Sennheiser IE 900


Reviewer at hxosplus
A Fine Piece of Art
Pros: - Very musical and engaging
- Realistic timbre and lifelike tonality
- Excellent, reference quality bass
- Sub - bass extension and dynamics
- Holographic and wide soundstage
- Highly resolving but not analytical
- Discrete, lightweight and comfortable
- Great build quality
- Three cables with different plugs
- Quality hard carrying case
Cons: - Slightly lacking in scale
- Treble can be a touch hot but not bright
- Cable is a little microphonic and smelly
- Limited selection of ear tips.
- May not fit well larger ears
- You may need larger sized ear tips than the included
- Custom design MMCX+ connectors will not fit after market cables
The IE900 was kindly loaned to me by Sennheiser Greece for domestic reviewing purposes and the sample unit has been returned back.
This is a translated version of my review made specially for Headfi.

I am going to skip the usual introduction and technical information that can be found in detail over here


Build quality and appearance

The IE900 is the first product to be released after Sennheiser consumer division was acquired by Sonova.
It is 100% handmade in Germany with top craftsmanship and excellent finish quality.
Aluminum is the only material used and a five-axis CNC machine precision cuts each housing individually from a single block of aluminum.
I have been reading about a handful of units with some assembly problems, mainly some kind of gluing issues at the plugs or something like that, but this wasn't the case with the review sample which was perfectly assembled and finished.
The IE900 is beautiful looking with a minimal design reminiscent of modern cut jewelry.

Fit and isolation

The earpieces are so small and lightweight that they literally vanish in the ear to the point that you forget if you are wearing them.
The fit is very comfortable, relaxing and discreet with the only footnote concerning the fact that you may need ear tips larger in size than those included in the package.
Some people with deeper, than average, ear cavities may encounter some issues getting the proper fit due to the shell shape and the short length of the nozzle, so getting deeper insertion might be a problem.
Sennheiser should have included larger and double flange ear tips to better suit individual needs
Choosing the right size ear tips is of vital importance since if for some reason you do not achieve the perfect fit then the low end just disappears.
I have achieved the best results with the supplied memory foam ear tips.



The detachable cable is of good quality, reinforced with para-aramid for better durability and it offers a great handling experience although it is prone to microphonic noise and the material is a little smelly.
The IE900 is worn around the ear and the cable features, the now out of fashion, memory bend ear hooks that offer a secure fit but are a little cumbersome.
Sennheiser, instead of designing a modular plug cable they opted to include three different cables with 3.5mm, 2.5mm and 4.4mm jacks to cover all types of plugs.
This is a little bothersome if you frequently switch sources but then, three cables are better than one in the long run.
Sennheiser uses Gold-plated Fidelity (+) MMCX connectors for improved stability and durability but while the supplied cables are of good quality, users who love cable rolling will have some trouble finding aftermarket options.


The IE900 comes with three different cables, three pairs of silicone ear tips and three pairs of memory foam ear tips (arranged in a nice plastic shorting card), a hard carrying case of high quality and a cleaning cloth.
I perfectly understand Sennheiser not including fine tuning ear tips because the IE900 tuning was done with the included ones in mind, but then they should definitely have included a couple of large sizes and some kind of double flange ear tips.


Listening set-up

As per usual practice the IE900 was left burning for about 150 hours prior to critical listening.
The acoustic evaluation was done with various sources but for the main portion I have used the iBasso DX300 with the AMP12 module and the FiiO M11 Plus.


Sound impressions

After testing dozens of iems with large, bass shaking, dynamic drivers in single and hybrid configurations, the truth is that I looked at the tiny 7mm IE900 drivers with half an eye and some kind of distrust.
I have already reviewed the Sennheiser IE300 featuring the same size drivers and I wasn't disappointed but come on, a flagship with 7mm drivers when the competition comes with huge 12mm ones?
Being skeptical and slightly biased, I started the listening tests with bass stretching material to discover in my greatest surprise that the IE900 passed all the tests with flying colors, not only offering a state of the art performance but it also outperformed most of the competition.
The quantity and quality of the low - end is just amazing to the point that one wonders how it is possible for such a small unit to produce that big sound.
Bass sounds full, visceral and weighty, deeply extending into the lower notes without rolling off, offering great sub - bass rumble, a versatile performer that feels at home from classical to bass boosted electronic music.
The tuning is balanced with a touch of warmness and the bass doesn't cloud or mask the rest of the frequencies, moreover it is exemplary layered with perfect separation between the various instruments of the bass line.
Quantity is delivered in spades but not at the expense of the quality characteristics as it is tight, controlled and crystal clear with large impact and a grand scale in dynamic contrast that is unbelievable even without considering the size of the driver.
The continuation of the auditions revealed without any doubt that I was dealing with an iem of the highest level where technical performance was top notch and addressed at birth, allowing the designer to concentrate all his efforts and know-how in manufacturing a musical communicating instrument rather than the average transducer.
With the IE900, fidelity and transparency are a "de facto" and not worth analyzing any further so we can discuss in depth about the timbre and tone of the sound.
Here the classical sound analysis into bass - mids - treble is vague and rather unnecessary since the timbre flirts intensely with the ideal, with the tonality of all instruments and voices touching reality not only in their harmonic wealth but also in their textural quality.
The IE900 is particularly resolving and finely articulated without being analytical at all, standing out by the ability to offer a deep gaze into the recording venue and masterfully communicate the inner space and time domain, virtually teleporting the listener into it, making him a part and not a mere observer.
The stage extends beyond the ears and creates a deep, three-dimensional illusion with the performers occupying their desks with pinpoint accuracy and ample space between them.
If there is something to criticize is that the picture is missing in size and scale and there is the feeling that we are listening to the music like sitting in the balcony of the concert hall.
Sennheiser's decision to stick with the time tested single dynamic driver principle paid off because the IE900 sounds incredibly homogeneous, there are no phase shifts nor frequencies overlapping and the sound is coherent and solid.
The driver is fast and agile, the iem has excellent timing and fast transient response, a sense of inherent rhythm that can keep up when the music gets busy without losing its pace.
Percussion instruments fade away and decay with the most natural and shimmering reverb, not too fast nor too slow and above all without losing in body while reaching the higher frequencies.


At the end

Well, it is not a coincidence that Sennheiser is considered to be the leading headphone manufacturer in the industry and that seems to hold true even after the transition to Sonova.
The IE900 is in my opinion, Sennheiser's best creation after the legendary Orpheus and the iconic HD650, it is more like a rare musical instrument of the highest rank committed to connecting the listener to the music.
Don't let the size fool you as it did with me and make no mistake that the IE900 is easily the best single DD iem on the planet and among the best of all kinds.

Test playlist

Copyright - Laskis Petros 2021
Last edited:
@gLer , @lmf22
Thank you very much, I am glad that you have liked the review!
Codename john
A great review makes you want to blow your money and bury your head in the rabbit hole. This was a great review!
  • Like
Reactions: Ichos
Thank you very much.
Well I have regrets that I didn't buy it but I was sort of cash back then.


Headphoneus Supremus
Sennheiser IE 900 – A Miniature Musical Marvel
Pros: Balanced, natural, lifelike sound.
Utterly coherent and musical.
Excellent build quality, comfortable fit.
Lush tonality with excellent technicalities.
Probably the best single dynamic driver bass in the business.
Spacious stage with excellent imaging and detail.
Cons: Treble can get spiky with some recordings.
Cable is prone to microphonics.
Stock tips aren't suited to everyone.
Not the most technical performer compared to multi-kilobuck IEMs.
If you haven’t read my first impressions preview of the new Sennheiser IE 900, feel free to do so here.


The opinions expressed in this review are just that – subjective opinions, based on my personal music choices, listening preferences, and even my mood on the day. As such you should consider this (and really any) review as just another data point. If you have any questions about my preferences, the music I used, or anything else you’d like to discuss, feel free to leave a comment or PM me directly.

Full disclosure: Sennheiser loaned me the IE900 in exchange for my honest review, without fear or favour, or any expectations from me. I am required to return them to Sennheiser once I’ve written my full review, and have already purchased a pair of my own. That’s probably a bit of a spoiler for what’s to follow…



Sennheiser is a name synonymous with headphones, some of which – like the famed HD600 / HD650 series and flagship HD800 – have earned their place as benchmarks for high-fidelity in the head-fi world.

The company has dipped its figurative toes into the IEM world too, but never quite attained the same stature in the smaller format of the game as it had with its lauded headphones. That’s not to say it hasn’t been successful, and its flagship IEMs did for a time earn widespread appeal and pioneered notable engineering firsts.

But it’s been a while since the IE 800 (2012) and IE 800S (2017) were flagbearers, superseded by a new generation of multi-driver IEMs from boutique manufacturers in the US, Europe and Asia. Despite releasing a series of new IEMs in recent years, purportedly for the ‘pro’ stage and music mixing market, the company waited until earlier this year to launch its first updated ‘audiophile’ IEM, the consumer-friendly IE 300, before surprising the market with its new flagship IEM, the IE 900.

