CURVI HIFI UNIQUE SPEAKERS
The Curvi story
By 2004 I had quite a lot of experience in loudspeaker cabinet design and construction, I have a PhD
in composite materials and am a lecturer and researcher in polymer science.
I applied my materials expertise to a one-off statement three – way design that is made from a laminate of in-situ cast highly filled filled polyurethane foam between birch ply skins. The use of a birch ply skinned
structure was partly inspired by the de Havilland Mosquito aircraft. This statement design wascompleted in my uncle’s furniture workshop in September 2003.
After moving into a new house in 2005 my parents needed an aesthetically appealing speaker that did not have an excessively large floor foot-print. For this design I explored the idea of using a full
range drive unit; balanced mode radiator (BMR) drive units were still in development and not commercially available at the time.
I therefore chose the last – generation approach to full range drive unit design, namely the E J Jordan contro-flex full range JX92S drive units.
The cabinet of the speaker had to be different and offer a visual statement whilst embodying transmission line loading for maximisation of bass extension and effective absorption of rear radiated sound. I wanted to get away from the rectilinear line geometry used in most TL designs and go as far as possible towards elimination of rear radiation reflections.
After several iterations, I arrived at a design which resembles a person sitting with their knees drawn up – the curved back encourages mid and high frequency sound to be reflected round the line and be efficiently absorbed by the strategically placed line damping. The curved profile with no sharp corners also facilitates smooth air movement.
This was too good a design for just a one-off – I therefore applied for the design to be registered and registration was granted by the UK Patent office on 27 th March 2006 (registration number 3023981), The registration has subsequently been renewed and will continue to be renewed.
The geometry of the design suited a CNC cut laminated construction approach. Birch ply was the
obvious material choice from an aesthetic and acoustic standpoint. The 90 degree opposing grain
directions combined with significant vibration energy propagation transverse to the direction of the
ligno-cellulosic wood fibres and the differing mechanical impedances of the adhesive layers all add
up to rapid energy dissipation.
The Curvi Model 1 and Curvi Model 1v2 then followed, the latter was launched at the 2010 Sound and Vision Show in Manchester and received critical acclaim and was the subject of a CineNow
At this point I engaged Christien Ellis of CE Electroacoustics to carry out the voicing of the Model 1v2 and all subsequent designs.
BMR drive units become commercially available in 2010, I was the first to use these in a commercial
full range loudspeaker design (the Etude 1). The Etude 1 was launched at the national audio show
2011 and received many positive comments in show reports and a HiFi Critic Review.
Using the second Curvi prototype, I experimented with BMR drive units. At the time the largest unit
available was 85 mm. I therefore used two of these units, driven full range – one pointing forward
and the other pointing upwards, set into the top of the cabinet. The low bass was augmented by
two JX92S units driving the line 1/3 way along its length. Christien evaluated the concept and
decided a tweeter (ring radiator) was needed to augment/balance out the top end. This augmented
full range approach worked very well and has been progressed in the form of a more conventional
design which will be part of the Etude range. It was ultimately considered that this approach was
not in the true spirit of the Curvi design philosophy, as aesthetically the speaker was rather cluttered
A 128 mm BMR unit then became available and was evaluated in Curvi cabinet, with substantial
input from Christien Ellis. The cabinet needed some re-working to accommodate this drive unit and
the line damping required complete revision. An simple all-pass equalisation (Eq) network was
necessary (as was the case with the JX92S) to compensate for the baffle step. In the case of a
speaker with a narrow front profile there is no way this type of network can be avoided –
introducing the correction acoustically via resonance based methods, leads to undesirable
colourations and incomplete correction. The Eq network is constructed from high quality Mundorf
components and the internal wire supplied by Gekko cables.
The BMR drive unit offers key advantages over the already very effective Jordan drive unit. The
main advantage is more controlled delivery of upper-mid and treble frequencies. The sound is
smoother but also faster in this region, giving an even more natural effortless sound devoid of
edginess. At high frequencies the BMR unit is a bending wave transducer, this leads to much
superior off-axis coupling and reduced need to be in the hot seat for optimal imaging – the bending
waves in the diaphragm also provide the very fast, yet fatigue-free transient response. The radiating
area of the 128 mm BMR drive unit is also much larger than the JX92S – this contributes to a
significantly more powerful and more impactful bass response. The lower compliance and higher
resonant frequency of the BMR suspension necessitated changes to the line damping but the results
are impressive – the tendency for excessive excursion at low frequencies has been substantially
eliminated and there is much more punch, reach and authority in the bass.
The Curvi-BMR can give a very realistic view of organ music including that from a large cathedral / concert organ. Thanks to the 128 mm BMR drive unit the Curvi has now come of age and is realising its true potential. There is scope for further development including active wireless designs with DSP room
correction as well as the traditional passive separates based purist approach.
Contact for more information:
Designer of the Curvi speakers