German Physiks HRS120 Carbon

German PhysiksThis is assuredly not your average assemblage of conventional moving coil drive units in an MDF box, but then again at £16,000 you wouldn’t expect it to be. The German Physiks HRS 120 is a unique omnidirectional designed powered by the exclusive Dicks Dipole Driver (DDD) – meaning that it’s like absolutely no other loudspeaker on sale.

After years of mathematical modelling and physical experimentation, Peter Dicks created his first design concept in 1978, but it took until the early 1990s until Mainhattan Acustik, run by IT expert Holger Mueller, licensed the design and German Physiks was born. It took two years to make the first commercial product, refining the Dicks Dipole Driver to fit the Borderland loudspeaker. In 1993, with sales continuing to rise, Mueller established a new company to exclusively manufacture the German Physiks range of loudspeakers, and since then it has prospered, especially in the Far East.

Used on all models right up to the top of the range Gaudi, the DDD comes in two flavours – titanium or carbon fibre. These loudspeakers sport the latter, which are said to be a better ‘real world’ compromise (the former are easy to disfigure, their foil being so thin than one touch pushes them out of shape). The unusually shaped unit, described as a “bending wave convertor”, runs all the way from 24 to 24,000Hz, obviating the need for a crossover point in the midband (where the ear is most sensitive) and maintaining phase coherence right where it’s needed. Its omni directional dispersion is a further welcome benefit, making it work well in many types of listening room.

The trick was getting the DDD driver to work in box with a bass driver. The tall but slim (320x1145x320mm) cabinet uses heavy panels of MDF with reinforcements fitted to critical points within the structure, in an octagonal shape so the individual panels are smaller and therefore stiffer than they would be if a conventional square or rectangular cross section had been used. Hawaphon damping material is applied to the inside of each panel – a polymer sheet containing a matrix of small cells filled with very fine steel shot, originally developed as an anti-surveillance measure for use in military buildings. It is said to add mass to the panel and reduce the resonant frequency. Onto this is added a lining of high density felt. Finally, at the bottom of the 29.7kg cabinet, a 250mm moving coil woofer takes care of the last few octaves.

The HRS120 is a single wired design, with handy jumpers at the back next to the binding posts to offer a degree of treble trim in four steps (-2dB, flat, +2dB and +4dB). This is an excellent, welcome feature; providing it doesn’t impede the signal, I have no problems with level controls to get a speaker to work well in a listening room – given that the latter are so variable. Overall construction quality is very good – with fine cabinetry in the customer’s choice of hand matched, hard wood veneers. There’s also a carbon fibre panelled version at a considerable price premium.

Despite the fact that the HRS120 is an omnidirectional loudspeaker, and thus theoretically easier to place, I must confess to spending more time than usual moving my review samples around. In my medium-to-large (by UK standards) listening room, I found they worked best about 3.5m apart, and about 0.75m from the back walls, although the stereo imaging can be improved by moving them further out into the room and closer together. Another issue was that of partnering ancillaries – with only middling efficiency these won’t work with any old 3W single-ended triode tube amp. I found Quad 11-40s just about coped, as did Sugden’s IM4 Class A integrated, but they really liked the firm underbelly of NuForce’s Reference 9SE 250W monoblocks, allied to the superb MF Audio Silver Passive Preamplifier.

Despite sounding quite poor at first, the aforementioned fettling finally pushed these German Physiks columns into their zone, whereupon there was a ‘night and day’ transformation, and I suddenly realised they’re very high resolution transducers with all the spatial prowess that you’d expect from something that doesn’t fire sound at you from a very specific angle via multiple, often tenuously matched drive units! Put simply they offer a ‘cathedral-like’ listening experience, throwing images way, way out of the box (or, ermm, octagonal cylinder) and apparently dissolving into thin air. The recorded acoustic that they unleash is certainly well lit, but in my system at least – complete with some very smooth source components – never sounded harsh.

Most striking was the seamlessness of the sound; not only is it vast in scale but utterly even and all-of-a-piece. Hearing these omnis shows you how intrusive multiple drivers of different sizes firing right at you can sound – there was no sense of listening to a loudspeaker. The tone is startling – beautifully clean and direct, yet lightning-fast and ringing with harmonics. Vocals are also eerie – completely unspoilt by the sound of little cones heave-ho’ing in front of you – and tonally dry but vibrant all the same.

