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The importance of impedance for headphone listening
Electricity is a complex thing (literally—it’s described using complex numbers), and the interaction of the electrical characteristics of a headphone amplifier and connected headphones, quantified by impedance, can alter the resulting sound. Using devices with compatible impedance ensures that the drivers on a particular set of headphones are properly controlled and that their frequency response isn’t altered. A rough rule is that a headphone’s impedance should be at least eight times the impedance of the amplifier. However, this estimate isn’t universally agreed upon, and low-impedance headphones will still work with the higher impedance amps, though often with flabby bass and altered frequency response.
The MicroStreamer, DacMagic XS, and DragonFly (as well as the previously reviewed Arcam rPAC) have an output impedance of around 0.5 Ohms, so they’ll partner well with headphones with impedance of 4 Ohms or higher. This means that these products are suitable for low-impedance headphones such as many in-ear models. The Meridian is rated at about 5 Ohms, making it borderline for use with lower-impedance in-ear models, while the DACport and D3 are rated at 10 Ohms, so they’re ideally suited for higher-impedance (80 Ohm or higher) full-size models. (CEntrance can optionally modify the DACport, if you request, to reduce its impedance to 1 Ohm.) But, again, the 8:1 recommendation is just an estimate, so if you’re in doubt about a particular pairing, the best thing you can do is test a particular device with your favorite headphones before committing to purchase.
Listening in: DACs alone
In my testing, I found all of these models to be solid performers. If you aren’t listening side by side, it’s tough to discern major differences—even comparing their performance directly is to some extent splitting hairs. But a review like this is aimed at such comparisons, so let’s split some hairs!
I conducted my first comparative tests using my big rig (my home stereo) in order to evaluate each unit’s DAC apart from its headphone circuitry. I started with the Audioengine D3 (which, prior to the DragonFly’s recent price drop, was the-least expensive model), using it to establish a baseline level of performance. Compared against the D3, the DacMagic XS sounded more timid: It was less well-defined, and it didn’t sound as sharp. Bass, in particular, seemed quieter and looser through the XS.
In contrast, the MicroStreamer showed an improvement over the D3. The MicroStreamer fleshed out the sound, adding stronger, tighter bass; more clarity and detail; and an improved sense of rhythm and pace. All three of these units, priced around $190, sound good, but the MicroStreamer offers the best sound quality at this price.
Comparing the MicroStreamer to the DragonFly revealed obvious differences, but choosing a favorite was more difficult. On first listen, the MicroStreamer seemed clearer and more detailed, while the DragonFly had a smoother, more-natural sound that wasn’t as instantly impressive, but that I preferred over longer listening periods. Ultimately, the DragonFly’s smooth presentation gave instruments an “in the room” aspect, whereas music played through the MicroStreamer sounded more like recordings. I personally tend to prize clarity, detail, and accuracy over a smooth, romantic sound, so I would have expected to prefer the MicroStreamer, but nevertheless I found the DragonFly to sound more satisfying.
Sonically, the DACport resembles the DragonFly more than the MicroStreamer, but its DAC performance doesn’t quite match that of either of those units. In my testing, the DACport lacked the clarity and detail of the MicroStreamer, but it also didn’t sound quite as natural as the DragonFly. It did manage to best the D3 and the XS, though.
The Explorer also resembles the DragonFly more than the MicroStreamer, but unlike the DACport, the Explorer bettered those DACs. In my listening tests, the Explorer offered a fuller, more-realistic sound than either, and it gave music a more-driven, exciting feel than the DragonFly—it was clearly the best of these DACs. On the other hand, the Explorer couldn’t match the performance of my reference, the full-size DacMagic, which made the music sound better-defined and even more in-the-room. I found the difference between the full-size DacMagic and the Explorer to be more dramatic than the difference between the Explorer and the other portable models here. In other words, while the portable, computer-focused DACs tested here can do double duty in a traditional stereo system, traditional stereo components don’t struggle to outperform them.
In summary, when it comes to just the DACs of these units, I liked the Explorer the best, followed by the DragonFly, the MicroStreamer, the DACport, the D3, and then the DacMagic XS. I also reconsidered the Arcam rPAC, which I’d slot in between the DragonFly and the MicroStreamer. The rPAC has a more full-bodied, believable presentation than the MicroStreamer, but sacrifices some clarity and speed versus the DragonFly. It doesn’t match the portability of either model, however.
