This is the most innovative headphone I've ever seen, and it sounds great. Its low-frequency reproduction is especially impressive — better than any headphone in my collection. But before we delve futher into the sound, let's start by describing the Mo-Fi's stand-out features.

First, there's an onboard 240 mW Class AB amplifier that's been carefully matched to the custom-built 50 mm drivers. If you're listening to music on a mobile device, you'll be very impressed with both the volume and the sound quality this amplification stage adds to the experience. The amp runs off an internal Li-ion battery that is rechargeable with a bog-standard micro USB cable. (A charging cable is included, as is a tiny 1.0 A output USB charger.) The amp will last for about 12 hours of listening, and after that, the Mo-Fi simply becomes a passive headphone. A rotary switch that surrounds the port for the removable headphone cable turns the amp on and off, and it also allows you to put the amp into a bass-boost mode (4.5 dB bump at 60 Hz), which uses a good ol' analog filter — no DSP wizardry here. This boost is nowhere near as obnoxious as the B.S. bass on "DJ" headphones; it's more like turning up a subwoofer a wee bit. Personally, I would have traded away the bass-boost feature for an analog attenuator instead, because the amp adds way too much volume, forcing you to turn down the output of your source too far; if your source is a mobile phone, you're turning down the pre-DAC level, reducing the bit-depth of your signal. Smartly, the amp turns off when the headphone is taken off your head and the earcups are allowed to close in on each other, which means that the headphone doesn't leak any sound if the amp switch is turned on but the headphone is off your head. This feature not only extends battery life, but it also facilitates A/B'ing a mix between headphone and speakers without having to turn up/down the headphone level as you go back and forth.

Second, the earcup cushions are shaped like upside-down teardrops. Most of us have earlobes which are bigger up top than down bottom, and the Mo-Fi's cushions mimic this shape. The result is a much better seal behind and below the ears, where the skull and jaw transition to the neck. The cushions, which are user-replaceable, are made of dense memory foam and are covered in a very supple, premium vinyl that doesn't absorb sweat or skin oil and is easy to clean. Importantly, the earcups offer the best seal I've ever experienced — even with my eyeglasses on.

Third, there's a multi-articulating headband with various joints and arms to precisely position the earcups over the ears. The center of the headband is padded with the same vinyl and memory foam as the earcups, and there's a tension knob there that varies how much squeeze is put on your head. Leading to each earcup is a near-parallel, 4-bar linkage, which was inspired by the double-arm suspension designs of Formula One racecars. Between each linkage and earcup is a pivoting secondary arm with a ball joint for independently tilting and automatically adjusting the camber of each earcup to the ear. On a car, the suspension works to optimize the contact patch of the tires as the car turns, leans, and reacts to the changes in road surface. Similarly, the "suspension" on the Mo-Fi keeps the earcups in line with your ears, no matter the size and shape of your head. Every moving part and joint moves smoothly in a well-damped manner, and Blue took great care to make sure there is no mechanical resonance. My son commented that I looked like I had an alien insect on my head when he first saw me wearing my Mo-Fi headphone. I agree that it looks like some crazy alien tech, but apparently, these aliens are experts in luxury materials and finishes. In reality, the Mo-Fi is a result of a 3-year development partnership with AWOL.

Now that we've covered the major innovations, let's talk about sound. I've owned my Mo-Fi for many months, and on top of all the casual listening I've done on it, I've also used it on many critical listening sessions, as well as spent some time playing test tones through it.

The Mo-Fi is not at all a "lifestyle" headphone for the street and subway crowd, and therefore, it's not stupid bassy. Bass from 200 Hz down is what I would call "emphasized" — like going through a 5 dB linear-phase shelf EQ — but, it's the clearest of any headphone in my collection. Driven with a good headphone amp, I can hear the fundamental tone of bass notes with less harmonic distortion than I hear from my other headphones, even at 20 Hz. When the Mo-Fi is driven from an anemic headphone output (like on a mobile device), the harmonic distortion easily swamps the fundamental for low bass notes — until you turn on the headphone's built-in amp, and then, the harmonic distortion drops away. With music, the bass is articulate and punchy, a testament to the superb drivers and electronics, as well as to the perfect earcup seal.

The midrange sits back slightly from the bass, but it's there and represented with clarity. Harmonic distortion in the critical 300 Hz to 1 kHz region is exceptionally low, which explains why the midrange, despite playing backseat to the bass, sounds so clear and doesn't get lost.

The treble has a bump in energy at 4-6 kHz, and then from 7 kHz on up, it's essentially shelved down a few dB. The response then starts to slope off further at 14 kHz. Crucially, phase response is near linear from 20 Hz all the way to 16 kHz, which is the upper limit of my hearing anyway.

Keep in mind that we all have differently shaped heads and ears, and therefore, your experience with this or any other model of over-the-ear headphone may differ from mine. Therefore, I think it's prudent to listen to any headphone before making a purchase. With that said, here's my recommendation.

If you need a headphone that will force you to work hard to rid your mixes of sibilance, the Mo-Fi is not it. On the other hand, if you prefer a headphone that sounds big and full, without the midrange getting lost, the Mo-Fi should be on your short list, especially if you appreciate all of the innovative engineering invested in its design. Also, the Mo-Fi is a perfect complement to nearfield monitors, since its bass response is pretty much as good as it gets. Even if your monitoring setup includes a subwoofer, unless your room was purposefully designed with perfectly effective bass-trapping, room resonances will reduce the accuracy of the low-end reproduction in the room — not a problem if you're listening on the Mo-Fi.

Included with the headphone are two straight cables. The shorter one is perfect for use with an in-pocket mobile device, and a three-button iOS-compatible remote is mounted in-line. Both cables terminate in a skinny, case-compatible 1/8'' connector. A 1/4'' adapter is included, as is a two-prong airline adapter just in case you want to go back in time and fly on an outdated jet. If you do, make sure your time machine has extra room, because the Mo-Fi doesn't fold up for travel. The headphone fits into a large carry pouch, inside which is a pocket for holding the cables and accessories.

Tape Op is a bi-monthly magazine devoted to the art of record making.

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