If you’ve been following my content over the years you’ll know that Knowledge Zenith (KZ) has played a big part in my journey from total newb to whatever I am now. I was around for their early models like the ANV, Micro Ring, and R3, and saw them finally break into the mainstream to set things alight with affordable hybrid iems like the ZST and ZS5.
You also might have noticed my lack of coverage of their most recent generation of earphones as a result. The reason being? The lack of forward momentum just wasn’t there and everything ended up sounding like an iteration, albeit iterations with improvements (some vast), of that original ZST sound. When I was invited to check out the S2 I had to accept. My only experience with Bluetooth gear from KZ was limited to their original 2-pin cable. While I got lucky in that mine still works perfectly and usually spends it’s time powering the equally aged Rose Mojito earbuds, KZ’s record with wireless products has been a little spotty. I was curious to see if they got it right with the S2, and for the most part, the answer is yes.
Let’s take a look at the new true wireless earphone from KZ, and see why this one is a solid budget friendly option in what has quickly become a very crowded market.
What I Hear If you like the KZ “house sound” you should be right at home with the S2 since it brings nothing overly new to the table. That’s not a bad thing since I quite like the v-shaped signature Knowledge Zenith has been touting since they started releasing hybrids.
Treble is well-extended and has a distinct brilliance region focus to my ears. This gives the presentation a bright, airy, shimmery feel that is fun and vibrant, if not potentially fatiguing. Treble sensitive listeners need not apply. In the past I’ve found KZ’s with this bias to sound somewhat loose and splashy, so I was pleasantly surprised to find notes tight and well controlled with a reasonably realistic attack and decay. Detail is good, if not slightly exaggerated given the shift in emphasis to the upper treble regions. While still a bit too bright, I’m glad KZ dialed in and cleaned up the output of their 30095 armature for this application. Overall treble quality is quite good for an inexpensive hybrid, and a wireless one at that.
The midrange is recessed and plays second fiddle to the treble and bass regions. While vocals are less prominent than I’d like and somewhat overshadowed by frequencies at the extremities, they still remain clear and coherent with good tonality. Timbre is somewhat light and bright with a hint of plasticity to it, especially noticeable when a drummer taps their stick on the edge of the drum, but not so far off that I found it distracting in any way. Sibilance is present but not extreme and is handled much better than one of KZ’s more popular recent models, the ZSN Pro. In general, I found the mids here to be satisfying, I just wish they were either pushed forward a bit more or the other frequencies were dialed back a bit to change the perceived recession.
The bass performance out of this earphone should satisfy a lot of listeners. Extension is quite good with the S2 able to delve out some decent visceral feedback on deep, rumbly notes. Midbass is quick and provides good punch, something that seems to be common to the dual-magnet design KZ has gone with this time around. Notes feel textured and detailed as evident running the S2 with some grimy tracks from Tobacco and The Prodigy, something that can often be an issue with wireless sets. Speed isn’t an issue either with quick transitions being handled with tact and grace. Bass isn’t often an area where KZ falters, and the performance here is right in line with expectations. Good stuff.
For a truly wireless earphone, I was quite impressed with the sound stage. The S2 feels quite expansive with a wide and deep stage that has sounds transitioning from channel-to-channel quite accurately. Testing it out with gaming I found sounds dead centre to feel a little off, but as soon as they moved to either side the movement was smooth and reliable. I actually wouldn’t be entirely opposed to using these for some light, competitive gaming. Laying and separation are also better than average for a TWS, only faltering at high volumes where the staging begins to compress and sounds start to meld into each other and lose definition. I never listen at those volumes though, so while it was never an issue for me beyond the few minute I cranked the volume that loud, you might find it intrusive.
Overall I am quite happy with the sound coming out of the S2. While nothing new and special, this v-shaped signature is smooth and detailed with good staging qualities and deep bass that can really carry a track. It definitely sounds best when paired with the artificial elements inherent to electronic music and most modern pop, but it can still provide a good experience with rock and other genres. It also performs best at moderate to high volumes to avoid hiss which is audible at low volumes, and stage compression which occurs at very high volumes.
