disclaimer: The KZ S2 has been much anticipated and having enjoyed the E10, I was interested in seeing how this new model would fare. I was provided the S2 by LinSoul Audio for purposes of this review. The S2 is a bit different from most KZ models as it was crowd-funded and to some degree crowd-sourced as much discussion has gone into what the S2 should be and the specs have shifted considerably since the early discussion with a different bluetooth chipset as well as other changes, so I am interested to see how this product will perform. If you have an interest in the KZ S2, visit Linsoul Audio or their Amazon Store.
Unboxing / Packaging:
The S2 ships in a white lift-top box with the line drawing on the front and the KZ address on the rear, details of the drivers etc are not on the box as is typical for KZ. Lifting the cover reveals the case in a plastic tray, under the tray is a short (6 inch) USB type-A to type-C cable, a warranty card, the user manual, and a single spare set of tips. Earpieces are in the case and do have a set of tips installed so you get two medium sized sets of tips in the package. This is probably the single biggest complaint here as for $29 I don’t expect miracles but a full set of tips to allow for better fitment is a must.
The shell on the S2 is a 4 part design made mostly of black resin with a brass nozzle. The outer faceplate is made of two parts: the shell itself and a large central button with the KZ logo. A large slot vent is cut in the rear face of the faceplate near the upper edge. The LED is visible through this vent so we have to assume it provides an ingress for sweat although the S2 is listed as IPX-5 water resistant. A second small vent exists below the nozzle on the inner shell. The inner shell is the semi-custom ergonomic shape that has become the norm in recent years. The joint between the faceplate and the inner shell is easily visible and felt readily with a fingernail but is uniform with no glue or slop present. The nozzle exits the body at nearly its lowest point with an acute forward rake for fairly deep insertion. I found the S2 fairly comfortable for longer listening sessions but did have to do some tip-rolling to find a slightly larger tip than those provided to get the seal I wanted. Even with those larger tips, isolation is only average.
The heart of the S2 is a 7mm dynamic driver coupled with a KZ made 30095 balanced armature driver. I mention the maker as increasingly the numbers alone are becoming generics and several makers now produce a 30095 series driver. The Dynamic driver is listed a dual magnet, with a composite diaphragm but no further details were available at the time of this review. Connectivity is hadnled by the Realtek 8763 chipset and offers bluetooth 5.0 support with SBC and AAC connectivity, but lacks the Apt-X HD and LDAC some had hoped for. Per KZ, this was done to improve compatibility as AAC was more readily available on a broader spectrum of devices and battery life as it was a bit more efficient than the Qualcomm alternatives.
The touch controls are better on the S2 than some recent models with a single touch being used for play/pause. dual tap on left is back, dual tap on right is forward, triple tap is mode switch between high performance and standard modes, and press-and hold is turn off/on/pair. Controls react quickly which is also appreciated as some other touch models I have tested left me wondering if I had hit the right button by the time they reacted.
Early discussion of the S2 had included a Qualcomm chipset that would have included Apt-X HD support and possibly LDAC but at some point in the prototyping it was decided to move to the Realtek chip and focus on AAC protocol support instead. This is probably due to the fact that the S2 is positioned as a direct competitor to Apple’s products as can be seen in KZ’s marketing materials (shown below). I did find the S2 worked well when connected to devices that supported AAC, but suffered some with devices like the Hidizs DAPs that support LDAC, and AptX protocols but not AAC. Distance between source and earpiece was roughly 10 meters before break up started and a single layer of drywall often did not defeat the signal. Longer distances or heavier walls did fairly easily defeat the signal. I did appreciate the low latency option (triple tap to engage) as it did a good job of reacting instantly to commands and keeping video in sync with audio on my devices.
The case is fairly typical of TWS offierings of late with plastic all the way around. The upsides are it does have a proper metal hinge and a magnetic closure on the lid. A single button on the reverse is used as a battery indicator prompt, but the LED indicator that displays charge status is unfortunately on the inside of the case. This is a bit odd in that the button is most easily seen by turning the case to orient the rear toward you, but then the LED is blocked by the lid of the case unless you change orientation of the case to view it. When the button is pressed, the LED will display Red if the case is between 0-30%, yellow for 30-70%, and Green if over 70%. The button does not work when charging the case as the light stays on solid red while charging and turns green on full charge. Another odd feature of the case is the USB type-C port which resides on the bottom of the case for charging. You cannot set the case on its base and charge it at the same time, this again seems like whoever designed this cared very little about ergonomics.
The case sports a 500mAh Li cell battery that measured 429mAh in my tests and each earpiece has an internal 50mAh battery. I didn’t attempt to test these as my equipment’s minimum discharge rate is high enough I was afraid of damaging the tiny cells. KZ lists the S2 as having up to 4 hours of listening time or 2 hours of talk time if the microphone is engaged. I found both of those numbers believable but perhaps slightly ambitious with my listening times being closer to 3 hours than 4 when using the S2 at normal listening volumes (82dB). Recharging the earpieces takes roughly 2 hours from drained to full charge. The case is able to charge the four times before the case has little enough remaining capacity that a full charge cant be delivered. A fifth partial charge may be possible depending on depth of discharge before the earpieces were returned to the case. Using the phone does reduce the battery life to closer to 2 hours and for my use it was slightly under that. A low battery vocalization will be heard in the earpieces as it approaches cut-off. I found that usually I started getting cut-outs about this same time.
