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The Mo-Fi's unique cantilevered design is unlike anything else out there. The Mo-Fi phones come with a nice selection of accessories.
The Mo-Fi's unique cantilevered design is unlike anything else out there.
The Mo-Fi phones come with a nice selection of accessories.

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Blue Mo-Fi
By Mike Metlay
Date: November 2014

Blue first appeared in our magazine in November 1996, in a small article about then-Editor Nick Batzdorf's visit to what started out as a mic-refurbishing business. With a factory in Latvia doing the heavy lifting and an office in the Los Angeles area pairing mics with buyers, Blue's intent was to take vintage mics and restore them to fighting trim for use in real-world studios rather than moldering away in collections.

Not long after that, Blue started making its own uniquely designed and cool-sounding mics. We've premiered any number of Blue products in our pages, including reviews of the now-classic Mouse and Dragonfly mics before anyone else got them, and we've watched the firm expand into new areas: mic preamplification with Robbie, USB miking with the Snowball, and podcast-friendly I/O solutions for miking and monitoring with the Yeti.

For nearly a year, we've been waiting on Blue's newest effort: a promised re-imagining of headphones that Blue calls Mo-Fi. The wait is over, the Mo-Fi headphones are here, and here's what I found after living with a pair for a few weeks.

From hi-fi to Mo-Fi

The guiding principle behind Mo-Fi is simple, and relates directly to the idea behind powered studio monitors and active ribbon mics. If you put the critical amplification stage inside the product, right along with the moving transducer (whether said transducer is a mic element or a speaker), you can assure that they are perfectly matched, no matter what they're connected to.

That's what Blue purports to have done with Mo-Fi. The headphones can operate as an ordinary pair of passive cans, or you can turn on the internal amp for more volume and greater dynamic range. While Blue has been pitching Mo-Fi to any listener who wants consistently great audio, the primary push is for mobile listening -- an attempt to overcome the shortcomings of the relatively weak audio circuits in many mobile devices. With that in mind, I tested the Mo-Fi with a variety of budget and high-end audio interfaces, and with my Apple iPhone 5 and iPad Retina Mini.

Out of the box

The Mo-Fi phones are very unusually designed; rather than the usual padded headband or spring-loaded sling that adjusts to the skull, the Mo-Fi headband is a 5-piece articulated metal design with spring-loaded joints. The horizontal top piece with its thick padding contains a dial to loosen or tighten the tension in the two metal pieces at the sides of the head, and the earcups themselves are mounted to joints that allow up-and-down movement just above the ears. The overall intent is a sturdy design that conforms to any head shape.

The closed-back earcups themselves are teardrop-shaped to fit the ears fairly closely, rather than being round or oval. The luxuriously thick padding around the earcups creates a tight seal when combined with the spring action of the articulated frame, making these the best-isolated headphones I've heard in a long time. When listening at normal safe levels, no one standing near the listener will even be able to tell if they're on, and they block outside audio better than any headphone short of a dedicated isolation phone like the Direct Sound EX-29.

Both earcups have small green LEDs that illuminate when the headphones are powered up and flash slowly when they're plugged into the wall and charging. The phones sense whether the earcups are close to one another, turning themselves off when you take them off. This prolongs the battery life of the amp, which gives about 12 hours' audio playback on a single charge (my results matched that estimate reasonably well) and takes 3 to 4 hours to charge fully.

The Mo-Fi comes with two straight cables, a 1.2-meter cable with a standard 3-button iOS volume/pause control and a 3-meter cable sans controls. The cable plugs into a deep socket on the left earcup, and the other end is terminated in a standard TRS or TRRS minijack depending on the cable chosen. A 1/4" TRS snap-on adapter is included, along with a wall charger, 1-meter micro-B USB cable for charging the phones (the charging port is on the left earcup near the cable socket), airline 2-prong adaptor, and a large pouch with a magnetic closure to carry it all.

Before we get to my listening sessions, here are a few specs for your interest. The Mo-Fi has drivers with a very generous 50 mm in diameter, a frequency response of 15 Hz to 20 kHz (no tolerances given), and a 42 ohm impedance. The internal amp claims a Total Harmonic Distortion + Noise below 0.004%, a Signal/Noise ratio greater than 105 dB, and a power output of 240 mW, a pretty hefty jolt for something strapped to your ears.

Switched Off, switched On, switched On+

The amp in the Mo-Fi is controlled by a rotary Off/On/On+ switch that surrounds the cable socket. When Off, this is a conventional passive headphone; when On, the amp kicks in, and the On+ setting adds a "fun/exciting" low-mid boost. The gain structure is fixed -- there's no volume control on the phones themselves.

Blue warns in several places that the amp makes these headphones really loud, and they're not kidding. As a rough rule of thumb, I found that on my iPhone and iPad, which have a 16-click volume adjustment from silence to full blast, the difference between Off and On was about four clicks. So, for example, if you usually run your iPhone with its volume set anywhere from 12 to flat out, the On setting lets you hear at the same level with a setting of 8 to 12.

