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Acoustic Research AR-M2


I recently reviewed the Audioquest Nighthawks (much to my pleasure) and the Australian distributor of said Nighthawks surprised me by lending me 2 other products at the same time as the ‘hawks. Both products were from long-time audio manufacturer, Acoustic Research, with one product being a USB DAC / amp combo and the other being and AR-M2, Acoustic Research’s portable digital audio player (or DAP).


AR-M2-2844Acoustic Research are not well known in the world of portable / headphone music, but they are a well known manufacturer of top-end speakers so they’re no strangers to the audio world and know what it takes to make great-sounding products.

The M2 is actually their second foray into portable players (as far as I am aware) and my first direct exposure to their products. At around $2000 here in Australia, the M2 plays in the upper echelons of portable players with the likes of Cowon’s Plenue players, Astell & Kern’s AK240, and Calyx’s simply named M. In my experience so far, these top flight players sound amazing, but haven’t always justified their price to me given the amazing performance available in some of the sub-$1000 players on the market. I was keen to see if the M2 could change that trend.


  • Interface: Custom Android OS
  • DAC: Burr-Brown PCM1794a
  • File compatibility: WAV, AIFF, FLAC, ALAC, APE, DSD, and DXD
  • Memory: 64Gb internal with microSD expansion slot
  • Battery life: 9 hours (quoted)

AR-M2-2831Sadly, I forgot to measure the weight of the M2 while I had it, but it’s a hefty beast and weighs something similar to my cumbersome audio stack (HUM Pervasion strapped to FiiO E12DIY). Thankfully, the weight of the M2 is packaged in a much more compact and sleek housing than my Frankenstein stack so although it’s got some heft, the AR-M2 is very comfortable to hold and use and isn’t too heavy to be pocketed.

In terms of size, the M2 has roughly the same footprint as a smart phone, but it’s twice as thick as most smartphones to allow for the epic amplification circuit included, but I’ll get to that…

Overall, on paper, the AR-M2 offers everything you would expect from a flagship device so the next question for me was how it would look and feel.

Design & Functionality

As you can see from the photos here, the AR-M2 is a sexy bit of kit. Acoustic Research have used a nice combination of glass, metal, and high quality matte and gloss plastics to create the M2. It looks high class and feels just as luxe. All of the surfaces you interact with are either brushed aluminium or glass and everything feels incredibly sturdy and well-made.

Hardware Design

AR-M2-2833The M2’s design is accented by a central metal chassis that protrudes slightly on all sides and a little extra at the top. The metal chassis holds a microUSB socket at the bottom along with line out and headphone out sockets (both 3.5mm stereo). One side is blank while the other houses a microUSB slot and hardware buttons (power, play, forwards and backwards) while the top edge holds a ridged volume wheel that’s silky and smooth to use, but stiff enough to be mostly safe unless you really give it a good bump. In that event you might be in for a nasty, high volume surprise, but for the most part the volume control is a really nice design.

Placement of all of the buttons and connectors are logical and well-designed for the most part with the exception of the volume and headphone socket being at opposite ends. If you want to put the M2 in your pocket during listening, this places the volume control at the bottom of your pocket and proves a bit tricky to access. Based on this small oversight and one other that I’ll get to later I can only assume that the designers of the M2 didn’t really have this in mind as a pocket device so much as a plane, train, or office device where you want desktop quality sound without carrying around a desktop size rig.


AR-M2-2852The Android OS makes for a brilliant audio player interface and in the case of the AR-M2, Acoustic Research have designed their own player which bypasses Android’s normal sound handling to allow for a more direct link between your files, the DAC and the amp in the M2. This does mean that you’re locked into their app for your maximum music pleasure, but I found it to be a nice app overall so in my opinion it’s fine.

The only glitch with the app that I am aware of is a funky folder browser that doesn’t support nested file trees (files within subfolders within folders) so you get overwhelmed by seeing everything at once and navigation is pretty tricky. No doubt that can be fixed via firmware updates so I definitely wouldn’t let that put me off the M2, but it’s worth noting.

The Acoustic Research version of Android has had the Google Store removed so you can’t directly download other apps, but you can manually add them by downloading them elsewhere to transfer them across. That means that streaming services are viable with the M2 because it has WiFi capability so some people will no doubt want to add other apps to enjoy the Android flexibility, albeit without the simplicity of accessing apps via the Google Store.

Finally, the touch screen is responsive and the display quality is excellent so the whole interface is everything that a good Android setup should be.


I’ve already shared the file compatibility in the specifications so you know that the M2 can play all major file types, including DSD and DXD. What I was very pleased to see though was that Acoustic Research have successfully implemented playlist support – something that is apparently not always as easy as it sounds. Thanks to this, Acoustic Research have largely overcome the folder browser issue I mentioned above because you can always access your music via simple playlists (assuming you use them of course).

A function that isn’t currently available with the M2’s own player app is true gapless playback. Once again I believe this is a question of firmware only so it likely won’t be a long-term issue and can also be solved by converting any “must-be-gapless” albums into single files. Sure, it’s not ideal, but while you wait for a gapless feature it allows classical albums and progressive music to be enjoyed without breaks.

One final feature I would like to see added to the M2 in the future is some form of volume levelling or ReplayGain feature. Once again I believe this is a firmware function so it probably shouldn’t prevent anyone buying the M2 as it could well be added later. I certainly feel like it’s an important feature on a player of this calibre so I hope Acoustic Research add it in the near future.

Amp Stage & Power Output

AR-M2-2831I’ve already alluded to the quality of the M2’s amp and there’s no denying it is outstanding. It comfortably powered my HD800s, LCD-2s, and every other headphone in my collection. This is clearly an amp designed to power the best headphones money can buy and would likely manage with all but the most challenging loads (like Abyss headphones perhaps).

