Astell & Kern T8ie MKII Earphone

Selling Full Set of Astell&Kern AK T8iE MkII Tesla Driver In-Ear Headphones by Beyerdynamic . Condition is excellent as I bought it only in July 2019. Use it for short while and bought an Airpod Pro shortly after. The T8ie has been in my drawer since then.
Reviews From "Absolute Sound":

Currently Astell&Kern has six universal-fit Jerry Harvey-made in-ears, two in-ears from Final Design, and two headphones and one in-ear from Beyerdynamic, the full-sized over-ear AK T1P, the AK T5P, and the AKT8iE universal-fit in-ear monitor. The AKT8iE, which is the focus of this review, retails for $999 and is the first Beyerdynamic in-ear to miniaturize Beyerdynamic’s latest “Tesla” technology. Astell&Kern is the only source for this in-ear monitor just as it is the only source for universal-fit (as opposed to a custom-fit) Jerry Harvey in-ear monitors.

Technical Tour
Depending on whom you talk with, dynamic-driver-based in-ear monitors are either the best or worst technology for in-ear monitors. Dynamic drivers, as compared with balanced armature designs, have higher mass. Their design requires more power and is therefore less efficient than a BA driver, plus dynamic-driver in-ears often sound “slower” and less detailed in direct comparison with BAs, as a result of having higher-mass diaphragms. But to its credit, a single-dynamic-driver design doesn’t require a crossover, which eliminates all the sonic issues caused by phase shifts at the various drivers’ crossover points. The “best” full-sized headphones are almost all full-range single-driver designs, so why not in-ear monitors as well?

Currently most conventional single-dynamic-driver in-ear monitors are entry-level rather than state-of-the-art, but they are all based on something other than Beyerdynamic’s Tesla technology. The Tesla driver utilizes a ring magnet that has a high magnetic flux density. This higher magnet strength is combined with a new multi-layer diaphragm driver technology that has lower mass and less weight, as well as better damping than conventional dynamic drivers. According to Beyerdynamic, “additional attenuation at the heart of the Tesla driver eliminates even the last traces of resonance in the high-frequency range. Beyerdynamic has also optimized the geometry of the baffle design and replaced the single-layer baffle material with a more stable, high-tech compound. This reduces the vibration of the material to a minimum, which in turn delivers even clearer sound combined with ultra-precise bass.”
What you have with the T8iE is a single-driver system whose performance has been pushed well past what could have been obtained from an off-the-shelf driver motor. The new driver system is housed in what Beyerdynamic calls a “special alloy used in high-tech medical products.” Neither Astell&Kern nor Beyerdynamic published a sensitivity specification, but the T8iE proved to be sensitive enough to be driven easily by the least powerful player I have, my iPhone 5. While I understand Astell&Kern and Beyerdynamic not wanting to release too much proprietary information that could tip off competitors, I do see the lack of detailed technical info about the T81E on either manufacturer’s website as part of the unfortunate and almost universal trend toward publishing colorful prose in lieu of revealing technical information about new audio products.

Ergonomics and Fit
While fit is certainly important in full-sized, over- or on-ear headphones, it is even more critical for in-ear monitors. The T8iE comes with eight different tip options. Five are different-sized silicone tips while three are various Comply compressible foam tips. The T8iEs are lightweight and compact (especially when compared to a multi-driver balanced-armature design such as the Noble K-10) and are “anatomically shaped” with an oval molded design that rests in your ear’s auricle and puts the cabling over the ear so that light pulls or tugs won’t dislodge the phones.

The T8iEs come with two cable options. Along with a “standard” 1.3-meter cable terminated with a 3.5mm stereo plug, Astell&Kern includes a balanced cable terminated for the AK100 II, AK120 II, AK240, AK300, AK320, and AK380. This cable uses a 2.5mm 4-pole termination. Also, as you would expect from a premium offering, the T8iE comes with a nice hard leather case and a metal shirt-attachment clip. Astell&Kern also has several other cables available from Crystal and Mundorf at additional cost on its website.

I tried all the tips included with the T8iEs and settled on the largest of the Comply. My ear canals start wide and narrow quickly, like those of many other people, so I usually need to use either the largest tips for my outer canal or the smallest ones if the in-ear monitor’s design calls for a deeper insertion, such as with the Etymotic 4P monitors. The T8iEs’ design required the former because of where it sat in my ear and its fairly large diameter barrel. When properly seated the T8iE isolated me from the outside world nicely. Astell&Kern has no published isolation specifications for the T8iEs and I lack an ear coupler for measurement, but I will take a WAG (wild-a** guess) that it’s somewhere between -18 and -20dB.

