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
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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Signing UpStep 1: Prep the cable
One end of your cable will connect to your amplifier or other audio source, and depending on that source, you may want to leave the 1/4" phono plug as is, remove it, or replace it with some other type of connector. The other end of your cable connects to the speaker and will need to have the plug removed and the cable leads exposed.
The easiest way to remove the plug is to just cut it off a short distance behind the ferrule with a pair of sharp scissors. Toss it in your spares box and desolder the inch or so of attached cable when and if you use it, later. If the waste bothers you, of course, you can go ahead and unscrew the ferrule, cut away the heat shrink tubing, and desolder the connections now.
Once the plug is gone, slit the rubber cable sheath with a hobby knife for an inch or so at the end. Try to cut between the wires, but don't worry too much if you nick one. Once it's cut, grab the two halves of the split sheath and "banana peel" it back three inches, or so, exposing as much of the wire pair as you need. If you nicked the wires while cutting through the sheath, snip the ends off far enough back to remove the damaged part(s). Once you've got two inches of good wire pair exposed, trim away the excess sheath bits.
Tie a strain-relief knot in the cable another two inches back, or so. This knot, which is much too wide to pass through the narrow opening where the cable will exit the cabinet, will bear the weight of the hanging speaker.
Finally, strip about 3/4" of the insulation from each of the wires, exposing the copper strands.
The easiest way to remove the plug is to just cut it off a short distance behind the ferrule with a pair of sharp scissors. Toss it in your spares box and desolder the inch or so of attached cable when and if you use it, later. If the waste bothers you, of course, you can go ahead and unscrew the ferrule, cut away the heat shrink tubing, and desolder the connections now.
Once the plug is gone, slit the rubber cable sheath with a hobby knife for an inch or so at the end. Try to cut between the wires, but don't worry too much if you nick one. Once it's cut, grab the two halves of the split sheath and "banana peel" it back three inches, or so, exposing as much of the wire pair as you need. If you nicked the wires while cutting through the sheath, snip the ends off far enough back to remove the damaged part(s). Once you've got two inches of good wire pair exposed, trim away the excess sheath bits.
Tie a strain-relief knot in the cable another two inches back, or so. This knot, which is much too wide to pass through the narrow opening where the cable will exit the cabinet, will bear the weight of the hanging speaker.
Finally, strip about 3/4" of the insulation from each of the wires, exposing the copper strands.
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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 !
Thanks again ...
I wish I had a 3d printer ....
I'm wondering how the whole thing sounds?
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.
(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.
i don't even......
good job-good job
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.
I recently just upgraded my setup to the dodecaquadraphonic sound! It is amazing, and I feel that it is the sound for me.
Terrific to see 40 year-old ideas coming to life.
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.
http://en.wikipedia.org/wiki/Icosadodecahedron
and place small tweeters in/on the added equilateral triangles.
R.
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.
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(Ï) or approximately 116.5650512 degrees
Therefore the angle of the surface undercut for each edge is 58.2825256 degrees,
I presume.
The Johnny Cash artwork caught my eye as well. Can you tell me where can I get one?
http://www.graffitiwestern.com/
The prototype was commission by Tower Records in Austin, TX, and is still visible on what used to be their building:
http://www.flickr.com/photos/saintmurse/61605085/
Dunno if he still has the stencil or is spraying new ones, or not.