A Survey of Digital Audio Players Part 3 Acoustic Research M-2


Acoustic Research M-2 ($1199)
I imagine most InnerFidelity readers have at least a casual knowledge of the old Acoustic Research brand name. That company has a history dating back over 60 years. And a big part of that history involves buyouts by other firms who, unfortunately, didn't always make the wisest choices with their new acquisition. AR only operated on their own for a mere 15 years before being purchased by Teledyne, who eventually sold to Jensen Electronics. Then came Recoton Audio who swooped in and bought Jensen, getting AR along with it. Finally Audiovox, who now goes by the name Voxx International, picked up the brand in 2003, and retains ownership to this day.

Voxx actually has quite a roster of current or formerly well-known audio brands: Advent, Jamo, Klipsch, and RCA to name just a few. To be honest I had no idea the company was so large—at over $600 million in annual revenue last year, it's significantly larger than audio conglomerates like D&M Holdings (Denon, Marantz, Boston Acoustics) and World of McIntosh (formerly Fine Sounds Group—Sonus Faber, Wadia, Audio Research, and of course McIntosh). Voxx doesn't seem all that interested in competing in the higher-end audio space, but that may be changing. Despite owning Acoustic Research for well over a decade, the company is finally doing something interesting with it.

AR re-enters the market with the M2 DAP. From my discussions with their engineers and designers, it seems like they've assembled a potent team who is really taking this venture seriously. A plethora of firmware updates over the past year confirms their dedication to the device. So too does the more recently launched M20, a relatively more affordable DAP at $699. I believe there's a USB DAC/headphone amp in the lineup as well though I don't know much about it. Bottom line: Acoustic Research is "back", even though it may not be doing what most people would have expected.

External Design
The M2 is moderately large DAP with very nice build quality, as would be expected for the price. Unlike many competitors, this one looks roughly like a thick, somewhat blocky smartphone, and I've actually had several people make that assumption while seeing me use it. The whole thing is dominated by the 5" display which sports a 1280x720 LCD of reasonably high quality. This isn't spectacular by smartphone standards yet feels pretty satisfying compared to the lower resolutions found on much of the competition. There are transport buttons along the side which have a nice tactile feel to them, and the small volume wheel on top avoids accidental movement by virtue of its low profile. I thought the smaller volume wheel might hamper precise adjustments but it works out just fine in actual use.

Nothing ground breaking here. The device looks and feels smartly laid out, and build quality is high if not outrageous. Again, from many angles this looks like a phone, as opposed to the HiFiMAN and Cayin and Pono players which are very obviously something else. Whether this is good or bad is up to you, but I was surprised to find that I appreciated the lack of "what is that thing?" inquiries while using the M2.

Internal Design
The name Acoustic Research implies some thoughtful design with respect to sound quality, and the M2 does its best to live up to that name.

On the digital audio side we get a TI PCM1794A DAC, a Cirrus CS8422 ASRC chip for upsampling, and a pair of voltage controlled, temperature compensated crystal oscillators (one each for 44.1kHz and 48kHz sample rates along with their multiples). The analog stage is comprised of dual TI OPA2134 opamps feeding a TPA6120A2 headphone amp chip. Volume control is handled by an Alps potentiometer rather than a digital volume solution as used by many competitors—I'm of the opinion that either method can be done well. It's worth noting that the output impedance is 10 ohms, which is a TI recommended value for their 6120 driver chip. Obviously this is not ideal for use with low impedance IEMs and I'll get into the ramifications shortly.

General system duties are handled by a Qualcomm Snapdragon 400 SoC with quad cores topping out at 1.3GHz each. Again, slow for a top smartphone but generally fast in this roundup and certainly quick enough for our needs. It feels snappy next to the slower Sony player, which hides its age well yet sometimes lags more than I'd like during more intensive activity.


User Interface
The M2 runs Android version 4.3 with very little in the way of aesthetic add-ons. It's basically a vanilla Android experience—and that's not a bad thing for the most part. It feels slightly more responsive than the Sony ZX2 but also a bit less polished in terms of visuals, though I can't say I really mind.

One important aspect is that the M2 doesn't support the Google Play store. AR says they made so many SQ-related modifications to Android that it would no longer be possible to run the Play store directly. It's therefore not as simple to customize in the same way as the Sony, but still doable in the end.

