Sony IER-M9 Review - The Kilobuck Benchmark

Review written by @Precogvision

Preface

I fondly recall hearing the Sony IER-M9 several months ago and being stunned with what I heard. It was incredibly solid to the point of which I struggled to find any major issues, and despite only a short time with it, I immediately placed the IER-M9 near the top of my personal tier list. 

But I don’t want to get ahead of myself. And of course, you might be wondering...what actually makes this the de-facto kilobuck benchmark? After all, there are other “value monsters” (I use this term loosely) in this price range like the Hidition Viento, Campfire Andromeda 2020, and the new Thieaudio Monarch and Clairvoyance IEMs. But see, that’s solely on the basis of sound, and sometimes I think it’s important to consider the entire picture. You know - build quality, accessories, and availability. Each of these other IEMs suffer (in this reviewer’s opinion) in one or more of these respects; I won’t dive into specifics to save myself the risk of attracting ire. Conversely, there isn’t a single thing about the IER-M9 that I can consider an outright “dealbreaker,” at least on the fronts I’ve specified; this is what makes it the benchmark. 

Now, if it sounds like I’m buttering up the IER-M9 or worse, shilling, fear not. I simply had to hear it again, so I arranged an IEM loaner swap with the local hobbyist I’d first heard it from. After more extended evaluation, the critic in me is happy to announce that there are a plethora of faults to complain about. So sit back, relax, get out the popcorn...oh, and along the way I’ll do my best to highlight all the good stuff too. 

This unit was kindly loaned for review by moa (RelentlesSausage). Thank you! At the end of the review period it will be returned; as always, what follows are my honest thoughts and opinions to the best of my ability.

Source and Driveability

• All critical listening was done off of the 4.4mm jack of an iBasso DX160 with lossless FLAC files. Stock hybrid silicon tips and cable were used. 
• The IER-M9 seems to be a bit more difficult to drive than most BA IEMs; however, I had no issues getting it to sufficient listening volumes. 
• My genres of preference include the following: K-Pop/J-Pop, Country music, EDM, and instrumental scores. 

The Tangibles

Normally, I’m not one to care about presentation too much because at the end of the day, let’s be honest: After I pry out my shiny toy, the packaging is going straight to my closet to collect dust. But Sony has outdone themselves here, and as such, they deserve praise. This is how you do presentation and make your customer feel like they’ve gotten their money’s worth.

You’re presented with the following:

• An assortment of ear tips including Sony’s Triple Comfort and Hybrid Silicon. 
• Approx. 3.94 ft, silver-coated OFC strands, ear hanger, L-shaped non-magnetic gold-plated stereo mini plug, Approx. 3.94 ft, silver-coated OFC strands, ear hanger, L-shaped non-magnetic gold-plated balanced standard plug
• Carrying case, cleaning cloth, and clip

The included cables are of excellent quality, and it’s great to see a manufacturer include separate cables terminated for both 3.5mm and 4.4mm applications. Perhaps most notably, there is very little microphonics with these cables, and I’m assuming that this is where the IER-M9’s intended stage-use comes into play. 

The IER-M9 has a sleek, understated aesthetic and exudes a sense of reliability not unlike the other Sony stuff I’ve handled. It is composed of a magnesium housing and on the outside there appears to be a carbon fiber faceplate for just a touch of flare. It is a lightweight IEM, and fit is very comfortable. It’s worth noting that I prefer not to deep-fit the IER-M9, as I notice an unpleasant suction effect; isolation is fairly average for me as a result. As usual, though, fit is wholly subjective, your mileage might vary and all that good stuff. 

Sound Analysis

Frequency response taken off of an IEC-711 clone; measurement is raw, matched at 1kHz, and there is a resonance peak at 10kHz. Look at that beautiful channel matching.

The IER-M9 follows a neutral-warm frequency response; in general, it has an agreeable, more laidback sound. One of the first things you may notice about the IER-M9 is its timbre. Most BA (balanced armature) IEMs suffer from a distinct lack of density to their notes, often described as “plastickiness”. Other phenomena include “grain” and transient edginess due to the driver’s faster speed. But Sony has worked some magic with the IER-M9, and be it by virtue of their proprietary BA drivers or the timbral warmth, many of these nasty quirks are mitigated.

And clearly, some of these benefits extend to the bass - those of you who have read my reviews before know my opinion on most BA bass responses; it’s not a kind one. On an intangible level, the IER-M9 has excellent density and texture for a BA. I make the distinction “for a BA” because it’s still not quite up to par with my (admittedly high) standards - I’ll delve into that later. Still, it certainly slams harder and decays slower than your run-of-the-mill BA, so much so that I could almost see it being mistaken for a DD. It flew nicely with every genre I put it through, including my bass-heavy EDM stuff. And contrary to the graph, the IER-M9’s bass sounds like it has a slight emphasis on midbass over subbass to my ears. 

The midrange goes for a thicker note weight and is close to dead-balanced. If I had to guess, though, I think most listeners will lean toward male vocals on the IER-M9 simply because of said thickness. Overall, it’s probably one of the most well-done midranges under $1000; safe to the point of which I struggle to nitpick it, so let’s move to the treble. The treble is reminiscent of the 64 Audio tia Trió I recently reviewed in that there’s a bit of a lower-treble suckout. I wasn’t the biggest fan of this on the tia Trió, but the IER-M9 sounds much more linear going into the highest frequencies. Would I prefer more stick impact? Sure. Would I prefer more air? Yeah, the timbral warmth can get borderline claustrophobic for my tastes at times. But in general? The IER-M9 has ample extension (up to 40kHz according to the specs!) while being easy on the ears and maintaining sufficient presence. 

