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First Listen: Sennheiser’s IE 900 Earphones Deliver Big Sound in a Tiny Package

The $1,300 components represent the top-tier of in-ear options.

Sennheiser's IE 900 earphones. Photo by David Daub, courtesy of Sennheiser.

I’ve been championing the virtues of headphones since the mid-1970s, which marked me as a real audio weirdo in an era when nobody but recording engineers and pilots put a pair on their head. From the beginning, headphones have possessed those rarified sonic attributes that, for me, define accuracy in reproduction—transparency, speed, detail and low distortion. These are qualities that were absent in most loudspeakers of the 1970s.

Save for Magnepan, or a few electrostatic outliers like Quad, KLH Nine, or Dayton-Wright (on the odd day the latter decided to work), most speakers were awful, with no real bass, sluggish, wooly midrange and screechy but attenuated highs. Of course, advancements came by leaps and bounds to the point where most speakers were sounding really good by the 1990s.

On a parallel track, by the 2000s, lots of headphone manufacturers had jumped into the fray, and today, headphones are the sound maker of choice, with a market value in 2020 estimated at $34.8 billion. But one can rest assured that few of those dollars will be earmarked—pun intended—for the thin slice of headphone sales occupied by products like the $1,300 Sennheiser IE 900. (Sennheiser Group captured about $900 million in turnover in 2019.)

Sennheiser's IE 900 earphones.

Sennheiser’s IE 900 earphones.  Sennheiser

Now, living with the IE 900 for a couple of weeks of extended listening has been a revelation, if only because these are in-ear headphones and not conventional “cans.” My go-to headphones are precisely that: donut-sized transducers connected by a headband that go over the ears. They range from electrostatics to dynamics—including Sennheiser’s own superb HD 800S—to true oddballs like the Ergo that use massive AMT ribbon drivers mounted in an armature that perches atop the head and floats inches away from the ears. (As an aside, Ergos are best enjoyed in private, as posting oneself wearing them on social media could jeopardize any future employment opportunities.)

So, having time to get acclimated with Sennheiser’s flagship IE 900 earphones has had me rethinking how convenience, comfort and fidelity converge in a new way. As with the automotive liberation of shifting with a dual-clutch automated gearbox, the in-ear concept makes things so easy.

When a pair of IE 900 are mated with a portable hi-res audio player like the new Astel&Kern SE180 ($1,499), it’s a match made in heaven. Most of my listening was done ensconced on the couch and through ripped high-res FLAC files stored on the NAD 50.2 digital music player. Alternate sources were analog: LPs with SS and vacuum-tube electronics. The Sennheisers will reveal whatever source they are fed, and reward a quality, vinyl-based system, though admittedly, 99.9 percent of users will likely enjoy them on-the-go or in front of a computer monitor.

Sennheiser's IE 900 earphones.

Listeners can choose their preferred cable, which plugs into the gold-plated connector on each earphone.  Sennheiser

The first glimpse of the IE 900s is when one lifts the lid of a smallish box and encounters the two tiny silver objects set in a black foam pad. It reminded me of a visit to Ripley’s Believe-It-or-Not museum as a kid, and seeing a glass case that contained a magnifying glass, under which was a grain of rice on which someone had written part of the Declaration of Independence. Looking at the diminutive Sennheiser IE 900 conjures the same disbelief, insofar as a device smaller than a shelled peanut can be engineered and then fabricated to do what it does.

That fabrication happens at the Sennheiser headquarters in Wedemark, Germany, a fully automated transducer manufacturing facility with tooling to accomplish machining feats in miniature. The quality control, according to Sennheiser, maintains the tightest tolerances and the lowest unit-to-unit variation possible. Precision cameras examine the housing and transducer components closely during production, and the completed transducers are tested before and after pairing. For optimal performance, the assembled left- and right-side earphones are paired by hand to work together.

The housing is milled from a single block of aluminum to create the earphones’ unique triple-chamber absorber (T3CA) system, which divides the internal volume of the device into three chambers with an acoustic vortex milled into the nozzle to counter the masking effect, an acoustic phenomenon in which the human ear cannot perceive high-frequency sounds at low volumes if a louder sound is present in a lower frequency range.

Sennheiser's IE 900 earphones.

For optimal performance, the left- and right-side earphones are paired by hand during the assembly process to work together.  David Daub/Sennheiser

Originally developed for the IE 800, the latter system has been improved upon with the IE 900, and by removing the energy from masking resonances, the absorber system prevents undesired peaks and reveals the subtlest details within the recording. The motor that actually makes the music is the X3R, which is engineered to tighter tolerances and is an altogether more refined version of the 7 mm wide-band transducer used in the IE 800 and other Sennheiser models. A new membrane foil results in a high degree of inner dampening, reducing natural resonances and distortion.

A note about sound pressure level. These things play loud enough to make your ears bleed, and that’s precisely why listeners need to take care of their hearing and lay off the volume. Just as one doesn’t guzzle a bottle of good Bordeaux, there’s no need to turn the pleasure knob up to 11 as it will put you on a first-name basis with the guy at Costco’s hearing aid counter. Take it easy and listen responsibly.

Sennheiser's IE 900 earphones.

The para-aramid-reinforced cables can endure thousands of bending cycles.  David Daub/Sennheiser

Sennheiser specifies a frequency response of 5 Hz to 48,000 Hz, both extremes virtually impossible to hear. What one does hear is an all-important midrange that is lucid and lifelike, with the effortless transition to high frequencies and bass that provides an eerie simulacrum of real low-frequency energy, albeit within the volume of a nutshell. Because the transducer is, for all intents and purposes, weightless, transient attack is instantaneous without any overhang. Meanwhile, spatial cues are rendered as realistically as in-ear or on-the-head transducers can; the brain compensates for three-dimensional-soundstage cues so crucial to the character and performance of the best loudspeakers.

Listeners who like the top Sennheiser headphones will marvel that the IE 900 doesn’t miss a beat with respect to tonal accuracy, and shares a similar signature, to the extent that rendering of micro- and macro-details is simultaneously accomplished. Two completely different approaches to one “house” sound.

Comfort is key to usability, and it’s easy to listen with the IE 900 for a few hours without fatigue. I noticed this first-hand with four CDs of Friedrich Gulda playing Book I of Bach’s Well-Tempered Clavier (on piano), an undertaking for completists who can’t abide a “Greatest Hits” approach to listening. A massive work like Bach’s Mass in B minor (the old Karl Richter performance from 1969) is rendered as a grand landscape of orchestra and choir that has weight and substance, with pinpoint focus on solo voices and instruments as appropriate.

Sennheiser's IE 900 earphones.

Listeners who like the top Sennheiser headphones will marvel that the IE 900 doesn’t miss a beat.  Sennheiser

Ordinarily, I prefer listening to such recordings via loudspeakers, but the IE 900s proved their mettle when tackling complicated material that is well recorded and with thoughtful microphone placement. Ultimately, serious listeners will probably opt to use traditional headphones for personal listening when planted in the chair or on the couch, but for active listening, or for a discreet appearance in an office or public setting, these IE 900s represent the top-tier of in-ear options.

A Fidelity Plus MMCX Connector allows listeners to choose their preferred cable, which plugs into the gold-plated connector on each earphone that accommodates an unbalanced cable fitted with a 3.5 mm connector, and balanced cables with 2.5 mm and 4.4 mm connectors. Sturdy and made to last, the para-aramid-reinforced cables can endure thousands of bending cycles. Adjustable ear hooks and several foam adapters—that slip on the end of the housing—tailor the components to an individual’s ears. And when not in use, the earphones and cables fit in a compact case that’s ideal for portability.

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