Ok, lets just be honest up front, if you were planning on using these for office meetings and important business calls, you may be better served by something else. It picks up a fair amount of surrounding noise and even in quiet environments there is a background hiss produced by the mic. Voices are clear to the listener wearing the S2, and speech is easy to hear for those on the other end of the call but quite often they spoke of hearing a hiss or a noisy background. I think, for many, these will be used for music listening with only the occasional call thrown at them and I think this is the best use case as for call quality other models offer more in the same price space. The Dudios shuttle that I reviewed was a better in ear for calls, but won’t rival the S2 in overall sound.
Sub-bass has good extension, is elevated with a center around 80Hz and a mild roll-off that only becomes notable below the mid-30s. The S2 is able to deliver good rumble when called upon without getting really lose or sloppy. Mid-bass drops throughout its range and is a bit less pronounced than the sub-bass but retains good definition and presence in the mix giving the S2 no lack of slam at the low end. I think KZ has done a good job with the speed of the 7mm dynamic here as it quick attack and just slightly slower decay which give the sound good texture and a natural tonality that is lacking in a lot of TWS. I applaud KZ for a low-end with both good definition and some slam and rumble when called upon.
The lower-mids continue the decline from the sub-bass peak and while not emphasized like the sub-bass and treble, overall the mids still have good presence and don’t sound overly recessed. This step back does mean vocals are on the same plane with guitars and other instrumentation and don’t cut through the mix quite as well as one would like at times, but it also means they don’t sound artificially elevated either. Upper mids climb a bit forward and female vocals tend to be a bit in front of their male counterparts as a result. String timbre is not quite realistic, but one must remember the price point here as that is a lofty expectation. Midrange detail is good but the tonality is a touch bright and tracks that tend toward sibilance will show that and be a bit strident at times. This is not to say the mids have that bite if the track doesn’t take it that direction anyway, but it does little to attenuate that either.
Lower treble climbs fairly rapidly, continuing what the upper-mids started. This pushes the lower treble to the foreground and gives the S2 good energy and some extra life rather than sounding a bit dulled. It does seem that KZ has continued to work on tuning the 30095 (either internally or by crossover design) as this iteration is not as splashy and strident as several earlier models. The true treble retains the same energy level as the lower up through about 7.5kHz which gives snare rattle good realism and highhats just a touch of metallic sound but overall very good at the price point. Final roll-0ff is somewhere above 13kHz which is quite good regardless of price but exceptional at the asking price here. Detail is good throughout the treble with good air and sparkle at the top. The only caution here is the treble is still a bit hot and sparkle can and does become sizzle occasionally.
Soundstage / Imaging:
The S2 has good stage size with slightly better width than depth and does even muster some height in the mix. Seating the orchestra was fairly straight forward although the S2 has somewhat limited instrument separation when compared to the E10 or Zs10pro but still quite good when compared to other TWS models I have tried Thus far. Movement around stage is quite good but somehow never quite feels that it reaches dead center in front, but otherwise feels fairly precise. Layering is fairly good for TWS but again fairly limited in the overall. Compression becomes fairly evident as the volume gets louder and the tracks get busier so keep that in mind, the S2 is best at moderate volumes.
Thoughts / Conclusion:
There has been a race on to create a budget earpod killer. Most makers either have released or have planned some form of TWS product targeting everything from the casual listener, to the office user, to the gym rat. KZ through their hat in the ring with the E10 but quickly found that its form factor of earhooks was a negative for many, and its connectivity wasn’t as good as many had hoped. This go around, they backed off the sound quality a bit (The E10 was basically A Zs10 Pro sonically) and instead focused on giving the people what they had asked for. The S2 is IPX-5 rated, is a true TWS with no earhooks or appendages, has good battery life, and better connectivity than its predecessor. Sonically, it is a V shape with good lively sound for popular genres and enough call quality to be good paired to a phone. While the treble is still a bit forward, it is more refined than earlier efforts, and can be tuned back a bit with EQ for the more sensitive folks. The S2 may just be the best option available for those looking for a budget TWS. Yep, it beats the Sabbat, the Dudios, and Simgot models I have tried, and even its larger sibling the E10 in most respects. To get better than the S2, you’ll have to spend at least twice as much based on my experience to date. While I still wish for and LDAC model, this thing is well worth considering even without it.
- Bass - 6.5/106.5/10
- Mids - 5/105/10
- Treble - 6/106/10
- Soundstage - 6/106/10
- Imaging - 6/106/10
Pros: True TWS form factor, good battery life, respectable sound quality, improved connectivity, IPx-5
Cons: no LDAC or AptX support, odd location of charge port and LED battery indicator, noisy mic, limited kit