HEDD (Heinz ElectroDynamic Designs) was formed in 2016 by ex-ADAM Audio founder Klaus Heinz and Frederik Knop. Their range of hand-crafted studio monitors and headphones is fast gaining an excellent reputation in the pro audio community. We speak with Klaus about how he started out and the technology behind HEDD’s recently released Mk2 monitors…
How did you get started in equipment design, and what was the first thing you created?
As a student, I was a Hi-Fi fan and became intrigued by how different speakers could sound. One day a friend showed me a DIY 12“ bass unit, and the way it was constructed and worked was simply fascinating to me – you could say that was the start of my love affair with speakers! Then in the early 1970s an American speaker came along, the ESS 7, made with a British KEF B139 woofer - some of you guys may remember it - and cheap midrange and HF paper cone drivers from Peerless. The whole thing sounded so extraordinarily good that I really wanted to understand why. There were no Thiele Small parameters at the time (a set of electromechanical parameters that define the specified low frequency performance of a loudspeaker driver) and I had no idea about filters so it wasn’t an easy matter to analyze and quantify the performance. Still, I tried to improve the design by using a different midrange unit and to try my own filtering. That was my first half-attempt at creating a speaker.
A few years later, ESS came up with speakers based on Oskar Heil’s Air Motion Transformer (AMT) and that really blew me away. Back then, Heil’s AMT was a bulky unit that could only be used on top of a speaker as a dipole, which wasn’t very practical. Also, the sound had to travel through a horn-like pole plate setup, which didn’t help the sound. I thought it would be a good idea to adopt the same AMT principle but use it to make a tweeter that could replace a 1“ dome tweeter and still maintain, in my opinion, the superior sound quality. I travelled to meet Oskar and work on my idea but the patent was an issue as Oskar insisted on his original construction. However, once the patent had expired I was able to pursue the idea of a compact AMT (or “C-AMT”). In 1999 I managed to put my AMT version into production and founded ADAM to introduce this transducer to the pro audio world.
After ADAM Audio you left to form HEDD in 2015? How do your later monitor designs differ from your earlier work?
ADAM enjoyed a great reputation and the company was very successfull - I think mainly due to the open sound of the AMT tweeters. But from the very beginning there were some people who found the sound overly aggressive or shrill. So, in 2007 I came up with a revised version of the tweeter that performed better. The HEDD AMT tweeter uses better damping glues and more refined filtering. So far, the pro audio community seems to like these modifications.
The Air Motion Transformer (AMT) HF driver is at the heart of your monitor designs - why do you prefer them to dome tweeters?
It’s really down to performance. To my ears the HEDD AMT delivers more accurate transient reproduction. You can also achieve a more 3-dimensional soundstage – particularly with acoustic recordings.
Can you explain how HEDD's Lineariser software works?
All loudspeakers cause phase errors - ie. not all frequencies leave the speaker at exactly the same time. Fourier transform theory explains that corrections in the frequency domain will affect phase response and vice versa - you can’t have both linear phase AND frequency response at the same time. Also, a tweeter emits HF signal much earlier than a LF driver which is another source of phase problems. We mostly hear phase problems as a smearing of the stereo image - critical for mix monitoring of course. Essentially, HEDD Lineariser is a Finite Impulse Response (FIR) filter. Firstly, the speaker is measured to get its Impulse Response (IR) which contains all the non-linearities in both the frequency and the time domain. During music playback, this IR is continuously combined with the audio signal (convolution), and is hence able to correct time and frequency errors. The digital processing involved means there is a delay of between 5 - 50ms – this is required to achieve linear phase as the signal is “held” long enough in DSP to wait for the slower low frequencies to arrive. FIR filtering makes it possible to deliver the desired linearity in both the time and frequency domain. With the new MK2 monitor range, we found a significant improvement in clarity and more authentic room representation. This would all be impossible with traditional analogue speaker designs – it has only become achievable with the integration of DSP.
HEDD’s CoP technology means you can run the monitors closed or ported. Why did you feel the need to offer both?
I have listened to countless discussions on whether closed or ported is the best approach for low frequency reproduction. There are good arguments for ported (bass reflex) designs as they go lower and/or louder, but also for closed designs as, theoretically at least, they allow perfect transient response and avoid the unwanted resonances which can occur in port tubes. Of course, you usually don’t have the opportunity to directly compare as speakers will typically be designed as one or the other, but DSP now makes this possible. Our monitors incorporate mechanically tuned ports to ensure optimum performance in “Ported” mode (with or without linear phase filtering), then if users want to try the speakers as a closed system they simply need to seal the ports with the supplied plugs and select the “Closed” CoP filter to optimize the sound in this mode. This way, users can easily compare the results and decide what works best for them – the important thing for us was to give customers the choice.
On the other hand, when we designed the Tower Mains studio monitors, we used multiple LF drivers with high-powered amplification to overcome the shortcomings of a closed system and the results left us in doubt that this was the best way to go with this model.
As a long standing speaker manufacturer, what are your feelings on the longevity of DSP and AD/DA in speakers? What happens when digital technology moves beyond PCM?
The DSP features of our speaker designs do not affect the fundamental acoustic design considerations. Bear in mind that human audio perception is theoretically and practically already far exceeded by the quality of modern 32-bit/192kHz, and the fundamental requirement of coherency between time and frequency will not change whatever comes up digitally in the future.
Your HEDDphone is getting a lot of interest - was this originally designed for the hi-fi market, or predominantly as a “pro audio” headphone?
The HEDDphone is made for people who simply want to hear the most accurate music reproduction possible – that applies to users in both camps. For me, taste doesn’t really come into it - my colleagues and I focus only on creating the most natural reproduction. Of course, our personal opinion is used to make design decisions, and that is influenced by the hundreds of classical concerts that Frederik and myself have listened to. Now our AMT has been successfully implemented in the HEDDphone, it opens the door for other future headphone designs.