Acoustics Audio IEMs Knowledge Rants Thoughts Universal-Fit

Rant: Audio-Technica ATH-IM02 vs. ATH-CK90PRO MK2

The ATH-IM02 has been praised almost universally for being one of Audio-Technica’s most complete sounding products to date. But what has really changed?

I’m more of a whole wheat, multi-grain kind of guy, though, and I wondered about why there was so much enthusiasm surrounding the IM02. While the IM02 did indeed sound very nice, to me, it sounded very similar to the CK90PRO and CK90PRO MK2 that were introduced years ago. Yet, those older models didn’t receive nearly as much attention in four years as the IM02 got in a mere four months.

I was perplexed. After all, the ATH-IM02 actually sported technical specifications that were nearly identical to those of the ATH-CK90PRO MK2. Sure, the stated impedance of the IM02 was a single ohm count lower, and the sensitivity was a couple dB higher, but the fact of the matter was that the two earphones used the same exact driver assembly and outputted to an ‘acoustic horn‘ tube, canted at the same exact exit angle and opened to the same diameter. For all intents and purposes, from an acoustic design standpoint, these two earphones were the same.

All new outer design, same acoustic internals.
But the older ATH-CK90PRO and CK90PRO MK2 also utilized an acoustic horn in the outlet port…

But they sound different! How could that be?

Yes, the Audio-Technica ATH-IM02 features all-new ergonomic features over the older ATH-CK90PRO MK2, but retains the same driver assembly. It’s actually understandable that both the CK90PRO MK2 (and the original CK90PRO, for that matter — SONOVE’s measurements of the original ATH-CK90PRO bear close resemblance to those of the CK90PRO MK2 in impulse and impedance curve — frequency response isn’t directly comparable between different measurement apparatuses) and the IM02 share the same receiver — it’s a nice one. At the heart of both is the Knowles Electronics GQ-30783; this GQ driver has also been used in several other earphones, specifically the Westone 2, InEar StageDiver 2, Lime Ears LE2, and a few other products from China that fewer people are familiar with, such as the AudioSense AS-2.

The ATH-CK90PRO MK2 was an overlooked gem. (Picture from: Lyra Media)

So what accounts for the slight differences in technical specification, and the differences in subjective listening?

Well, if we take the example of the Westone 2 and InEar SD2 (see thoughts here), which both also use the GQ-30783, we’ll see that the electroacoustic measurements, as taken from InnerFidelity, are nearly identical:

Comparison of the frequency responses of the Westone 2 and InEar StageDiver 2, as measured by InnerFidelity. (All original rights belong to InnerFidelity.)
Comparison of the frequency responses of the Westone 2 and InEar StageDiver 2, as measured by InnerFidelity. (All original rights belong to InnerFidelity.)

Other than a minor few dB of variation here and there, the frequency response is nearly identical; the major mechanical resonance points are the same, and the other electroacoustic data, such as square wave response, impulse response, and electrical impedance/phase, are even more similar.

However, in a direct subjective audio comparison, the W2 and SD2 sound quite different from one another. The SD2 sounds tighter and more present, with more forward, less muffled vocals. The only difference between the two are an increased build quality, tighter fit rate, and isolation with the InEar SD2 — but these factors put together actually amount to a significant difference in sound quality. The difference in the plastic tubing used on the Westone 2, compared to the solid, 3D-formed acrylic in the Stage Diver 2 is actually enough to create measurable differences in frequency response and impulse. Sort of like opamps or DAC chips in a signal chain, balanced armature drivers are the same, in that even in very similar setups, small variations such as tubing material, housing stability will affect change in the most unpredictable of ways.

So let’s get back to the Audio-Technica models; I’ve compared the CK90PRO MK2 and the IM02 directly to each other — the audible difference between the CK90PRO MK2 and the IM02 is actually much smaller than the difference between the W2 and SD2! The IM02 gains a miniscule amount of added clarity and tightness over the CK90PRO MK2, along with slightly better instrumental separation. Possible reasoning for these improvements are (1) a better shielded cable (beyond ergonomic improvements such as flexibility and thickness) that allows for separate ground wires for the left and right channels all the way down to the 1/8″ plug, and (2) a large, denser, more vibration stable housing that stays more securely in the ear because of shape.

So what’s all the fuss again about the IM02 being the “gem” of the Audio-Technica IEM lineup, when they’ve had essentially the same earphone since 2010 in the ATH-CK90PRO?

