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KIH #69 – Enter Sandman

  • The speaker builder’s sandbox. How to print a speaker cabinet. Between each other, Ondrej and Martin have many years in Skoda’s R&D department and shorter projects at Aston Martin, McLaren, Honda and Airbus under their belts. This has them fluent in the disciplines of design engineering, prototyping and 3D printing with selective laser sintering, fused deposition modeling and stereolithography. Between their Akemake prototype to Deeptime the Czech design studio and its first commercial project, five years were spent on R&D into acoustics and the hifi industry. This included learning how to print from sand and master so-called binder setting. In general, this type of printing was used for casting molds, not finely finished freestanding objects. Hence Deeptime had to develop their own compound hardener to turn an otherwise fragile silica structure into a strong acoustically inert object.

    Ondrej: “With both of us being design engineers in the automotive industry, we first met at the Auto Design and Styling Conference in 2011. This would eventually lead to Deeptime the design studio. Our first joint project became Spirula. It was birthed in part from my obsession with music and marine biology, fossils, geology, concepts of geological time and other scientific fields that trigger our imagination. Also, there was never enough space to put proper conventional reference speakers on my office desk. I lived in London at the time where spacious rooms are quite unaffordable. With no room for proper monitors, my computer speakers and headphones weren’t up to par. My experience with product development and a degree in computer-aided engineering which means a lot of applied hard math came in handy to look for a more personalized solution.”

    “Martin too was used to working with 3D modeling and printing in his day job. Thus 3D printing became a logical avenue to try and materialize the Spirula concept. Our 2014 Akemake prototype attracted a lot of attention and demand but its FDM technology did not allow us to manufacture wooden Spirula in series. Process reliability, printing time, manufacturing cost and above all sound quality were all far from ideal. We had to look elsewhere for a technology that could generate efficient low-volume production and improved sonics. Around that time we discovered sand printing and began experimenting. This method is mainly used to print molds for the casting industry so the printed form is very fragile and porous. It took us a few years before we perfected hardening the printed product into the silica composite we now use. We had to develop our own compound hardeners to give the material rigidity, durability and perfectly airtight acoustics.”

    “Once we perfected our sand printing, we developed Thunderstone the subwoofer. The process took us through five stages of development to pick the right drivers, design and model the enclosures, prototype then develop the electronics and test everything over and over again. The testing looped us back to the drawing board several times so the final shape and features of the Ionic system resulted from several rounds of iterations, optimizations, tweaks and upgrades.”

    “The goal of our driver research was to identify premium specimens with high power output relative to diameter, the greatest bandwidth and outstanding response characteristics. Spirula wanted a 3″ or 4″ unit loaded into a minimum air volume for a Qtc of 0.707 usually considered the optimum alignment for excellent transient response, low bass performance, high power handling and flattest response. The ideal companion woofer had to hit 40Hz at -3dB. Using three types of professional design software, we benchmarked and verified parameters to calculate a wide variety of cabinet types whilst tracking performance with a cabinet calculator of our own design. We benchmarked over 40 different types of 3″ and 4″ widebanders and over 40 different types of 5″-8″ woofers. We looked for the best combination of sound parameters, cost and availability to end up with our final 3″ Tangband and 5.75″ Wavecor. In Thunderstone, the ports and driver together create the desired response in a 4th-order Chebychev alignment.”

    “Using one of the most advanced CAD programs widely adopted by the automotive and aviation industries allowed us to develop a styled design package and visualization modes to create, modify and validate complex innovative shapes almost on the fly. In the beginning, we designed and developed over 10 different fully parametric CAD subwoofer concepts to evaluate the overall cabinet shape, size, packaging (electronics, drivers, volume knobs) and the possibility of multiple bass ports.”

    “We started rapid prototyping with basic FDM as a 3D printing process which uses a continuous filament of thermoplastic material. The initial speaker and subwoofer prototypes were printed from PLA, ABS or Timberfill mainly to determine appearance and packaging feasibility. Yet the acoustic properties, printing time, cost and quality of these plastic prototypes were not acceptable. This led us to binder jetting, an additive process where a liquid binder is selectively deposited to join sand particles. Layers of material are then bonded to form an object, with the print head strategically dropping binder into the silica and powder. Over the years we tested a wide variety of post-processes for infiltration and coating to harden the brittle raw printed components. Due to the need for deep infiltration, stiffness, absolute air-tightness and the finest surface finish, we decided to collaborate with an established chemical laboratory to develop our own bespoke hardener. This was probably the most difficult part of the process. After years of developing about 100 prototypes, we finally perfected a solution that covers all the requirements: full infiltration, material rigidity, airtightness, cost-effectiveness and outstanding visuals.”

