Viper's general concept of a compact 2-way with sidefiring passive bass radiators enjoys a current surge. The Radiant Acoustics Clarity 4.2 and 6.2 from Denmark embrace it as shown. So do the German Wolf von Langa Serendipitiy+ and Joachim Gerhard Surveyor. The first three change Greg's dipole for a monopole AMT, the fourth for a monopole ribbon. The Chesky Audio LC1 from the US does a classic soft dome. Buchardt's E50 from Denmark relocates its passive radiators to the rear then wave-guides its dome tweeter. So do Acoustic Science Lab from South Korea and Amphion's Argon 3X from Finland. GoldenEar's American BRX and Aon 3 put two radiators on opposing cheeks again.
Regardless, loading up cone surface with auxiliary radiators whilst replacing the ubiquitous port and cramming the lot into the tidiest possible cab is becoming more popular around the globe. Now Poland marks its spot with currently the only dipole AMT and 3D-printed cabinet of my bunch. There likely are more which fit this general niche but to my knowledge, Viper's particular execution is unique. Given how overcrowded the 2-way monitor speaker segment is, unique is hard to do. It makes Viper just a bit of a VIP; a very interesting proposition.
"For many years I've wanted to build a small bookshelf speaker mainly for desktop use. I spend a lot of time at my desk and not listening to music at its best while working feels like a missed opportunity. As you know, I'm a widebander fan. I grew up with small bookshelf speakers using 4" full-range drivers so naturally that's where I started. After trying nearly every promising off-the-shelf 3–5" widebander, I found that while they offer a lot of fun and musicality, they just don't deliver the sound I need. Then a few years ago I discovered Mundorf's AMT tweeter which we now use in the Qualio IQ. It quickly became my all-time favourite tweeter and I think it's yours too [correct – Ed.¹]. So the goal became to find a bass driver that behaves like a widebander with an amazing midrange, capable of a high crossover point and deep bass all in a cabinet of ~7 litres.
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¹ It's why I secretly rooted for Viper to use the AMT over a broader bandwidth than just the top octave. "This crossover point needs to be lower. I still need to calculate the final choice but at the moment it's ~5-6kHz with 2nd-order filters on either end." The performance graph below the break shows why. At 4kHz, the response begins to rise so needs to be welcomed with an inverse roll-in.
"That's when I found this Dayton Epique E150HE-44, a dual voice-coil 15cm driver with carbon-fibre cone that reaches to 10kHz, has a beautiful midrange, low distortion and most importantly, is a subwoofer in disguise. With huge 14mm stroke, in my small box it goes well below 40Hz. The only trade-off is efficiency but I was instantly hooked. I love this driver."
Dayton's response graph for their driver.
"Did I mention the amazing midrange and killer off-axis response? It's seriously impressive. Dayton also offer passive radiators with matching carbon-fibre cones. For my needs of big sound from a small box, their two 150mm radiators weren't quite enough so I use two 180mm ones which are technically made for the Epique's bigger brother but do the job beautifully here." This exceeds the base recommendation whereby passive radiators should be able to displace twice the air volume as the active driver/s they augment. Not only does Greg use two passives to double his throw, he also uses larger diameters for more cone surface. In the bass, his three drivers combine to the area of one 11½" woofer.
"So the drivers were locked in a while ago but I didn't yet have a cabinet I liked. I didn't want to make yet another MDF box. Plus with the pressure a big-stroke 15cm/6" driver creates in a small box, you need thick walls and heavy bracing. Those eat up internal volume and make the whole thing less compact. Then earlier this year I started to experiment with 3D printing. That's when I knew I'd found the solution. I ran through loads of ideas: hollow walls filled with resin; composite materials; mineral or stainless steel inserts – you name it. Some of them worked pretty well but all were complicated to execute and still didn't hit the sweet spot.
"Then I realized that it's 3D printed so why not work in actual 3D? It's how the pyramid structure was born outside and in. It makes the cabinet incredibly rigid. I chose PET-G² for the print material because it allows for high-speed printing at around 300mm/s (though one cabinet still takes over 120 hours to print!), has excellent internal damping and is UV resistant. The pyramid wall structure has an effective wall thickness of 10mm and thanks to its geometry, measures about 15mm from the inner wall to the peak but occupies no more volume than a standard 10mm flat wall. The result? Absolutely awesome."
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² From Acme Plastics: "Polyethylene terephthalate glycol is a thermoplastic polyester with significant chemical resistance, durability and excellent formability. PET-G easily vacuum- or pressure-forms as well as heat-bends thanks to low forming temperatures. This makes it exceptionally popular for consumer and commercial apps that involve 3D printing or other heat-forming fabrication techniques. PET-G is also well-suited for die-cutting, routing or bending. PET-G is strong and cost-effective compared to acrylic or polycarbonate. Its unique characteristics make it preferable for impact-resistant glazing and high-strength display units. In general PET-G is a food-safe plastic commonly used for food containers and beverage bottles. Like acrylic and many other thermoplastics, PET-G is fully recyclable. It is thermo- and vacuum-formable and tolerates tremendous pressure without cracking. Although PET-G is naturally clear, it easily takes colour during processing. It can be injection moulded into a variety of shapes or extruded into sheets. Its damage resistance is far higher than that of acrylic to rival polycarbonate's impact resistance. However, PET-G fabricates readily, making it an easy material for practitioners and professional fabricators alike."