Some audiophiles have come out and declared the ATH-IM02 to be the most capable IEM of the new lineup, but the fact is, Audio-Technica did not hire some new acoustical genius to design the IM02. The IM02 is merely a minor, incremental improvement over its immediate predecessors, the CK90PRO and the CK90PRO MK2 — mostly in aspects of ergonomics. Is it the best one yet? Yes. But it’s no reinvention of the wheel, and it’s certainly not a big leap in improvement.

We all like new products; they’re shiny and eye-catching, but don’t let new products and new marketing pull wool over our eyes — just because it looks new, doesn’t mean it’s actually different.

Product Links
  1. ATH-CK90PRO
  2. ATH-CK90PRO MK2
  3. ATH-IM02
About Mr. T

Mr. T is an in-ear fanatic by day, and writes SOAP notes by night. He pities the fool who actually has the patience to read through his stuff.
(Full Author Bio)



  1. Interesting article. Agreed about the CK90 series being overlooked, though I haven’t tried them. Have you managed to try the ATH-IM03 as well?

    Also, what do you have to say about the bass response of the IM02 (and 03, if you’ve tried it)? I’m very wary of IEMs with a lean bass that ends up being misrepresentative of the authentic weight and fullness of the music and instruments.


    1. Yes, I did try the IM03. It is similar to the former Audio-Technica flagship CK100PRO, but with a less finicky top end. The IM03 is slightly more robust in the low end than is the IM02.

      However, the IM04 will definitely impart the deepest bass out of all the IM series. It uses two very high-quality vented woofers that allows its bass to be set apart from the rest. However, in terms of tonal balance, it is also the darkest of the lot.

      My recommendation would be to give anything that seems initially “lean” in the bass region a chance for about a week, listening to it exclusively. That week will allow you to get used to the signature, and allow your brain to readjust. It’s true that certain earphones are unable to transduce weight as authentically as others, but the effect is perhaps less pronounced than what most people think.


      1. Thank you, that definitely increases my confidence in the IM03. The IM04 is definitely beyond my budget, and I also don’t want a DARK IEM.

        Here’s a bit of background, if it matters. I’d appreciate if you could help me out.

        I’m a musician and music producer. When I’m at home working, I have my studio monitors (Yamaha HS7) and headphones (Beyerdynamic DT880 Pro) for all listening, and I love them both. That is my general reference point for neutral sound – NOT lacking fullness, realistic weight and body in the bass. It seems most ‘neutral’ IEMs however, suffer from a lack of the above, and I understand the IEMs seem to need to be tuned with a gentle-to-moderate, but controlled boost in the low-end to achieve a similarly realistic representation of the bass regions.

        I own a VSonic GR07 MkII that I find to not represent the general low-end to my satisfaction. My production references, and my own mixes, sound thin, realistic fullness and body in the low-end, when listening through the GR07 MkII. EQing helped a bit, but I want to stay away from EQ as far as possible. I also found the treble to be uneven, spiky and a bit unrefined.

        Within a budget of say, $300, I’m looking to find a pair of IEMs to give me a balanced, fairly neutral sound, but with that realistic body, weight and fullness in the low-end. Which will probably imply the IEM having a general low-end boost, which I am okay with. I definitely do not want bassy IEMs though. Balanced but with a full-bodied, realistic low-end. I also would like the top-end to be smoother and more refined, without peaks and resonances (to whatever extent is achievable in my budget).

        Isolation is a priority, as these are strictly for use while commuting. Also would like an airy, open, large soundstage, with good imaging.

        Is there anything in your experience with IEMs that will give me these? What are your recommendations?

        Thank you!


      2. Yes, for IEMs there’s a “missing 6 dB” in the bass response that usually prompts IEMs to be tuned with more bass, but the discrepancy is more of a lack of “training”, so to speak. Because IEMs are generally a “closed” system with your ears, psychoacoustics plays a big part of the equation, and thus accurate monitoring with IEMs requires you to “hear” the bass signal, rather than “feel” it, and if you’re able to decouple the two, it really helps you not need bassier IEMs. However, most people find this psychological decoupling to be a chore (because it must be goal-directed), so most manufacturers just turn up the bass, as most people are “all about that bass” anyway.

        One disadvantage that you have with the GR07 is that it is a dynamic driver IEM, and the venting prevents it from being as isolating as it can be. I am surprised by your statement that you find the GR07 too thin-sounding, however. It could be that you’re hearing the treble harmonics, and attributing its sharpness (the GR07 tends to have somewhat sharp and defined treble) to overall thinness of body. In a quiet environment, the GR07 will probably sound a lot more full-bodied.