Compared To A Peer
SoundPeats Truefree+ (~35 USD): While both have a v-shaped signature, the TrueFree+ is less extreme. The S2’s upper treble is more prominent giving it a more shimmery presentation and airier feel. Notes are also more controlled with overall a much higher quality presentation. The Truefree+ sounds somewhat rough and unrefined in comparison. Overall detail and clarity are in the S2’s park, despite the exaggerated treble that makes then feel even more detailed than they already are. The Truefree+’s midrange is thicker, more forward, and more natural, but lacks the clarity of the S2. I still prefer the Truefree’s presentation regardless since it feels more coherent and better integrated into the overall signature. Bass between the two is quite comparable with similar levels of extension and texturing. The S2’s low end is a bit smoother and comes across a little more organic, but doesn’t feel quite a quick. Sound stage is where the S2 is much superior providing a significantly wider listening experience. I was quite surprised as this since the Truefree+ was already quite good for a TWS. Even so, the Truefree+ obviously lacks the width and the S2’s ability to toss sounds way off into the distance. It also has a more intimate default position for vocalists which tends to have the effect of pulling the stage in further. Imaging I found tighter and more accurate on the Truefree+, but layering and separation in the S2’s camp thanks to all that space the music c an play around in. While there are aspects of the Truefree+ I appreciate more, like the mids, I found the S2’s sound stage and treble refinement to provide the better listen. That said, the Truefree+ has a cleaner background in places where there is noticeable hiss through the S2, and might be better is you often listen in quiet areas at low volumes.
In terms of comfort and usability, I’m split. The S2 is more ergonomic and provides a more stable fit in my experience, but the Truefree+ has a more common bean shape that has been shown to provide a more universal fit among various ear types. Despite the S2’s more form fitting shape, it also doesn’t passively isolate quite as well. The Truefree+ also has physical controls vs. the S2’s touch-based controls. No surprise, I much prefer the physical controls which are very difficult to activate by accident. Comfort when using them is sacrificed slightly, but it’s worth it to avoid the finicky nature of the S2’s interface.
Both of these earphones have the same 3.5-4 hours rated battery life. However, battery performance out of the Truefree+ well exceeded my expectations back when I first tested it giving me over 5 hours of listening time. The S2 has been fairly consistent in giving me around 3 hours and 45 minutes of listening time. The Truefree+ has also provided a more stable wireless connection. The S2 suffers from occasional stuttering. At times it almost feels like the two earpieces are quickly re-syncing since volume will drop in the right earpiece, then pick right back up. All of these imperfections pass by in a fraction of a second and honestly do little to hinder the listening experience, but since they’re not really present at all on the Truefree+, well, you know which gives the superior performance.
Overall I like the sound of the S2 more, it looks nicer, and fits my ears better, but the Truefree+’s battery life and connection quality are superior. The physical controls are also much nicer to interact with in my opinion. Whatever it is you value most, pick the one that offers that.
Astrotec S80 (89.00 USD): While both earphones have a v-shaped signature, the single beryllium-coated divers of the S80s aren’t as skewed and have a warmer, thicker feel top to bottom. Where the S2 skewed balanced towards the upper treble the S80 rolls off and focuses on lower treble. Overall detail is similar but the S2 feels more nuanced on first glance thanks to it’s leaner more spacious note presentation. The midrange is dominated by the S80 which is more forward and audible with a more accurate timbre and tone. It does a better job representing a wide variety of vocal styles and artists. Bass on the S80 is a bit more tame compared to the S2 with less low end rumble to it. It is also a bit smoother and less textured with a slower, softer attack. That more relaxed presentation gives note more body though, and things like a slow, chugging guitar riff hit in a way the S2 can’t match. The S2’s sound stage is notably wider and deeper with more space between notes. Imaging performance is similar off-centre with the S80 showing none of the on centre quirks of the S2, though layering and instrument separation are mostly on par.
When it comes to comfort and usability, the S2 wins hands down. I find the S80’s shells somewhat awkward and unstable to wear due to the stubby shape and short nozzle, particularly with the stock tips. Comfortable though. The large touch pad also means I pause my music by accident constantly. That happens with the S2, but not to the same extent. The S2’s controls are also much more in line with the rest of the industry using more traditional actions to perform functions. The S80 can control volume though, so while its functions are less intuitive to access, it has more of them.
Battery life out of the S80 is quite a bit better. 6 hours isn’t unattainable and you get it from the same 2 hour charge time. The case also adds an extra 25 hours of play time vs. the 14 of the S2’s case. When it comes to connection stability, the S80 is more reliable and less prone to the occasional hiccup. The S2 managed to best the S80 with its impressive range though.
Overall I prefer the more natural sound, less skewed sound of the S80. However, the S2’s ergonomics, more intuitive control scheme, and seriously good range have me leaning in it’s favour simply because it is nicer to wear and use, even if connection stability isn’t as reliable. Oh yeah, it also lacks the clean background of the S80, so there’s that too.