It does support sideloading of apps in APK form which is not at all difficult. Loading the Amazon Appstore APK puts automated app installing back on the table—they don't have everything Play Store has, but there's still a lot to choose from. I was able to run Spotify and more importantly Tidal without issue, which is a huge benefit as far as I'm concerned. I do a ton of Tidal listening and it's a perfect fit for a device like this. It even supports offline downloads which means I can load up a couple dozen albums and play them later. This is in contrast with the Astell & Kern players which recently gained Tidal support but lack offline mode.

Aside from that, the M2 is pretty basic. There's a built in player app which does the job in a rather simplistic fashion, offering a 5 band integrated EQ which is merely passable at best. I didn't try, but I imagine a better EQ app could be obtained if the user really felt the need. Personally I don't mind the simple stock player, and I tend to split my time between it and the Tidal app.

AR gives us 64GB of internal storage along with a microSD card slot which cleverly hides behind a sliding door. They claim support for up to 200GB cards but I only tested 128GB (which worked fine). There's the usual 1/8" headphone output along with a separate 1/8" jack for line-out. For whatever reason, Acoustic Research chose not to add a digital output for SPDIF connections, and there's no provision for acting as a USB DAC either. So expandability is a bit limited compared to the standard in this field.

On the plus side we do get WiFi connectivity which enables the use of streaming music services. Did I mention that's a big deal to me? Bluetooth capabilities are absent thus far—apparently AR didn't think anyone would miss that function, and they ended up being wrong based on customer feedback. I'm still not sure why anyone would buy an expensive DAP and use it for lossy streaming though...your phone can probably handle this part just as well.

The M2 stays on par with the average DAP in this roundup, going about 8 or 9 hours on a charge. Due to the class A bias of the headphone stage, it doesn't vary much based on playback volume, though higher resolution PCM and certainly DSD playback will bring down the total significantly. AR says DSD gets about 6.5 hours and I can't say I disagree. As usual, I would have loved an increase here, yet I can't complain too loudly about something meeting the class average.

Sound Quality
First things first—headphone pairing; it's absolutely crucial here. The Acoustic Research M2 has a rich, dynamic, yet generally neutral presentation, but only when we avoid certain low impedance headphones. More specifically, multi-armature based IEMs are a real problem for the M2. Those in particular will sound quite different than their true signature as heard via another DAP with low output impedance. Once in a while it's an interesting variation, but the vast majority of the time it's a clear downgrade. So unfortunately I avoid all my CIEMs with this DAP, as well as my low impedance Grado and Ultrasone headphones.

The good news is that the M2 has a powerful output with plenty of voltage swing, and it loves high impedance headphones. The classic Sennheiser HD650, as done by Massdrop with their HD6XX release, sounds exceptional. I hear punchy lows and a silky smooth midrange, but also a really well balanced top end. The HD6XX can sometimes come across as being "veiled" and that's definitely not a term I would choose with this pairing. The varied trumpet styles of Chet Baker, Toshinori Kondo, and Nils Petter Molvaer all have an extended sweetness to them with just the right amount of bite. The list of DAPs which pair this well with the HD6XX is very small indeed, and the M2 might just be the best of the bunch.

The powerful M2 also excels with planar magnetic headphones. My LCD-2 (non-Fazor) has never sounded this good from a DAP—the HiFiMAN 901S with the Minibox Gold amp comes the closest, and the Cayin N6 isn't far behind, but I think the M2 does better than both in terms of dynamic swing and deep low end impact. The LCD-2 isn't the brightest headphone and the M2 seems to impart a generous sense of detail without artificially inflating the top end. It's a wonderfully musical presentation that I actually prefer to the newer Fazor edition—the M2 drives that pretty nicely as well, yet the result leaves me a little flat in comparison. It takes a step forward in detail retrieval yet a step back in organic tone, sounding overly polite and perhaps even boring compared to the non-Fazor. I've heard other setups where the newer Audeze pairs better so this is by no means a definitive preference, but in the case of the M2 I do prefer the LCD classic.

Lastly, the HiFiMAN HE1000 with its buttery-smooth presentation. Again, plenty of drive; low-end authority for days; rich textures and a nicely formed soundstage too. That's one aspect the big HiFiMAN does quite a bit better than the LCD-2 or the Sennheiser HD6XX—as it should for the price increase—and the M2 really takes advantage of its capabilities. Imaging is precise and performances are beautifully layered, sounding very "out of head" at times. This is an excellent pairing, again among the very best I've heard from a DAP.