When you leave the mobile world, the amp quickly becomes overkill. On every audio interface I tested that had any sort of real juice in its headphone circuit, more than a tiny nudge above dead silence was enough to make the Mo-Fi too loud for comfort.


In the review process, I spent about 30 hours under the Mo-Fi phones. I found the sound of the Mo-Fi to be quite enjoyable; it's a very mid-forward and present phone, well suited for rock and roll. On the low end, bass is well-defined and abundant, thanks in part to the large drivers and sealed earcups. The highs are smooth and even; they're not muffled or hashy or smeared, delivering excellent results even in comparison with phones that have a lot more treble extension according to the spec sheet.

While most of my mobile listening was done on Apple gear, I did manage one informal test with a Samsung Galaxy S4 smartphone. The phone's owner confirmed that the On setting was a significant improvement over what he was used to hearing from his phone.

Interestingly, the On+ setting does not make the Mo-Fi a lot louder; it's a subtle but very pleasing EQ tweak (Blue proudly states that it's all-analog, no DSP involved) that brings the bass and low mids a hair upward and is well-suited to dance music, hip hop, or anything you'd like to hear with more boom and thump. I wouldn't engage it for critical listening, but it's a lot of fun in casual use.

Blue markets Off mode as a sort of fallback position for when the amp runs out of charge, but I actually liked it better than On mode! The phones were no longer overly loud when used with audio interfaces, I felt the sound quality wasn't compromised in the least on my Apple hardware, and the 42 ohm impedance allowed the phones to get plenty loud even when connected to an iPhone. Also, with one or two poorly shielded "semi-pro" audio interfaces, the On mode produced a faint background whine, which vanished in Off mode.

Carry that weight

There's one more number on the Mo-Fi spec sheet that I haven't discussed yet: a weight of 466 grams, a hair over one pound. It's not impossible to build a headphone that is heavy yet comfortable -- the AKG K812 weighs nearly 14 ounces and you barely notice you're wearing it -- but the sensation of weight is the first thing you feel when you pick up the Mo-Fi phones, and when you put them on your head, it intensifies.

The weight of the Mo-Fi combines with its headband design to create a divisive ergonomic experience: you either love the comfort and isolation, or you find the weight and pressure distracting. I got the most comfortable results for my head when loosening the top bar all the way; tightening the headband added pressure behind my temples but didn't ease the weight on the top of my skull.

The lower joints, above the earcups, allowed for a tight seal regardless of where the top bar was placed, so I could move it back and forth in a search for the most comfortable fit, but they didn't help support any weight that I could feel. I couldn't wear the Mo-Fi for more than a half hour before the discomfort above my forehead and the tension in the back of my neck from the weight demanded a rest; frequent breaks were the order of the day.

I needed to be sure that it wasn't just me, so I took the Mo-Fi to a gathering of local musicians, set the phones on a table with an iPad, and let people try them on their own without any introductory commentary beyond "Here's how you adjust the headband, here's how you turn them on, mind your levels." Pretty much everyone enjoyed the Mo-Fi's sound, and one or two of the attendees flat-out loved how they felt, but almost everyone else commented on their weight and/or uncomfortable feel, and only one person was eager to wear them for more than a few minutes. (It was the guy with the Samsung smartphone, if you were wondering.)

On balance

All of my listening sessions with Mo-Fi ended the same way. I would be listening happily, totally immersed in the sound of the phones, and I'd be yanked out of the moment by my aching head and sore neck. I have been known to sigh with relief when taking off headphones, but usually after four or five hours, not 30 minutes.

As for sound, we've given thumbs up to other strongly mid-forward phones before, but when we do, we have to advocate caution before using them for mixing or editing. The Mo-Fi might sound fun and engaging, but I wouldn't call it studio-neutral.

The Mo-Fi technology, cool as it is, seems to me to be a solution in search of a problem. Adding the extra gain stage -- even one well matched to the drivers -- doesn't seem to offer sonic benefits that counterbalance the added weight and discomfort. It's not impossible to build a great-sounding passive headphone that coexists happily with even the tiny amplifier in a mobile device. I would even say that Blue's already done it... just listen to the Mo-Fi with its amp turned off!

Ironically, setting aside the amplification and headband that make the Mo-Fi unique might well produce a better headphone. The earcups and drivers on the phones sound great without the amp stage; a passive version at half the weight (and half the price) would be an amazing competitor in the world of pro audio headphones. But the current design is simply too heavy and fiddly to be a slam dunk, at least for this reviewer.

Only time will tell if this technology will be refined to the point where it's as common as active studio monitors, or if it becomes a historical footnote along with multitrack MiniDisc recorders and Digital Compact Cassettes. In the meantime, Mo-Fi is certainly a bold endeavor for a company with a history of exciting innovations, but one that definitely falls into the "you need to try it for yourself" category.

Price: $350

More from: Blue,

Kef America

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