Incidentally, behind the scenes, Sennheiser sold off its consumer audio division to Swiss-based Sonova, and despite suggestions that Sennheiser’s design teams will continue working with the new owners to develop future products, could the IE 900 possibly be the last original head-fi release from the famous German brand?

Considering how the IE 900 came to be, the legacy it represents, and the fact that the HD800 was the culmination of my personal four-year journey to find the very best headphone for the music I listen to, I immediately signaled my interest in the IE 900 almost as soon as it was announced. To my utter amazement, Sennheiser answered the call, and with the generous help of one of the best industry spokespeople I’ve had the pleasure of working with (thank you, @Evshrug), I had an IE 900 delivered direct from Bavaria to my review desk at the tip of Africa.

The Sennheiser IE 900 is an outlier of sorts in the modern IEM world, particularly at the pointy (read rather expensive) end of the market where only the most enthusiastic (read well-heeled) enthusiasts dare to go.

For one, it sports a single full range (or wide band, as Sennheiser calls it) dynamic driver, instead of the mix-and-match of dynamic, balanced armature, e-stat and other exotic driver combinations common to its competitors. It’s uniquely small, unusual even for a single driver dynamic. And it uses MMCX (rather than the more popular 2-pin connector) for its plastic-sheathed (rather than braided) stock cable.

But as you’ll soon see, all these design decisions have a purpose. While they may initially frustrate some users, who may prefer the contemporary ear-moulded aesthetic or take issue with the inability to ‘roll’ their existing, expensively-acquired collection of third-party cables, once you get to know the IE 900 (and navigate around some of its ‘quirks’), you’ll find yourself rewarded with an IEM that elevates, rather than stymies, the state of the art.


What’s in the box

The IE 900 comes in a compact box adorned by a classy image of the distinctive earpieces on the cover, flanked by the Sennheiser logo and ubiquitous Hi-Res Audio emblem, a must-have accreditation for any self-respecting audiophile in the 21st century. Inside the box you’ll find…another box, this time with no imagery, just a sleek, dark-grey motif, silky smooth finish, and embossed Sennheiser logo, with a velvety pull tab on the side that releases…yet another box with the contents you’re by now desperately trying to get to.

The first thing you see after you’re done playing Russian Dolls is the two glistening silver earpieces, looking ridiculously small in their pre-cut foam enclosure. Another tab lets you lift the foam away, exposing a date-stamped certificate of authenticity with a serial number and handwritten signature of your personal QC checker, a very nice touch befitting a premium product.

Digging deeper you’ll find a smorgasbord of standard-issue accessories, including a stylish gold-brown zippered carry case, three stock cables (one for each of the 3.5mm, 2.5mm and 4.4mm termination types), a selection of silicone and foam eartips (in small, medium and large sizes), a shirt clip for playing crocodiles while listening to music, a Sennheiser-branded cleaning tool for flicking your co-workers with the earwax that accumulates in your tips, and a plush cleaning cloth to offer your co-workers by way of apology when you’re done.

I’ve seen more lavishly presented flagships (Empire Ears comes to mind), and laughably spartan ones too (Oriolus Triallii, anyone?), but on the whole, I’d say the IE 900’s is a very pleasant unboxing experience indeed. You get everything you need in the box, and what you don’t get isn’t too expensive to source elsewhere (more on that later).


Form follows function

A closer examination of the IE 900 earpieces reveals exceptional build quality and precise craftmanship. The IE 900 housing is CNC-milled from a single block of aluminium with a finely ridged ‘fingerprint’ pattern making it both very distinctive and easier to grip. It would have been cool for every set to vary the pattern slightly, like its own unique fingerprint, though that would have no doubt added unnecessary complexity and cost to the process.

The earpieces are shaped in the fold-over style common to on-stage monitors, and even though that’s not their primary purpose, it’s a design that lends itself to a very comfortable, if somewhat intimate, fit. Sennheiser opted for industry standard MMCX connectors for the IE 900, but used slightly recessed earpiece sockets to improve contact longevity at the expense of compatibility with many third-party connectors.

If you’re going to cable roll, make sure to stipulate IE 900-compatible connectors, or risk your new cable not being able to latch on to the earpieces (as was the case with a spare set of MMCX to 2-pin adapters I tried to use unsuccessfully).

Inside the shells, Sennheiser stuck with their tradition of using a single 7mm dynamic driver, made of unspecified materials, extending a lineage that dates back to the original IE 800, and possibly even earlier. While the driver itself has undergone several iterations since then, the standout features of the current implementation is the addition of two important engineering advancements created specifically for the IE 900:

X3R technology – a fancy acronym for the three Helmholtz resonators milled directly into the earphone enclosure, designed to eliminate resonance peaks that can otherwise colour or adversely affect the sound coming from the driver. The resonators work in combination with the specifically shaped nozzle structure to regulate the airwaves generated by the driver and smooth out any errant peaks in the frequency curve.

Acoustic back volume – this small ‘space within a space’ sits behind the driver and supposedly affects the tuning of low-end frequencies, helping better shape and separate them from the midrange and further reduce resonance from the enclosure.

In the lead-up to the IE 900 launch, Sennheiser released a promotional video to highlight these specific features. Check it out below:

I’m no engineer, but to my layman’s ears, one of the standout qualities immediately apparent in the IE 900’s sound delivery is a silky smoothness with an almost complete lack of resonance, particularly in music where shouty vocals or aggressive piano strikes often result in fatiguing peaks with other IEMs (especially those tuned brighter, with strident treble, or over-abundant midbass).

I’ll make more mention of these qualities in the sound impressions part of this review, but as part of my research, I asked the man who led the IE 900 design team, Jermo Köhnke, how the specific function of these tuning technologies impacts real-world performance (in a way that you and I can better understand it). This is what he said:

“The resonator chambers primarily dampen several peaks in the treble range. To me, a peaky treble is most annoying when it makes the headphones lisp and the singers ‘s’ sounds become too sharp to enjoy the music. A second effect can be unnaturally aggressive percussion, but lisping is my litmus test for peaks, which varies from song to song. Sometimes the song itself is mastered too liberally in those frequencies, in these cases a revealing headphone should transport that as well.

The back volume…gives us complete control over the tuning, so we can worry about everything else when developing the earphone housing, the assembly process, etc.. For example if you just overdo it with the mids, the sound becomes closed-in, undynamic and generally unenjoyable for music listening.
It gives us a lot of flexibility during development, but it also means outstanding quality control for the end user to get exactly the sound they listened to in a store.”

Whatever the IE 900 is doing or not doing, and regardless of whether or not what it’s doing suits your preferences, the one thing I think we can all agree on is that it’s been precision engineered by a company that knows a thing or two about tuning headphones. Sometimes the smallest innovations make the biggest difference, and this seems to be the case with the IE 900.

For more information on the various components, frequency response, THD and other technical aspects of the IE 900 design, you can download the full spec sheet from Sennheiser here.


Finish, fit and comfort

The IE 900 makes a change from the larger, bulkier, heavier multi-driver IEMs that have dominated the high-end and mainstream market for some time now. It’s a welcome throwback to more compact single-driver designs, and I applaud Sennheiser for sticking to their proven design aesthetic with the IE 900 rather than blindly following current trends.

The aluminium shells are well made, and feel refreshingly cool to the touch. They seem very resilient too, though I still wouldn’t want to drop them, and their fragile internals, from any sort of height.

I generally keep my IEMs permanently attached to their cable and stored inside a hard case or pouch, and the IE 900 is no exception. The included case is protective on the outside and softly lined on the inside, with ample room for the earpieces, cable, extra tips and even an extra cable if you need to carry one around with you. I normally like to prevent my earpieces from clinking against each other, so use a mesh case from Campfire Audio (product link here) for extra protection.

All of this contributes to what I consider to be one of the most comfortable IEMs I’ve had the pleasure of using. Comfort is a non-negotiable for me when it comes to the gear I use for several hours at a time, and the combination of small size, smooth finish and relatively shallow insert makes the IE 900 an easy recommendation in this regard.

That said, the ergonomics of the IE 900 don’t make for a seamless wearing experience for everyone. I’ve heard of several instances from very experienced IEM users I know and trust that have struggled to get a good fit with the IE900. For one, the earpieces are very light, and since they’re attached to the cable using MMCX connectors, they swivel (or helicopter) quite easily. The cable itself, while very smooth and supple, terminates in a memory wire-shaped hook that’s fairly thick, and somewhat bulkier and heavier than the IEMs themselves. If not seated properly, the cable and hook will simply yank them out of your ears with the slightest movement, especially if the tips don’t grip your ears like they should.

There’s an art to properly fitting the IE 900 that, once mastered, makes it quick and easy for me to slip them in every time. Hopefully this will help some of you who are still struggling with fit (with thanks to my wife, the ear model):
  1. First, loosely flatten out the earhook, facing the cable entry forward (in front of you and away from your face). Don’t worry about shaping the earhook before inserting the earpiece. It’s going to deform anyway, so rather save your energy.

