Introduction - what is the Sennheiser IE 900?
The Sennheiser IE 900 is an in-ear, looped fitment earphone. It is visually similar in overall design to the IE 300 and where the IE 300 comes in at a consequential but not outrageous £260, the IE 900 is a rather more significant £1,099. This is the first time a Sennheiser earphone has broken the four figure barrier and it means that the IE 900 is the most expensive earphone that the company has ever made.
This is fitting to an almost cinematic narrative level because the IE 900 was revealed at the same time as the news that the company's consumer division had been sold off broke, as per the announced intention to do so earlier in the year. The nature of this sale is not a ‘clean break’ and Sennheiser looks like it will be involved in the development of future product but, until we know how that truly works in practice, what you see here is very likely the last of the Sennheiser home audio division products developed in the ‘old way.’
Of course, while there’s scope to be nostalgic about this, there’s some more prosaic things to consider as well. The IE 900 sits above the IE 800S which remains one of the best all round earphones on the planet. It is also roughly the same price as the Campfire Audio Andromeda 2020 which is an exceptional piece of kit in its own right. Can the IE 900 be more than a line in the sand, marking when things changed? Let’s find out.
Specification and Design
Key to the IE 900 is that Sennheiser hasn’t changed its basic preferred configuration to make them. Where many rivals are armature designs, with multiple drivers on each side, often supported by a dynamic driver handling the bass, the IE 900 has a single dynamic driver in each enclosure. This is responsible for the entire frequency response and the IE 900 uses an all new one called the X3R. This builds on the ‘Extra Wide Bandwidth’ principles that have been seen in the IE 800 and IE 800S and begins by increasing the size of the driver from 7mm… but only to 7.7mm.
Now, it’s easy to look at this figure against a 10mm driver (something which is routinely encountered in rivals) and feel that the difference is little more than a rounding error. It really isn’t though. That 10mm driver is considerably bigger and notionally more authoritative. The trick to the X3R is not the size or even what it’s made out of (although Sennheiser isn’t willing to give too much away about that so we can presume that some of the material choices might be unconventional). Instead it is about how the driver is used.
In each of the aluminium housings, between the face of the driver and the nozzle to which you attach the dome, there are no less than three heimholtz resonators. By carefully choosing the shape and relative position of these, Sennheiser can shape the driver output in a way that a ‘straight pipe’ arrangement simply couldn’t match. This air management is joined by something called the acoustic vortex principle which ensures that air movement through the resonators themselves is controlled and consistent.
Then, behind the driver and separate to the three aforementioned chambers, there is an additional chamber called an acoustic back volume. This controls the space and air movement behind the driver and helps to shape the low end performance. Unlike the forward chambers, this one is filled and damped. Effectively, it is necessary to look at the IE 900 as a driver in an enclosure but as a driver with a wearable air management system. The result of this work is that a pair of 7.7mm drivers have a frequency response of 5Hz-48kHz which covers off absolutely everything you’re ever going to hear and as much again, all without any need for a crossover or any other additional hardware. This in turn means that the sensitivity of 123dB/1Vrms and 16 ohm impedance will not present any significant issues to most devices with a headphone socket.
With the IE 300 being more of a design origin point for the IE 900 than the IE 800S, it isn’t too surprising to find that Sennheiser has moved to a structured fit style cable that loops around the top of the ear. This is achieved via deformable sections that bend to your specific requirements. The cables terminate with the housings via a MMCX connector that provides a notional break point if the cable is snagged. This also of course means that the cable is detachable as well and here, Sennheiser has been very canny. The IE 900 comes as standard with three cables. The first has a conventional 3.5mm connector (which via adapter will become a 6.35mm one). The other two provide for both the 2.5mm four pole connection and the 4.4mm ‘Pentacon’ connector which means that unless you suddenly need a four pin XLR in your life (for which adapters for both 2.5mm and 4.4mm connectors exist), the Sennheiser has you covered.
The housings themselves are something that photos cannot do justice to because they are exquisite. Machined from aluminium in two sections, each one looks like a tiny turbocharger and the execution is utterly flawless. The seal in the ear canal is via a choice of silicone and Comply domes (and here, as ever, is your standard caveat that my abiding hatred of Comply means these have stayed in the box) and the IE 900 is extremely comfortable to wear for extended periods. Here it’s very hard to argue with Sennheiser’s decision to stick with a single driver because, where the Campfire Andromeda is comparatively large, the IE 900 feels svelte by comparison.
Not everything is perfect though. The case supplied is closer in pattern to the IE 300 and while it is well finished and does a good job of storing the earphones, it isn’t a patch on the one supplied with the IE 800S which ranks as one of the best of its kind I’ve ever seen. There’s also a… for want of a better word… showiness to the IE 900 that it’s older brother doesn’t have and that I have long appreciated them for. It would be wrong to describe the IE 900 as gaudy but it’s more obtrusive than Sennheiser often chooses to be. Compared to many devices at the price though, it’s still nice and subtle.
Unless you suddenly need a four pin XLR in your life (for which adapters for both 2.5mm and 4.4mm connectors exist), the Sennheiser has you covered
How was the IE 900 tested?
The Sennheiser has largely been used with the Astell & Kern KANN Alpha which has all three of the connections it supports. It has additionally seen testing with an Oppo Find X2 Neo via USB dongle. Some additional testing has then taken place on the Chord Electronics Mojo and Poly and Hugo2 and 2Go both running as Roon Endpoints. The test material has been FLAC, AIFF, DSD, Tidal and Qobuz.
