The curv ball. From Mike Klasco's paper: "An innovative and superior-performance cone is now available globally with performance comparable to woven composites yet pricing just above extruded PP sheet cones. The material Curv®, manufactured by Propex, is light, stiff, with a high Young’s modulus and high damping, not hydroscopic and provides high temperature tolerance. Curv is relatively inexpensive at least when compared to carbon fiber or Kevlar. What is it made of? In a nutshell, pure polypropylene (PP) is extruded, drawn into tapes, woven and heat-treated to produce a self-reinforced PP composite. In this unique patented process, the surface of the tapes is selectively melted to bond the fabric together, providing a single polymer composite. The drawing process provides higher stiffness by orienting the polymer. As the surface facings are melted and re-crystallized to form the matrix, an ultra-stiff and smooth skin sheet is produced. The resulting sheet material properties are enhanced through this molecular orientation rather than mineral loading. Typical polypropylenes for speaker cones have talc, mica or glass compounded into the PP that increases the material density about 10%. Curv is pure PP without mineral loading. While the stiffness is 30% higher than conventional glass-filled PP, Curv’s density is .92, about 10% lower than glass-loaded PP. The processing not only results in a stiffer and lighter cone but also increases temperature tolerance... Highly oriented polymerization is one of the secrets the Japanese brands such as Sony have used to achieve superior sound in their headsets by biaxial stretching and heat annealing (crystallization) of the polyester diaphragms such as PET and PEN films. The Japanese material suppliers have not offered this processing outside of their Keretsu group(s). Now this sophisticated molecular processing is readily available in PP sheet material for speaker cones. Steak at hamburger pricing."

The driver. Though Dayton's above ES140Ti-8 unit looks the likely suspect, it's not, exactly. "Our actual supplier is a factory in Taiwan. They do OEM drivers for Dayton's Esoteric line if I remember correctly. Our woofer is a custom variation of a product that exists in multiple versions because this supplier will change parts and parameters as the customer specifies. The curv membrane is less stiff than the glass fiber in Dayton's unit and in my opinion more suitable for midbass use because of its softer breakup behaviour with our shallow filter. The driver's general architecture is from the old Dynaudio and Morel styles but with a Titanium former, neodymium motor etc. The parameters of that type driver fit well with transmission line loading but not always bass reflex. Sensitivity is low however, about 84dB."


Transmission. Massimo's brief comment reminded us. Different loading schemes want different driver parameters. In my review of the soundkaos Libération, we'd learnt how for open-baffle use, the surround/spider of its Enviée widebander previously used in a box had to be stiffened. This made up for lack of standard box pressure on the back of the cone though it drove up its resonant frequency. This was compensated by a beefy 18" woofer. Identifying the perfect driver for a given design is key to minimizing any wrinkles a filter has to iron out. With the Amira, 1st-order filters and time-aligned drivers walk softly in the time domain. So does a narrow baffle with round-over edging via diffraction control. A hidden damped steel stalk to which the drivers and plinth torque establishes a path to earth for structural resonances. All of it is an attempt at removing sonic clouds. If effective, the sun of the sum would be left to shine unhindered. And that would return us to Albedo's tag line about brightness in sound. That's clearly not about pleasing colourations. It's about a transparent transmission of what's fed, with minimal distortion. About distortion, Massimo had an interesting comment. It arrived when I asked whether he had ever tried any of the crazy-money diamond drivers.

"Regardless of cost, I'm starting to think that diamond is the only way to avoid even subtle treble hardness completely. It might seem contrary but the really annoying issue of hard membranes is their high breakup distortion. Meanwhile their distortion in the audible band is low; exactly what you want. Ceramic tweeters push their breakup beyond our hearing threshold, to ~30kHz depending on size. Even though that seems sufficient, it's not. Sometimes, a little harshness creeps in despite a low-pass filter. Diamond tweeters push their first breakup mode up by 10kHz or more. Now breakup effects in the audible band are less. That's why diamond tweeters sound softer than ceramics. Because of their high cost, the retail price increase of such speakers is extreme. A few years ago, some brands sold diamond and ceramic versions of the same speaker. Some crazies, even dealers, used to swap ceramic with diamond drivers to have or sell a diamond version at the far smaller increase of raw parts cost. Obviously, the xover for diamond and ceramic is not the same to cause a worse-sounding speaker. Today this is impossible. Accuton stopped selling diamond drivers to the spare parts market. For a customer or dealer, it has become quite impossible to source one. As a manufacturer, we of course can. In fact, our new tower above the Alecta is planned to include one. Our first pair of diamond tweeters just arrived. My wallet still hurts." Chasing ever lower distortion means superior parts. It eventually becomes a game very few can afford to play. A happy exception are new materials like Curv® when they incorporate desirable traits of costlier variants at a lower price. By using a silk-dome tweeter, the Amira also avoids ceramic tweeter challenges.