  2. Grip the earpiece between your thumb, index and middle fingers to prevent it from swiveling around the MMXC connector, then gently insert the tips into your ear canal and corkscrew the earpieces counter clockwise while using your free hand to hook the cable around your ear. Don’t force them in, you just want enough pressure for a good seal. If pushing them in hurts your ears, or they’re going in too easily and not creating a seal, you’re either pushing too hard or the tips you’ve chosen are probably too small. Swap tipsand try again.

  3. While holding the earpiece in place, use your free hand to gently pinch and mould the earhook around the top and back of your ear. Not too tight so that it clamps your ear, but tight enough so that it keeps the earpiece in place, with the rest of the cable falling away weightlessly.

  4. If you’re still finding the earpieces aren’t perfectly seated, push the ‘bottom end’ of each earpiece (the part that goes into your ear) slightly forward (in other words, deeper into the ear). The earpieces will now sit at an angle, but should hold firm, albeit with a slightly deeper fit.

Now that you have the earpieces and cable in a comfortable position, no amount of head movement, jaw movement or light cable tugging should shift them out of place. Feel free to use both your hands to pat yourself on the back for passing the Advanced IE 900 Fitment Course with flying colours.

On cables and eartips

Before we move on to the substantive part of this review, a quick note on cables and eartips. Newcomers to the hobby sometimes get despondent when they crack open their IEMs only to find the cable sucks and the tips don’t fit as well as they should. As an experienced (read battle weary) IEM user, I almost expect to ‘roll’ the cables and tips of a new IEM to see if I can change the sound, fit, or both for the better. In fact, I’m now at the point where it’s rare that I even take the stock tips and cable out the box with most IEMs.

The IE 900 is slightly different in that the tips it comes with are rumoured to have some sonic characteristics important to the sound. According to Jermo, that’s not the case:

“The foam within the ear tips has been implemented solely to protect the transducer from cerumen or other ingresses. Foam is necessary to catch even small particles, but it’s also nearly impossible to prevent foam from building up some acoustic impedance if you compress it. If you look closely, the foam is very large-pored.

If we wanted an acoustic impact, we’d choose a finer, better-defined material. If the IE 900 were a relaxed earphone that might turn dull with a bit of impedance, [and] we would have chosen a different solution. But the IE 900 is a brilliant earphone and a slight change of 1-2 dB in the treble doesn’t change the character to the worse for most people.
Long story short, you can use whichever ear tip fits.”

So, there you have it folks, from the man himself. Stop worrying about sonic filters and proprietary tips and tip roll the IE 900 to your heart’s content!

Fortunately, I have a war chest full of third-party tips I can choose from, so when none of the included IE 900 silicone tips sat comfortably in my ears, I was able to quickly find an alternative that fit better and (as I would later discover) sound better too. Do note that the stock tips have a clever two-slot system that allows you to position the tips further forward or back on the nozzle, for a deeper or shallower fit, and that you lose this feature by switching out to third-party tips without these slots.

As for the cable, I happen to quite like the stock cable, and the fact that you get a 4.4mm-terminated cable in the box is a big plus. Yes, the included cable is microphonic when you’re fiddling and fitting the IEMs in your ears (for the uninitiated, microphonics are the loud scraping sounds you hear when the cable rubs up against your sweater or skin as it dangles from your ears).

Thankfully this is not an issue once the earpieces are seated and I’m sitting down to listen, and if I get up to walk with the IEMs, the chin slider mostly prevents any errant sounds from the cable too. But, if you’re super sensitive about cable microphonics, get ready to roll.

I’ll compare various tips and the effect they have on the sound of the IE 900 later on in the review, but I’m glad to say the IE 900 may be one of the first IEMs I’m unlikely to cable roll for the foreseeable future.

Sound impressions

In my first impressions preview I went on a musical journey of discovery with the IE 900. Now that I’ve had a few solid weeks listening to it almost daily, I have a much firmer handle on what I’m hearing and will hopefully be able to describe it without resorting to images of rainbows and unicorns.

All listening was done with the stock cable and Acoustune AET07 tips, using a HiBy R8 DAP in high gain Turbo mode at a volume setting between 36 and 44/100. I’ve also included some notes on different tips and source matching.


The IE 900 is a very balanced sounding IEM. There’s nothing in its tuning that jumps out and screams for attention at the expense of everything else. In this regard it’s not a wow tuning like you’d find with some specialist IEMs. Instead, the more I listen, the more I’m asking: ‘wow, why aren’t more IEMs tuned this way?’.

While it’s difficult to gauge how fatiguing (or not) an IEM will be after a few quick sessions, on the whole I found the IE 900 to have a fatigue-free, natural sound over the time I’ve used it. Tonally at least, I’m struggling to think of anything about the IE 900’s tuning that will fatigue even the most sensitive listener. It may not be to everyone’s preference in terms of aggression or in-your-face energy, for example, but fatiguing it simply is not.

I’ve seen the IE 900’s tuning described as V-shaped, but I don’t think that’s right. This is not an IEM that pushes excessive bass and treble energy and leaves the mids to dangle in the middle. I’m hearing a much more uniform U-shaped tuning, with a slightly lifted but otherwise linear bass, a very natural midrange that is neither too forward or too recessed, and treble with plenty of sparkle and air up top that pushes close to – but generally doesn’t cross – the brightness threshold to my ears.

All three strike a very cohesive – and importantly for a single-driver IEM – coherent balance. If there’s something prominent in the mix, you’ll hear it as prominent with the IE 900. If vocals are pushed back by the artist, they’ll stay pushed back. What you’ll get in return for this ‘hands-off’ tuning approach is exceptional quality, from the lowest sub-bass rumble to the tiniest flutter of high-frequency air. Like I said earlier, this is not a specialist IEM, it’s the consummate all-rounder.

One of the ‘tuning tricks’ the IE 900 seems to employ very successfully is a dip in the upper mids and lower treble (the so-called presence region) that lends a more relaxed tonality to the sound. It’s probably not so much a trick as it is a tuning choice, and is likely what gave me the initial impression of a laid-back listen. While I’ve since discovered the IE 900 is very capable of oomph when it’s called for, this laid-back quality is very much part of its DNA, and also what makes it so appealing to me personally (I’m not a fan of overtly aggressive transducers in any format).


Bass. The baseline measure of quality for any IEM, for me, is its bass response. With only one exception (Oriolus Traillii) I’m yet to hear any IEM that delivers perfectly natural sounding bass without dynamic drivers, and among the dynamic driver IEMs I’ve heard and own, the IE 900 is very close to the best. By ‘best’ I don’t necessarily mean fastest (it’s very fast for a dynamic driver though), or biggest (it’s plenty big, but there are bigger bass cannons out there).

By best I mean the IE 900’s bass is a delicious feast for any true bass lover. I find it very balanced between sub-bass and midbass, with a very deep sub-bass extension and healthy but not overdone midbass lift that adds just enough kick and punch.

Regardless of what’s playing, the bass seems to occupy a space just behind or just around other instruments and vocals, and as such remains distinct yet infused from and with the rest of the track. It’s a presentation that I’ve rarely heard with other IEMs, so I asked Jermo about it and he told me it has less to do with tuning than I assumed:

It has not as much to do with tuning or design… for the most part, we’re standing on the shoulders of giants here. Producing the lowest distortion sound consistently and matching channels precisely in a single transducer gives you much of the more natural impression of space.”

I’m yet to find an example where the IE 900’s bass lets me down. Not one. From synth drums to real drums, bass guitar and classical bass, woofer rumble and kick drum kick. This is a masterful bass presentation that’s impeccably tuned. There’s zero midbass bleed, and even when the bass goes big, it somehow manages to occupy a space behind or around the vocals and supporting instruments without the usual cost to microdetails.

This spatial quality of the IE 900 is clearly evident in Lana Del Rey’s Dark But Just A Game( The track has two electronic bass hits, the first at 0:26 (a soft but definite thud that should decay into the sub frequencies) and a much deeper, more resonant double-bass hit at 0:38 which then repeats throughout the track but spreads out around the vocals and instruments to give a very natural impression of the stage.

Another litmus test for bass quanity and quality is James Gillespie’s What You Do(, a track that literally opens with one of the biggest bass hits I’ve heard in a modern pop. The track’s signature synth drum explodes four seconds into the track, them repeats a few times from 0:48 onwards, and the IE 900 delivers the full, uncensored impact every time.

Unlike some IEMs that favour midbass over sub-bass or vice versa, the IE 900 doesn’t compromise either, but also doesn’t overdo the midbass to the point of midrange bleed or bloom. In Katie Melua’s Red Balloons(, for example, the track opens with a deep midbass hit and sub-bass rumble that persists through the track but never overpowers Katie’s delicate vocals at any point.

Likewise the droning bassline that makes Massive Attack’s Angel ( a go-to bass test for many people is deftly handled by the IE 900, never obscuring any of the smaller instruments or vocals and avoiding the muddiness this track can exhibit with lesser drivers. Feist’s Tout Doucement( is another track where a repetitive bassline can quickly turn into bass soup if left controlled. The IE 900 gives me an enjoyably thick, meaty rumble that underscores the sweet vocals with ample contrast and delicious texture.