More: Audio Formats
Let’s kick this off by making two statements that are notionally contradictory but I’ll unpick in due course.
- The IE 900 sounds very much in keeping with the IE 800S and IE 300
- The IE 900 also does things I’ve not experienced from a Sennheiser earphone before
How can this be? Put simply, listening to the IE 900 alongside the IE 800S, the shared design philosophy of a single, exactingly engineered driver covering the whole frequency response is what defines the performance of Sennheiser earphones more than anything else. Multi driver IEMs are often wonderful things, possessing a space and airiness that is frequently addictive. Listening to Making Water from the Martian score, compared to the Campfire Audio Andromeda, the IE 900 has to give a little ground in terms of the sheer soundstage on offer.
Where Sennheiser’s philosophy hits back is that the coherency of the IE 900 is, at times, other worldly. The orchestra responds with a speed and dynamic impact that leaves pretty much anything else sounding a little confused. The IE 900 (and indeed its more affordable brethren) serve to remind us that crossovers are a necessary evil and, if you can get shot of then, the performance on offer is ‘right’ in a way that very little else is. If you listen to faster, smaller scale pieces, this difference only becomes more pronounced. Dodie’s gorgeous Hate Myself in the hands of the IE 900 is a direct link to the recording booth with nothing so base as electronics in the way.
So why does the IE 900 then go on to sound different? The answer is best experienced using the Mojo with its pair of 3.5mm outs and having the IE 800S and IE 900 connected at the same time. Listen to big, euphoric Catch Me When I Fall by UNKLE on the IE 800S and it’s brilliant; big, addictively fast and tonally believable. Switch to the IE 900… and your perception of ‘brilliant’ has to instantly shift. The IE 900 just sounds bigger. There isn’t just ‘more bass’, there’s a wholesale gain to the realism of the recording. To be clear though, the low end of the new earphone is something else again. All good earphones rejoice in the ability to deliver low end shove that you’d need a monstrous pair of cabinets to achieve outside the ear canal but the IE 900 delivers it with the speed of an electrostatic. Going back to the IE 800S after time with the IE 900 is a night and day experience - and I remind you that I still consider it to be one of the very best earphones under £1,000.
And, as if that wasn’t enough, the gains to be had from switching to balanced have to be factored in as well as doing so brings some of the three dimensionality that the IE 900 lost to multi driver rivals back into play. Running the IE 900 via 4.4mm connection from the Astell & Kern KANN Alpha has been a joyous experience. I revisited the 24/88.2 download of Dead Can Dance’s Rakim - one of my longest running test tracks - on the pairing and the result is something that is genuinely ‘high end’ in presentation and experience. There’s the same perception that, roughly a minute in, you’re no longer listening to the delivery system. The IE 900 and KANN Alpha have ceased to be and you are instead somewhere in the Mayfair theatre in November 1993, right there, surrounded by enraptured goths experiencing one of the greatest live performances of the last fifty years. I’ve no problem with acknowledging that £1,099 is a lot of money for a wired earphone but for a device that allows you briefly transcend the limitations of space and time… it’s not too bad.
Against this, the limitations of the IE 900 are admirably small but interestingly, they are most consistently shown up by its precocious older brother. This is a sensitive earphone and I have been able to drive it happily on the end of the USB-3.5mm dongle connected to my Oppo phone. Unlike the IE 800S though, the IE 900 does make it rather clearer that there are some limitations to the source in this situation. Likewise, it’s no more cumbersome or tricky to use than the IE 300 and getting a comfortable fit and decent seal in the ear canal is easy enough… but neither is as comfortable or as easy to use as the older model with its simpler cable arrangement.
I’ve no problem with acknowledging that £1,099 is a lot of money for a wired earphone but for a device that allows you briefly transcend the limitations of space and time… it’s not too bad
- Big, astonishingly cohesive sound
- Beautifully made
- Impressively flexible
- Not cheap
- In some ways not as comfortable or convenient as the IE 800S
- Maybe not as spacious as multi driver rivals.
Sennheiser IE 900 In-Ear Earphone Review
The easiest way to reconcile this is to view the IE 900 as further evolved and a little more specialised than the 800S. It has lost some of the day to day useability but in return, the performance on offer is at another level altogether. Making an objective call between the Editor’s choice winning Campfire Andromeda and the IE 900 is something I’ve wandered back and forth over in the time the IE 900 has been here. For now, I’m content to say it’s objectively a dead heat with subjective preference of the listener making it likely you’ll prefer one over the other.
Right now, as I type this, I’m listening to the IE 900 playing Brian Eno’s An Ending (Ascent) both because I have a mild flair for the dramatic and because it contextualises where this headphone sits in the wider scheme of things. This is among the last, if not the last domestic Sennheiser product we’ll see before the new ownership arrangement starts to make itself felt. On the one hand, there’s a degree of sadness to this because, not only is the IE 900 the best earphone Sennheiser has made, it might well be the single best thing of the company's I’ve ever tested (it’s a three way tie between this, the original IE800 and the PXC550). If this is an ending, it is truly going out on a high.
On the other hand though, this sure as hell doesn’t feel like an ending from here. Packed with new technology that must have some interesting trickle down potential and with the announcement that Sennheiser will continue to work with the new owners to develop product, the IE 900 comes across not as a last hurrah but instead as a statement of intent for the future. Not only is that statement a wholly convincing one, it means that this peerless earphone is an unquestionable Best Buy.
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