Inside Martin Gateley's head.What if any mechanical changes were made to the Enviée widebanders for open-baffle use? What, in general, makes a given driver suitable for OB applications; or not?
These Enviée drivers are different to the ones in the Waves. As they work in free air with little or no back pressure, at higher SPL their cone excursions could get out of hand. To control this, we stiffened the suspension of spider and surround. This however did move up the resonant frequency from 55Hz to ~70Hz. Since we aren't actively driving our 18-incher, Chris insisted on a high Q driver to keep sensitivity as high as possible.

The Libération runs two Enviées side by side bracketing the Raal ribbon rather than being vertically arrayed above and below it. One has a whizzer, the other one doesn't. Please explain the purpose of this layout and why only one carries a bicone. Do both of them cover the same bandwidth? Are they low-pass filtered at the handover to the Raal ribbon but then allowed to run wide open at the woofer? Or are they high-passed as well? If so, are both filtered the same?
With the second prototype, I explored the horizontal versus vertical mid/tweeter/mid config. Whilst vertical sounded perfectly acceptable, I was struck by the panoramic soundstaging and imagery which the horizontal layout exhibited. Particularly on classical music the wider presentation got my vote. It also made perfect sense from a design point of view. Aesthetically the vertical configuration did not look as pleasing. But for me this really was a case of form follows function.

Galm Audio offer three versions of the Enviée, two AlNiCo motor versions with and without bicone and a midbass version with Neo magnet. We tried every which way except for the double bass driver version. That was 10 drivers to find optimum performance. For the Wave 40, we'd already established that the bicone was largely responsible for the forward projection of the sound. That was more or less a given. Using two whizzers per side simply got too hot in the 8-10kHz region. From a system's point of view, two AlNiCos would have been preferable due to the same motor design but the bass version brings extra body and warmth to the upper bass. We had originally planned to run the widebanders in series to keep impedance reasonable but with two different motor systems, we got feedback and intermodulation issues. We had to go parallel. To overcome lower impedance, we then reverted to some voice coil trickery which Armin Galm the driver designer was happy to do.

Keeping to my low-order filter ethos, I was planning to run the widebanders filterless but extensive listening revealed something not quite right. It seemed that the dual mids where fighting each other with an edginess I couldn't live with. Chris investigated. He first thought it to be a baffle mesh resonance but it turned out that the voice coil trickery had introduced a 750Hz blip not present in the 8Ω driver. On standard measurements this did not seem significant but the waterfall plot made it obvious. Now we have a notch filter to correct it. I also realized that whilst the filter sorted out the inter-driver issue, there was a strong case to be made for introducing some quality caps and components. It brings a general feel of sonic calm and sophistication not there before. In researching various filter parts, I came across this statement from Troels Gravesen, a Danish DYI guru and reviewer: "Super caps can almost make the music sound just a little bit better than life by adding a certain sheen, glare, brightness or radiance particularly to HF content. English is not my native tongue and different words may describe the effect better so take your pick. I wouldn't use the word lush. To my way of thinking, 'lush' is more related to 2nd harmonic distortion." I fully agree with this.
• What woofer did you end up with? What kind of filter did that require to integrate seamlessly with the Enviées? Do you perform any low-end response trim or just allow the driver to roll off naturally? What type filter slopes are used?
The 98dB 460mm/18" Beyma 18LX60V2 has no low end trim, it gently rolls in with a 2nd order slope at 200Hz with an additional Zobel filter for phase linearization. The two 210mm/8" Enviées run wide open but with a notch filter at 750Hz. The dipole Raal dipole ribbon comes in at 12kHz with a 2nd order filter.

What are the benefits and disadvantages of not back-loading the Enviée drivers which you previously used with enclosures?
Benefits: More openness, better staging and imagery which clearly are lost by the box. With careful placement, you can also get better vertical staging.  
Disadvantages: A little less of that beautiful midrange warmth and richness we both love with the Waves.

What sonic changes arose with the move from HDF to real wood baffles?
Ah, my cardinal sin. Two main observations on that. Firstly, that projection of sound into the room you described in your Wave 40 review was stronger with the wood. To me it just sounded more alive. And secondly, the absorption of resonances must be superior since it sounds cleaner. This may be partly due to the thicker baffle. Our CDF was 19mm. At 36mm, the Spruce is nearly double but I'm always surprised by how good solid wood is at absorbing and shedding unwanted resonances.

Three augmented Enviée widebanders, three very different executions, one speaker house.

What set you on the course of investigating an open baffle to begin with when you had such good success with the Wave 40 and Skiny 16 tonewood cabinets?
A lot of folks where confused when I first came up with the OB concept in the wake of the Wave 40 and SK16. Looking at our lineup photo above, I can see why. For me, it's simply always been about sonics and aesthetics, in that order. Whilst the Waves can sound magical in the right setup, they, like a lot of widebanders, struggle with large orchestral music like Mahler which I have a weakness for. Something had to be done. You may also recall a brief conversation we had, about me suffering an attack of Grössenwahn [delusions of grandeur] driving back from the 2014 Munich show. It basically came down to doing it bigger and better and moving up the food chain. Before soundkaos came into being, I had cut my teeth on an OB project some years earlier. From the photos it will be painfully obvious that sonics where not my primary concern at the time. Enough said.

I did learn some valuable lessons though, the primary one being that if you want any meaningful bass from a dipole, you must move serious amounts of air. Why not have a couple of full-range drivers in a horizontal d’Appolito arrangement with a dipole ribbon? Seemed obvious to me. It took some time and a few mock-ups before I plucked up the courage to let Chris have a listen. To my surprise he felt that I really had something there! That fast midbass reminded him of a pair of electrostatic speakers from about 15 years ago which he would have loved to have owned. A few prototypes later we had the basics nailed but as I mentioned earlier, the last hurdle is always the hardest. Top and bottom integration was relatively easy but the important midband took a bit of hard work.

In your experience, do the low-impedance Libération want more or less amplifier damping and power than your other models regardless of their higher efficiency?

They do need more power. That's partly down to the 18" woofer. My preferred amp for the Waves remains the Bakoon AMP-12R closely followed by the FirstWatt SIT1. Those will drive the Libération's mids/ribbon very well but can't cope with the bass. I have been doing most my listening with the FirstWatt F5 but in larger rooms I'd need more power. It will be interesting to see what preference you come up with. This is actually the reason I introduced biwiring but it will need careful gain matching.