Author: Kim-Niklas Antin

Introduction

It is striking how often 3D printed speakers take the shape of a sphere and that is also how RD Physics started with the FR1 full-range speaker. What are the benefits of spherical loudspeaker enclosures and why are they so popular?

1. Rigid and void of panel vibrations
2. Minimum material use for a given volume
3. Potentially avoid edge diffraction
4. Omnidirectional up to a relatively high frequency and controlled baffle “step”
5. Aesthetically pleasing with a single circular driver
6. Difficult to manufacture any other way than 3D printing

As RD Physics has extensive experience in these types of enclosures, we have decided to share our learning in one blog post. The models are presented in chronological order allowing the reader to understand the development that took place over the years of building and listening to various versions of the FR. Most of the designs are offered open-source to the community.

FR1 – Full-range bliss in a compact form

The FR1 is a spherical (180 mm diameter) full-range loudspeaker with a sealed enclosure. Internal wall stiffeners are used in order to maximize internal volume as opposed to simply increasing wall thickness, which robs internal volume. We use Noise Killer paint to both seal the enclosure and also to add mass and damping. The sound of the FR1 speakers is very unique and quite tricky to get the most out of. The full-range emitters are very directional and the listening distance also changes the sound markedly.

Model	RD Physics FR1
Driver	Mark Audio Alpair 6M 2.5″
Enclosure	3 liters sealed
Material	UPM Formi3D
Construction	Internal webbing with Noise Killer damping
Tilt	Fixed at 15 degrees

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FR2 – Exotic carbon fiber skin reduces resonances

Additive manufacturing (AM) has many benefits over traditional construction methods, such as design freedom, fast product development, and integration of functions into one part. There are drawbacks as well. The plastic AM parts tend to be low in mass and not very stiff. Air-tight walls are sometimes difficult to achieve, too.  Adding mass by increasing the fill density of the print is not a good solution, since it adds build-time and material cost. Stiffeners and bitumen paint were used in FR1. However, the stiffeners were cumbersome to paint with bitumen and it did not add significant weight. For FR2, we used the vent as a part of the mechanical structure and used a thicker wall. But some additional means were needed to bring 3D printed enclosures on par with traditional cabinet materials.

Carbon fiber in loudspeaker building

Dry carbon fiber tow was wound around the enclosure and then wetted with epoxy resin. The composite skin was sanded after curing and additional coats of epoxy were added. The result is a unique unidirectional carbon fiber surface finish. The composite shell adds mass and stiffness to the enclosure. The loudspeaker sits on four feet printed from TPU material, which allows rotation.

Model	RD Physics FR2
Driver	Mark Audio Alpair 7MS 3″
Enclosure	5 liters vented
Material	UPM Formi3D + CFRP
Construction	Structural port and carbon fiber skin
Tilt	TPU feet allow tilt ~0-15 degrees

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FR3 – Metal-filled filament for mass and rigidity

The FR1 used internal ribbing and Noise Killer paint to reduce enclosure resonance. The FR2 used an external carbon fiber shell. Both approaches were a bit cumbersome and laborious. For the third version, we wanted to fully use the capabilities of 3D-printing. Therefore, a high-density metal-filled filament was used an internal gyroid-shaped support was used even where overhanging surfaces would not have required it. In addition, height and tilt can be adjusted using three threaded rods that form a tripod. The finished enclosure with three 14 mm trapezoid-threaded nuts bonded to it weighs 1.2 kg. The RS100 drivers have a distinct on-axis peak at the upper treble, which actually works nicely for those who like a bright sound. Those who don’t should toe-in the speakers a bit.

Model	RD Physics FR3
Driver	Dayton Audio RS100 4″
Enclosure	2 liters sealed
Material	Colorfabb steel fill
Construction	Gyroid infill as an internal stiffener
Tilt	14 mm leadscrew tripod

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FR4 – Refining the concept further

The metal-filled filament used in the FR3 was too brittle and difficult to post-process. The FR4 uses wood-filled filament, which is more ductile and easier to sand if needed. The surface is quite nice straight out of the printer thanks to the matte surface. A quick touch with an orbital sander gives a smooth finish. Leadscrew nuts are bonded into recesses in the enclosure and allow for adjustment of the legs. Small TPU feet can be printed and placed at the ends of the leadscrews in order to avoid scratching the desktop. These are satellite speakers and need a subwoofer to complement the lower frequency spectrum.

Model	RD Physics FR4
Driver	Tangband W3-1878 3″
Enclosure	1 liter sealed
Material	AddNorth Textura
Construction	Gyroid infill as an internal stiffener
Tilt	12 mm leadscrew tripod

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FR5 – Returning to square one

Reviewing the FR project so far, we came to the conclusion that all things considered, the original FR1 is the DIY project that was the most fun to build and listen to. It’s simple but rewarding once dialed in. For the FR5 we went back to basics by ditching the tripod and returning to a simple white spherical enclosure. The tilt adjustment is handled by a TPU mounting ring that allows a large adjustment range. The Scan Speak 10F driver is one of the best for voice reproduction, but our subjective view is that it needs a tweeter in addition to a subwoofer making it suitable for three-way builds only.

Model	RD Physics FR5
Driver	Scan Speak 10F 3″
Enclosure	2 liters sealed
Material	AddNorth Textura
Construction	Stiffeners and alu-butyl sound-deadening mat
Tilt	TPU ring +-30 degrees

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3D files and components

In the table below you’ll find links to the drivers used in each version as well as the geometry files needed for slicing the toolpaths. Support us by clicking on the Soundimports affiliate links before buying anything from them (we get a small commission and it won’t cost you a dime). Thank you!

Model	Components	3D files
FR1	Alpair6M at Soundimports	FR1 at Thingiverse
FR2	Alpair7MS at Soundimports	FR2 at Thingiverse
FR3	RS100 at Soundimports	FR3 at Thingiverse
FR4	W3-1878 at Soundimports	FR4 at Etsy Shop
FR5	10F at Soundimports	FR5 at Thingiverse

Videos

Acknowledgements

We wish to thank UPM for the Formi3D materials and support. Photos taken by J-P Virtanen and Markus Markkanen. Erell Bodinier handled the carbon fiber skinning.