Our previous subwoofer, the SW1, is a 13 liter subwoofer with a 6.5″ driver, a matching passive radiator and a plate amp. We wanted to develop something smaller that would still offer the bass extension that satellite speakers so badly need. The result is the SW2 using a 5″ long-throw driver and the same passive radiatior as in the SW1. The enclosure is now only 5 liters and much easier to place on the desktop. The passive resonator allows tuning the resonance frequency to match room modes, for example. The spherical shape is optimal for material use and stiffness. Combined with the small diameter driver with large surrounds, the appearance is quite unique. If a traditional box is what you want, then this build is not for you.
The measured resonance frequency of the passive radiator indicates that some air-coupling occurs. Simulated resonance frequency matches the measured value (53 Hz) when 16 grams of added mass is used. Mass can be further added using washers to avoid room modes. Practical lower roll-off frequency is 50 Hz. The Arylic amplifier offers DSP capabilites and using a computer as the source allows unlimited DSP with zero cost. Therefore, frequency response in not that meaningful especially when considering the room effects, but we have included some measurements to give an idea of the natural response especially around the knee.
The enclosure is printed in one part (234 mm diameter) and takes approximately 1.5 kg of filament. Print time is about 48 hours. The mass can be increased by lining the walls with sound deadening mat. Although the external wall is spherical, there is a cylindrical inside wall that braces the woofer with the resonator and, thanks to single curvature surface, allows easy placement of thick sound deadening mat. The drivers are fastened using 4.2 mm wood screws and there is a geometry file for a gasket for the woofer which can be printed from TPU. Traditional gasketing methods will work obviously, too. The binding posts are recessed deep into the enclosure and only accept banana plugs in that configuration. An O-ring under the binding post washer is recommended and there is a chamfer for it. Wood-filled prints can easily be sanded for a smoother finish. The photos show 15 minutes worth of post-processing making this a very easy and fast build without compromising in function and looks.
The subwoofer was compared to the much larger, THX certified Logitech Z623 subwoofer. The sound is very similar, but in a much smaller package. The SW2 is a great companion for small satellite speakers and brings fullness to the bass. Electronic music will benefit from the “boom” offered by this small unit, while other types of music may require turning down the level a bit for a tighter bass.
Links and video
The 3D files can be found in Etsy store:
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