• In 2015 currency, what are the retail prices for the standard Ampeggio and the flagship Ampeggio Dué?
€27'000/pr for the Ampeggio Signature with wood-cone drivers, €88'000/pr for the Dué with upcoming new HEML driver (short for Hybrid ElectroMagnetic Loudspeaker).

So the 9.87 system offers more bandwidth for less coin than the Ampeggio. That seems like a real benefit.
It is and yes, the Pi has more bandwidth. This successful math of course includes far simpler enclosures which are easier to build; and the AC-PiFe driver with Ferrite motor which lowers the price. However, the Pi can take the Ampeggio driver in the 9.87 system. That raises the retail to €27'800. Even our AC-X type drivers fit.

Does one assume rightly that the Pi driver would make less bass in the Ampeggio cab than the stock Ampeggio driver?
Yes. As one scales up within our catalogue, the drivers become more and more ambitious all the way up to our current battery-powered field-coil version. The Pi driver makes less bass than the Ampeggio AC-4X and also has lower resolution. The Pi enclosure also won't support bass as low as does the Ampeggio's but it is linear to 60Hz.

From that follows that to maximize bandwidth in your costlier enclosures, the quality hence price of the associated drivers has to increase accordingly. That's another obvious reason for how the new active bass system of the 9.87 system can lower the price of full-bandwidth admission. The widebander mustn't have record-breaking bass output and thus can be a bit 'simpler' than its equivalents in your unassisted top models. Here the interesting question becomes, can the Pi bass cab migrate successfully to the bigger models? Given their intrinsic rear-horn lines, one assumes not? How about the Pi's own rear-line loading? Is it being sealed off when docked atop the Pi bass unit? How is that done? If one purchases the four-piece system from the very beginning, is there a different Pi version whose enclosure is fully sealed already?

Correct, the price of our wideband drivers increases as one pursues more LF bandwidth. But in the 9.87 system, we don't relieve the widebander at all. It remains unfiltered and runs wide open. Only the horn mouth of the upper Pi enclosure gets a bit closed off with sheep's wool to insert an acoustic filtering function at ~80Hz. And yes, the 9.87 woofer system can assist all our loudspeakers systems. For this our plate amp has all the necessary regulators for crossover frequency, phase, bass boost etc. For the 9.87 application however, we only use the 80Hz low-pass and level control. All other regulators remain at zero to give the best linear sound without typical subwoofer boom.

It's highly unusual to find a subwoofer of your rated 99dB sensitivity. Did you once again roll your own driver or is this an existing pro woofer? We know that driver efficiency is a function of low moving mass (cone + voice coil + suspension of surround and spider) and high magnetic field strength in the gap. For a large-cone woofer with sufficient excursion and cone surface to do low bass, the challenges of cone stiffness and low weight seem mutually exclusive. Can you tell us how this particular driver manages that stunt? Tell us more about your R&D into widebander-specific active bass systems and some of the dead ends you explored before arriving at the final folded open-baffle design.
The 9.87 woofers are modified 12-inch pro drivers with special suspensions and voice coils. They use strong Neodymium motors. They arrive with a raw 96dB value which in our loading nets 99dB [2 x 96dB woofers per channel = 99dB - Ed]. That loading is a completely open dual-woofer isobaric dipole based on the Ripol design by Axel Ridtahler. We optimized it with our Acoustic Stealth technology and now call it AST-Ripol. The low air volume helps to get fast bass. Without any electrical correction, it does a linear 30Hz and 20Hz at -3dB. At first we tried simple Ferrite magnet woofers. The results were sorely disappointing. What we got was a slow-pumping system which sounded like a typically sluggish subwoofer, hence absolutely not what we wanted. Once we started using professional woofers, speed and control improved but extension still didn't reach low enough. Now we purchased unassembled pro woofers and added our own voice coils, surrounds and spiders. That finally gave us the desired results. No longer does one discern any added woofers. Of course the price for this bass system isn't cheap but it sounds great. And that's the only interest I have.
For plate amps, I tried many commercial class D solutions but they all sounded like glass. I can't easily explain that glassy quality but basically, the bass must be musical. I want to distinguish a bass drum from a bass string. Here all the cheap plate amps gave bad results and poor differentiation. They simply were not good enough for a product with our name on it. Subsequently we used an old Glockenklang power amp with a Marchand tube crossover which I'd had in storage for years. Wow, what a difference! Really, you have never heard such bass - very powerful, very detailed, very fast. Alas, the combo of Glockenklang/Marchand wants about €7'000. That was too expensive for a regular customer. But now that we knew what was possible, we kept looking. A bit later we found a class A/B amplifier module at a reasonable price that was far superior to the standard class D options. So that's what we are using. If someone wants the bigger stuff, no problem of course.
24'000 gauss in a 9mm gap.