Technical Performance

One of the things you’ll always hear people raving about is the IER-M9’s imaging. The bulk of the IER-M9’s imaging is predicated on its “holographic” quality (the ability to shape the walls of the room around you) and positional cues. In these respects, it certainly is well above average, but admittedly, I wasn’t too impressed when I first heard it - more on that later. No, what’s more impressive to me is the level of technical capability in general. I firmly believe there are very few, if any, IEMs in this price range that can top the IER-M9 for its overall technical prowess. 

Details, subtle nuances in tracks are simply laid out for you to depict; the IER-M9 isn’t the type of IEM to slam details in your face, and here-in lies a pleasant contrast with the IER-M9’s excellent positional cues. Perhaps most interestingly, the IER-M9 also doesn’t feel very fast. However, it stands that its sheer resolving capability is impressive - perhaps a step shy from being at the top of the IEM game. Coherency is stellar in my opinion, although I’m not especially sensitive to this stuff. 

I think most would be hard-pressed to take issue with a specific instance of the IER-M9’s frequency response or technical capability so much as to call it a dealbreaker. You might be noticing a theme here, and it’s that for better or worse, even on an intangible level, the IER-M9 is safe, safe, safe. If you’re sensitive to BA timbre but don’t want to sacrifice technical capability, I’d highly recommend giving the IER-M9 a shot. 

Unforgiving Explication

Let’s talk about why I don’t own an IER-M9 as much as I once considered purchasing one. If this type of more critical talk offends you, please just consider me a salty boi who wishes I had more disposable funds to swing. That or, you know, skip to the end of my review. 

• First, it just sounds borderline dull. I find it suffers from macrodynamic compression, failing to appropriately scale decibel gradations in tracks and sitting somewhere squarely in the middle. But the compression isn’t remotely bad for a BA IEM. More than anything, said dullness is exacerbated by the IER-M9’s attack transients. There is a distinct lack of vigor, urgency to the IER-M9’s initial leading edge that contrasts strangely with its tonality and good resolution. It’s like you’re somewhere between a stupor and awake; this quality is disconcerting. The IER-M9 is close, but ultimately fails to escape all the undesirable characteristics of a BA IEM. It likewise presents its own, separate set of issues outlined above. 
• The way the IER-M9 images vocals is unsatisfactory to my ears; vocals sit in a pseudo-limbo failing to break the headstage much less surpass the depth “wall”. I suspect that this largely has to do with the ear compensation peaking at ~3.5kHz (but don’t quote me on this). I’ve noticed that most IEMs that “diffuse” for me peak at around 2-2.5kHz. Along these lines, for an IEM touted so heavily for its imaging capability, sheer diffusal of the image is middling at best. The IER-M9’s soundstage is subsequently fairly average, if not well-distributed, to my ears. 
• Oh yeah, let’s go back to the bass. See, the thing about the IER-M9 is that it’s not a particularly fast IEM to my ears. There is a certain fanning of the attack, particularly to its punch, that results in a slight muddiness - diving into bloat at times - to the IER-M9’s bass transients in tandem with the slower decay. This is helped in no part by the fact that its only real competition is the 64 Audio U12t, my benchmark for BA bass. The U12t has better texturing, speed, and nuance in the low-end. I’m not saying this is by any means a fair comparison, nor is it a deal breaker on the IER-M9 - far from it - but it’s undeniably there to my ears, and it stands that comparisons will be made under less forgiving eyes.

But these are mostly quibbles. Above all, they serve as a fitting precursor for the main reason, and I stress this is more personal preference than anything, why the IER-M9 isn’t my cup of tea. Note my frequent use of the word “safe” in this review. It’s prevented me from going as in-depth as I would like at times, and to me it almost feels like the IER-M9 errs too closely to the side of caution. So closely, in fact, that it borders on offensive of itself, and I feel obligated to articulate why (as seen above) at every instance. Most of the issues I’ve cited are minor in isolation; however, they add up. Like so, I can’t help but find the IER-M9 lacking in that special engagement factor that keeps me listening in the long run.

The Verdict

Don’t get me wrong. The IER-M9 is the de-facto kilobuck benchmark for good reason, and I’ve been critically assessing it like I would a flagship - yeah, it’s that difficult of an IEM to knock. I should also make a distinction between the terminology I often sling around. A “flagship” IEM for me is a reflection of price and status - it does not necessarily have any bearing on sound quality. There are expectations that come with this status, though, and I likewise hold said IEMs to a higher standard. Conversely, a “top-tier” IEM is an IEM that stands at the audio summit on the merit of its sound quality alone (of course, these IEMs tend to be flagships). 

So I think there are a couple ways of interpreting the flaws that I’ve outlined. On one hand, the IER-M9 is simply not a top-tier IEM. It makes too many little errors here and there that a top-tier IEM would not make. But on the flip side, these are all minor issues that I’ve come to expect even at the flagship level. The IER-M9 is, in essence, an IEM that easily trades blows with most flagships at a fraction of the cost. And as if that doesn’t say enough, the IER-M9 comes highly recommended from this reviewer. I think what it mostly comes down to is if you’re willing to trade some engagement factor, musicality to your sound. If this seems like a worthy sacrifice to you, then by all means look no further; I can wholeheartedly empathize with those who choose to die on the hill that is the IER-M9. 

-@Precogvision

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