One slight problem with the amp though is that it is sometimes too powerful. This links back to my previous point about the intention of the designers when they made the AR-M2. I strongly believe they were designing for people listening to headphones while sitting down rather than people on the go. When I look around me during regular commutes I would say that less than 10% of people use headphones when they’re out-and-about with most opting for earphones and IEMs. Nutters like me take that one step further and go for CIEMs to really get in touch with the music, but the point is that commuting and headphones don’t go together as much as commuting and IEMs.

The M2 doesn’t play particularly well with most earphones I tried. It’s better with ear buds (the ones that sit in the cup of your ear) than in-ear designs that seal the ear canal, but overall it seems to be a headphone-focussed design for two reasons. Firstly, the amplifier is just a bit too powerful and the result is very limited usable range on the volume control before the music gets too loud. Secondly, due to their low impedance and high sensitivity IEMs reveal an obvious processor noise from the M2. There’s also some screen noise, but that disappears when the screen is off so it really isn’t an issue (because the screen is mostly off during listening). The processor noise sadly never goes away and is audible during quiet moments of tracks and between tracks. It’s just enough to distract you from the magical experience of listening to music from the M2 which is a real shame because that’s a place you want to stay forever.

Imagine sitting in the most beautiful place you can think of, with a basket packed with all your favourite food and drink, and your favourite person by your side. Are you there? Feeling good? That’s what listening to the M2 is like with headphones…

Now, imagine a mosquito is flying nearby – just close enough that you can’t help but hear it, but far enough away that there’s nothing you can do about it. That’s what listening to the M2 with sensitive earphones is like and it’s such a shame. Seriously, this thing would be perfect if it weren’t for that tiny, but audible sound. Sure, you could connect an external amp with lower gain (and higher impedance), but that would be a waste of the M2’s epic amplifier and frankly makes the whole package too large and heavy.

Before you click away in disappointment, let me clarify. The noise is minor and I know of some people who are happily able to ignore it. Furthermore, the noise is completely inaudible with headphones. With headphones you’re back in that perfect spot and all mosquitos for a 10km radius have been nuked – you’re free to relax and enjoy some of the most magical sounds you’ll ever hear so consider carefully how you would most often use a device like this – if it’s commuting with IEMs / CIEMs then you might be disappointed, but if most of your time will be spent with headphones, this is a device you should absolutely consider buying – in fact, don’t even take the time to consider it – just do it!

Let me explain why…

Sound Quality

AR-M2-2856The sound from the AR-M2 is astounding. For a long time now I have been demoing various DAPs at various price-points and I continuously reach the conclusion that the HUM Pervasion is one of the best sounding players on the market for both its pure sound quality, but also at its price. I’m not suggesting the Pervasion is the best on the market, but it’s good enough that I haven’t been able to justify the cost of other, more expensive players. Well, the AR-M2 completely smashes the Pervasion and I mean obliterates, destroys, outclasses, and demolishes it. That’s in no way a slight towards the Pervasion which remains the best bang-for-buck player I have heard to date, but the M2 is in another league (and it should be for more than twice the price of the Pervasion).

The sound from the M2 is perfect. It is warm in the sense that everything is perfectly balanced so there is no hint of treble fatigue or sibilance, but all of the details are rendered with clean, clear and extended treble. Bass is full and powerful, but without bloat or enhancement and the mid-range performance is equally as impressive with vocals and instruments all possessing both a clarity and warmth that is beguiling and seductive.

The first time I listened to the AR-M2 I couldn’t wipe the smile from my face. Its sound quality really is amazing and only in part thanks to the perfectly balanced frequency response and performance I just described. What separates the AR-M2 from other players I have heard is its combination of balanced sound and incredible presentation. The AR-M2 presents a sense of space and depth around the sound that allows each and every note to ring true and it creates a level of nuance and realism that’s an absolute pleasure to hear. The soundstage isn’t exceptionally wide or deep, but it feels like there’s an endless amount of space around each sound. In fact, much like the Noble Savants I recently reviewed, the AR-M2 keeps its soundstage small enough to be 100% coherent and realistic while being large enough to grant room for each sound to be fully expressed and realised within the overall sonic image.

For a while now I had been thinking that the DSD-capable Burr Brown DACs produced a rather flat sound, albeit with oodles of resolution, but the AR-M2 proves resoundingly that the implementation of the DAC is crucial and the results in the AR-M2 are extraordinary. I haven’t specifically addressed the sound quality of the line out, but it’s safe to say that the glowing comments I have made about the M2’s sound apply to both the line out and headphone out.

Summary & Conclusion

The AR-M2 shows signs of sheer genius and a few signs of immaturity in portable audio design. There is no denying that the sound quality from the M2 is on par or better than any of its competitors (AK240, Calyx M, etc.). The interface is excellent and requires just a few firmware tweaks to really shine. In fact, the only thing holding the AR-M2 back from perfection is the processor noise that’s audible through IEMs and the slight excess of power / volume from the amp.

I can’t stress enough that if you’re predominantly a headphone user and occasionally (or never) use IEMs, the AR-M2 is a must have player, but if you predominantly use IEMs, the AR-M2 might not be a good fit unless Acoustic Research find some way to pull back the gain on the amplifier and somehow attenuate the noise via a firmware update.

I posed the question early on of whether the AR-M2 is worth its $2000 price tag where other similar players haven’t quite managed to convince me. Well, the answer is a resounding yes… if you’re mostly a headphone user. There is no doubt in my mind that the sound quality, interface quality and ability to drive any headphone you’re likely to throw at it makes the AR-M2 worth every cent if you have the budget available.