Tech Inside Depending on what you are connected to, the S2’s connection is either quite good or somewhat flaky. Stuttering was fairly common when connected to my ASUS FX53V laptop, especially in the low latency high performance mode. Things were much more stable connected to my various smartphones, like the LG G5, G6, and Q70, regardless of the performance mode. The first few runs though the battery I found that every once in a while the right earpiece would briefly drop in volume, then raise back up to match the left. It felt almost like the two sides were resyncing. This issue hasn’t cropped up during the last two complete charges so I’m not overly concerned. Despite the occasional hiccups when paired to my laptop, the S2 has been fairly consistent and never fully disconnected without being prompted to do so. The two sides have also never had any issues connecting to each other. Range was also excellent. Regardless of where the source device was, I could walk around my apartment and the connection would remain strong and clear with no hesitating (beyond the occasional stutters mentioned earlier), regardless of how many walls and rooms were in the way. Pretty impressive for a budget TWS.
Latency is another positive. Even in the low latency mode I find the S2 satisfactory for watching videos. Connected to my LG Q70 there was a very mild desync with voices, but nothing unwatchable. Tossing the S2 into the performance mode lowered latency to the point where any delays weren’t audible/visible to me. Connected to my laptop the desync was more prominent and while switching to the high performance mode fixed this, it introduced connection instability. I guess my advice it to ensure you’re using the S2 paired when paired to more up-to-date products for the best experience.
Battery life out of the S2 is fine, but nothing spectacular. It is rated for 3.5 to 4 hours. Connected to my LG Q70, I’ve been seeing around 3 hours and 45 minutes on average, usually at or below 1/3 volume. The S2 gets very loud very quickly, and I listen very quietly for the most part.
In The Ear With the S2, KZ has done a wonderful job translating their recent designs into the TWS world. The shells are very similar in size and shape to the ZS10 Pro in profile, with added depth to enable the necessary electronics to fit inside. While the inner portion of the ZS10 Pro is smooth and featureless, the S2 takes a similar approach to the ZSR with custom-like protrusions that help lock the S2 into your outer ear. This goes a long way towards keeping stable during movement. This design feature is very important in my opinion, because the S2 is fully wireless and does not utilize ear hooks or any other feature with a similar function to keep the product in place. This lightweight, form fitting design has been very comfortable in my time with the S2, and I have no problems wearing it for the entire duration of it’s battery life of around 3.5 to 4 hours. I’ve been averaging around 3 hours and 45 minutes when connected to my LG Q70 with the sound quality preference enabled, and the S2 on its regular latency standard mode. Not amazing battery life, but quite satisfactory for most use cases.
When it comes to build quality, the S2 doesn’t look or feel like anything special, but it has proven to be durable. I found out the hard way when the left earpiece slipped out of my fingers and over our balcony on the fourth floor, ricocheting off a second floor balcony on the way down. Evidence of the trip was limited to a couple small scuffs. While tough as nails, the plastic used for the ear pieces has that distinct washed out look and oily feel you commonly get with inexpensive, slippery, glossy plastics. The logo on the face plate is a matte texture, something that would have been nice if carried over to the entire earphone. Regardless, fit and finish is fine, though my set did have a number of scratches on the rear of the right earpiece out of the box. I assume that since this is an early production unit, such mild blemishes will not be an issue on the the eventual retail models. After all, it is still going through an Indigogo funding campaign. Also note that the S2 is rated for IPX5 water resistance. I haven’t had the chance to test it yet, but those looking to use these while working out shouldn’t have to worry about sweat ruining them.
When it comes to the case, I’m quite pleased. First off, the matte plastics used are nothing special and feel about as basic as it gets, but they managed to keep it relatively compact and slender enough to fit comfortably in most pockets. While the placement of the USB port on the bottom (???) is an odd choice, I think this is appropriately countered by a proper metal hinge, the lack of which I’ve expressed concern about on numerous models from other brands and at much higher costs. This will certainly give the S2’s case a welcome durability advantage over much of the competition. Some other nice touches are the strong magnets that keep the lid shut, as well as hold the earphones in place and the contacts lined up when dropped into their charge ports. Lastly, there is a button on the back that when pressed lights up an LED under the lid advising the approximate charge level of the case.
