Insights Into Sennheiser's IE Pro Series

Jannik Schentek & Tom Vollmers share key thoughts on the making of the Sennheiser IE 400 PRO and IE 500 PRO.

This article is Authorized by the In-Ear Monitor International Trade Organziation

Members from the In-Ear Monitor International Trade Organization share their industry knowledge about the best ways to use in-ear monitors.


March 11, 2020


Jannik Schentek is a Product Manager for Professional Audio at Sennheiser.

Tom Vollmers is the Head of the Professional Portfolio for Sennheiser.

They were both instrumental in bringing the IE 400 PRO and IE 500 PRO to life.

How did the development for the IE PRO Series start? What were the design goals and principals?

(Jannik) The development of the IE PRO series actually started with the team realizing that we have been manufacturing wireless monitoring systems for several decades and have also had many successful consumer in-ears for decades. We even had audiophile models with sound-tuning capabilities that were also enjoyed by many audio engineers. But there actually wasn’t any true pro in-ear in our portfolio, no in-ear developed especially for the professional user. We decided that it was time for an in-ear that would do nothing less than redefine the in-ear concept.

We kicked off intensive talks with musicians and sound engineers about their daily challenges and actual needs. We also closely observed the marketplace and came across the claim “the more drivers the better” several times. Coming from dynamic driver design we found this a somewhat weird statement and asked ourselves “What if we use just one powerful dynamic driver that will do away with all the disadvantages of multiple balanced armature drivers?”

During the development of the pro in-ear series, we focused on three key aspects: (1) creating a natural sound signature to give musicians enhanced control of their performance (2) improving the reliability and ruggedness of the audio connector and (3) designing a generic earpiece that simply fits well.

How did your individual backgrounds play into this? Tom — I know that you have been a professional A-List monitor engineer before joining the Sennheiser team. Did this influence what you were looking for?

(Tom) I do hope my professional experience was helpful! Sound has always been my passion and I turned this passion into a living, first in live audio mixing and now here at Sennheiser as a portfolio manager for our pro products.

In the development of the IE PRO series, I tried to tune the driver towards the needs of musicians on stage, and this is not necessarily identical with the requirements of an audiophile model for home use. The noise floor on stage is very loud and the musicians need optimum sound – not only to be comfortable but also to control their performance and to harmoniously perform with their bandmates. Therefore, you need very strong and precise mids, more than a regular headphone can offer.

(Jannik) Tom’s field experience was a massive benefit during product development. It has not been easy to get such a sound signature from a single dynamic driver. You have just one membrane, and if you change the bass frequencies this will immediately influence the mids and the treble. The close development loops with our lead acoustical engineer were a big advantage in the fine-tuning of the system’s sound performance.

What sound signatures were you targeting?

(Tom) Oh, nothing too serious – just the best ever. We were looking to achieve a full-range frequency spectrum with high volumes, a tight low end, punching mids and brilliant treble. In fact, we tried to combine a very precise studio sound signature with that rock n´ roll feeling.

Why single dynamic?

(Tom) To understand this approach we have to dig a bit deeper into sound and technology. No matter whether we are looking at a PA system, your stereo at home or an IEM system, using more than one driver is always a compromise with unwanted side effects. There’s interference between the different drivers, there are crossover effects. In a nutshell: Such a system can never be as good as a single source for audio.

The reason for multi-driver solutions lies in the lack of a single driver that is able to cover the entire frequency range with decent quality. The same is true for IEM systems with balanced armature drivers. None of these drivers, which are actually taken from hearing aids, are able to cover the whole frequency range, so manufacturers had to develop the familiar multi-driver solution with a passive crossover.

(Jannik) For the Sennheiser IE 400 PRO and IE 500 PRO, we use a truly incredible 7-mm dynamic driver, developed and manufactured at our headquarters in Germany. I’ve brought you a graphical representation of one of the key USPs of the single dynamic driver principle compared to the balanced armature driver, and that’s low distortion. Some background: For measuring distortion, we mainly need to consider overtones up to the fifth order (K2 to K5) based on the fundamental tone (K1). When developing a new transducer, the target is – as always – to reduce distortion as much as possible.

However, some overtones– are beneficial for sound perception because they give sound this beautiful “analogue” and warm feeling. Therefore, we need to refine our development target: A transducer that sounds good requires well-dosed harmonic overtones like K2, K4,… plus we need to reduce unwanted distortion like K3 or K5. Unwanted distortion can be compared to foreign bodies: It is confusing or even annoying.

K3 does not sound natural at all, and it can mask the original sound signal, which in turn may encourage users to turn the volume up to damaging levels. Our extra-wideband drivers have very low K3 levels and therefore sound much more precise and warmer – we call this TrueResponse technology – which makes them ideal for long listening sessions.

What about the aesthetics, comfort and form factor? What decisions went into the product design?

(Tom) One major aspect was to develop a generic housing with a great, tight fit that would make customization obsolete for many applications. Customized IEMs are still a big topic in the pro world and mandatory for many musicians on stage but for many users it’s not an issue, such as backline tecs and engineers. And we even got the feedback from many performers that they feel that customization is not that important anymore with our housings. This reveals a further benefit of the single driver without crossover: We need less space, therefore the housing can be designed very slim and easy to use. Moreover, it’s just half the weight of a multi-driver solution, you can certainly feel this after hours on stage.

Lastly, what are your thoughts on True Wireless and on your MOMENTUM line? Do you see overlap between what you are developing for stage use and the sound signatures that consumers want?

(Jannik) There’s definitely a certain overlap regarding frequency range, distortion, dynamics. But you’ll also find many differences such as maximum volume, frequency response – especially in the mid-range – fit and design, servicing, cable solutions and reliability in heat and humidity. So, for Sennheiser it makes perfect sense to offer different solutions for pros and consumers. This generates synergies and is a true benefit in development.


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