Instructables
Picture of A Dodecahedron Speaker for Desktop Printers
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At normal listening distances, an array of twelve speakers arranged on the faces of a dodecahedron is a very good approximation of a point sound source, and the sound waves it produces are very close to perfectly spherical.  A dodecahedron speaker can be a useful tool in acoustics research, and is definitely a fun toy to pull out at parties.  They are available commercially, but very expensive.  Some people build their own, but the odd compound angles and the high degree of accuracy and precision required in the parts make for challenging work with manual tools.  But it's easy for a 3D printer. 

If you have a RepRap, MakerBot, Up!, MakerGear, Ultimaker, or other suitable fused-filament printer, you can print and build this speaker for just under $100 in parts and materials.  That includes speakers, hardware, wires, cable, plastic filament--everything.  
 
The high symmetry of the dodecahedron is amenable to a modular design, and this one consists of four basic parts: the face modules, the vertex plugs, the edge gaskets, and the bezels.  (NOTE: These models are also available on Thingiverse.)  The speaker grilles are made from hardware store window screen cloth installed in the bezels using rubber spline and a screen roller tool, just like a residential window screen.  

The assembled speaker array weighs 5.6 lbs, not counting the cable, and measures 7.5" across, from face to face, and 8.6" from point to point. The speakers are wired in a hybrid series-parallel circuit that brings the total array impedance to about 10 ohms (again not counting the cable) which should be a comfortable load for most amplifiers.

Non-printed parts ("vitamins")

12 pcs × speaker, square, ferrite 3", 8 Ohm, 3W, Jameco SP83W
10 ft × instrument patch cable, 18 AWG leads, such as Conquest Sound CS118
30 pcs × sex bolt (hehehe), combo truss head, zinc plated, 3/16" barrel, #6-32 × 3/8", Bolt Depot 14285
30 pcs × machine screw, combo truss head, zinc plated, #6-32 × 1/2", Bolt Depot 2887
60 pcs × split washer, #10, zinc plated, Bolt Depot 3023
108 pcs × wood screw, #4 × 1/4", black oxide or finish of your choice, such as McFeely's 0402-PSK
13 ft  × screen spline, vinyl serrated, 1/8", black or color of your choice, such as Home Depot 3028737
3 sq ft × window screen, black or color of your choice, such as Home Depot 3003947
36 in × hook-up wire, stranded, 18AWG, white or color of your choice, such as NTE
18 in × hook-up wire, stranded, 18AWG, red or color of your choice, such as NTE
2 pcs × craft foam, adhesive-backed, 8.5 × 5.5" sheet, black or color of your choice, such as Fibre Craft
2 pcs × wire nut, orange, such as Ideal 73B
1 cu ft × glass wool, such as Owens Corning PINK
6 in × electrical tape

Tools

3D printer -  I use and enthusiastically recommend the MakerGear Mosaic M1, but any RepRap-type fused-filament printer should work so long as it has a build volume of at least 122 × 122 × 14 mm.   Mine is equipped with a 0.35 mm extruder nozzle and a heated build platform.  I print onto a 1/8" aluminum plate covered in painter's masking tape.  To make models (CAD), I use Google SketchUp Version 8 with D. Bur's su2stl plugin for STL import / export functions.  To convert STL models to G-code machine instructions (CAM), I use Alessandro Ranellucci's Slic3r (v 0.7.1).  To actually control the printer (client), I use kliment's Printrun.  All of this is free software.  

2D printer (laser or inkjet)
Multimeter & leads
Soldering iron
Small butane torch, such as Bonjour Chef's Torch (optional, for flame-polishing)
Wire strippers
Hole punch, 4.5 mm, such as Harbor Freight #97715 (optional, for punching holes in gaskets)
Scissors
Spring steel shim, such as iSesamo (optional, but handy for removing parts from build platform)
Hex driver with basic bit set
#0 square drive hex bit (required for McFeely's wood screws)
Additional Phillips-head screwdriver (you will need two screwdrivers for tightening sex bolts)
Needle nose pliers
Hobby knife
Wire cutters
Tweezers
Screen roller tool (such as Prime-Line #P 7503)
Sharpie permanent marker
1/8" metal rod, 6+ inches (optional, for holding plugs during flame-polishing)
Long-sleeved shirt (for handling glass wool)
Latex, nitrile, or other protective gloves (for handling glass wool)

Consumables

Plastic filament - My extruder takes 1.75 mm diameter filament, and I prefer to print in polylactic acid (PLA).  Using my CAM settings, you will need 185 meters of filament which, at typical densities for 1.75 mm PLA, should weigh about 560 g.  So a 1 kg spool should be plenty, if you only want to print in one color.  If you're printing in multiple colors, you will need about 150 m / 450 g of filament to print the modules, 33 m / 100 g to print the bezels, and 3 m / 10 g to print the plugs.   None of these filament estimates includes an allowance for misprints or other losses, and in my experience you will probably want to add about 10% to account for these.  All my filament came from MakerGear.

