Audeze iSine 20

When I heard that Audeze was releasing a pair of in-ear planars, I perked up, especially given the prior success of the oBravo ERIB-2As, even though those were hybrids. I ordered them late January and waited excitedly.

Fit and Form
The headphones come in a magnetically clasped package with a soft leather case, a hard insert for same, three sets of ear tips (aside on the ear tips: as the canal that carries the sound is larger than most IEMs, regrettably, you can not just substitute Complys for the provided ear tips), two sets of ear hooks, and two sets of their proprietary EarLocks. I found that the EarLocks work best for me, although the smallest pair of ear tips is still slightly too large for my small ear canals. The EarLocks themselves lock into your concha, and when properly adjusted, offer a good hold.
The headphones themselves, though some may be turned off by the design, are very well constructed. There aren't any machining issues, and the design is cohesive. The included cables clip in satisfactorily and seem to hold well. The flat cable is a godsend and, while it may twist on itself a little bit, is fairly tangle-resistant. Microphonics are tolerably low.
The 1/8" connector is straight and good enough; it's nothing special.

Sound
Overall, these headphones sound absolutely stellar. For an IEM, they have a veritably jawdropping soundstage that is especially shocking with binaural recordings. It is both tall and radially large, with a surprising amount of there's-sound-coming-from-behind-you-better-whip-your-head-around ability. The detail is on par with over-ear planars, like the LCD-2. The immediacy and detail allowed by such a large planar driver in such a small form factor is tremendous.
I found that while it shines in the expected genres (e.g. classical and jazz), it does equally well and impressively with almost everything I threw at it (everything from modern pop, to trap, to German dancehall, to pastel house, to Southern rock, to gospel, to post-punk, to EDM, to post-hellenic troika).
Bass
Songs used: Copter by S U R V I V E, I Never Woke Up in Handcuffs Before by Hans Zimmer, and Show Me Love feat. Chance the Rapper (Skrillex Remix) by Hundred Waters
The bass on these is so clean. More than that, it is incredibly fast. I've yet to find a track that they can't facilely keep up with. "I Never Woke Up in Handcuffs Before" is one of my staple test tracks for speed, as the vast majority of headphones (and particularly IEMs) below TOTL simply struggle to keep up once the song picks up. As they are flat all the way down to 10Hz or so, they respond very well to equalizing, but I found that for my tastes, it was not necessary.
Key descriptors: detailed, fast, immediate, punchy, and lush
Mids
Songs used: While My Guitar Gently Weeps by Dario Marianelli and Regina Spektor, Past Lives by Børns, and Sound and Color by Alabama Shakes
The mids in the iSines can most easily be described as rich. There is no distortion whatsoever; they're energetic and open. Both female and male vocals sounded among the most natural that I've ever heard. They absolutely bring your focus directly to the vocals, without diminishing the instrumental aspects of any given songs (considering the separation and stellar imaging).
Key descriptors: rich, and energetic
Treble
Songs used: It's a Long Way to the Top (If You Want to Rock 'n' Roll) by AC/DC, 22 (OVER S∞∞N) by Bon Iver, and MONEY IS FOR THE RENT - NOT FOR THE SOUL by mr. carmack
The treble is slightly recessed compared to the other frequencies, and, to my ear, welcomely so. In songs where I usually immediately get a blaring headache from their treble (particularly 22 (OVER S∞∞N)), I found that I could tolerate it fairly easily. Exactly as in the other frequency ranges, they do not miss a single detail and are supremely fast and accurate, if (again) slightly recessed.
Key descriptors: smooth, detailed, and pleasant

Minutia and Miscellaneous
Although these IEMs are semi-open back (it feels strange to even type those words in the same sentence), and the isolation is near none, their leakage is not terrible. In my experience, they leak a similar amount to the Apple EarPods (whatever they call what Apple includes with new iPhones). If you are listening at a comfortable volume, the likelihood is that none of your neighbors will be bothered, unless you're in a sterile-silent environment. They certainly wouldn't be out of place in an office or otherwise slightly-noisy environment.
The carrying case is nice, but is slightly larger than comfortable. They are still very easily portable, they just require a little extra space in a crowded backpack. The EarLocks fit in a recess for the canals themselves in the bottom of the hard insert.

Wrap-Up
These headphones offer the sound of a much larger pair of cans in an extremely portable package. I have very little negative to say about them, and although they are expensive, I think they are very, very worth it.
A good summary, I think, is that these headphones make me feel a little guilty about skipping the end of a song just to get to hear what they can do with the start of the next.
Disclaimers
These headphones were not provided to me by Audeze, they were purchased purely of my own accord. I am not being paid by anyone to write this review, to endorse the product reviewed, or for the content that I put in the review.
These headphones were powered by an Astell&Kern AK Junior, a Google Pixel, and by whatever soundcard is in the motherboard of my computer.
I have had these headphones for about three weeks, and they have been my main driver for that time.

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