This review page is supported in part by the sponsors whose ad banners are displayed below

"A speaker's brain is its crossover. It defines its drivers' bandwidth, attenuation, correction and phase coherence. No common structure—Butterworth, Bessel etc—will match ideal parameters to a real-world environment. That only happens in simulation software. 25 years ago Christian Yvon developed a proprietary topology so flexible that it allows him to precisely shape the response of each driver. His DRIM filter can even cut at 90° with full phase coherence but isn't applicable to actual production because it is far too susceptible to driver discrepancies. Here we protect our IP since pale imitations are so many.

"Finally Apertura today are a family-type business of Stentor SAS located close to the city of Nantes on the western coast of France. Our cabinets are sub-contracted in Asia. The main reason is not cost but that the know-how and tooling required to manufacture cabinets as complex as ours have migrated to Asia. There they also have a long tradition of top-quality lacquering which is no longer common in Europe.

"We have two sub-contractors who work to our quality standards. Our drivers are from Seas in Norway for all our mid/woofers whilst the ribbon tweeters are from Fountek in China. China holds more than 80% of the world's reserves of rare-earth metals needed for Neodymium magnets, hence nearly all ribbon manufacturers are located in China. All our coils are from Jantzen in Denmark. Our capacitors are from various sources like Jantzen, Mundorf, LCR, Intertechnik and others. We use our own proprietary cables of OFC or silver-plated copper with PTFE dielectric. All our measurements, PCB assembly, speaker assembly and QC checks are performed in our Nantes facility."

About Christian Yvon's CV, "he was always surprised how existing loudspeakers were unable to recreate—from his point of view at least—the experience of live sound. In 1978 he created his own laboratory to conduct research on sound and acoustic. He then developed several new technologies of which the proprietary DRIM crossover topology is one. In 1979 he worked for Goldmund where he developed the Dialogue, Apologue, Analogue and Epilogue speakers. He also worked for Focal, Sonus faber and many others. In 1982 he decided to develop his own models under the brand name Apertura. Like the name, this became an opening towards a new concept of reproducing the purest sound with no additional resonances, colorations, phase errors or impulse response delays. The first Apertura model was 1983's Reference. It was soon followed by many others, amongst them 1990's Tanagra and the Kalibrator in 1999. Over 25 years then, Christian had developed a complete line of speakers.

"By late 2009 he ended his work with the company which manufactured his speakers when quality and strategy no longer met his expectations. By 2010 he and Eric Poyer set up Stentor to manufacture and sell a completely new line of Apertura models. Eric Poyer had worked for many years with a well-known high-end manufacturer before creating his own OEM firm 15 years ago. At Stentor Christian is responsible for all acoustic design, Eric oversees mechanical design and production. Between 2010 and 2013, their partnership has already netted the five floorstanders Armonia, Onira, Ariana, Edena and Enigma. 2014 will still see the production launch of the Kalya monitor previewed at the Munich HighEnd show in the La Rosita exhibit. Christian's early work on filters was prompted by dissatisfaction with the lack of attenuation, efficiency and versatility of then common crossover structures. He was looking for a subtle but powerful tool that would be capable of effective modeling, carving and slicing of the signal without erratic compensation.
Apertura Kalya from fairaudio's show report

"To exploit the trail of the resonators never used at that time appeared obvious to him. However he quickly realized that simple adaptation of the Cauer filter topology would not reach his goal of subtlety and precision on the razor’s edge. Some amount of adaptation and damping should be inserted into the ellipse to compensate for the non-linear profile of impedance and frequency. After much research it became clear to him that the configuration of the resonator to achieve the corrections and multiple slopes he wanted relied on a specific additional circuit. This finally created the dual-resonant intermodulation minimum or DRIM filter capable of a brutal 90° cut-off as well as complex compound-slope attenuation. Christian subsequently launched his first company Prologue Research & Development. Its purpose was not manufacture but the study and design of loudspeakers for various brands, occasionally direct competitors.

"His first project was the Dialogue Logos. It enjoyed great success in the US and was in fact the first speaker for Goldmund whose appointed designer he became for many years. Amongst his other clients were Focal/JM Lab, Point Source, Auditor, Joseph Szall of today's Capriccio Continuo, Einstein, Sonus faber and others for whom he oversaw crossover development for their luxury high-end models. During the early 1980s, nobody in the industry had experimented with such deep crossover attenuation yet. Thanks to his DRIM structure, Christian could design transition slopes which mirrored so closely that even reversing the polarity of a drive unit left the summing phase almost unchanged. The phase rotation was in fact there but occurred over a frequency range so narrow that it almost became a rotation in the void." For those mathematically inclined, here is US patent 6854005 for another form of elliptical filter which combines a notch and low-pass filter.