KZ (Knowledge Zenith) is known for producing excellent value high-performing earphones, including the popular ED range of dynamic driver IEMs and the hybrid series beginning with the ZST. Founded in 2008 in Guangdong by Keith Yue, a former Audio-Technica engineer, and Zen Li, a Western-trained classical musician, the company name KZ isn’t just a nod to the founders’ initials, but is also short for “Knowledge Zenith”.
The KZ AST is the company’s latest flagship and is the most ambitious design from the company to date. It is an all-balanced armature design featuring twelve drivers per channel.
The Packaging
The AST comes in KZ’s premium packaging, a charcoal-coloured box bearing the KZ logo. It opens bookwise, with the IEMs nestled in a foam insert along with a metal identification plate bearing the model name and configuration. Lifting the foam insert reveals the silver plated cable, spare eartips and documentation. It is perhaps a rather basic presentation for a flagship model.
Build and Design
The AST’s earpieces are formed from a clear resin through which the drivers can be seen and there is a CNC-formed zinc alloy faceplate engraved with the KZ logo. The earphones come in silver, green or black color choices. They appear to be very well made. The 2-pin socket is proud of the surface and accepts a QDC connector and the cable is a loosely-braided 8-core silver-plated copper type featuring a knurled metal straight 3.5mm plug and alloy Y split.
The ear guides are more relaxed than previous designs and there is no chin slider. This is probably the best cable so far from KZ.
The earpieces are, necessarily, fairly bulky in order to accommodate the twelve drivers. These are the new “s”-type balanced armatures which are as follows:
- Bass: 1 x 22955s
- Midrange: 1 x 29869s
- Mid/High frequency: 2 x 30017s
- High frequency: 6 x 50024s (matrix)
- High frequency: 1 x 30019s
- Ultra high frequency: 1 x 30095s
Fit and Isolation
Although the earpieces are bulky, the inner surface is subtly contoured. I have large ear canals and obtained a snug fit but those with smaller ear canals may find a problem doing so. The stock cable was very comfortable around the ears, but I found the AST to be very tip-sensitive.
The supplied tips proved unsuitable so I fitted a set of large original KZ Starline tips instead. I also obtained very good results with a set of KBEAR wide bore tips. Thus equipped, the isolation was very good indeed, and I would think the AST would make an excellent stage monitor.
Sound Impressions
I subjected the AST to a burn in period of 100 hours and I would say that burn in is absolutely essential for this model as the improvement was dramatic. In use, I found the AST quite power-hungry with a smartphone proving incapable of driving it successfully and a higher volume level being required on my DAPs.
I used three different DAPs and discovered that the AST revealed the differences in the sources very clearly. Further improvements were obtained with additional power from a Fiio A5 amplifier. For the purposes of this review, testing was carried out using an Xduoo X20 DAP without amplification.
Tonality
The immediate impression was of a largely neutral presentation, with perhaps a gentle “W” shaped profile and a wealth of detail across the frequency range and excellent clarity. The bass was well textured and clean, the midrange present and expressive and the treble extended, airy and precise. The soundstage benefited from the high levels of detail, as did the separation, imaging and layering which were all of a high standard. The overall tonality was cool with a bit of extra brightness.
Bass
The AST prioritised quality over quantity. Fast, detailed and with high resolution, it was typical of a BA bass driver. It did not display the visceral slam of a dynamic driver but still delivered a spirited performance. Sub bass was lower in level with good texture but a slightly reduced extension.
However, the bass in general was well balanced with the rest of the frequency range and possessed good transient attack. Mid bass was clean and well defined, did not bleed into the midrange and its lively quality brought out the rhythmic aspect of music very well indeed. Bass guitars cut through clearly, drums displayed a crisp strike and fast decay and orchestral basses were especially clear with a natural timbre.
This was very refreshing to hear compared to the heavily bass boosted and ill-defined presentation in many of the “V-shaped” models dominating the market.
Midrange
With its balanced profile, the AST’s midrange came over with little evidence of recession, in fact being a touch forward in nature with copious detail and a largely natural timbre. It was cool and a little brighter than neutral but blended well with the bass and treble and there was no warming influence from the bass region.
As a result, solo instruments and vocals were especially clear and well projected and stood out well from their accompaniment. Male vocals had the requisite weight with diction easy to discern whilst female vocals were light and airy with sibilance only occurring when present in the recording.