    “For the Thunderstone prototypes, we incorporated basic off-the-shelf electronics at first. Due to their lack of performance, connectivity and packaging issues, we then decided to design and develop our own modular electronics that would work not only for this but also future models. We invested a lot to deliver a solution that covers our requirements and customer expectations. We wanted class D with an extremely low noise level; a control board with integral high-res Bluetooth and automatic signal detection; and highly efficient switch-mode power for low consumption all assembled into one modular ‘hamburger’ mounted beneath the volume knobs which double as passive heat sinks. The electronics use no equalization. The only thing we had to fine-tune was the hardwired 200Hz crossover. Apart from the drivers, all the electronics are sourced and manufactured in the EU with the aim to achieve control over the supply chain and deliver the highest possible quality.”

    “In terms of acoustic testing and validation, we closely cooperated with the acoustic research lab of the Czech Technical University in Prague. Accurate measurements in their anechoic room were fundamental to all our R&D. We also cooperated with our country’s foremost specialist from the hi-fi industry to fine-tune and test our products and gather initial opinions and reviews to push the acoustic performance and design even further.”

    “Trilateral symmetry was a crucial part of Thunderstone’s design. The shape allows for three bass ports and the right amount of space for the ideal diameter and length of the resonant tubes. The flared ports are 1.618″ in diameter. Apart from being suspiciously reminiscent of the golden ratio which is a pure coincidence, it is the smallest possible diameter before unwanted noise would arise from air turbulence. The port tubes are an integral part of the enclosure and wrap inside it alongside the outer shell to double as internal reinforcements. This helps to reduce enclosure resonance for cleaner bass.”

    “Whilst we experimented with wool absorbers inside the tapered Spirula line, we ended up using vatelin absorber tampering. In Thunderstone there’s a sheet of Mylar foil between each PCB, all its capacitors are damped with silicone adhesive and all signal cables are shielded. The electronics packaging is by Petr Sladek, a friend who developed Bluetooth smartwatches years before Apple bowed their first Apple Watch and who works on the development of Tokamak fusion generators. Unlike our clamshell Akemake monitor, for the Ionic system, there is no gluing whatsoever. All three enclosures are printed from one piece respectively. There are no joints or seams, not even with the bass ports. These are all true monolithic structures.”

    “Also, the penetration of our proprietary hardening compound is 100%, not partial to leave a softer core. The final surface isn’t by any means scratch-resistant or unbreakable but not fragile or scratch-prone either. It is sandy, therefore rough like sandpaper. The material is solid and hard enough but you can, of course, ding it with metallic or hard objects like keys. We’ve done drop tests, flinging Spirula prototypes onto different kinds of floors to learn what the material will withstand as it falls from 1.5 meters to carpeted and linoleum floors without any discernible damage. Of course, we kept trying and if you drop the enclosure from that height straight onto a concrete floor a few times, it will obviously break. But should your kid accidentally swipe one off your desk, it’ll be fine.”

    So there you have it. Grab yourself a shovel, head to the nearest beach or builder’s emporium and bring home a few buckets full of sand. Spend 5+ years figuring out how and you’ll have yourself a super-advanced organically curvaceous seamless loudspeaker enclosure. Easy.

    The sandman cometh! So wipe that sleepy sand out of your eyes and get busy…

    Srajan Ebaen

    Written by Srajan Ebaen

    Srajan is the owner and publisher of 6moons. He used to play clarinet at the conservatory. Later he worked in audio retail, then marketing for three different hifi manufacturers. Writing about hifi and music came next, then launching his own mag. Today he lives with his wife Ivette and Nori and Chai the Bengal cats in a very small village on Ireland’s west coast, between the holy mountain Croagh Patrick and the Atlantic ocean of Clew Bay in County Mayo’s Westport area. Srajan derives his income from the ad revenues of 6moons but contributes to Darko.Audio pro bono.

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