Just to test things out, I switched to the line-out driving an Arcam rHead desktop amp. I heard a lot of the same qualities I mentioned above, but amplified (no pun intended) to a significantly higher level. As nice as the amp section of the M2 may be, I do think their choice of TPA6120 driver chip is a limiting factor. Based on what I'm hearing from the line-out, there seems to be a decent amount of untapped performance being lost due to the amp stage. As much as I enjoy the headphone out, and as competitive as it manages to be, I think there is more to be had from this device.

The output impedance issue also takes away from the experience compared to other DAPs—the M2 ends up being very selective about which headphones it pairs with. I inquired about this and was told the designer doesn't think the output impedance is an issue. Or at least, not the ONLY issue to focus on, but rather one of many attributes to be considered. I disagree on a fundamental level and believe most listeners would hear problems when using their favorite low impedance headphones—they just won't have the same signature you know and love.

Still, with the right headphones, this is an extraordinarily enjoyable device. With a big, bold sound and plenty of power, not to mention full Tidal support, the M2 is a unique entry in this field which may be just the thing for certain users.

tony's picture

This is one hell-of-a-summary!

Battery life, efficiency, Streaming, Quality, Design Integrity, you're hitting all the key points. What do I owe you for this? Buying the wrong feature Set is an expensive mistake.

Can you offer an opinion on the New Phones as Audio Players? the V20 for example.

It would seem that the World will be using their Phones as DAPs, I hope to encourage you to continue your "important" work in this new area.

Thank you for all this work!

Tony in Michigan

John Grandberg's picture

...are getting better (at least some of them). Unfortunately it seems like LG and others don't want to bother with us lowly audio journalists. I have a heck of a time getting replies from their PR people, which makes it tough to properly investigate. I'll keep at it though.

I'm currently using a ZTE Axon 7 as my daily driver and it's pretty impressive, both as a phone and in terms of audio quality. Not a true "DAP replacement" but very impressive for what it is.

flohmann's picture

A big omission, it seems to me, since the X1a is about $650, supports up to 400gb, and runs a newer version of Android than the Sony player (so runs all the apps that the Sony player does). Maybe Part 4?

John Grandberg's picture

I had the original DP-X1 when it first came out. Weird battery issues, and then the 3.5mm jack went sideways. I figured it was just an anomaly, but then a friend with a pretty decent measurement rig got some wild results with his DP-X1 - *extreme* deviation from the published specs. Those two experiences were enough to put me off when it comes to Onkyo.

Don't know if those issues are still present with the DP-X1a, and honestly I haven't kept up with it. But from now on I'll be doing updates one DAP at a time so I should manage to be more nimble going forward. Perhaps an Onkyo is in my future one of these days.

logscool's picture

I also had issues with my original DP-X1 and almost didn't get a second one after trying the not very good OPUS#1 I went ahead and got a second DP-X1 I've had no issues with the new unit. There is a pioneer unit coming out that looks to be identical (XDP-300R). There is also the single ended only version Pioneer makes (XDP-100R).

Meshail's picture

Why do you find the opus #1 bad or ( not good ) where is it lacking, I'm asking as I want to grab one now as price is like 290$ & you are the second person who is saying it is not good

logscool's picture

It just didn't have a lot of weight or dynamics to the sound pretty "digital" sounding in comparison to better sources. If you have a chance to try it then definitely try it as you might like it's signature.

Meshail's picture

Can you please suggest me a better dap in the sub 300 $ range as the opus#1 runs for 289$ on amazon

Long time listener's picture

I note you mention the Fiio X5, but they now also have an X7--disappointed not to see it as I would appreciate comparisons. I trust the Fiio brand, they use a good DAC chip, and the sound seems very good at the $600-700 range. But is there better?

Also, to Tyll, a review of the new Shure electrostatic IEM would be appreciated. Thanks

John Grandberg's picture
See, there's the dilemma I mentioned - always another worthy model coming out. I finally had to put my foot down and just go with what I had, else it all became irrelevant. But I definitely intend to catch up on newer models from Fiio, Cayin, Astell&Kern, and perhaps the new Sony models. One at a time though!
thefitz's picture

I use the DX90 because you can plug in a USB hard drive via OTG. Use Western Digital drives. 2TB+ at my fingertips!

