A velvet fist in a velvet glove…
By Roy Gregory
The planar magnetic driver is one of audio’s simplest and most robust transducers. A flat voice coil laid or etched onto a flexible diaphragm is suspended parallel to a field of permanent magnets. Run signal through the voice coil and it produces movement and hence sound. Magnets, wire and cling-film and away you go. Making a planar magnetic loudspeaker has to be just about the easiest project in audio. But making a really good planar magnetic loudspeaker – that’s a whole different proposition…
As well as its inherent simplicity, planar magnetic construction presents its own practical and performance challenges. The most obvious is the relative arrangement of the magnets and voice coil. Not only is does the diaphragm’s excursion dictate a relatively large gap between tit and the magnetic array, the further it moves from the magnetic structure, the less control those magnets have over it. Despite the fact that the diaphragm is driven across its entire area, the spacing of voice-coil and magnets translates to limited sensitivity and dynamic range. One solution is to place magnetic arrays on both sides of the diaphragm, in a push-pull arrangement. This certainly improves linearity in the ‘motor’, but also places a fairly substantial physical barrier between diaphragm and listener, with a corresponding reduction in any gains when it comes to sensitivity or dynamics: two steps forward but one step back.
Magnepan has long been the principal producer of high-end planar magnetic loudspeakers (although the technology has proved more popular amongst headphone manufacturers). Starting in 1971, their various Magneplanar models have built an enviable reputation for affordable performance and longevity. Early models used classic, single-sided construction, but later flagship designs moved to a double-sided, push-pull configuration. The Eminent Technology LFT speakers coupled double-sided planar magnetic panels with dynamic woofers to considerable effect, although whether they pre- or post-dated the double-sided Maggies I just don’t know. Meanwhile, Magnepan’s concentration on the US market (and a bizarre decision to install a European distributor, thus creating a four-tier sales structure and massive price differential between European pricing and their home market) limited international sales and market share. What was a high-value product in the US, became an expensive, high-end product overseas – where it simply didn’t have the fit and finish to justify the prices being asked.
And for many years, that’s exactly how the planar magnetic landscape looked – right up to the point where Gilles Douziech and Eric Poix of Diptyque launched their first speaker, the DP77 in 2013. Based in Montauban, they are right next door to Toulouse, centre of the French Aerospace effort and Airbus Industries, giving them access to considerable local technological and materials resources. https://gy8.eu/blog/visiting-diptyque-audio/.
That first speaker was quickly followed by other models, the entire Diptyque range being both affordable and used double-sided drive-units. It represented a step-change in planar-magnetic performance, making its benefits more accessible in a wider range of systems. But that was only the beginning. The company soon developed the first real advance in planar-magnetic technology since the 1990s – cross push-pull topology. In this arrangement, the driver uses magnets front and back, but also uses two voice coils, one arranged horizontally, the other vertically, with magnetic arrays disposed to match. It’s a construction that creates greater control over the diaphragm, but also over its mechanical behaviour, reducing unwanted resonance and increasing bandwidth. It’s the use of this construction in the bass-driver that separates the three-and-a-half way Reference II from other Diptyque designs. II? The current Reference model was preceded by an earlier, visually virtually identical version, but series refinements quickly led to the Mark II designation. Changes included improved, modular internal construction, with each driver enjoying its own separate, composite frame, a larger foot and upgraded components, cables and connectors. Early models can be upgraded to a Mk.I Evo version, incorporating many of these upgrades – of which more later.