Moving higher up, and the cymbal sound also impresses. Having a penchant for ribbons at this price point, with a strong second-choice preference for the sublime electrostatic panels of Martin Logan or Quad, I wasn’t expecting what looks like a moving coil driver with a stretched, down firing cone to deliver the goods in the high frequency department! Hi-hats are smooth and subtly etched; there’s no sense of listening to a large cone trying to ‘do’ treble, and the HRS120 sounds just as finessed as almost any small metal dome tweeter I’ve heard. This great subtlety and detail up top, allied to that vast spatiality make for a lovely listen.

Bass is impressive, if not quite the HRS120’s strongest attribute – there’s no sense of massive, swingeing power and subterranean lows you get from B&W’s 801Ds at almost half the price. Perhaps this is actually a boon for British rooms, the low frequencies offering a firm, no-nonsense underpinning to an exceptional midband and excellent treble. You’d certainly not notice this as a two-way, so well integrated the lows are with the rest of the frequency range. Properly set-up, these loudspeakers shine with almost anything they’re fed, but if there was one genre they love more than any other, it is acoustic jazz, where the size of the recorded acoustic is astounding.

This is a very distinctive pair of loudspeakers. Having tried every high end design in my house from Quad 989s to Meridian DSP7000s, via Perigee Acoustics FK-1F and Martin Logan Summits, I have confess that I’ve never been completely convinced by any of them. Yes, I’ve loved them all for different reasons, knowing that what they do, they do brilliantly. And so it is with the German Physiks HRS120 – they are superb in many respects, but not all. The interesting thing though is that in their inevitable weaker areas, they are less compromised than others. For example, B&W 801Ds give stunning visceral bass but are rather tonally ‘grey’, Quads 989s are lovely spatially but weak and compressed at frequency extremes. This loudspeaker’s least convincing aspect is bass, but even this is still good by class standards. There are other speakers at the price that do other things better, but I can’t think of any which is such a consummate all rounder. A brilliant appliance of science.

DDD THEORY
At first glance, the driver looks like a conventional pistonic cone, inasmuch as it has a voice coil/magnet assembly that serves as the actuator, and a cone – although this is longer and narrower than usual.  But with a piston driver, when the voice coil moves, the entire cone moves together with it (which is why the cone and voice coil structure is made as rigid as possible), and the sound wave produced moves in the same direction as the movement of the cone. The company says that the DDD “is rather more complex”. The lower frequency end of its operating range can be described with Thiele/Small resonant parameters, while in the next frequency band up to the coincidence Frequency, “it works like a pistonic driver”. Next, there’s an overlapping band where pistonic movement is “progressively replaced by bending waves until all the radiation is generated purely by bending movement in the cone”. Due to dispersion and the cone’s special shape, the Coincidence Frequency is spread over an extended frequency range, rather than occurring at a single frequency like the Dipole Frequency, says German Physiks. From the upper edge of the Coincidence Frequency band, it works like a pure bending wave converter where the velocity of the travelling waves in the cone increases with frequency. Finally, the last mode of operation commences above the bending wave band at the Dipole Frequency, when the first standing wave occurs and where modal break-up begins.

The idea is that, by optimising the key properties of the cone material, namely thickness, elasticity and specific weight, together with the cone’s bending stiffness, which is achieved by selecting the correct cone-angle, all four frequency bands may be very closely balanced. The last two modes cover the majority of the DDD driver’s operating range and are what differentiate it from conventional drivers. In these two modes, when the voice coil moves, the whole cone does not move together with it, as the open end of the cone is terminated by a rubber suspension and semi-rigidly attached to the driver chassis.  Instead the motion of the voice coil causes a wave to travel from the top of the cone down to the open end.  This occurs because unlike the piston driver, the DDD driver cone is made from a very light and flexible foil – 0.025 mm thick titanium or 0.15 mm thick carbon fibre. While the shape of the cone gives it rigidity at rest, it is relatively easy to excite waves in the cone material. The trick is in controlling these waves.

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