Back to your core widebander focus, you started with specialty paper but later migrated to actual wood cones. Tell us about that development. And explain why traditional widebanders champion paper over composites or metal (though smaller widebanders from Jordan and Mark Audio for example use aluminium). What is it about cellulose that makes it superior for these applications? From Lowther to Feastrex, AER to Rethm and Fostex, it's always paper or plant-based fibres. Is that due to controllable cone breakup behaviour by using dissimilar material thickness and cross-fibre layups across the cone profile? Other?

The migration to wood arose from a discussion with a guitar maker. Any material has its own behaviour well removed from what we can measure. We were happy with our paper and still use it for our entry-level units. It's very fine Japanese calligraphy paper. But for more bass you need more stiffness. The higher the stiffness, the more bass you get. The only issue? For good treble, the moving mass must be minimal. Here most materials are heavier than paper or cellulose. 

Other companies use aluminium, Kevlar and other modern materials. They are all good but we found them to be not very musical; plus too heavy. That luthier gave me a Spruce veneer which we cut down to 1mm thickness. After this we lacquered it from both sides to get a cone of the same mass as our paper but 100 x stiffer. For the HT cone, the wood was too hard and the drivers sounded hard in the treble. So we mix paper and wood. We still keep paper for the whizzer because it sounds best. It's the material mix which creates the final finesse in the mids and highs.

Dissimilar membrane thickness comes from elementary physical knowledge. We know of DIY guys who think that an increase from center to rim or the other way around are optimal. And we know of companies who claim to do just that whilst using ordinary paper without any alteration in thickness. Actually, the highest strength should be in the middle of the cone. If you increase its thickness, it's best to have it in the middle. That's what we do for our wooden cones. It is accomplished with a pressurized moulding process. With paper you can only do this when you start with raw cellulose pulp. With calligraphy paper it's not possible. It is already too thin. Anyway, we like the Stradivarius material of Spruce.

Relative to Ferrite motors and those with more exotic magnets like Neodymium and AlNiCo, what are the technical advantages of the various exotics? If it goes beyond measurable differences, what are the sonic benefits of for example AlNiCo which is popular for single-driver speakers? Could you talk us through your current driver options and how specific technical advances from one to the next telegraph as sonic upgrades?

We have them all: Ferrite, AlNiCo, Neodymium, field coil and hybrid field coil. Why? In the beginning, we simply wanted to show that we can do them all. Later we learnt that Neodymium has very big potential due to its low mass. Ferrite is not strong enough. With a 7mm magnet gap, you cannot go beyond 20'000 Gauss. With AlNiCo, Neodymium and field coils, you can reach 24'000. My favourites are Neodymium and field coil. AlNiCo must be cast like steel and it is very heavy. Some people prefer its sound but I think we can achieve the same with a really good Neodymium motor. Field coils are my favourite but very expensive. And you must use a very good power supply. All the qualities of a field-coil rise or fall with its power supply. Never use a switching power supply. The HEML is our latest idea. This is a mix of field-coil and Neodymium. It is extremely strong. You still cannot exceed 24'000 Gauss but this hybrid motor will drive a 9mm gap. The magnetic strength diminishes as gap height increases. A 9mm gap with an underhung voice coil is perfect for extreme highs when you have a bass stroke in phase. It's the best we've ever done. 

Finally, explain your Acoustic Stealth technology in layman’s terms. What is it; and what does it do?

That is proprietary technology but you're welcome to speculate whilst looking at that Stealth bomber and trying to figure out how its odd shape helps it to be invisible to radar. We use AST for all our cabinetry.