I use two specific tracks to check for bass bleed: Ingrid Michaelson’s The Way I Am( and Heidi Talbot’s Cathedrals ( Both have massive bass presence, bass strings in The Way I Am from the first note, and bass drums in Cathedrals from 0:55.

The reverberating bass plucks in The Way I Am give the track its signature weight but can damage vocal and instrument detail if it's not handled deftly. The IE 900 somehow manages to infer as much heft as I've ever heard with this track while somehow leaving every other element untouched. In Cathedrals, Heidi’s sugary vocals are interspersed with sparse guitar plucks until a cavernous bass envelops the music at 0:51. If there’s any bleed, some vocal and string instrument details become obscured at this point, but not with the IE 900.

Finally, realism is a big factor in bass quality for me, and it doesn’t get more real than in Batunde Olatunji’s Stepping (Isise) ( If you want to know what it feels like to sit in the middle of an African tribal drumming melee, this meticulously recorded track is for you. The incessant, swirling, sweeping drum hits will have you bobbing your head and tapping your feet to the rhythm, but take particular note of how articulate and lifelike the texture, velocity and position of each individual drum is rendered here.

To think that the single miniature dynamic driver in the IE 900 is capable of simultaneously conveying all the subtleties (and air movement) in these ultra-dynamic drums, especially as the drummers reach a frantic crescendo at the 5-minute mark, is quite something.


Midrange. While the IE 900’s bass is almost faultless, it also never pulls my attention away from the fundamentals of the music in the midrange. This speaks not only to the balance the IE 900 strikes with its tuning, but also to the natural voicing of the IEM.

The IE 900’s midrange is firmly in the Goldilocks zone for me: just wet and full enough (especially in the lower midrange), not too dry or thin, a very natural presentation in and of itself. It has an organic quality that makes me believe what I’m hearing, particularly with vocals, but also with physical instruments like guitars and piano. Male vocals reach deep with just the right amount of texture, and female vocals have a sweetness to them that I particularly enjoy without ever being too shouty (two things I definitely do not enjoy).

Listening to the IE 900 sometimes makes me feel like the recording disappears and the artist comes to life, sitting in the same room and singing directly to me. In fact, the IE 900 pulls off this disappearing act better than any other IEM I’ve heard (a mantle previously held by the 64 Audio U12t), and I attribute this mostly to the quality of its midrange.

When I think of midrange, I think of vocals, and since I primarily listen to female vocal-driven music, this is where most of my focus has been for this review. The IE 900 is a very human IEM, in that it renders both female and male vocals with an organic timbre that’s essentially lifelike. It’s something I keep coming back to but also something I feel needs to be emphasised, because so many IEMs that go for the spectacular fall short when it comes to lifelike vocals.

The IE 900 is like a warm blanket in this regard, not that its midrange tone is particularly warm – though it is warm in the sense that it sounds alive and full – but in the way it’s just instantly comfortable and relaxing at the same time, at least with the music I listen to.

And yes, I know that the fundamentals of most instruments also fall into the midrange bracket, but I’m far less attuned to ‘issues’ with instrumental midrange as I am to vocal delivery. That said, I’ve been very impressed by the realism (there’s that word again) of real instruments with the IE 900, though I’m probably not the right person to ask about instrumental accuracy, timbre and such.

One of the first tracks I use to test for vocal purity, as I like to call it, is Beryies’ Alone ( As you’ve probably inferred, a large portion of my music library is made up of sweet-sounding female vocalists, and one of my absolute favourites is Canada's Beyries. Alone, the opening track of her masterful album Landing, isn't perfectly recorded; there's a slight glitch in the annunciation at the start of the second line (‘…so long’, 15 seconds in), that the IE 900 presents unerringly, but for the remainder of the track - and indeed the album - the vocals are just pure emotive honey.

Katie Pruitt's It's Always Been You (, another one of my all-time favourite tracks, is recorded with too much upper harmonic energy for my liking on many IEMs. Listening to this song on the 64 Audio Tia Fourté , for example, was always a love-hate experience for me, loving the detail and hating it at the same time. The IE 900, with its fuller midrange, presents an altogether more organic rendition of this track without most of the upper harmonic hissiness. On balance it's one of the best renditions of this track that I've heard (bested only by the Legend X and Traillii), which is to say it's exceptional on the IE 900.

Another great litmus test for vocal purity, Eva Cassidy’s Songbird ( melds Eva’s velvety vocals with a sparse guitar accompaniment. When Eva hits her high notes from 2:35 to 2:45, any errant upper mid forwardness will have you wincing, but the IE 900 keeps this section in check, albeit still emotionally potent.

Combining husky male and sultry female vocals, Holly Throsby and Mark Kozelek’s What Do You Say?( exemplifies the balance and linearity of the IE 900’s vocals. It’s also a good example of the IE 900’s midrange clarity, the guitars (both acoustic and electric) supporting but never subverting the vocals. From 1:49 to 2:19, both Holly and Mark and trade verses with each other to an electric guitar and rhythmic tambourine backing, and not once are the vocals pushed behind the instruments.

While not the best recording, Jim Croce’s Time In A Bottle ( doesn’t make the vocals compete with the guitar strums, which are split neatly into each channel. While Jim’s isn’t the deepest of voices, it’s still indicative of how evenly the IE 900 renders male vocals, and I’m moved by the sadness of the words, knowing the tragic fate of the artist.

This emotional connection is a repeating theme with the IE 900, which is rare for me with male vocalists, and I think it’s a factor of the IE 900’s rich and realistic midrange delivery. From Neil Diamond’s gravelly Hello Again ( to Novo Amor’s ethereal Anchor ( and Radical Face’s sublime Welcome Home, Son (, I’m finding a renewed appreciation for the male vocal collective in my library.


Treble. Treble is probably the bottom rung on my list of tonal priorities. I only really notice the treble if it’s problematic (zingy and sibilant), or rolled off too soon (dull and lifeless). I’m fairly treble sensitive, so harsh treble that calls too much attention to itself is an instant fail, but I’m not as sensitive as I thought I was to a brighter tonality, as long as the treble is inoffensive.

The IE 900’s treble is fairly smooth and inoffensive, but not quite as relaxed as say a 64 Audio Nio or Legend X. Its treble tuning is such that the lower treble is fairly relaxed but the mid-to-upper treble can, on occasion, be strident, calling more attention to itself than I’d normally like. Some instruments, like cymbal crashes, can therefore seem more pronounced than they should be, at least compared to other instruments in a track, but this also lends itself to a liveliness and sparkle with most music.

According to Jermo, this is by design: the treble of the IE 900 is at the upper end of what I consider pleasant and fatigue-free. We spent most of the development time dampening the upper frequencies to the level they are now and had several discussions about whether we need to go further.

The most common feedback I get now is if there is a way to increase the treble again. So in the end we have a common goal at the audiophile team: distortion-free and natural listening experience. On the journey to that goal, we have to make some compromises, i.e. If we want to have a strong response beyond 10 kHz, we may also have to increase the critical area of 5-10kHz slightly more than we’d wish for.”

I can probably count on one hand the number of tracks that irked me to the point of distraction over the past few weeks of listening almost exclusively to the IE 900. But yes, if I have to be critical, they’re there to be found. Whether it’s the faintly metallic tone in a small number of upper harmonic female vocals, or the peakiness of a wayward cymbal or misplaced piano strike, the IE 900’s treble, unlike its bass and to a lesser extent midrange, can be fallible with certain types of music.

A very (and I stress very) small number of female vocal recordings have also come close to sibilance, hitting a treble peak that can be uncomfortable for some, so if you’re fairly sensitive to this, an audition is probably a good idea before buying.

If I have to mark the IE 900 down on anything when it comes to tonality, its occasionally over-exuberant treble would be it. But then I’m actively seeking out issues for the sake of this review. Overall it’s still what I consider to be a very good treble response, given the single driver design that doesn’t have the benefit of multiple dedicated BA or e-stat treble drivers.

To my ears, the balance the Sennheiser team struck with the treble tuning of the IE 900 is just about right, even though I’d side with the team asking about further dampening if possible. That extra dampening would be mostly appreciated on brighter recordings, like Boston’s More Than A Feeling(, where the snares can get just a bit too splashy for my liking, and even Brad Delp’s (RIP) vocals teeter on the edge of sibilance – almost unheard of with male vocals.

On the flipside, tracks that I typically associate with sibilance, like Missy Higgins’ outstanding cover of Shark Fin Blues (, is actually very smooth with the IE 900. With the wrong IEM, Missy will ess you into submission in the opening verses, but the IE 900 seems to tame the worst of it and I find this track thoroughly enjoyable, especially when the bass rumble kicks in.

Another artist that often crosses the sibilance line is 80s starlet Sandra. I think this is more a case of her recording style, because her bright, almost hissy delivery is consistent across her albums when played back with multiple IEMs. The IE 900 actually manages to keep Sandra’s Loreen( sounding quite sedate. The pseudo-sibilant vocals are more sugary sweet than startling, and the overall balance is actually very pleasant. Who knows, I may have to dig up all my childhood favourite Sandra albums now that I can tolerate them again.

