Dear Troels!
 
After >6 weeks of listening and working on room, speaker placement and bass integration I am finally ready to share my experiences with your community! I hope you enjoy the read :-)

Thanks for your work! As you can read below, I am absolutely stoked by the final result!
Getting everything right was a challenge, but also a fun learning experience.
 
Kind regards, George

 
About a year ago I started looking for new speakers, and after 8 months of research I decided on attempting to copy Noam Geller's version of the ATIRI with added bass module. I used CAD to design my own version of the cabinet, and was lucky to find a Makerspace close to my home with access to professional machinery and expert advice throughout the 2 month build process. It was quite a journey, I spent between 200 and 300 hours learning woodworking and building cabinets, but the end result turned out way better than I had hoped. And having Noam's support throughout the process was the icing on the cake. The end result are heavily braced cabinets made from 21mm birch plywood, reinforced with 10mm MDF in the bass section, weighing in at 30kg each. Equipped with the ATIRI drivers, Fusion FA501 amplifier, Faital 10RS430 bass drivers and upgraded crossovers (copper foil MR coil, Cornell Dubilier bypass capacitors across all Caps, and Pathaudio resistors in the critical positions), the total weight of each speaker is around 50kg.
I documented my decision and build process on DIYAudio here:
https://www.diyaudio.com/community/threads/build-thread-troels-gravesen-atiri-plus-was-ellipticor-2f8.433379/
 
Sound:
Speaking of sound, I need to differentiate between the 2-way Atiri, the active bass, and the room integration. Troels' description of the Atiri sound characteristics is spot on, it has clarity, detail, speed and (for the size) very impressive, fast, punchy and textured bass. The soundstage is deep and imaging is sharply defined and stable. It really delivers shock experiences when there's suddenly a sound element so clearly defined in space in front of you! And with all the clarity and detail it still sounds smooth and emotional. Treble was a surprise, super detailed yet smooth, stunning in its ability to deliver texture, and almost never sharp. Overall the Atiri creates a very lively musical image that invites to explore details, texture and nuances from top to bottom, without sounding too analytical.
 
The next big factor is the room influence. Speaker positioning in my room is limited, and after some experiments with mixed results I used a methodical, measurement based approach to dial in speaker positions and toe-in. That improved imaging and made the ideal listening area larger. Placing experimental damping panels on the wall behind the speakers significantly increased microdynamics and detail. But I am well aware that I have more work to do on the room.
 
And finally the elephant in the room - bass support.
Let me say that finding good settings for bass was challenging and at times frustrating. It was a steep learning curve to find settings that improve bass extension, add more body and energy to upper bass and lower midrange, and blend well with the Atiri. I finally settled on a 1st order LP at 70Hz followed by a 2nd order LP at 180Hz.
The second task was finding timing settings for the Faital combining good summation, phase- and impulse response alignment. It was quite a challenge to get this to work with the room instead of against it, and maintain the fabulous resolution and microdynamics of the Atiri.
But the result is really, really nice!
 
Atiri without and with bass support
I think this is the key question - is it worth the significant extra effort and expense of adding the active bass to the Atiri?
Without the bass support, the Atiri creates beautiful music like a bubble in front of me, everything clearly defined with a great balance of precision and emotion. Excellent performance for a 2-way with 6,5" midrange. And did I mention that the bass is astounding?
But adding the bass module changes the energy in the room, and not only with bass heavy music. Bass extension feels powerful, controlled and even, without significantly exciting the room modes. And bass remains really fast, punchy and textured. Organs rumble, Kodo and kettle drums have impact and textured reverb, percussion is snappy and energetic.The soundstage expands but imaging remains in sharp focus. It's like the music bubble expands, instruments and vocals get more body, foundation and energy. Vocals have more expressive power, not just male but also female vocals, they feel more life-like, there's a stronger emotional connection to the music. It's a bit creepy, but very powerful. Listening to good recordings is tremendous fun, and I just want to turn the volume up way higher than with the Atiri alone, it stays clean up to really high SPL and just keeps adding energy. And I find it difficult to stop listening.
Are there any downsides? Yes. Setting up the speaker and dialing in the bass is way harder to get right than with the 2-way Atiri, and with the wrong setup there’s loss of detail, speed and texture, and avoiding excitation of room modes is the other challenge. Oh – and building a pyramid cabinet with angled sides all around is quite a challenge too!
But to summarize, I am SUPER happy with this speaker. It's been very challenging and rewarding to build, I love the looks, Troels' Atiri 2-way is a phenomenal speaker, and adding the sealed bass module (and dialing it in) just takes it to another level, delivering "High-End Audio Show" sound in my home.
Thank you Troels and thank you Noam!