        Thus, my recommendation would be to get a pair of budget custom IEMs. It sounds ridiculous, but since you’re a musician, investing in a pair is worth it — my default recommendation for any other kind of listener would not shoot straight to customs.

        Granted, they’re not as convenient to put on and remove, and have poor resale value, but you’ll find that the added comfort and isolation will get you to be able to hear the details better than ever before — don’t worry about the driver count (it should never be considered an indicator of sound quality when considering any balanced armature IEM, despite marketing — more drivers means lower distortion, more input headroom, and room for more tailored frequency responses, but most dual drivers do a good enough job).

        Keep in mind that you’ll also have to go to the audiologist to get ear impressions, which will run you between $35 to $100, typically, unless you attend a trade show like NAMM and get them done with the company itself.

        Also remember that Thanksgiving is coming up, and many custom IEM companies will be discounting their models by quite a bit. 1964Ears typically slashes their prices by quite a lot, and the 1964-V3 will likely be slashed into a price range that you can consider. Noble Audio holds a sale as well, but the products that most suit you are perhaps in the higher end of things (8C, K10). The Ultimate Ears UE4 Pro is a great choice, though it’s typically not discounted and only comes in clear. JH Audio does hold Black Friday sales, however, and the JH5 should be a great starter monitor.

        The extreme budget end for CIEMs is with Perfect Seal Labs in Kansas, and Fisher InEarz in Florida. The Perfect Seal Silver and the Fisher IE-P250 both the Sonion 1723 AcuPass dual driver, which is a great setup for value priced IEMs. Both should come in at a raw price of less than $300, which is absolutely affordable. Granted, I’ve heard neither, but it has been well-received by other reviewers that have heard them, and I know the capabilities of that 1723 driver. It’s difficult for that driver set to sound bad.

        For silicone monitors, currently my only recommendation would be Poland’s CustomArt, as they really hit the sweet spot with respect to value and balanced sound signature. The Music Two (read shotgunshane’s review: is a truly great all-arounder; both shotgunshane and I bought a pair. It’s accurate enough for monitoring, but is really able to express music really well also. It has energy and depth in the low-end, but does not get bloated. It’s brighter than a conservative monitor tuning, but pulls back when others can get really harsh. It’s truly an excellent value. It’s near the ceiling of your budget, but I’d still recommend you give Peter an inquiry. He’s a personal friend, but I can state objectively that his products are excellent.

        If you’re not ready to take the custom plunge, EarWerkz is slated to launch their “Project Supra” next week on Kickstarter ( Supposedly, it is their EP-2 model in universal form, but official details have not come out yet. From his listen, shotgunshane highly recommends this model (read about his experience here:

        Keep in mind, however, that the universal fit might not necessarily be perfect. As the universal shape has not been determined as of yet, it’s difficult to deal out a definite recommendation. Of course, you could go for the custom version (which also has a slightly more bass-enhanced EP-2+), which is currently on sale until the end of the year, and costs just a bit more than the IM03.

        Slightly higher up the price food chain is the German InEar Monitoring SD2. It was mentioned in this article as being extremely similar to the Westone 2/W20, as well as the IM02 on account of all of them having the same exact dual driver GQ unit from Knowles; however, with the benefit of a good fit (the fit is near perfect for an universal IEM), the bass gets fleshed out really well. Expect a similar timbre and midrange presentation to the IM02, but with better rounded bass, as the SD2 isolates as well as any custom IEM, given the right fit. Read my quick impressions on them here:

        Honestly, your ideal in terms of sound signature would probably be something like a FitEar MH334, but that’s almost certainly out of your budget, I’m sorry to say.

        This is just a primer. Don’t hesitate to let us know if you have further questions trying to narrow things down. My recommendation for you is to go for a pair of CIEMs, because they will come in handy for your music career, though if you’re not ready, we’ll continue to help you with alternatives as well.


      3. Thank you very, very much for that detailed, painstakingly elaborate reply. I really appreciate you taking the time to write that out!

        Unfortunately, custom IEMs are not what I’m looking for at the moment, for multiple reasons – first, I only use IEMs while performing when I am absolutely required to, because I dislike the presentation of in-ear monitoring while performing, as opposed to using regular stage monitors. So the appeal of custom IEMs for professional use doesn’t draw me all that much. Second, I live in India, and the additional cost of shipping impressions overseas is something I’d prefer to avoid entirely.

        So for now, I’m looking for a set of universal IEMs.