In truth, while the IE 900 can push my treble tolerance to the limit, it very rarely crosses it. High-energy dance tracks like Fragma’s You Are Alive ( are full of sparkle and shine, and I quite like what the IE 900 does with it. It’s fun, almost spiky, but not to the point of fatigue, and I find myself turning the volume up to get even more of the energy, not something I usually do with brighter music.



The IE 900 is a solid technical performer that doesn’t quite reach the lofty heights of multi-kilobuck, multi-driver IEMs at the very top of the tree (with pricetags to match). But, what it might ‘lack’ in technical excellence, it more than makes up for in one very important and often overlooked ‘measure’: musicality.

This is not an analytical microscope of an IEM I’d use to dissect the music, like Fourté , or a detail monster like Odin or Traillii. Instead, the IE 900 gives a good account of itself on every technical metric, even surpassing some far more expensive IEMs in some areas (as you’ll see below), but it’s less an IEM I’d pick on technical merit and more an IEM I’d pick for musical enjoyment.

Soundstage and imaging. Of all the technicalities us audiophiles typically like to compare, soundstage is my personal barometer in an IEM. While some people struggle to hear any ‘stage’ at all with IEMs, for me the very best IEMs are able to break down the typical in-my-head stage and trick my brain into believing the sound is much bigger than it actually is.

Some IEMs, like Fourté and Traillii, have earned a reputation for a particularly wide sound, with the tiniest of details easily audible at the extremities of the stage. While the IE 900’s stage doesn’t quite reach out as wide as those two, it’s still wider than what I’d call average, and much wider than what I’d call intimate. It also has fairly good depth and height for IEM stage (more depth than height), and with some music borders on holographic, with sounds being projected all around my head.

Closely related to stage, imaging defines how accurately (or not) an IEM positions different sounds on the stage relative to each other. For me, this is one of the real strengths of the IE 900, and part of what makes it sound so effortlessly lifelike in my opinion.

Another attribute of the IE 900’s stage is what I call ‘room feel’. Listening to the IE 900 is akin to listening to music with loudspeakers in a room. While you can’t really compare the sound of an IEM, even a great IEM, to speakers, the IE 900 is one of the few high-end IEMs I’ve heard (alongside Fourté and Legend X) that gives me a room feel sensation with some of my favourite music.

I think the best way I can describe the IE 900 soundstage and imaging characteristics is lifelike and natural, and if those words are already familiar to you, that’s because these are also the defining characteristics of the IE 900 for me.

I’ve heard Amber Rubarth’s Strive, an instrumental track off her seminal Chesky Records recording, Sessions from the 17th Ward, sound far wider and more diffuse with some IEMs than I do with the IE 900. The opening drums in particular sit a little closer in than I’m used to, but when the strings come in at 0:17 in the right channel, they are positioned farther right than the drums, almost behind my ear.

Yosi Horikawa’s Bubbles ( is another staple stage test for me (and many others), with its mesmerising drop-ball effects echoing around the stage. I’m hearing quite a bit of depth with this track, a few of the more prominent echoes decaying deep into the ink black background, but left and right I’m only hearing slightly above average width.

Al Di Meola’s Tracks of a Tear (, the opening track off his hypnotic Cielo e Terra LP, with its gentle guitar strings overlaid with swirling cymbals and a shaker that pans right to left, left to right across an ample stage, is a case in point. Some IEMs image with a three blob stage (left-centre-right) with very little information in-between, but on this track I can easily follow the shaker as it pans in both directions, not once losing its clarity or definition. Likewise I can almost reach out and touch every single cymbal strike because of how precisely they’re placed on the stage.

Vocal imaging is just as natural. Rosie Thomas’s duet with her male backing vocalist in Why Waste More Time( is notable for many things, but for me the way the two vocalists are offset from each other, just to the right and left of centre, speaks to how perfectly the IE 900 is recreating the overall image of the song.

In Kristin Hersch’s Your Ghost (, a deep, almost subterranean rumble, first heard at 0:59 and again at 1:07, echoes to the extremities of the stage and gives me a real sense of the size of the ‘room’.

A similar effect is audible at the start of Dadawa’s Sister Drum, the prominent bassline sketching out the dimensions of the stage. Then, the interplay between the larger drums at 1:59 and smaller hand drums all around them (including a prominent and surprising smack left of centre at 2:34) combines all the different elements of stage size, width, precision imaging and room feel to create a startlingly vivid image of the soundscape.

Separation and layering. I never thought a single-driver IEM like the IE 900 would stand a chance against multi-driver IEMs when it comes to separation and layering of vocals and instruments, and technically speaking I was right. I don’t think the IE 900 has the same space and air between instruments and vocals as Fourté, for example, and is a rung or two below the Trailli when it comes to layering the different sounds in a track (but then again, most IEMs are a rung or two below Traillii in this regard).

That said, the IE 900 does not sound congested, even on busier tracks, and there’s more than enough air between and around instruments and vocals so they don’t trip over each other. I’ve already covered this aspect in some detail above, but vocals are particularly well separated from instruments, and the IE 900 somehow manages to render bass on a separate level to most other sounds while still sounding completely cohesive.

Two minutes into Agnes Obel’s The Curse ( she starts to sing over a crescendo of oboe, cello, piano and some nondescript background strings and I could still make out the fundamentals of each instrument and accompanying vocals without too much trouble. It’s not as spacious or crisply delineated as I’ve heard it with the best multi-driver IEMs, but then with the IE 900 I’m generally not trying to dissect the music (as I’m doing now for this review).

Owl City’s The Saltwater Room ( is another great track with a whole range of elements vying for attention: synths, strings, drums, electronic effects, and both female and male vocals, often playing simultaneously. On some IEMs I can almost walk around the song, taking in all the different elements from different perspectives. The IE 900 is not that type of IEM. Instead I find myself listening to the music as a collective, with the different elements fitting together rather than separated and spaced apart, but at no point sounding congested.

A perennial favourite of mine, Daft Punk’s Giorgio By Moroder ( is a horrible track to use for reviews, mainly because I always get lost in the music and forget what I’m listening for. But…I did stop long enough to listen for how the IE 900 handles the busier parts of the track, starting with the sped-up section from 5:50, where drums and effects overlay some classical strings, all of which I could easily follow as separate elements if I wanted to. Then, as the track hits its crescendo at 8:05 with the introduction of electric guitars and splash drums, the IE 900 takes it all in its stride and never makes anything sound confused or congested.

Details and clarity. I’ve already suggested that the IE 900 is not a detail monster like some of the better-known high-end multi-driver IEMs with their fancy e-stats and whatnot, but that’s not to say the IE 900 doesn’t do detail. It actually sits comfortably at the upper end of the detail scale for me, but unlike some IEMs that shove detail in your face for fun, the IE 900’s details are there to be enjoyed at leisure.

Overall clarity is also in the upper echelons, with vocal clarity particularly impressive. Even though I suffer from moderate hearing loss, and sometimes struggle to make out certain softly spoken words in a loud environment, I’m hearing vocals much more clearly with the IE 900 than I do with many other IEMs, even IEMs that supposedly have unnaturally elevated mids (which the IE 900 does not).

The level of detail in the guitar strumming and plucking in Nils Lofgren’s live rendition of Keith Don’t Go( is an absolute marvel to hear. I always listen to this track right through, but if you want to jump to the highlights, the finger picking from 3:23 onward is so pin sharp it feels like the strings will cut you if you’re not careful. I can almost tell how tightly each string is wound, such is the resolving power of this IEM (and the quality of recording). The best thing about it is that it’s not harsh detail, just naturally rendered as if I’m right there at the live performance.

Fine details are also evident in the Eagles live recording of Hotel California(, which appears on the band’s Hell freezes Over LP. From the opening crowd effects that put you right in the centre circle, to the subtle differences in timbre of the shakers in the right then left channels, to the differences in tone in the three guitars used for the intro sequence, and even the deep texture of the kick drums that precede the signature guitar riff, the IE 900 gives you absolutely everything there is to hear on the recording (and even some stuff you may not have heard before).

Switching pace and genres, there’s a part in Pink Floyd’s Hey You ( that never fails to send shivers down my spine with its creepy subtext. As Roger Waters delivers the iconic line: “…and the worms ate into his brain…” (3:18), I can vividly make out the electronic effect the band used to mimic just how that must feel, and the detail with which it’s rendered by the IE 900 is utterly satisfying.

I didn’t expect the IE 900 to compete technically with some of the top dogs on the market, so I wasn’t prepared when I heard it doing just that. Listening to the IE 900 for the first time, and now even weeks later, I’m still struggling to comprehend just how it manages to pull off some of the things it does with its seemingly simple yet deceptively complex design. While it may not win every race from a purely technical perspective, it’s so far ahead musically than mostly everything else I’ve heard, price irrespective, that I question how much this actually matters.

Still, if you’re someone that favours technical performance above all else, I don’t think the IE 900 will let you down, even though I don’t consider it an IEM best suited to the analytical listener.