Listening in: With headphones
I then tested all the products using headphones in order to evaluate each unit’s combination of DAC and headphone amplifier. Listening through the JH13 in-ear headphones, I came to similar conclusions in terms of sound quality and relative rankings, although the differences between products weren’t as pronounced as they were through my stereo. I did notice looser bass in the D3, DACport, and Explorer, likely due to the relatively high impedances of these units in combination with the relatively low impedance of the JH13. However, these changes didn’t alter my overall preferences.
The AKG K701 is less picky about impedance than the JH13, but more picky about amplifier power and quality. Most of my comments in the previous section hold, though the DACport and rPAC’s better headphone amplifiers assert themselves with the K701—both made these headphones sound more lively, offering tighter bass and better definition in the mids and highs. With the K701, the DACport and the rPAC best even the Explorer—keep this in mind if you’re using full-size headphones that are difficult to drive.
As I mentioned, the Explorer has an optical output, which can be useful for bringing an optical-audio output to computers (such as the MacBook Air) that lack it—or, from the opposite perspective, for adding high-quality USB compatibility to other DACs that lack this feature (or have older, lower-quality USB inputs). I used the Explorer to ferry USB audio into my full-size DacMagic’s optical port, and I then compared the result to a direct optical-to-optical connection between my Mac and the full-size DacMagic. I detected no difference in audio quality between the two configurations. In contrast, I find the DacMagic’s USB input lacking compared to its optical port, so I also compared the full-size DACmagic’s built-in USB input to the Explorer/DacMagic combo: In this configuration, the Explorer handily bested the full-size DacMagic’s mediocre USB input—USB audio interfaces have improved substantially in the last five years! If you have a use for it, the Explorer’s USB-to-optical bridge feature is a great way to ensure that a high-quality but USB-deficient DAC remains useful.
Phones and tablets
Finally, I tested the MicroStreamer (running the new, lower-power firmware) with an iPad mini, an iPad mini with Retina Display, an iPhone 5, and a third-generation iPad using Apple’s iPad Camera Connection Kit and Lightning to USB Camera Adapter. All three sounded great when listening to high-quality audio files, handily besting the devices’ built-in audio circuitry. And the MicroStreamer is portable enough that I’ve made extensive use of this capability. I was even able to use iTunes Home Sharing to stream 96 kHz/24-bit files from my Mac to the iPad mini under iOS 6. (Unfortunately, under iOS 7—at the time of this writing, iOS 7.0.4—playback stuttered, which I’m assuming is a bug in the OS.) I did notice that the MicroStreamer’s power draw had some impact on battery life: I lost a couple hours of playback time on my iPhone when using the MicroStreamer in this way.
As I mentioned previously, none of the other models here work connected directly to Apple’s adapters, but they do work when connected via a powered USB hub. This is a nice option to get high-quality sound from an iOS device at home, but it’s obviously not particularly portable.
What about Android devices? Well, it’s complicated—perhaps unsurprisingly. If your device supports USB-on-the-Go, these DACs may work. When I briefly tested the DACs with the Samsung Galaxy Note 2, only the MicroStreamer worked immediately. I’ve seen reports of other devices working, particularly with third-party software. If you’d like to know if your Android hardware and software will work with one of these DACs, my best advice is to do some research—this post (and thread) on Head-Fi is a good place to start.
A few years ago, any of these models (along with Arcam’s rPAC) would have been best-in-class. You really can’t go wrong with any of them—each provides great sound quality and will improve on your computer’s built-in audio hardware. The differences between them can seem subtle, particularly if considered in isolation. However, the Meridian Explorer offers the best audio quality overall, befitting its $300 price, and its optical output can be useful. AudioQuest’s $149 DragonFly offers the next-best overall sound quality, and the fact that it does so at half the price of the Explorer makes it the best value here. That value, combined with the DragonFly’s convenient design, make it my favorite model overall.
In a few cases, however, I would recommend other models over the Explorer or DragonFly. HRT’s $190 MicroStreamer almost matches the DragonFly’s sound quality and price, and some listeners may prefer its clear sound or find its cool iOS compatibility worth the price premium. If you primarily listen to difficult-to-drive, full-size headphones, the CEntrance DACport and Arcam rPAC will outperform even the Explorer with those headphones, and each costs about $50 less. The Arcam has the better DAC, while the DACport has the better amp.
While I liked both the Audioengine D3 and Cambridge Audio DacMagic XS, it’s difficult to recommend them given that each is more expensive than the DragonFly but neither matches its sound quality. However, the DacMagic XS is the least expensive model that plays 192 or 176.4 kHz files.
Audioquest DragonFly DAC
Audioengine D3 Premium 24-bit DAC
Cambridge Audio DacMagic XS DAC
High Resolution Technologies MicroStreamer
Meridian Audio Explorer DAC