GGerman Physiks HRS-120’s unorthodox appearance is the first clue that it is unlike other loudspeakers.  The driver on the top of the cabinet is our DDD driver, which is proprietary to German Physiks and can be regarded as the heart of the design.   The same driver is used in all German Physiks loudspeakers.

The DDD driver was developed by German engineer, mathematician and sociologist, Peter Dicks.  In 1978 he began to investigate certain fundamental problems of loudspeaker driver design.  He was particularly interested in the Walsh driver, designed by the American engineer Lincoln Walsh and used in the famous Ohm F loudspeakers. To assist his research, Dicks developed a computer model to describe the behaviour of this driver.  He then spent several years building and testing prototypes of an improved driver and refining his computer model, until eventually he had produced an extremely impressive sounding new design, together with a complete theoretical model of its operation.  The new driver had a very wide operating frequency range, comparatively high sensitivity and was physically rugged.  The latest version uses a carbon fibre cone, which is relatively immune from the attention of straying little fingers and those doing a bit of over zealous dusting. 

Dick’s driver came to the attention of Holger Mueller, the owner of a German loudspeaker company called Mainhattan Acoustik.  Mueller was intrigued from the start.  He was himself the owner of a pair of Ohm F loudspeakers and always believed that the Walsh driver had enormous untapped potential.  He agreed to license the DDD driver and formed German Physiks to develop the design. Two more years were spent further refining the DDD driver, before, in 1992, it made it its debut in the first German Physiks loudspeaker:  The Borderland.   This is still in production today, though in its Mk IV iteration and it is from this model that the HRS-120 has been developed.

Although the DDD driver bears a superficial resemblance to a conventional pistonic driver, both types having a cone, voice coil and magnetic circuit, the way the DDD driver operates is rather more complex. 

At low frequencies the DDD driver works like the pistonic drivers in conventional designs.  Then pistonic operation is progressively replaced by bending wave operation.  The cone on the latest DDD driver is made from 0.15mm (0.006 inch) thick carbon fibre sheet, which is very flexible and the termination of the cone is much stiffer than that used in a conventional driver.  Consequently, if the voice coil acceleration is sufficiently high, instead of the voice coil and cone moving uniformly together, the carbon fibre bends and a wave travels down the cone wall toward the open end.  This is referred to as bending wave operation.  

At the frequency where a standing wave is established on the cone wall, the cone goes into break-up and then the sound energy is radiated using modal radiation.  You can imagine this as vibration patterns on the cone surface much like those seen when a pebble is dropped into water.  A more detailed description of how the DDD driver works is available on the German Physiks web site. 

The use of use of these modes of operation provides two important advantages:  

Firstly, it gives the DDD driver a very low moving mass and consequently an exceptional transient response. This is easy to hear in the life-like “snap” that percussion has when reproduced on the HRS120.  There is no sense of the dynamics being compressed.  With sufficiently fast electronics like Spectral, transients can make you jump, even when you know they are coming.

Secondly, it allows a very wide operating frequency range.  In the HRS-120 the DDD driver operates from 240Hz up to 24kHz and thereby avoids the need for the crossover point in the mid-range commonly found in conventional multi-way designs.   This gives a very significant improvement in the overall clarity of the sound, as our hearing is very sensitive in the mid-range and anomalies here are most easily heard.  The consequent purity of the mid-range combined with the DDD driver’s high degree of phase linearity, enables it to very accurately reproduce the timbral characters of the instruments in a recording.  

Another feature of the DDD driver is that it is very transparent and it is able to maintain this transparency at all signal levels.  When you play back complex high-level passages of music, you will be able to follow all the threads of music, rather than being presented with a confused mixture.

A happy consequence of the DDD driver’s construction is that it radiates omnidirectionally.  This more realistically recreates the type of sound field one would experience in a live performance, where most of the energy from a broad range of frequencies is reflected before it reaches your ears.  This also means that the timbral balance of the sound is much more even throughout the room than is possible with conventional drivers, due to their tendency to beam at higher frequencies.  In addition, the exceptionally well-focussed and realistic stereo images that the DDD driver produces can be enjoyed from a wide range of listening positions in the room.  This makes it much easier to share the enjoyment of your favourite music with friends and also helps to make listening more relaxing, as you do not have to worry about staying in the small “sweet spot” that most conventional designs produce.  It can also help to prevent marital strife.

The simple looking cabinet also conceals a few clever ideas.  Most of its volume is taken up by the bass system.  This consists of a sealed enclosure with a downward firing 10-inch woofer fitted at the bottom end. This covers the range from 240Hz down to 29Hz. The energy from this system emerges from the openings at the base of the cabinet, so the low frequencies are radiated omnidirectionally, matching the radiation characteristic of the DDD driver.  The use of an octagonal cross-section for the cabinet means that individual panels are smaller and therefore stiffer than the panels of a square section cabinet of the same volume would be.  Stiffer cabinet panels vibrate less. Vibrating cabinet panels can severely degrade the performance of a loudspeaker system.   The only things we want vibrating are the drivers and your feet.

To minimize any residual panel vibration, a special damping material called Hawaphon is applied to the inside surfaces of the cabinet. Hawaphon is a polymer sheet containing a matrix of small cells filled with very fine steel shot and was originally developed as an anti-surveillance measure for use in military and government buildings. It adds mass to the cabinet to reduce the resonant frequency and the ability of the shot in the cells to move against each other provides a very effective way of converting vibration energy into heat. Hawaphon achieves a broadband attenuation of structure-borne sound of more than 50dB.

The HRS-120’s cabinet has a small footprint, talking up just over a square foot on your floor.  This is more impressive when you hear the quality of the bass that the HRS-120 can produce in terms of depth, speed and control and how loud it can play.  However, when it does play loud, it maintains the delicacy, detail and finesse it shows at other levels.  

One more useful feature of the HRS-120 is that it is not overly critical of room positioning.   Like all loudspeakers it will benefit from extra time and care taken in fine tuning, but a good sound can be quickly produced without the need adjust the position to the last fraction of an inch, and being an omnidirectional design, you never have to adjust the toe in.

If I may I would like to add a few subjective comments about the sound. In nearly 25 years in the audio industry, in both the professional and high-end sectors and having worked in the UK, USA and Japan, I have heard a lot of loudspeakers.  Many were good hi-fi, but very few were exciting on an emotional level.  Music is fundamentally an expression of emotion and without it music lacks meaning.  With their transparency, speed and sheer musicality, the German Physiks designs manage to reproduce that essential emotion.  I have lost count of the number of hours I have spent listening to music on my own set of HRS-120s, when I should have been attending to urgent jobs, but they have drawn me into listening to just one more track.

It gives credit to Walsh for the inspiration of the design of the DDD driver.  At the time that Walsh was working he would not have had access to the computer modelling techniques that Peter Dicks used, so he could only improve his driver by making changes and building a prototype to see if they improved things or not.  Once Peter Dicks had developed his equations to define the device's behaviour and which are quite complex, he was able to more clearly see how to optimise the design.  That said,  a considerable amount of time was spent in making prototypes and using the test results for these to refine the accuracy of the computer model.  Peter also had access to more powerful magnets than I think were available to Walsh and these were crucial in obtaining a more useable efficiency.

Everything best for „High Fidelity” readers!

Robert Kelly
German Physiks, Manager