- Red – 0-30%
- Yellow – 31-70%
- Green – 71-100%
When charging the light remains a solid red, and when fully charged switches to green
Using the device is mostly a solid experience, though as is always the case I find touch controls on such compact devices somewhat finicky. The logo on the face plate is the touch point and quite sensitive. As such the various control options are response, pending you tap the right spot. I found it helpful to grip the tapered front of the earpiece with your thumb and middle finger, leaving your index finger to tap accurately. While you can’t control volume, other common functions are present like answering and hanging up calls, and playing/pausing and skipping through music tracks. Oddly, I found the triple press needed to activate the high performance mode the most reliable function. If any of the functions were to be changed, I request the single tap to hang up phone calls. I routinely found myself hanging up on my callers by accident. A single long press would resolve this. For those calls I was able to complete, the call quality was decent. Those on the other end found my voice clear, if not a little quiet. The S2’s active noise cancelling feature during phone calls seems to work fairly well.
In The Box The S2 arrives in a bright white lift top box similar in style to other similar products in the same price range. On the lid is an image of the earpieces in a wireframe style art form along with their new brand logo and model name. On the left and right sides is one of KZ’s original logos. As a long time fan of the brand, I really appreciate this nod to their history. Flip the box over and you find numerous contact and location options for the brand, as well as an important notice.
“In order to ensure the service life and safety of the equipment, do not use fast charger for charging.”
Lifting off the lid you find the charge case tightly held within a stiff, plastic tray. Lifting the tray out reveals the included accessories, a warranty card, and a surprisingly well-written instruction manual. In all you get:
- S2 earphones
- Charge care
- Silicone ear tips (m x2)
- USB Type C charge cable
In all a very basic unboxing experience. While the included tips are very high quality and extremely comfortable, you only get two pairs and only in one size (not small and medium which I originally thought) which will be an issue for some. Hopefully KZ decides to toss in some of their community named “Starline” tips, or at least multiple sizes of the existing tips, once the S2 is done its Indiegogo campaign and is up for regular retail sale.
Final Thoughts Taken as a complete product, the S2 is a very solid true wireless earphone. My favourite aspect is that KZ managed to cram all the electronics and drivers into a familiar and comfortable design, without much compromise beyond the shell being a little thicker than it would otherwise need to be. If you like the comfort that this style of low profile shell provides and is used by brands such as KZ, FiiO, TFZ, Dunu, and various others, you will feel right at home with the S2.
The sound quality is also quite enjoyable with good end-to-end extension and plenty of detail, pending you enjoy a v-shaped signature and vibrant upper treble. There is some background hiss that requires moderate volumes to cover up, but after a couple minutes I always forgot it was there and it did little to ruin my enjoyment of my music. This isn’t the sort of earphone you hook up to your pricey hi-fi setup and analyze the hell out of after all.
Connection stability is decent with minor hiccups here and there, but it’s backed by a very strong hold that remains that way over good distances, even with obstacles in the way. I can deal with blips as long as the connection never actually drops, and it hasn’t yet. Battery life is pretty average, however, with me seeing around 3 hours and 45 minutes per listening session.
Overall I think KZ has done a good job with the S2. Given the sub-50 USD price tag (even less right now through the Indigogo campaign) you have to keep expectations in check and with that in mind, the S2 is a success.
Thanks for reading!
Disclaimer: Thank you to Lillian with Linsoul for reaching out to see if I would be interested in reviewing the S2, and for arranging a sample for coverage. The thoughts within this review are my own subjective opinions and do not represent Knowledge Zenith or Linsoul. At the time of writing the S2 was going through an Indigogo campaign. You can check it out at the links below.
- Driver: 7mm dual-magnet dynamic + KZ 30095 balanced armature
- Chip: Realtek 8763
- Codec: AAC
- Bluetooth: 5.0
- Range: 15+ meters
- Frequency Response: 10Hz – 20kHz
- Earbud Battery: 40mA
- Case Battery: 500mA
- Charge Times: 2hr earphones / 2hr case
- Battery life: 4hr music (up to 18 with case) / 2hr talk time (up to 12 with case)
Devices Used For Testing LG G5, LG G6, LG Q70, Asus FX53V
Some Test Tunes
Supertramp – Crime of the Century
Slipknot – Vol 3 (The Subliminal Verses)
Daft Punk – Random Access Memories
Aesop Rock – The Impossible Kid
King Crimson – Lark’s Tongues in Aspic
King Crimson – Starless and Bible Black
Infected Mushroom – Legend of the Black Shawarma
The Prodigy – The Day is My Enemy
Steely Dan – The Royal Scam
Porcupine Tree – Stupid Dreams