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.