John Grandberg's picture
The literature for the Acoustic Research M2 also mentions the same OTG functionality. I never actually tried it but I can see how that might come in handy in some cases. Thanks for the info!
jcheadphone's picture

Thanks John. Really enjoyed reading your three part series on DAPs. I used to own the Calyx M and agree it sounded wonderful. I ended up selling it because of the shortcomings that your mentioned and others. I currently own a ZX2. It sounds great and is able to drive all my headphones from my Shure SE846 to Audeze LCD-XCs with good results (although the XCs as expected certainly benefit from a desktop headphone amp). I also picked up a pair of Sony MDR-1000x wireless noise cancelling headphones for travel. The LDAC streaming with the ZX2 sounds very good. In A/B tests with 16/44 ALAC and FLAC tracks I can't distinguish a difference between the wired connection and the LDAC wireless streaming. I note that Sony has now made LDAC available on the licensing market so maybe we'll see it on other non Sony Bluetooth products in the future.

Three Toes of Fury's picture

As a big fan of better quality sound on-the-go, the ever evolving DAP market is of big interest to me. I very much appreciate you taking the time to review so many entries. Its great to see this site evolve in its review and wall-o-fame offerings.

Great stuff...keep it up...even if you dont do the huge comparison reviews (takes loads o time im sure), drop in with a 1-off review of a DAP every now and then. Would be much appreciated

Peace .n. Living in Stereo


GlennT's picture

I own a Questyle QP1R and I love it. However, I agree that the scroll wheel's functionality is disappointing. Before I bought the QP1R I had the expectation that the scroll wheel on it would be as useful as the old iPod scroll wheels used to be, but that's not the case. I find that the touch-sensitive buttons around the outside of the scroll wheel as well as the button in the center of the wheel become usability obstacles when scrolling. It's too easy to accidentally brush against the touch-sensitive buttons when scrolling. It can be very frustrating when trying to scroll to a specific selection only to suddenly be dumped back at the home screen because your finger accidentally brushed against one of the touch-sensitive buttons surrounding the scroll wheel. The wheel is also pretty slippery, making it sometimes difficult to grip. However, they have an adhesive film that goes over the scroll wheel that Questyle will provide to you upon request at no cost that mostly solves this problem.

husafreak's picture

I am a huge fan of my QP1R. It is beautiful and sounds fantastic. Clean, dynamic, and detailed. Your review is on the money. I would say that the scroll wheel cover is a must to facilitate its use. I believe the unit ships with them now but they are free and easy to get, actually something as simple as a generic stick on rubber dot can solve this design flaw.
I use mine with a set of 64 Audio U6's, TH-X00's, and now Mr Speakers Ether Flows. It is amazing to me how much detail and life I can hear with the Ether Flows. I had to comment because my son is a drummer, a professional now, and so I really get into the nuances of drums and cymbals. I swear I could hear the double bass chain mechanism rattling away when I was auditioning the Flows through my QP1R! I look forward to hearing the Spark album you used in your review.
By the way there is a very active QP1R thread on the Head-Fi forums and the company has been very proactive in releasing timely updates. In only one year they have solved many requests.

John Grandberg's picture
...for the comment. Glad you are enjoying the QP1R. The firmware aspect is yet another category which I probably could have used to judge each model, or at least each brand. Questyle is indeed one of the better ones in terms of frequent updates.
Jayhawklaw's picture

I love comparisons like this. I hope you (and your sister publications) do more. So much more meaningful data for the "everyman." I would love to see a similar survey for portable dac/amps (e.g.: Audioquest Dragon Flies Red and Black, Oppo HA-2SE, Chord Mojo, etc.)and how a smartphone with one of said dac/amps connect compares to the dedicated DAPs.

jcheadphone's picture

At first I was disappointed that Sony decided to go with a proprietary WM port rather than micro USB. When I contacted Sony tech support via phone to ask about this the tech rep said the WM port was intentional because it allowed the left and right channels to be separated for optimum line out sound quality. Don't know how much this explanation holds water but thought I would mention it.

John Grandberg's picture
They say the same thing about their 3.5mm jack. Not sure it really makes a notable improvement of any sort in terms of SQ, but it's a perfect example of Sony being Sony.
Martin.'s picture

The only DAP that seems "consumer friendly" in my eyes is the Sony NWZ-A17, which is priced at 300$. Is it even worth buying a DAP for 300 usd when you can save a bit more for a mojo at ca 500? The real question being, other than portability, what advantage would a 800$+ DAP have over a 500$ portable DAC like the mojo and, most importantly, would it make a discernible, audible difference? Thanks for any answer :)

John Grandberg's picture

Different folks will have different priorities, and each solution has pros and cons.

