Sennheiser IE 900

Sennheiser list the IE 900 in the “Audiophile headphones” category. At first glance, I would have classified them as the flagship of the professional in-ear monitor series. However, according to Sennheiser’s own statements, this audiophile product series relies on different sound characteristics and tuning than their professional models. The areas of application are also different: the professional in-ears are optimised for monitoring, while the audiophile models are aimed at hi-fi connoisseurs.

In fact, no corners have been cut on the flagship of the manufacturer’s wired in-ear range. The IE 900 is manufactured at Sennheiser’s main factory, assembled by hand and matched in pairs. High-quality materials, technology and an optimal fit should result in the best sound quality. The dynamic design relies on one optimised true-response driver with a diameter of 7mm per side. Sennheiser intends to eliminate any problems in the transition between different channels.

The integration into the overall X3R system is also noteworthy (to the manufacturer’s website). The driver is housed in a casing that is ergonomically adapted to the shape of the ear. This consists of milled, anodised aluminium with a so-called vortex structure, into which three Helmholtz resonator chambers have been integrated. The manufacturer addresses the problem of the interaction between the driver and the sound energy emitted from the rear, which influences the frequency response, especially in closed cabinets. These chambers are intended to further linearise the frequency response and improve the treble reproduction in particular. So the IE 900 is much more than a conventional earpiece!

In practice

Functionally, there is little to complain about because the IE 900 does not offer any extras. Neither a remote control nor an integrated microphone can be found in the design because it is simply a matter of sophisticated sound reproduction. These lightweight headphones fit securely and stay in the ear. The over-ear guide with a flexible wire bail may not be the fastest way to wear them (especially if you’re wearing a facemask), but these headphones are always held in position. Several fitting pieces made of silicone and memory foam are included and ensure the necessary sealing of the ear canal. When you’re not using the IE 900, you can put them in the carrying case, which is also included.

The external attenuation is high, as are the level reserves. However, Sennheiser does not offer variable attenuation in the form of inserts like competitors 64 Audio (review of the U6t).

The cables, reinforced with para-aramid, are, of course, interchangeable thanks to gold-plated MMCX connectors. Generously, three versions are supplied, all angled at 90 degrees on the connection side: one version with the common 3.5 mm jack plug, one with a balanced 2.5mm plug and one with a 4.4mm Pentaconn plug. The lack of a 6.3mm version and the cable lengths of 1.2 metres suggest that the IE 900 is more suitable to use with (sonically underpowered) smartphones, mobile players and DACs, such as the FiiO M11 Plus Ltd.

Sound

The manufacturer says the low-impedance Sennheiser IE 900 is an in-ear counterpart to the HD 800 S (or the closed HD 820, author’s note). The sound tuning is neutral with an analytical character – this is already shown by the wide frequency response and the low distortion factor.

From an acoustic point of view, the manufacturer emphasises the slightly accentuated but uniquely smoothed highs, which often exhibit disruptive resonances or overdamping in dynamic in-ear solutions and which are precisely addressed here via the resonator chambers in order to accurately convey the quality of the premium driver. In a sense, the acoustic measures for “room optimisation” are already built into the IE 900. Sennheiser also emphasises the low-frequency tuning: the IE 900 are supposed to sound emphatically clean but still powerful, which requires careful tuning. So much for the manufacturer …

In practice, I found the sound to be extraordinarily balanced, but perhaps for that very reason not necessarily spectacular, in the sense of being showy. What at first seems a little sober, after a short familiarisation, shows real monitor qualities over the entire frequency response. You quickly learn to appreciate the precision, speed and dynamics of the built-in drivers. I’m always amazed when I notice how clear the jump is between Bluetooth and a wired connection, especially when it’s with a headphone in this category.

I can fully attest to the IE 900’s exceptional resolution in the treble range. In fact, a dimension opened up that is rarely audible with an in-ear monitor. In the upper range, details were revealed that are not audible with cheaper headphones and even less so with wireless solutions. It’s as if there was another silky layer of information. And at the same time, this increased detail results in a spectacular stereo panorama as well as high comprehensibility of spatial effects. With good mixes, the IE 900 fans out the mix enormously and, with Kraftwerk’s “3D Catalogue”, even beyond the limits of the ears. Movements are clearly attributable. Speech intelligibility was also simply first class. And finally, the IE 900 was absolutely unerring when it came to the limits of harshness (Erosion: 70th Floor). A tour de force!

At the lower end of the frequency response, the IE 900 reaches cleanly down into the deepest depths. Basses sound tightly contoured and are tonally and dynamically traceable. Depending on the mix, they deliver warmth or the desired dry kick. The fact that it never sounded overemphasised was a positive feature – the IE 900 is not a lifestyle product.

The IE 900 also show off its strengths in the midrange: Lots of details, especially with voices and acoustic instruments. But dense pop, rock and electronic mixes are also differentiated and, depending on the quality, transparent, with close cohesion or just with small weaknesses – the IE 900 shows all these characters, strengths and weaknesses very comprehensibly. And even in the dense rock/metal genre, the IE 900 did not fall out of step and always hit the tone of the mixes and the intentions of the productions: “Check my Brain” by Alice in Chains sounded thick and round, “Repentless” by Slayer was emphasised in the mids but without nasality, “Shovel Headed Kill Machine” by Exodus, on the other hand, was more aggressive with a slight thinning in the mids. Finally, Meshuggah’s “Bleed” came across as coherent and not metallic and tinny like with some of the competitors.

But of course, the IE 900 are in no way dedicated to these genres. Rather, they demonstrate their talents equally with intimate singer-songwriter works, dynamic jazz recordings and room-filling classical recordings. An important virtue here is the ability to bring out not only the dynamics but also the timing of the elements involved so that layered elements are clearly discernible. Ultimately, however, it is less a matter of individual areas than of a coherent overall performance in sound reproduction, which the IE 900 indeed delivers in an exemplary and analytical manner, but never in a glossy or even cold way.