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Community Interview: Axel Grell

A few weeks ago, we asked members of the Audiophile Community what they would ask one of the world’s top headphone engineers: Sennheiser’s Axel Grell. Following an overwhelming response, we chose some of the most frequently asked questions and shared them with Axel. Here are his answers:


How did you get into headphones and headphone engineering? Did you study anything related in college with a plan to pursue this career path, or did you stumble into it after?
I have been building speakers since I was 12 years old. In my 20s, I had a mainly self-built PA system that I rented out for several different events, and I toured as a mixer man with some rock bands—never being famous ;-) … In parallel, I studied electrical engineering with a focus on electro-acoustics. So I knew a lot about sound and acoustics when I started working for Sennheiser, but nothing about headphones.

Did you always know that you wanted to work with Sennheiser? What has your journey at the company been like?
Sennheiser had a factory in my hometown and its headquarters were just 20 miles away. When my then-girlfriend (and now wife) decided that I should work more seriously than touring with rock bands and soldering PCBs on the weekends, Sennheiser was my first idea of a cool company to work for. I started working as a development engineer for headphones, and today, I am responsible for the audiophile product portfolio. In between, I did a lot of different things, all related to headphones.


What does your setup look like at home and in the office? Do you have go-to headphones or different pairs for different sounds?
I change my setup quite often. But this is something I have used for years now:
Sources: Telefunken S600 and Thorens TD160 turntables (different pickups, different preamplifiers), MacBook Pro, Denon DVD-3930 (CD, SACD, DVD-A)
Amplifier: HDVD 800
Headphones: All! With the preferred being HD 580 Jubilee and HD 800 S
Sources: AK 240, AR M2, iPhone 6 with Arcam MusicBoost
Headphones: IE 800 (always with me!), HD 630VB, Momentum over-ear wireless, PXC 550 (great for traveling)
Sources: Transrotor Dark Star, T+A MP 2000 / MP 3000, MacBook Pro
Amplifier: HDVD 800 or HE 1
Headphones: All! HD 650s, HD 800 S, HE 1
Good headphones can reproduce everything. The better they are, the better they transport the emotions in the music. I don’t need boom-boom headphones for hip-hop, for example. I prefer HD 800 S or HE 1.

Can you tell us about a pair of headphones you really admire that you had no hand in?
Sennheiser HE90 (the legendary Orpheus—my benchmark for over 20 years), Sennheiser HD 560, Beyerdynamic DT 831.


What kind of testing gear and procedures do you use?
Ears! Ears! Ears! Listening sessions. Audio Precision stuff, starting with System One up to their newest analyzers. Klippel measurement systems. B&K measurement microphones, artificial ears, and dummy heads. Anechoic chambers, diffuse sound fields, laser vibrometers, and a lot more.

How do you feel about the Harman Target Response Curve? Does it have any influence on your design when working on a headphone’s sound signature?
It is interesting. We did something similar 23 years ago. And we had very similar findings. When you tune a headphone only following these findings it sounds okay, but a bit boring. As headphones should transport the music, the emotions, we tune them using our ears, knowing all these findings.


In your opinion, which qualities make a great DAC/amp combo? Are there any plans for a DAC/amp from Sennheiser?
A sophisticated circuit topology, the right components, and a great PCB layout. One is already available: Sennheiser HDVD 800.

How did the idea for the Orpheus project come about? Are there any plans for a pair of consumer-level electrostatic headphones in the future?
The motivation to develop the HE 1 was the same as for the legendary Orpheus. We just wanted to make the best that is possible with the actual technologies. HE 1 is at the avant-garde of today’s technology—this is audible.


With Apple dropping the headphone jack and a general trend towards wireless, where do you see the future of headphones? Are there limitations in wireless audio?
Wireless transmission gives you the freedom to move around when you are listening. The limitations for audiophile transmission are given by RF bandwidth and battery lifetime.

Any advice for aspiring audio engineers?
Trust your ears!

Nov 4, 2019
Axel knows everything. Sennheiser for life
Nov 4, 2019
I am still waiting for the interview!
Feb 6, 2017
He is an engineer, I would have liked to see far more technical questions than simply a fluff piece for Sennheiser.
Jan 1, 2017
this post got a shitload of sennheiser brainwashing materials. hey lets buy hdvd800, hdvd800 and hdvd800, and lastly don't forget, get an hdvd800
Jan 2, 2017
Spartan117you said it more than he has :P
Dec 30, 2016
That interview was way too short. I would have liked to hear a lot more of a personal take on the wireless headphone thing as an audiophile. He basically gave us the definition and the well known technical limitations.
Dec 29, 2016
I liked this article, when it comes to music...... just enjoy
Dec 29, 2016
"Following an overwhelming response "... here's an underwhelming interview.
gn77bYou betcha!
Dec 29, 2016
Seriously? No mention of a new flagship headphone to replace the hd800?
Dec 29, 2016
AnotherYearThey did with 800s and they are selling good.So I do not think we will be seeing any flagship anytime soon.What bother me is there is no mention of next gen HD600.
Dec 29, 2016
tareq.haiderThey added an acoustical absorber inside and painted it black. Nothing special. What we need is a new electrostatic headphone for the consumer at a reasonable price.
Dec 28, 2016
Dec 28, 2016
I'm a little disappointed that my marshmallow question didn't make the cut.
It's critical information.
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