When I caught up with Kaiser at Munich, Rainer explained how Mini's flat and high impedance is a result of using Kondo's EL34 Overture during R&D. Internal Mini wiring plus wiring for its ribbon trafo's primary was Kondo's famous silver made available to an outside firm for the first time in 40 years. A pre-show email from Rainer was signed Director of NVH, Continental Automotive GmbH came with a PDF article showcasing his work at Powertrain-BU Engine Systems under the header "a man who literally hears quality. When it comes to the solving of acoustical problems, the principal expert for NVH is in demand across the continent".
It sketched out the backdrop against which Rainer develops Kaiser speakers: industrial well-funded measurement-heavy R&D on lowering automotive cabin and other noise. NVH is short for noise, vibration and harshness. That condenses focus and purpose. It explains Rainer's unique expertise and approach to enclosure design. He looks at it like a car cabin. That's exposed to all manner of noise from its own engine and tyres. How to reduce it so that we hear less of the box, more of the music? That's germane especially with small speakers of full-range ambitions. The louder we play them with bass-heavy music, the more they pressurize internally to escalate stress on the box, its drivers and also the filter components unless those seal into a sub chamber.
More on passive radiators, "they of course cost a lot more than a cabinet hole with an attached tube. By using four, Mini's raw parts cost already eclipses equivalent ports by a factor of ten. That still reflects a lot higher in the final price. Also, a port not only works at its tuning frequency but as a kind of organ pipe with two open ends. So it exhibits a lambda/4 resonance often clearly audible in the midrange.
"A passive radiator doesn't. It does however create a useful additional null in the transfer function below cabinet tuning. That causes less energy in a band where the room already acts a bit as a compression chamber. In the bass, you're correct to think that one adds the cone surface of the radiator/s to that of the active mid/woofer. For Furioso Mini, this sums to around 500cm², more than a 12" woofer. Due to this large surface, its acoustic coupling to the air is far superior to a small port. It's why an auxiliary bass radiator usually enjoys more linear high-volume behavior. To match a port's dynamic output to that of a radiator, you'd need big port area/volume. Then high SPL nonlinearities stop being an issue. Think of the old Onken enclosures. They used 90% port vs. cone area. Also, an ABR is very easily tuned to a customer's room." Here we remember that a passive radiator's functional principle is mass. Increasing or decreasing it by changing variable weights on the cone alters its tuning.
By September 20th, "for your eyes only" showed in my inbox with this terse message accompanying the above photo: "Test cabinets. Will send pics with drivers mounted this weekend. Looks rattenscharf. The new Mini." I'd not heard that German colloquialism in ages. Rattenscharf. Literally hot as a rat, it derives from Rattenschaf or 'rat sheep'. Due to favorable climatic conditions, sheep on the Falkland islands exhibit unusually frisky behavior. Like rats, they copulate and give birth thrice a year. Clearly Rainer thought Mini an unusually turned-on box. Shown here in his workshop next to Chiara, I had to agree. Mini's cosmetics were much improved.
By September 26th, "I'm testing Silvercore autoformers to attenuate the ribbons. Sound very good but expensive." Rainer was leaving no stone unturned. By October 6th, "making big progress. Went away from the Silvercores. Above 5kHz, they had less harmonic distortion than a resistive solution. However, despite high-passing the autoformer with just 1.1µF, I encountered high distortion below 1kHz. That probably was core saturation. A resistive solution performed much better and was 30 x cheaper. I still tested expensive Duelund cast copper capacitors but in this application, the less costly red Jantzen Superior Z caps were better. Next week I’ll get the final tankwood baffle. My prototype cab wasn't the very best. The actual enclosure will still improve bass and clarity. But already with the proto cab, Mini outclassed Chiara." Talk about fratricide carefully engineered by the pater familias. Shakespeare would have been proud.
Rainer wasn't done. On October 12th, his terse message was "ScanSpeak Ellipticor eats Viawave ribbon. HJ is changing cab to fit new tweeter." HJ was obviously Hans Jürgen Kaiser. And the ScanSpeak was a premium Danish silk-dome tweeter which just had had a Russian ribbon for breakfast. When I told Rainer how interesting it was that originally, Mini had adopted the Viawave as an improvement over the ScanSpeak Beryllium tweeter in the first Grande, "yes, funny, isn’t? I was always a big fan of ribbons and I like their non-homogeneous radiation with less energy aimed at ceiling and floor. And I like natural tone colors. Ellipticor delivers. With regards to radiation pattern, it is better also than a spherical dome. Do you remember the old Audax elliptical tweeter from 30 years ago, piezo with a gold surface?"
I did. Pat McGinty whom I'd worked for used it in his Meadowlark Heron model. Furioso Mini was taking final form. What other wrinkles lay ahead before the design would lock in? At this stage of the narrative, my book on it closed for a year. Then it opened again.