1 pc × printable paper label, adhesive back, 8.5 × 11", 2 × half-page label each, such as Avery 8126
8 in × solder, 60/40 rosin core, such as Alpha Metals 13460
35 ft × painter's masking tape, 1.5", to cover build platform
 
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jlandreth12 months ago
Did you know that your project is in the unofficial android magazine this month... They did a feature on 3d printing and your project was one of them!!!
dgateley2 years ago
What do you think of the sound? I've read conflicting opinions on point sources.

For your next effort, you could get vastly improved high frequency performance (dispersion as well as reach) by scaling up a bit and placing mountings at the vertices for small tweeters.

Great work! For 40 years I've contemplated this design but was daunted by the fabrication details.

Should you get that far I have a lot of experience with time domain sound compensation via DSP and would be interested in applying it to your device to idealize its frequency response. I do believe, however, that the inclusion of tweeters at the vertices will be absolutely necessary since the HF lobes from just 12 faces will leave deep holes in the polar response pattern.
What I meant by "scaling up a bit and placing mountings at the vertices for small tweeters" I meant use an Icosidodecahedron

http://en.wikipedia.org/wiki/Icosadodecahedron

and place small tweeters in/on the added equilateral triangles.
60cyclehum (author)  dgateley2 years ago
I have at least one more prototype in mind that will have larger icosadodecahedral faces positioned at the dodecahedral vertices. In the next model, I want the vertex ports to be at least slightly larger, so that they can accomodate short threaded 1/8" lamp pipe nipples. This would allow for more overhead mounting options--using, say, swag lamp hardware--as well as making it easier to mount the speaker from below on, say, a movable tripod or other stand.
staida 60cyclehum3 months ago

The stand should be a ported 10" downfiring sub in a nice enclosure. Then the dodec (or other config) speaker would rise up from it on a stalk rather than hanging. Place your crossover and other electronics (even pre-amp so you can change your wiring without affecting overall impedance) in the sub enclosure portion.

2 of these outdoors and you're set for the block party.

Probably easier to use drivers with concentric HF units.

R.
60cyclehum (author)  dgateley2 years ago
It sounds great! The bass response is limited by the size of the speakers, but I knew that going in. And the designed-for quality, the omnidirectionality, works as advertised to the best of my ability to hear it. I really do need to figure out some kind of proper sound-level mapping procedure to see if I can test it more scientifically.
You could use some coaxial, or triaxial speakers?
rbuesst6 months ago

The speakers themselves don't seem to be available at Jameco anymore. Does anyone know where I can get something of the same size/shape and power rating?

klubow10 months ago
Whats the resistance of the whole set of speakers?
They are in parallel or some combination to get 4 or 8 Ohms ?
how much would it be to buy one?
fretted1 year ago
On the orange pieces that hold the speakers what is the angle on each of the five edges ?

The reason i ask is i'd like to try and build one of these from some scrap oak i have !

Great Ible this is some awesome work ! bet it sounds great too !
If my math is right, it should be 58.285 degrees
I came up with 58.280 * for some reason but i'm trying to play with it in google sketchup so it may be a bit off
Thanks I'm going to try and cut these out of hardwoods I think a nice oak or some walnut would be nice i think i have some hickory in the shop just might be the thing 58.285* is exactly it great math ! i may have to start working on a jig for my table saw this is going to be tricky to cut ...

Thanks again ...
hertzgamma1 year ago
Amazing!

I wish I had a 3d printer ....

I'm wondering how the whole thing sounds?
AnJo8881 year ago
Really beautiful. Congrats.
captcol2 years ago
Can I ask why you have each "pod" wired I series then running them in parrallel? I have only every used speakers in parrallel. From an electronic point of view (with my limited knowledge of electronics and audio) I can see no issue with using series but from an audio point of view it doesn't quite ring true (pun kind of intended)
kai.h captcol2 years ago
You need to take into account the impedance of the speakers.

Wiring two speakers (say 8Ω each) in parallel will present a 4Ω impedance to the amplifier. All other things being equal, this will play louder, and draw more current to an 8Ω speaker.

Most amplifiers are rated for 8Ω speaker loads (note too that this is not the straight up resistance, but the impedance, which is different and depends on the frequency)

By wiring two 8Ω speakers in series, you get a 16Ω load presented to the amp.