Select comparisons

Unfortunately I can’t compare the IE 900 to any IEMs in its price bracket and the only other single dynamic driver IEM I own is BLON’s BL-03, which costs less than the IE 900’s spare tips. My ‘other’ IEM is the legendary Empire Ears Legend X, and while I hear many similarities between the two, the Legend X has seven drivers and costs $1000 more than the IE 900, so it’s not exactly a level playing field.

Also, while I no longer own it, I did manage to briefly compare the IE 900 to 64 Audio’s Tia Fourté side-by-side, but at almost three times the price of the IE 900, it’s in a different category of IEM altogether. That said, if anyone owns or has heard any of these IEMs, the following notes could be useful.

BLON BL-03. Say what you like about one of the most hyped IEMs in the history of hyped IEMs, but when it comes to the BLON BL-03 (BLON for short), the hype is real. This has to be one of the best tuned IEMs for my personal preferences, with a spacious, punchy and tonally even sound that shames some kilobuck IEMs I’ve compared it to (I’m looking at you, Andromeda).

Compared to the IE 900, the tonality of the BLON doesn’t deviate too far from what I consider ideal. Both are U-shaped to my ears. There’s some sub-bass rolloff with more midbass energy in the BLON, but I still find the bass very clean and with just the right amount of oomph, though not nearly as clean or textured as the Sennheiser’s. The midrange of the two is similarly close, with the BLON exhibiting a little more upper mid energy, but not much, and both pull back in the presence region just enough to create a greater sense of space and prevent female vocals from getting shouty. The IE 900’s mids are significantly better defined and detailed however, while the BLON is prone to some smearing with less-than-ideal recordings. The two also share a similar treble trajectory, though the BLON is a touch more peaky and rolls off sooner, while the IE 900 can be more intense.

Where the IE 900 pulls away, in a big way, is technically, leaving the BLON to huff and puff while it sails through in every category. Both share a fairly large stage, relatively speaking, but the IE 900 is easily more expansive, wider, deeper and better defined, while the BLON is just naturally comfortable. The IE 900 images better, separates better, and its detail retrieval isn’t really fair by comparison. All that said, the BLON is still no slouch, and what it lacks in absolute technicalities it makes up for with a warm, smooth, full and easy listening sound, and is the only IEM I find even more comfortable than the IE 900 for all-day listens.

Empire Ears Legend X. Of all the IEMs I’ve owned and loved, none have matched my personal preferences more than Legend X. Widely considered to have the best bass in the business, the Legend X is actually a very balanced IEM, with an organic tonality ideal for just about any genre of music, and technicalities that sit firmly in TOTL flagship territory.

Compared to the IE 900, the Legend X – like the BLON – is not too dissimilar tonally. I hear the Legend X’s tuning as distinctly U-shaped rather than the more commonly suggested bass-dominated L-shaped curve. The Legend X definitely has more bass energy than the IE 900, but only if the track calls for it. It’s definitely more extended into the sub-bass region, with a healthy but linear midbass elevation that only gets back down to IE 900 levels around the 400Hz mark.

The IE 900’s midrange is slightly flatter and more balanced with its bass and treble, but the Legend X’s isn’t far behind. Where the Legend X improves on the IE 900’s midrange, in my opinion, is detail, being able to bring out slightly more subtle nuances without being too forward. It’s also wetter and more organic compared to the IE 900, but always clear and, to my ears anyway, never recessed. The Legend X doesn’t have quite the same treble energy as the IE 900 so makes for a smoother, slightly warmer listen overall, but still manages to outdo the IE 900 when it comes to treble detail.

Technically the Legend X improves on the IE 900 in every metric, from stage width to imaging, separation and detail. This is probably the part that surprises most people on first listen, combining an understated power and organic tonality with world-class technicalities and a balanced tuning, especially with the right (neutral) pairing and right (wide bore) tips. It may not have quite as much air or shine up top to satisfy the true treble heads, but then neither does the IE 900, and that’s just fine by me.

64 Audio Tia Fourté. This IEM probably needs no introduction, other than to say it’s one of the best and also one of the most polarising IEMs I know. With an eye-watering price of $3600 (which buys you a junk cable and a very average accessory selection), Fourté remains a technical marvel almost five years since it was first released.

Compared to the IE 900 – and BLON, and Legend X – Fourté couldn’t be more different. It has a bright-leaning U-shaped tuning that favours treble energy and clarity over midrange fluidity or bass impact. Until I heard the IE 900, Fourté was my ‘reference bass’ benchmark, with a full, impactful (when required) bass response that gives it an immensity of sound akin to full-size floorstanding speakers, though it never quite satisfied my big bass cravings. It’s not the fastest bass, but is so detailed and textured it’s almost palpable. That the IE 900 was able to match and exceed Fourté’s bass in both quality and quantity was the biggest surprise for me on hearing them together for the first time. The IE 900 also does a better job at projecting the bass coherently across and around the music, whereas Fourte’s bass is somewhat separate from the other frequencies.

Midrange is where the IE 900 eclipses the Fourté to my ears. I’m one of the few (and fortunate) to hear Fourté as fairly natural, but even I won’t pretend it’s anywhere near as natural or realistic as the IE 900, especially when it comes to vocals. The Fourté’s vocals are airy, lofty, slightly dry, and typically float around its massive stage projection, whereas the IE 900 is more grounded, lifelike, with a dead centre stereo image (when called for). A sharp dip at around 800Hz makes some male vocals slightly hollow with Fourté , and female vocals can sometimes err on the brighter side of comfortable, although the latter is more recording dependent than a flaw in Fourté’s tuning. Treble is where the two IEMs differ the most, with Fourté using its unrivalled treble extension to infuse the sound with air and detail, and doing so exceptionally well. The IE 900’s treble is still fairly energetic by comparison, but not quite as smooth or refined as Fourte’s.

Technicalities is where Fourté really flexes its muscles (and justifies its price tag). It has one of the widest, most holographic stages of any IEM ever made, combined with clinically precise imaging, masterful separation, and more detail than the human ear could possibly resolve. This isn’t always to Fourté ’s advantage, however. The IE 900 is far more forgiving of poor recordings, for example, and is also more consistently musical. The IE 900 is also more natural as a result of its slightly narrower stage, and to me sounds more lifelike too.


Odds and ends

The IE 900 is fairly source agnostic, which is to say it’s going to sound great from just about any source. While I normally only use it with HiBy’s flagship R8 DAP, with its detailed, balanced, and slightly warm-of-neutral reference tuning, I enjoy the IE 900 just as much from my LG V30+ smartphone (with its drier, brighter Sabre DAC delivery), and even, on occasion, with EarMen’s Sparrow (review here) and TR-Amp DAC/amps (review here).

Interestingly I find the IE 900 to be both easy to drive and very power hungry at the same time. With a 16-ohm impedance and a sensitivity of 123 dB (at 1 kHz and 1 Vrms), it should be very easy to drive, yet requires the longest turn of the volume dial of all my IEMs to get it to my comfortable listening volume. To me that suggests the IE 900 is scalable, and will probably take well to even more powerful desktop amplification, though I have no such amplification on hand to verify my suspicions. I can say for certain it’s not sensitive to the point of exhibiting any hiss whatsoever with the HiBy R8, even on full power, and the R8 is prone to hissing with overly sensitive IEMs.

Eartips, on the other hand, can and do affect the sound profile of the IE 900. As mentioned earlier in the review, the included tips are not required to filter the sound of the IE 900 or tame its treble in any way, so whatever you may have read to the contrary is incorrect. Out the box I didn’t like the fit or sound of the stock silicone eartips, and since I don’t enjoy using foamies, didn’t even try the stock foam tips for size. But I did try several different tips with the IE 900, each with its own quirks and qualities, so thought it might be useful to include some of my findings below.

Acoustune AET07 – this is my preferred tip for the IE 900, which I hear as clear and exceptionally detailed (especially in the midrange), with a powerful, almost visceral bass response that travels through the stiffer stem and tickles my ears across the super soft umbrella-like silicone. It also gives me the widest, deepest stage of all the tips I’ve paired with the IE 900. The 07 can be quite revealing though, so poorly recorded brighter tracks may have you reaching for one of the warmer tips below.

JVC Spiral Dot – this is easily the most comfortable tip, with its soft, pillow-like silicone and pliable stem. The IE 900’s nozzle lip (which really should be standard issue on all IEMs) ensures the tips don’t slip off in my ears like they do with most other IEMs, and there’s enough of a gap between the IEM nozzle and tip opening for the ‘dots’ to do their sonic magic – i.e. soften and shape the treble and accentuate the bass decay. Compared to the Acoustunes, Spiral Dots do indeed soften the sound, making vocals slightly more ethereal and ‘distant’, but also smoothening the treble peaks while retaining most of the bass impact. If you’re finding the IE 900’s treble a bit spiky for your liking, try on some Spiral Dot tips.

Sedna EarFit/Light Short – closer to the Acoustune sound but with more contrast between bass and treble, the Sednas are a great choice with the IE 900, if you find them comfortable. The harder silicone of the Sednas makes them more noticeable over longer listening sessions (and not in a good way), and while I still find them comfortable with the IE 900 compared to other IEMs I’ve used them with, the combination of harder sound and harder fit compared to the Acoustunes makes them only third best for me.