I like a dedicated DAP because it's smaller and easier to manage than a phone-plus-Mojo type solution. Also many phones don't have expandable storage so a DAP with 128GB or 200GB (or more) can be useful if your phone is stuck at 32GB or even 16GB. If we're talking Sony ZX2, then battery life is supremely better than a Mojo. Last but not least, there are various sound signatures to be had with different DAP models. Not everyone loves the Mojo presentation, as popular as it seems to be. The target market who prefers the sound of a Cowon Plenue 1, for example, is not likely to be thrilled with the Chord.

On the other side, it could be argued that you always carry your phone with you anyway, so a DAP isn't really saving any space over a Mojo setup. And a decent phone is usually superior when it comes to display quality, ability to run apps, etc. In some (many?) cases the Mojo sound will be superior depending on your criteria.

I agree that there aren't enough affordable options right now. I'm still looking for a true replacement for the Sansa Clip/Clip+/Clip Zip. Only reason I can't put those on the Wall of Fame is the fact that they are long since discontinued.

Martin.'s picture

Thanks for your answer. Being a novice, I usually want a "this is best" answer because I feel I need to be told what is best by veterans in the field. It is nice to be reminded that audiogear is personal and that "different strokes for different folks". Your well balanced answer is much appreciated.

br777's picture

has convinced me yet to give up my sansa clip zip.

Rblnr's picture

Very comprehensive and useful reviews. I've been using the Plenue 1 for a couple of years after testing it against others at the time of purchase and am still very happy with it driving JH Audio Angies and some over the ear headphones as well. Surprised that Cowon doesn't get more attention. The sound is as described, smooth and easy, but by no means lacking dynamics micro or macro. Sometimes I want a more 'in your face' sound and the BBE and other profiles ( as noted in the review) can provide that to a point.

I also have to say that I have little tolerance for wonky interfaces anymore -- time for those manufacturers to enter the 21st century, whether or not interface is really their expertise. The Cowon's ergonomics, while perhaps 'merely' utilitarian, are at least direct and unfussy.

Peragulator's picture

No love here for the X7 I see.

John Grandberg's picture
I just had to stop accepting or seeking out new models at some point, or else I'd never get this thing finished. I intend to revisit different models from time to time, so a Fiio of some sort is certainly on the horizon.
Trebor74's picture

Hi, great review! Are there, or will there be, any measurements available at some point to complement the reviews? I'm especially interested in the Cowon measurements - Cowon and a couple of other sites have posted THD figures for the player but these are probably not with any load. I'm curious to see how well it performs (in terms of THD both in earphone and headphone modes) on some low impedance cans. Thank you!

Peragulator's picture

AK300 ($899.00) Sony 1a ($1,199.00) FiiO X5 3rd gen ($400.00) Pioneer 300r OPUS #2 ($1,400.00)

yc627's picture

I'd Love to see some flagship phones' real world comparison in their ability to reproduce sound through headphones... Such as:

Sony Xperia XZ premium: they say it can do 24bit 192kHz audio. And Sony's own LDAC bluetooth codec. How does it sound like with Sony h.ear go SRS‑HG1 bluetooth speaker compared to other devices... + Sony Xperia Z series and to the XZ lineup, they had this noise cancelling earphones that needs no battery boxes like the Sony MDR-NC750 and MDR-NC31E I also wonder what you guys think about those earphones.

Samsung Galaxy S8: I hear it can do 32-bit/384kHz audio and I wonder what audiophile people would think about that.

LG V10, V20, V30: I heard they got 32-bit/192kHz audio and B&O Play certified. LG seems like they don't really do a lot of marketing on the audio parts what do you think about the B&O Play certification?

Just a question from a college student who is somewhat regretting getting a Sennheiser Momentum 2.0 just because it had a huge discount on Amazon and is thinking that I should have gotten the V-Moda M100 or Sony H.ear on MDR100ABN or just go crazy and go with Sennheiser Momentum Wireless...

trl's picture

Based on https://reviewzorro.com/wp-content/uploads/2017/08/HifimanHM901s3.jpg seems that Hifiman 901S has 2 x ES9018S inside. Quite impressive, so that explains the price indeed.