By carefully wiring in series and in parallel, you can present a reasonable load to the amplifier. If the impedance is too low, the amp will distort and/or blow up. If the load is too high, it will be very quiet.
And in this case, each pod will have 32 Ohms of impedance in series, with three in parallel, that leaves roughly 10 ohms of equivalent impedance when all is said and done.

(4x8=32)
((1/32+1/32+1/32)^-1) = 10.666......)

Most amplifiers will state what ranges of resistances they support (e.g 8 ohms - 16 ohms, or 4 ohms - 8 ohms).  Going over or under those ratings will result in what you said in your last sentence.
knamey-11 year ago
this.is.so.sick.

i don't even......

good job-good job
TRANSLTR1 year ago
It's a privelidge just being a member of this site. What a fabulous Instructable.
luis23061 year ago
I have a replicator g, and the faces and bezels are a little too big for my printer. someone could explain me how to divide the models to print them by parts???
luis23061 year ago
I have a replicator g, and the faces and bezels are a little too big for my printer. someone could explain me how to divide the models to print them by parts???
luis23061 year ago
I have a replicator G, but the faces and bezel are a little too big for my printer. Can someone explain me how to divide the models, to print them by parts ???
looks great, yea, i like how you made those grills, i'm going to remember that.
danzo3212 years ago
Amazing, I guess. You have a 3D printer on your desktop?
If all those little woofers pull inward at the same instant, and push out likewise, the air in the sealed chamber will act as a spring that keeps each unit from full movement.
60cyclehum (author)  danzo3212 years ago
The vertex plugs can be removed, I should point out, to port the enclosure. I have not experimented with this yet, but mean to. My next prototype will have larger vertex openings, for a couple of reasons, one of which is that they will allow for better porting.
I doubt that the enclosure is air-tight enough for the effect to be all that noticable.

I recently just upgraded my setup to the dodecaquadraphonic sound! It is amazing, and I feel that it is the sound for me.
bboyes2 years ago
Wow, I am really impressed by this. What a cool use of 3D printers and open source software. I have similar questions about when a sound source like this would be a good choice. It also seems like a lot of thought went into the design. Plus, it looks awesome. Thanks for posting this!
60cyclehum (author)  bboyes2 years ago
Thank you very much. This is not, I should point out, really a piece of equipment intended for hi-fidelity "entertainment" audio (though commercial dodecs are often marketed that way). A dodec is good for outdoors, where there are no walls, or for exciting an entire room for acoustic mapping.
Voyager032 years ago
Victor Papanek would be proud!

Terrific to see 40 year-old ideas coming to life.
60cyclehum (author)  Voyager032 years ago
Yes, Nomadic Furniture is exactly the inspiration for this idea. I've been obsessing about how to make one of these since I first read it more than a decade ago. When I finally got my MakerGear Mosaic, I realized this was the tool that could make it happen.
djsc Voyager032 years ago
I have that book too, fantastic.
leschwartz2 years ago
Very interesting project.

I do not have all of the software you mention installed and I do not have a 3D printer, which I am sure would make your work offered here much easier to re-create.

I down loaded / installed Autodesk 123D, which is able to load some of your files.

However of course there is a learning curve to the program.

To get to my point finally, do you have a dimensional drawing of these parts, particularly the "face" parts?

Then I will not have to spend weeks dealing with the software since at the moment I am not contemplating getting a 3D printer.

Thanks again sincerely for this project information.
60cyclehum (author)  leschwartz2 years ago
I'm sorry, I don't. If you can learn to use Google Sketchup, you should be able to import the STL files either from the 123D gallery or from Thingiverse, and extract dimensions that way. Working in SketchUp, for instance, is more like constructing with a compass and ruler than it is like designing with traditional mechanical drawings. I don't know many of the dimensions or angles at all, and never had to, because the software figured it out for me as I went.
Just looking this up to work out the basic angles and relationships myself, from the wikipedia;

http://en.wikipedia.org/wiki/Pentagon
In a regular pentagon, all sides are equal in length and each interior angle is 108°

http://en.wikipedia.org/wiki/Dodecahedron
The dihedral angle of a dodecahedron is 2 arctan(φ) or approximately 116.5650512 degrees

Therefore the angle of the surface undercut for each edge is 58.2825256 degrees,

I presume.
edmondson692 years ago
I am very impressed with your design and would like to purchase a copy. Would you consider selling a kit without the speakers and if so how much?
60cyclehum (author)  edmondson692 years ago
Thanks. I have been thinking about it, actually. I will let you know if I go ahead with that plan.
grepper2 years ago
Really cool project... Great work!
The Johnny Cash artwork caught my eye as well. Can you tell me where can I get one?
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