Spinfit CP500 – I got these tips more out of curiosity than anything else, since I’ve never really gelled with Spinfits for some reason. These are longer than the other three tips above, and even though they’re made of soft silicone and have the trademark Spinfit bend when inserted, I still find them less comfortable to wear for longer sessions. Sound-wise they have a softer bass response than the three tips above, but also a more balanced tuning, so if you think the IE 900 is too dynamic and powerful for your liking, the CP500 might tame them for you – assuming you manage to keep their very wide stems seated on the earpieces and not in your ears.


Closing thoughts

I still remember when, in my early days in the hobby, Sennheiser’s IE 800 – with its black ceramic shell and twin-turbine aesthetics – was an aspirational IEM for me. When I finally got to hear it for myself, I was won over by its warm, full sound, ample bass and great staging, but left disappointed by its permanently attached, jangly, single ended-only cable and less than ideal, bottom-ended fit.

The IE 900, if it is to be the IE 800/S successor, is a major and worthwhile upgrade in every way. From styling to build quality, sound quality and accessories, it takes pride of place as not only the best IEM Sennheiser has ever made, but in my opinion, the best headphone Sennheiser has ever made, bar none. It even eclipses the HD800 which, for me, is the pinnacle of dynamic driver headphone design.

Whether or not Sennheiser will continue raising the bar in headphone design under new ownership remains to be seen. What we do know is that, in the IE 900, they have created a flagship worthy of the brand, and worthy of the heritage. A single dynamic driver design that’s both effortlessly musical and technically excellent, without ever sacrificing the former for the latter like so many other flagships (and even some of their own headphones) tend to do.

Like any IEM, the IE 900 is not without its flaws. The flipside of its easy going tonality is a treble that pushes too close to overexuberant for my personal liking, though it’s only ever crossed that line once or twice with the music I regularly listen to. Other nit-picks I could point to would be the occasionally microphonic cable, odd tip selection, uncommon MMCX connector design, and occasionally unconventional fit.

All that said, the IE 900 is one of the only high-end IEMs that’s truly engaged me from the very first listen, not with the spectacular, but rather with its balanced, natural, lifelike and completely non-fatiguing presentation of the music I love. It’s an IEM that, more than most I’ve heard before, removes the artificiality of the recording chain and connects me directly to the music. I’m in the room with the singer, on stage with the band, in the studio with the mixer. I’m hearing real drums and real guitars and real voices in an utterly realistic space, and not for a minute is my attention drawn away from the experience.

Put it in your ears, hit play, and you quickly forget you’re listening to an IEM. It’s a human experience that has less to do with technology and more to do with the people behind it:

I couldn’t devise an acoustic target that makes off-the-shelf transducers sound good enough that they practically disappear. It’s 90% the transducer technology and all the developers and engineers working for decades to make this performance possible.

The [real] stars for the IE 900 in particular are Grit Bonin, the acoustic engineer who implemented my target and requirements into the product, and Heinz Epping and Maike Faulhaber, who made world-class simulation efforts to optimise the last bit [of performance] of the transducer. Finally, André Michaelis, who initially headed the development of our 7mm transducer 16 years ago, and also convinced upper management to make a ten-digit investment to build the most advanced transducer assembly line in the world.”

The IE 900 is now the first IEM I reach for when I want to relax, want to connect, or want to explore new music for the first time, knowing I’ll be hearing it like it’s meant to be heard. It’s my miniature musical marvel, and comes with my highest possible recommendation.

Dust by Monday
Are you worried about using aftermarket tips since there's no protective filter between the tip and the nozzle opening? Wax might fall into the IEM itself. Is it an issue or not really?
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@Dust by Monday not worried at all. I have an IEM Vac from FiR Audio that I regularly use to 'clean' my IEMs. As long as you're careful and practice good ear hygiene you'll be fine. If you're concerned, you can take the foam inserts from the stock tips and put them in your aftermarket tips.
Dust by Monday
@gLer Won't the foam inserts fall out into my ears if there's nothing to stop them? The sennheiser tips have a cross shape in the tip opening that prevents this piece of foam from falling out.


1000+ Head-Fier
Sennheiser IE 900: One of the Best I've Heard
Pros: Excellent all-round.
Realistic soundstage and imaging.
Deep, detailed bass with great textures.
Cons: None for my usage (but if you plan to use these on-the-go, the cables are microphonic).
I had the IE 900 for two weeks, with over 150 hours. They are so aaamaaazing! Not only do they sound great, they are so light and comfortable. The IE 900 is so good that I sold my other IEMs, including the Campfire Audio Polaris II, Dorado 2020, Solaris 2020, and gave my UM Mest II to my dad. All of these IEMs are excellent in certain areas or genres of music, but I feel the IE 900 is the best all-rounder across the board, from musical qualities to comfort.

I’m using the Sony WM1A (MrWalkman custom firmware Dawn Plus). DSEE AI on, DC Phase Linearizer Type B Low, low gain, 4.4mm balanced output.
My music preferences are: Pop, country, jazz, and occasionally classical.

I'm skipping the unboxing, technical description, and walkthrough of the accessories. Other reviews are much better at doing that than me. Let's just get right to the sound!

The bass
The IE 900 has the best bass I’ve heard in an IEM. It goes deep when needed, but doesn’t artificially make every bass note deep and big. They are clean, detailed, and beautifully textured. The same goes for bass quantity; there is plenty of it, but only when the music has it, and never interferes with the lower-mids and mids. The bass quality reminds me of my home stereo system (PSAudio DirectStream Jr DAC, Octave V70SE tube integrated amp, Dynaudio Contour S3.4 speakers).

The mids
So beautiful, articulate, and detailed. Both female and male vocals come through strong and natural; never shouty or thin. The small details of familiar singers’ voices come through better and has better textures without overwhelming my ears with too much details. They are much more natural than other IEMs I’ve heard.

The highs
Extended and very smooth. Silky smooth. Some burn-in (either the IEMs or my ears or brain) is needed for the treble to shine. Initially, they seemed bright, even when using foam tips. After about 100 hours, they calmed down and became well extended and smooth. Instruments sound natural and non-fatiguing. This is important for me because I use IEMs when I work, so don’t like IEMs with distracting and fatiguing treble.

Soundstage and imaging
Both the soundstage and imaging are very beautifully done. The soundstage is moderately wide and deep, with a good amount of height. Sounds extend slightly outside my ears and around my head. What I like is that the soundstage is natural. It’s intimate if the music requires it, and extended if the music has it. More importantly, the soundstage doesn’t extend too far out where it can become unnatural, like an artificial 3D effect. Imaging is excellent. Every instrument and vocal has their own space and music rarely sound crowded. But please keep in mind these are not magical IEMs; poorly recorded/mix/mastered music still has poor soundstage and imaging. I would say the IE 900 presents the soundstage and imaging as they are in the music.

One of the most comfortable IEMs I’ve ever had. I can use them throughout my workday and rarely had to take them off or adjust them. I also like how extremely light they are. The comfort and weight don’t distract me from the music, which allows me to get more immersed in it.

The cable
I really like the cable. They are light, hard to tangle, and has a nice neutral color with a slight shimmery look under bright lights. They are more microphonic than other IEM stock cables, and may not be good when you’re using the IE 900 on-the-go. The shirt clip helps a lot. This drawback doesn’t bother to me because I use these in the office or at home.

Accessories and ear tips
Love the small case. The Sennheiser logo on the front looks great. The serial number on the back is a nice touch, and makes me feel special 😊

I’ll write some brief impressions of the ear tips I’ve tried. Keep in mind these are highly subjective (I tend to like sounds can be described as smooth, slightly on the warm side of neutral, and even slightly rolled off highs while retaining airiness). The sound descriptions may not apply to your ears, but hope they will give you an idea of how each tip can change the sound of the IE 900.

Stock ear tips
Out of all the stock ear tips, my favorite is the foam (size S). I like them with the small foams in them, which gives the sound a very slightly smoother treble.
I got a good fit with the medium silicone ear tips with a shallow insertion. I was not able to get a seal with the small or large sizes no matter the kind of depth of insertion.
+ Light and airy sound.
+ Excellent detailed and deep bass.
+ Very extended highs.
+ Very comfortable. They seem to just sit in my ear and doesn’t exert much pressure.
– Poor isolation (this can be plus if, for example, you’re working in the office and need to hear colleagues when they try to get your attention).
– The highs can get fatiguing for long sessions with poorly recorded music, but it’s fine with well recorded music.

I got a good fit with the small foam ear tips. The medium and large sizes put too much pressure in my ear canals, resulting in discomfort after about 15 minutes.
+ Full bodied sound.
+ Deep bass (but not as detailed as the silicone tips and can sound muddy with bass-heavy music).
+ Fuller sound, especially great for vocals.
+ Very comfortable. Slight pressure but never got uncomfortable.
+ Good isolation.
– Slightly rolled off highs (can be a plus because they are more forgiving of poorly recorded music, and good for long listening sessions).

