on the amplifier stage, which introduces a whole lot of distortion that’s clearly audible throughout most tracks. This distortion manifests itself not only in the strong background hiss that’s always present, but also in the smearing of details and in the muddied up sound. The background hiss is the most problematic bit, though, as it is strong enough to drown the music when the latter is relatively quiet (say, H.U.V.A. Network’s Access to the Long Fields). In that same track, around 2:50, the high-pitched synths are completely drowned in the distortion and noise to the point you actually can only hear a garbled mess. I doubted my hearing, but on other headphones I can hear the track just fine.
Soundstage is average in width, but it surprisingly has some depth. Imaging is never more detailed than “left-centre-right”, so you don’t really get the full immersion treatment. Instrument separation is good in the lower area, but mediocre at best in the mids and highs area due to the high distortion.
Bass is preponderant and decently deep. For $30 earphones it’s not bad at all: it’s decently physical and detailed, with enough control to come through as adequately clean. It’s satisfying, not only because it’s abundant (and fun) but also because its execution is done well. It’s got good control, as shown by transients which are relatively clean and fast; in the aforementioned H.U.V.A. Network’s track bass is impactful and well controlled enough to display some smaller details. Bass is actually quite good, even for wired earphones in this price range – though it’s much more present than fans of neutral tunings will like.
Midrange is where issues start to come up. It’s dominated by the upper area, which takes the top spot and leaves the rest almost in the background. The emphasis is strong, as in KZ’s tradition, to the point it’s often fatiguing. Detail is difficult to assess because of the background hiss, which smears most of it. Speed appears to be good.
Treble is the single biggest issue in the KZ S2’s tuning. It’s concentrated in the lower part, with some presence in the middle part and then a cliff in the highest area (which is practically non-existent). The peak in the lower part, coupled with the high-pitched background noise, could be used as an effective mean of torture if you really wanted to – but you shouldn’t, because torture is immoral. Jokes aside, it really is fatiguing as there is a constant sharp hiss poking at your eardrums. They’re not happy about that, as you can imagine. Due to the high distortion, detail is also smeared and treble comes out as a fumbled mess with little identity.
The KZ S2 epitomise what is wrong with “true wireless” earphones: you don’t have fine volume control, there are issues with the connection, the amplification stage is crap and the battery is not exactly long-lasting (and it’s not replaceable). They are okay-ish considering they’re $30, but considering the cabled alternatives for the same price include the Tin HiFi T2, that gives you some perspective on how much difference there still is between wired and wireless.
It’s not that they sound bad, although I find their tuning highly questionable, but it’s more about the quality. The connection is not high quality, but that’s what really defines wireless headphones – it’s their essence, if you wish – and this, together with the constant issues I’ve faced using them, make the S2 really frustrating. I can’t be bothered using wireless headphones whose connection stutters, is frequently interrupted or has issues like those weird tempo changes – it just makes me furious and nothing else. The S2 are cheap and that’s a very good thing, but the problem is that “cheap” is not only about money with them, it’s also about what you get.
So while the KZ S2 might be earphones you may want to consider to try the “true wireless” experience for little money, I find them to be too distant from an acceptable standard in general terms. They’re good as a novelty, but apart from that? I would rather be stuck with wired earphones or save to buy something more expensive. The Lypertek Tevi are around $90, so decidedly more expensive but not unaffordable, and are much, much better on every single front. It’s still three times the price, a fact which raises another issue: the TWS tech isn’t ready for prime time in the lower end yet, and the KZ S2 is the clear demonstration of that.
I agree with pretty much everything you wrote on these. I really wish I’d seen more people note the weird warble pitch fluctuations on these things. It is creepy and happens quite a bit. Most notably when battery is lower. Treble isn’t to bad for me but the background hiss is very noticeable. Like the TWS concept so bought a pair of Buds+.
Kygo E7/1000 uses the same chip RTL8763BFR and has none if these problems. It is a mystery how Linsoul managed to mess up this very good chip. Stuttering seem to be reduced a bit if disabling AAC, or maybe it is just random… Another problem not mentioned is volume/gain is too high, after 6 of 15 steps on my android media volume, it is maxed out for my ears. Other tws does not behave like this. And yes, the pitch problem is absolutely insane.
I did not mention the volume/gain issue as I thought it was just my own personal preference and/or a problem with my source devices having too high a base volume… but you are right, the lowest volume setting is just too high. Thanks for bringing that up.
“Stuttering seem to be reduced a bit if disabling AAC, or maybe it is just random…” Both stuttering and pitch problem has gone away for me after disabling AAC, so don’t think its random.
But found a new annoyance: buds will drain itself empty when not in use. Kygo E7/1000 does not drain, I can pick them up after months and they are still full. KZ S2 will drain itself empty in a few days. Also when the box become drained, the buds will stay on forever. Buds are not put to sleep when being put into a box that is drained. This is the same problem that Sennheiser Momentum buds had (fixed with FW upgrade), so probably a bug in some old Realtek SDK (default firmware). Unfortunately, China does not have a word for “support”, so there won’t be any FW upgrade to KZ S2:-(
Great review, I wish I read this before purchasing these headphones. They are terrible, the connectivity is so bad that I can’t wear them in public. I too have experienced the weird pitch fluctuations, I wouldn’t even take a set of these for free, they are that bad. Do not purchase!!
Could the item be defective ? Just received mine today and the stuttering is very noticable even with my phone sitting in my desk. Reviews on Youtube does not say the same though (Sponsored Content maybe?).
Also i dont experience the volume/gain issue when playing music because I use Poweramp, conveniently its has a 100 step volume wheel. Otherwise on youtube and video clips though, they use the phone’s volume/gain.
I don’t think it’s defective. It’s just poorly implemented. I don’t know why other reviewers do not mention that and I won’t delve into their motivations; I will just say they might not be as pedantic as I am (for better or for worse).
Buyer beware! The quality of this product is poor. I supported the Indiegogo campaign for these earphones and was excited to receive them. When I did, one of them was defective and would not charge or switch on at all. I returned them to the manufacturer in China at the cheapest possible shipping method ($17), but the manufacturer would only reimburse $5 of the shipping cost because that is what it cost them to dispatch from China in the first place. So I got poor quality goods and paid $12 for the privilege.