Sennheiser IE 40 Pro Review

Sennheiser is by all accounts a true high-end headphone brand. Their HD600, HD800, and variations thereof have obtained legendary status over the years, being used and enjoyed by countless audiophiles. I'm still in awe at how high my ancient HD650 scales when paired with amps and DACs costing many times as much as the headphone itself. And at the higher end, keep an eye out for Rafe's upcoming review of their latest, the HD820, which sells for $2,399 USD… to say nothing of their ridiculously expensive HE-1 electrostatic system. 

Meanwhile, at the more affordable end of the price spectrum, Sennheiser recently launched the IE 40 PRO in-ear monitors ($99 USD). I've been living with them for a couple months and while I've never been a huge fan of the company's in-ear monitor products, the IE 40 PRO has me seriously rethinking that stance. 

Initial Experience

Sennheiser's packaging is always well executed on their high-end products, and the little IE 40 PRO gets a surprisingly similar treatment. I'm not a fan of "unboxing" videos so I won't go too far into it other than to say the experience would not be out of place with an IEM costing double, or triple the price. The bundled accessories are adequate in quantity but above-average in quality – I particularly like the included foam tips, which fit my picky ears quite well. There's also the usual S/M/L silicone tips, a cleaning tool, and a storage case which is actually useful (unlike many others on the market). 

A closer look at the actual IEMs reveals a level of workmanship commensurate with the Sennheiser name. The tiny plastic shells are flawless, with tight build tolerances and a smooth matte finish that again brings to mind more expensive competition. My review unit is black but there's also a clear version which may be less obtrusive looking for stage performers. Yes, Sennheiser has positioned these for pro use, though of course music aficionados can still enjoy them too. 

I broke out my old Sennheiser IE 8 (original MSRP $449) and the more recent IE 80S ($349) for a bit of comparison. In terms of build quality, the IE 40 PRO is every bit their equal, despite the price difference. And when it comes to fit – a subjective aspect to be sure – I find the IE 40 PRO clearly superior. These little guys fit my ears just about perfectly, and I have to break out a set of custom-molded IEMs to achieve any improvement in comfort. Again, fit is very subjective, but I find many universal IEMs uncomfortable these days... whilst the IE 40 PRO gets it just right.

Let's talk cables - a critical aspect of any headphone or in-ear monitor design. Sennheiser talks up the cable of the IE 40 PRO as using an "innovative internal cable duct" for which a patent is pending. I can't find info on the patent, and nothing about the cable seems particularly out of the ordinary, but it is a reasonably nice cable in general. It's flexible, fairly resistant to tangles (though of course they still happen from time to time), and has a soft rubberized coating which helps minimize if not quite eliminate microphonics. The cable attaches to the IEMs by way of a customized metal connector which looks vaguely similar to the MMCX standard but extends farther out and is thus not compatible. Unlike the older IE 80S and predecessors which could be worn multiple ways, the IE 40 PRO requires the cable to be routed over the ears, which makes total sense for an IEM marketed for stage use. The memory-wire in the over-ear portion is a far better solution than the detachable ear hooks used in the IE 80S – this is a very comfortable system as far as I'm concerned, though folks who wear glasses may not get along with the memory-wire (a common problem not unique to the IE 40 PRO). 


Sennheiser IEMs have always been centered around a single dynamic driver, and the IE 40 PRO continues that trend. Without giving us too many details, the company refers to it as a "next generation broadband dynamic driver.” At 10mm in diameter, a nominal impedance of 20 Ohms, and a sensitivity rating of 115dB, the specs are very similar if not quite identical to those of the higher-end IE 8 series. I do notice that Sennheiser rates top end extension to 18kHz rather than 20kHz as seen on those far more expensive older models. What to make of all this? I can only speculate that the IE 40 PRO is using an updated, trickle-down version of those drivers, with perhaps a bit of sacrifice involved in attaining this lower pricing. 

Worth noting: Sennheiser has two higher-tier models launching any day now, to round out their new IEM lineup – the IE 400 PRO ($349) and flagship IE 500 Pro ($599). They appear nearly identical to IE 40 PRO from the outside, so it will be interesting to see (and hear) what improvements they bring with an expanded budget to work with. 

Sennheiser Electronic GmbH & Co
Am Labor 1, 30900 Wedemark, Germany

Rmusic's picture

Thanks John,
Your reviews are always jam packed with useful information.

crazywipe2's picture

It's always good to find a $100 product that is very well performing.
Can you compare with the ety er4xr?

charlesx31337's picture

Great review, very impressed with these for the price!
Would love to get your thoughts on / see a review on the Sennheiser ie400 pro in comparison.
Keep up the great work :)

Benjdbs10's picture

A friend very interested in this new babies (he's a treblehead, hence the interest). Got Eric Bibb's album, too. so i could relate, but in the real world Not all albums are made like that Superlative. I reckon an upgrade cable perhaps a hybrid one, could just do the trick. thanks...