Third-party ear tips
My favorites are the Final E (size S). I also like the Symbio F (size S).
Final E
+ Deep and bold bass with nice textures (but not as detailed as the stock silicone tips).
+ Full mids (much fuller than the stock silicone tips).
+ Smooth highs (need to have a deep insertion, otherwise the treble rolls off too much and you lose sparkle and air).
+ More body across the board.
+ Comfortable for long sessions.
– Slightly rolled off highs, but can be a plus because it’s more forgiving with poorly recorded music.

Symbio F
+ Detailed mids.
+ Great highs for foam tips; only slightly rolled off (less roll off compared to the stock foam tips).
+ Comfortable.
– Mids can sound grainy depending on the music.
– Bass doesn’t go as deep and there’s less of it.

Campfire Audio Marshmallow
+ Comfortable.
+ Forgiving sound for modern pop music.
– Rolled off bass and treble.

Symbio W Peel
+ Comfortable
+ Great bass quantity, but I not as textured as the stock silicone or Final E tips.
+ Smooth mids
– Treble doesn’t sound natural.

Azla SednaLight (regular and short versions)
– Easy to lose the seal in my ears.
– Bass sounds strange. I can’t put my finger on what it is.
– Highs can be fatiguing with modern music. More so with the short version.

Spiral Dot ++ and Spiral Dot regular
+ Comfortable
+ Forgiving sound for modern pop music.
– Diffused imaging. No solid center image. The vocals are too spread out.

Spinfit 145
+ Comfortable
– Muddy bass and midrange

(Photos have the Symbio F ear tips because the orange color looks great in photos :stuck_out_tongue_winking_eye:)


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Thanks for making the review so easy to find! If you ever want to share a link directly to this with someone, copy the link on the review date.
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hello vs sony iem z1r which one is better? I'm interested in these two

Scuba Devils

Headphoneus Supremus
Sennheiser IE 900
Pros: Incredible all-rounder
Excellent fit/comfort
Wonderful bass
Non-fatiguing crisp treble with stunning detail
Perfect width soundstage
Cons: Silicone tips aren't great...

I want to share some thoughts on the IE900 after almost two weeks of daily use. I’m sorry to say I’m not sufficiently technical to address in a way that many look for, as such, it will be a layman description with the knowledge I do have where possible. I am a music lover for many years (and once upon a time 90s DJ...) and up till last year, mostly listen via my separates systems and a variety of headphones and earphones - as of last November, I didn’t even know what a hybrid IEM was, let alone a single DD or an EST driver, they were all just earphones, headphones and some were Bluetooth (of which I've a few gathering dust)! My journey over the last few months with IEMs has certainly been obsessive, expensive and incredibly enjoyable - I’ve heard music in ways I’ve never before and I now rarely listen via my main system or full-size headphones. I admit to being a fan of Sennheiser and have had a few of their products over the years - HD-25-1 being a go-to back in my DJ days, HD650 (which I never use) in more recent years and a trusty set of IE8 that served me well for about 8 years, only actually finally retiring them last year as this hobby took hold. I’ve learnt a lot (but not enough) in the last few months and met many great likeminded music fans, I plan to continue this voyage of discovery and strive to be more proficient to articulate what I ‘hear’ into words that are useful to others… but for now, this is about as good as I can give!

I have a demo unit as I worked in consumer electronics for many years and still in touch with old colleagues. The unit is on loan but I will certainly be buying.


Most home listening has been via the Sony NW-WM1A or Sony ZX507 for out and about portable use. Some listening later on via the L&P W2. They are hungry enough compared to the MEST MKII, on the Sony NW-WM1A, I need to crank up to the late 50s (out of 120) somewhere on high-gain, versus maybe early 40s on the MEST. Still plenty of room though.

Current IEMs in order of purchase:


So what do I think?

First and foremost, I absolutely love the IE900 - right now, if I could only keep one of my IEMs, it would be this - mostly due to being the most solid all-rounder of any IEM I’ve heard in terms of its ability to handle any genre. In addition; the size, weight, form factor are perfect for any situation - walking, in bed, wandering about the house etc. I walk 5k every morning with my dog and I look forward to getting up at 6am to get these popped back in my ears - likewise during the day while working, finding moments to get lost in the music for a few minutes, even just while making my lunch or getting through some admin that doesn’t require much brainpower. I keep looking at others in my collection and thinking I must give them a shot, but then nah, IE900 it is…


Sound Impressions

Soundstage feels wide and natural, a well-positioned ‘stereo’ sound, instruments very well positioned and where I expect to find them relative to general listening experience of music over the years. The MEST MKII in comparison is somewhat wider but absolutely ‘taller’ too and much more 3D - this is good for some music but definitely not all - for example, I love it on well recorded ambient music, especially very cinematic albums - I’m not as keen with a lot of rock albums though, I find it can sound a bit unnatural at times, instruments a bit off in terms of positioning - a thought though in this regard, is it just I’m not used to hearing a delivery of this nature and need to get used to it?! But on MEST with genres that suit, that 3D tall and wide delivery is stunning and certainly a keeper in that regard.

In spite of the wide soundstage, I still feel a very centrally focused low-end delivery - I feel like the focus zone is in the middle of my head but separating out as appropriate for the instruments. I actually love how it ‘sits’ in my head, I really feel with kick drums for example that they thud in both ears perfectly to land a central delivery… reminds me of beat-matching kick drums back in the good old DJ days and I actually crave this position with other IEMs at times.

IE900- ZX507.jpg

Some of my test tracks had deep sub bass sitting alongside pounding kick drums - all wonderfully controlled and I keep wondering how the heck something so small is capable of this. I find the bass more obvious compared to the MEST MKII, not sure if its better per-say - I think going back to my reference to its position is where it shines - potentially a personal preference as opposed to one being better than the other.

The higher register of treble is an area that I tend to shy away from in music delivery - often choosing with audio system over the years to EQ bass up and treble down, probably the techno/house DJ in me. I’ve been concerned about this and look out for comments in reviews when considering purchases that might suggest an IEM is bright. Much to my surprise, yes the treble is more evident than I would expect to like, it feels like its fine-tuned marginally below a point where it could be an issue, but instead sounds wonderful and adds so much to a detailed, pristine and analytical delivery - I’ve yet to find it harsh on any music and again, often amazed how there is so much detail from a single driver.

IE-900 Package.jpg

There is a sense of being slightly recessed vs the MEST, a more forward centre on the MEST for sure which means for some vocal tracks, especially male vocals on the lower end of the scale that they can feel slightly back - not to the point that it bothers me personally but I do note at times.


The cable is excellent and very similar to the IER-M9, looks almost the exact same - slightly stiffer though and a small amount of microphonics if not correctly positioned around my ears and with the chin thing (what’s it called?!) - but easy to position and when out walking, I get zero cable feedback. The ear hooks are quite stiff and bend well around my ears - a slight concern here is when bending them over my ears, I wonder is this putting strain on the MMCX connectors that might damage over time?


The tips didn’t work out that well for me, I couldn’t get a good seal with any of the silicone tips and they sounded pretty poor as a result - I tried them first and was incredibly underwhelmed, bass was absolutely feeble as best. Switched to the included large foam tip and a whole new world opened - wow! I did ultimately switch to Comply TSX-500 in medium as I get an even better seal and no impact to SQ, unlike with some others where bass becomes way too much and overall too dark, not the case here at all - the TSX-500 seem to have a relatively medium bore size. Isolation is great - when walking, I can hear louder traffic but not enough to interrupt my listening, at home sitting in my kitchen as I am right now, I can’t hear any other noise in the house, including my wife talking to me… is it terrible to admit my frustration with having to unplug an IEM and ask my wife to say whatever she said again, only to find its a reminder I need to cut the grass or something? - she should know I have important listening to do.


Anyway, I would struggle to say whether I prefer the MEST to the IE900, they are both incredible IEMs in their own right but as noted, the IE900 would probably take the prize given how they can be a jack of all trades with any genre in any listening situation. I’m not exaggerating when I say they often take my breath away, I’ve stayed up way past my bedtime several nights over the last couple of weeks as I just want to keep listening, I’ve even broken my no wine during the week rule and had to pour a glass to accompany my listening bliss! They definitely complement each other well though and I will certainly be submerging myself in the MEST again soon for longer sessions.

They are unbelievably addictive and in my humble opinion, absolutely worth the price tag. Apologies again that I can’t address areas that a lot of folks here would like to know and I hope this was somewhat useful. I’m conscious there is a lot of interest in this IEM and I’m very lucky to have one before launch, as such keen to share what I can. Still early days too but I do feel comfortable at this point with my findings.

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So far I am truly enjoying my IE 900, and now I am afraid that I will be using my IE 800 S and IE 800 rarely in the future.

For me both silicon and foam adapters work perfectly fine. I use small size and both snuggly fit into my year. I primarily use silicon and swap it with memory foam. Memory foam give me slightly more isolation. I really wish if the adapters are a bit longer to have deeper in-ear fit. Will see if Comply would release any professional series in the future.
How's the IE900 compares to M9?
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hello vs sony iem z1r which one is better? I'm interested in these two