Pianos sounded natural and bright with an emphasis on the percussive element. Orchestral solos were portrayed very naturally, displaying an excellent balance with the rest of the orchestra, and the tonality of woodwind and strings was just on the cool side of natural, but there was no “metallic” BA timbre in evidence. The quality of the imaging and separation was notable.
Treble
The AST was very impressive in the treble. With a high level of detail, an airy and open presentation and good extension, this was perhaps its best feature. There was an attractive spaciousness which allowed the music to breathe and the precision of the reproduction ensured that the subtlest elements were delivered in an accurate and revealing manner.
This did mean that shortcomings in poor material were more evident so the use of a good source and high quality recordings is recommended. The large number of drivers handling the treble appeared to be very well integrated with the transition from the midrange seamless.
Percussion was crisp and clean in nature and the harmonic reproduction in violins was precise yet remained smooth. The high frequencies in electronic music were well separated with a sparkly quality and the soundstage was enhanced by the excellent detail retrieval.
Soundstage and Imaging
As mentioned above, the clarity and precision of the AST was responsible for creating an expansive and airy staging. Recorded ambience was very clearly conveyed due to the resolution in the bass whilst separation and imaging were class-leading owing to the superb levels of detail on offer.
There was an oval stage with a little more width than depth, and a good impression of height. The width extended beyond the ears with excellent stereo separation and the precise nature of the presentation delivered detailed layering enabling the production in complex pieces to be appreciated.
This showed in large scale classical pieces where the various sections of the orchestra could be easily identified and their relative positions clearly visualised. In popular music lead vocals were effectively projected above the backing musicians with an appropriate balance between the two.
Comparisons
KZ BA10 ($60)
The BA10 is KZ’s former flagship model. It has an all-metal construction and is very well built. It is a five-driver design and the BAs used are one 22955 for the bass, one 29869 for the midrange, one 31005 for the upper midrange and two 30095 units for the treble, in a four-way configuration.
It has a well balanced sound with a solid bass more reminiscent of a DD driver yet possessing the speed and detail of a BA. The midrange is nicely contoured with a natural timbre and good separation.
The treble is clean and does not suffer from a metallic tonality which can be imputed to there being no drivers placed within the nozzle. The AST is brighter and more immediate in character with a more urgent quality and better detail retrieval whereas the BA10 in contrast is warmer sounding with a deeper and more impactful bass.
Its treble is smooth, and although not as extended, is well balanced. The choice between the two is more of a matter of taste as each has its considerable merits.
CCA C16 ($99)
The C16 is an eight-driver design employing two 22955 units for the bass region, two 29869 BAs for the midrange and four 30095 drivers for the high frequencies. The CCA C16 has a measured and balanced profile which may be termed neutral/bright and has a powerful bass provided by the two 22955 drivers.
Midrange is not as detailed or as open as the AST but is warmer in tonality, and its treble is brighter and not as refined, occasionally displaying that metallic timbre associated with the original 30095 BA. The staging is much less expansive.
Aiderlot M5 ($199)
The M5 is a high quality five-driver IEM using premium Knowles drivers. It is equipped with one 22955 bass driver, one 29869 midrange unit, two 30017 mid/high BAs and one 30095 ultra high frequency armature. It also features three different tuning nozzles, “Reference”, “Bass” and “Treble”.
I found the bass tuning to be the best balanced and in this mode the Airderlot M5 proved itself to be an ultra flat IEM with a linear bass profile, a midrange which was not recessed at all and a very extended treble.
Soundstage was of average dimension, smaller than that of the AST. Bass output was reduced in comparison, mainly focusing on accuracy and detail. The overall tonality was clean but somewhat sterile. The AST is far more engaging and entertaining in style.
Conclusion
I was very impressed by the AST. I consider it to be one of the finest designs so far from KZ, joining the former flagship, the BA10 at the top of the tree. Its combination of high levels of detail, speed and accuracy, coupled with a fine soundstage and technicalities, should appeal to the majority of listeners except perhaps bassheads who would find the bass wanting.
It is a very revealing earphone so do bear in mind that because of its accuracy, the best results will be obtained with a high quality source. To get twelve BA drivers to work in harmony successfully is quite an achievement and KZ must be praised for this and the excellent tuning they have achieved here.
KZ AST Specifications:
Driver Units: 12 Balanced Armatures
Bass: 1 x 22955s
Midrange: 1 x 29869s
Mid-high range: 2 x 30017s
High frequencies: 1 x 30019, 6 x 50024s (matrix)
Ultra high frequencies: 1 x 30095s
Sensitivity: 103dB
Frequency response:10Hz – 40KHz
Impedance: 30 ohms
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