        About the GR07 MkII, I’ve used them in studio-quiet environments as well, and I always find the low-end lacking in the expected, natural weight and body, both in the timbre of bass instruments and percussion, and in the general presentation of the low-end of mixes. As you said earlier, this can be attributed to the missing 6db effect, which I’ve read about earlier. I also sensed a general mid-bass dip in the response of the GR07, which is a definite contributor.
        This lack of fullness is also possibly a result of the kind of bass decay that a very fast driver might possess, though I haven’t looked at the measurements and charts of the GR07 MkII in much detail, to confirm that.

        Now something like the HiFiMan RE-400, I found more natural in its presentation of the low-end. I haven’t directly compared FR charts of the RE-400 and the GR07 MkII, but the RE-400 did seem to have a fuller, and to my ears, more natural mid-bass, which lent a more realistic body to instruments and sounds in the bass region. The main drawback of the RE-400 was the gently but noticeably recessed top-end, which took away some brilliance from the representation of cymbals and some air from the overall presentation.
        To my ears, the RE-400’s frequency response can be summarised as ‘neutral with a gentle shelf lift in the low-end, and a gentle shelf dip in the upper treble’.

        What I’m looking for is roughly something not far from the RE-400, but without the gentle dip in the treble. In a universal IEM. Close to neutral, but with a mild lift in the mid-bass and below, and with a neutral, but clean and well-behaved top-end.

        Any universal IEMs within the $300 dollar mark or so that come to mind?

        Once again, I greatly appreciate your replies and their thoroughness. 🙂


      4. I understand your perspective on customs; as a person whose day job is in healthcare, however, I merely want to remind you that hearing preservation is paramount. With that said, universal IEMs can help with that to a certain extent.

        Living in India will certainly complicate things. Unfortunately, the market for higher-end earphones is simply not very mature there.

        The RE-400 is great for balance. The XBA-A3 (not H3) that I recently heard will probably fit your bill, but its fit doesn’t lend itself any favors when it comes to isolation.

        The Ostry KC06 and KC06A might be worth considering, as they’re pretty affordable (but sound great). Drawback is isolation, which isn’t terrible, but no better than the GR07.

        I hesitate to recommend products that I haven’t personally heard, but it might be worth considering the Brainwavz R3. It should have what you’re looking for when it comes to sound. The only questions are comfort and isolation.

        The DUNU DN-2000 is also a worthy choice. The sound will be to your liking, but while I personally had no issues with fit or isolation, others have.

        Out of the “big company” offerings, the Logitech UE900 is one to consider.


  2. Hi there! Just came across this article recently and I have some questions that I hope you can clarify.

    According to the article, it says that both the ATH-CK90PRO and IM02 actually shares the same driver, and that is why the measurements share some kind of resemblance. Even the Westone 2 and InEar SD 2 gave similar measurements and the reason is that they all use the GQ-30783.

    The reasons given to explain the technical specifications and differences in subjective listening (in the context of the SD 2 and W2) is that there is an “increased build quality, tighter fit rate, and isolation” for the SD2 as compared to the W2. However, I am just confused as to how build quality actually affects the technical specifications. Shouldn’t the drivers be the only factor that affects sensitivity and impedance? I am new to this so please be patient… 😦

    SD 2: Driver: Dual BA | Imp: 40Ω | Sens: 119 dB | Freq: 20-18k Hz |

    Westone 2: 117 dB SPL @1mW Frequency Response: 20 Hz -18 kHz Impedance: 33 ohms @1kHz

    Also, from what i understood from the article (correct me if I am wrong), it seems that if I were to send both the ATH-CK90PRO and the IM02 for re-shelling into custom IEMs, (suppose that the ear molds sent were identical, and the manufacturers managed to produce identical CIEM shapes, cables are the same too), will the two models now sound exactly the same? And applying this re-shell to the W2 and the SD2 too? Will all 4 of them sound the same now?
    If that is true, it definitely isn’t wise for SD2 users to go the custom route since they could have just got a W2 and re-shell it at a lower total price.

    The point I am driving at is that: are there really no difference in the drivers used in all 4 models? Maybe the companies have done some tweaks (to driver or crossovers etc) that made a change in sound quality? I understand that the housing of the IEMs will affect the sound quality, but is it really true that it is the only factor that that caused all the IEMs mention above to sound different?

    Once again, I must say that I am rather new to these topics and am still learning so please be patient, if these questions sound amateurish… Thank you for your attention!


  3. I’ve tried a pair of CK90PROMK2 and liked them, but ergonomics and the actual price tag of the seller is worse than IM02. I have no opportunity to try IM02 but can order them. Would you say they sound close(similar) enough to order IM02 without listening them if I liked mk2?


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