August 2019 | Newsletter No. 5

More German Physiks Facts

Firstly we would like to thank our existing subscribers for their support and welcome all the new subscribers to our newsletter.

In this newsletter we would like to tell you a bit more about what is probably our most unusual loudspeaker.

The Unicorn Mk II

Unicorn Mk II

How was the Unicorn born?

The Unicorn is the only German Physiks design that uses a single DDD driver to cover almost the entire audio range: 40Hz to 24kHz. 

It started life in 1998 as an experiment to produce a DDD driver based design with improved integration of the very low frequencies, hitherto handled by a conventional bass driver and the range normally handled by the DDD driver – approximately 200Hz to 24kHz.  Whilst the integration our designs offered was good by the standards of the time, it had not reached the levels that we now achieve after 25 years of experience.

Early Ideas

A bit about the German Physiks
DDD driver

Underside of the DDD driver

The DDD driver has a surround that is much stiffer than that used in a conventional pistonic driver. This is required to ensure that the driver transitions from pistonic mode to bending wave mode in the correct frequency range.  The stiffness of the surround limits the maximum excursion of the cone, consequently, the DDD driver produces a reduced output below about 100Hz. For this reason, in other German Physiks designs the DDD driver is rolled off at about 200Hz and the low bass is handled by one or more conventional woofers. 

Initially, modified DDD drivers were tried in an attempt to produce a more extended bass response, but these did not produce the required performance. 

Instead it was decided to drive the DDD driver “full-range” and bring up the very low-end response by coupling the energy radiated from the underside of the DDD driver to a horn.

The Challenges

This however, was not so simple.  A horn could provide more than 10dB of lift and so compensate for the DDD driver’s falling bass response, but achieving perfect integration of the DDD driver and horn posed three major challenges:

  1. In the region where the DDD driver’s response was falling off, the horn would provide too much lift. 

  2. When the DDD driver’s response had fallen by more than the horn’s acoustical gain, the system response would drop noticeably.

  3. The horn would also boost the mid-range, up to several hundred hertz and this would produce a time smear effect due to the path difference between the energy radiated by the horn and the direct radiation from the DDD driver. 

The Solutions - Acoustical

The first part of the solution was to combine a high gain horn with a bass trap located in the throat of the horn.  The bass trap itself consisted of two parts:

  1. A damped Helmholtz resonator similar to that used in the Borderland Mk IV and HRS-130 models.

  2. A pressure-release system like a Tube Trap.

The bass-trap keeps almost all of the mid-range out of the horn and also attenuates the region from 70Hz to 140Hz.   At the point where the attenuation provided by the bass-trap is falling off and the DDD driver’s response has also dropped significantly, the horn is coming into effect, thereby lifting the response and providing a smooth transition from the direct radiation provided by the DDD driver and the output from the horn.


Because the horn provides an extremely fast transient response, the bass is very fast and very precise and this provides an excellent match with the fast transient response offered by the DDD driver. 

The Solutions - Electrical

Unicorn equaliser network

An equalisation network placed between the power amplifier output and the loudspeaker was used to protect the DDD driver from being damaged by large low frequency signals. This was especially important with the early version of the DDD driver that used a titanium foil diaphragm, as this was easily damaged when subject to large excursions. The current carbon fibre diaphragm DDD driver is very much more rugged in this respect. The network also provided adjustment of the low frequency roll-off and the high frequency level, similar to that now provided on many other German Physiks designs.

Into Production

Unicorn Mk I and Mk II

Unicorn Mk I
The plastic film on the DDD driver is to protect it during shipping

In 1999 prototypes of the design, now officially known as the Unicorn because of its single DDD driver, were given a number of private demonstrations. These produced enough orders to convince German Physiks to put the design into production. The Unicorn Mk I sold steadily, mostly in the Far East, where horn loudspeakers were very popular and the unconventional looks were not a barrier. In fact, compared to what some customers were using, the look could almost be considered conservative.

In 2005, the Unicorn Mk I was replaced by the Mk II version, which featured a modified horn design.  This continues to sell today, still mostly in the Far East.

While the limited very low bass rules the Unicorn out for devotees of death metal, its exceptional coherence, clarity and speed enable it to provide a wonderfully involving and enjoyable musical experience with jazz, female vocal and small to medium scale classical music. Many Unicorn owners comment that the clarity and agility of the bass it provides is more than adequate compensation for its reduced very low bass response. If you want a demonstration of this, please look at this You Tube clip from High End Munich 2012, showing two visitors to our room seriously getting in to a pair of Unicorn Mk IIs doing a very good job with Pink Floyd’s iconic track Money.  

Latest improvements

The original passive equaliser has been replaced by a DSP based unit, which sits between the preamplifier and power amplifier. This allows the Unicorn to be connected directly to the power amplifier. The passive equaliser is still available to special order.

Conclusion

The essence of the Unicorn has best been summed up by the late Wes Philips, who wrote in his CES 2009 report for Stereophile magazine:

“I initially listened to the Unicorns waaay over against the wall, but I still got a coherent, solid soundstage. When I sat in the sweet spot, I essentially heard what I'd heard over to the side—only a tad more of it.
 

The more I learn about hi-fi, the more I find I need to unlearn. I always thought I didn't like 360° speaker designs, but it was specific designs I didn't care for. The Unicorns were fast, focused, and convincing.”

There you have it. Thanks Wes

Further Information

Visit the Unicorn Mk II web page.

Visit the DDD driver development web page.

A selection of Unicorn Mk II reviews is available on our web site.

 

Until next time…

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If we can be of help with anything at all, please do not hesitate to get in touch with us here. You can find your national distributor here.

Holger Mueller | German Physiks