Sound
The most impressive aspect of the T8iE’s sonic performance was its cohesion. Not only did it speak with one voice throughout its frequency range, but it also produced one of the most cohesive soundfields I’ve experienced. It’s easy to understand the T8iE’s harmonic cohesion because of the single full-range driver and lack of any crossovers, but what about its spatial characteristics? Since I have no aspirations to design headphones I won’t speculate on why the T8iE’s imaging is so precise and dimensionally convincing, but I can confidently state that once you hear the way the T8iE places each instrument in space it’s hard to go back to a less three-dimensional headphone’s presentation.

I am among one of the least head-transfer-function-sensitive humans on earth [see sidebar]. Years ago Sony had a military-grade HTR calibration device at CES, which tested and dialed in your HTR settings. The device could never get the image to move all the way from the top of my head to the front. It got halfway there and stalled. But when I listened to the latest DTS-X demo through the T8iEs I was surprised to hear not only the front channels coming from in front of me, but also the front and rear height channels above me. On my own field recordings, most of which were made using the Ultimate Ears In-Ear Reference Monitors (IERM), the T8iE in-ears proved to be slightly more “real” in terms of their overall spatial rendition than the IERMs.

The T8iE’s second most impressive sonic characteristic was its bass response. I’ve never considered myself much of a “bass head,” so I wasn’t prepared for what I heard from the T8iEs. They have the deepest, most extended, most precisely detailed and controlled low bass I’ve heard from any in-ear monitor. This should not be confused with the sort of bloated “big” bass you’ll hear from some popular in-ears. Instead of “phat” bass the T8iEs generate true low bass. If you listen to EDM, techno, or modern pop, the T8iEs’ bass control will render what used to be low bass “stuff” into discernable parts and tracks. Unlike many headphones that are known for their “generous” bass response, the T8iEs’ bass rendition does not muck up its lower midrange response. The T8iEs’ upper bass and lower midrange resolution is just as articulate and detailed as the low bass.

Moving up to the midrange, you will be hard-pressed to find an in-ear monitor with a smoother, more even-handed presentation from the lower midrange up through lower treble. This even-handedness extends to the way the T8iE handles musical details. For example, the rhythm guitar’s flutter (as in tape wow and flutter) and the muffled piano in the left channel on James Taylor’s “Sweet Baby James,” from the same-named album sourced from the 96/24 AIFF from HDtracks, were quite obvious through the T8iE. On older recordings you will hear all the warts along with getting closer to the sound than you thought possible. Just as great singers have, seemingly, all the time in the world to finish a phrase while luxuriating in a song, the T8iEs’ give your ear-brain ample time to examine the music’s inner fabric.

The T8iEs’ upper-mid and treble regions were as smooth and resolving as its midrange. The leading edges of the string section, especially the first violins on my own live concert recordings, had just the right amount of sheen and sparkle. The treble (up to 14kHz, which is where my hearing ceases) was airy and incisive and I never felt any desire to turn up the treble or add additional treble energy with eq. In comparison to the AudioQuest Nighthawk headphones, which also have excellent bass extension, the T8iEs’ don’t sound as dark or hooded on their top octave.

The T8iEs also do an impressive job on dynamics, both micro and macro. Take that old/new audiophile demo workhorse Daft Punk’s “Get Lucky” from an 88.2/24 version of Random Access Memories from HDtracks. The bass is big and plumbs the depths but is never slow or turgid. The multiple synthesizer lines each have their own individual dynamic emphasis, and the T8iEs preserve all of them. On modern pop the T8iEs excel, keeping the rhythmic drive pulsing while retaining the subtle dynamic interplay between parts.

Conclusion
The Astell&Kern AKT8iE’s most outstanding sonic attribute is undoubtedly its wonderful bass, which will appeal to both EDM fans as well as any classical listener into pipe organs. The T8iEs go deep, cleanly without bloat, and they do it with dynamic acuity. After its killer bass the AKT8iE’s second outstanding sonic trait is its cohesive, three-dimensional, and exceedingly specific soundstage. While not the biggest soundstage, the T8iE’s level of dimensional precision is exemplary.

If you’re considering a $1000 universal in-ear monitor, obviously you’re pretty darned serious about portable audio and you have well-developed tastes. The Astell&Kern AKT8iEs were created for people just like you. Once you overcome the principal weakness of any universal-fit in-ear, which is obtaining optimal fit, the T8iEs perform on a level that closely approaches the best I’ve heard from any headphone technology, including custom in-ears and full-sized reference headphones.