Has anyone tried an Icosahedron (20 sided with triangular facets.)

[jgaupel]

I share my ~shop with my brother and he is making these for fun.

https://en.wikipedia.org/wiki/Icosahedron#Convex_regular_icosahedron

What would anyone think the downfalls of using this shape for a cabinet be?
I,m thinking that a four inch bezel, 3 to 3.5 inch cone full range might be fun. To have a facet big enough to mount a four inch the inside edge (using 1/2 inch material) is 8.5 inches giving a volume of 0.7753665740741 cubic feet.
(I love to leave all those digits as if my measuring devices are N.A.S.A approved and calibrated.)

Any thoughts??

Jeremy

 

[rayma]

Design Acoustics D-12 dodecahedron omnidirectional speakers.
Sometimes they were hung from the ceiling.

 

[jgaupel]

Rayma,
I'm less interested in the dodecahedron and I am not going omni. Believe it or not Icosahedron is easier to make. Especially for me as my brother is just knocking them out. Also you have to make them BIG to get a facet that can accept even a smallish driver.

Thanks for replying Rayma.

Jeremy

​

 

[rayma]

Yes, that's the advantage of the duodecahedron. Good luck.

 

[planet10]

I recently brought the icsohedran up in the duodecahedron thread. If the driver fits in the panel it makes more sense to me than the 12 sided polyhedron.

It also allows me to use up more of the 35mm Foster FRs i have.

The sub might by a duodeca… with 8 woofers.

dave

 

[jgaupel]

Dave,
How did you know that I have four Visaton w200s drivers?
I could make two duodecahedron bass bins with Icosahedron FR. up top.

Wow I am realizing that there is a fine line between art decor and 70's disco.

I am going to stick with the FR just for now as I have a feeling that getting the sound out of this will take lots of effort and advice.
This is a shampoo situation. Measure, adjust, and repeat.

Now if anybody can tell me how to hold 20 sides in place for gluing!

Thanks
Jeremy

 

[Johno]

Now if anybody can tell me how to hold 20 sides in place for gluing!

Thanks
Jeremy

Select one of the "points". It has 5 facets that, when joined, have a planar (ie flat) lower edge. The next point around and its 5 facets ditto, and the next 2 sections of 5 facets. These 4 facet sections can thus be assembled with a straight forward flat jig that stops the lower edges sliding outwards. Think of a five sided pyramid. The 4 sections can then be joined and held in place with elastic strapping, carefully.
Each of the joints between each triangular piece should be keyed for stability. The easiest key is a biscuit inserted in a pair of cuts across the joint. About 1/3 and 2/3 along each side. The exposed part of the biscuit can be sanded off when the glue is dry.
Each of the sides of each of the 20 triangular pieces should be beveled inwards to 69 degrees.

 

[jgaupel]

Dave,
Just re read your post and I thought you were suggesting 8 inch woofers. But hey I think a large duodeca would be fun with an 8 inch sub or two.

Also I can't seem to find the duodeca thread?

thanks
Jeremy

 

[jgaupel]

John,

Are you suggesting to put the biscuit across the facet seam? Or along the seam?

thanks
Jeremy

 

[planet10]

https://www.diyaudio.com/community/threads/how-to-build-a-spherical-speaker.374278/

dave

 

[planet10]

... thought you were suggesting 8 inch woofers

Probably the way i worder it.

I plan on using 8x4” woofers pulled from Monsoon multinedia systems.

dave

 

[Johno]

John,

Are you suggesting to put the biscuit across the facet seam? Or along the seam?

thanks
Jeremy

Hi Jeremy,
Yes across the seam. Occasionally you will come across this method in old furniture, easier than dovetails. The biscuits can be in contrasting colour and appear like an inlay.
On reflection, the main challenges will be 1/ accurately cutting each bevel edge and 2/ accurately cutting each slot.
1 - bevels with the router if you can find a 69 degree angle else a wedge at 21 degrees to hold each facet at the right angle in a table saw.
2- I am thinking a table saw with a blade about 3mm wide and cutting multiple pairs of facets held in a jig, or clamped, supporting them cut edge down. Can repeatedly cut 20 at a time to the same, correct depth this way. Then making the biscuits from hardwood stock cut to the required thickness.

Interesting challenge and hope you succeed. In case you are wondering, I am an EE but my Dad was the carpenter and taught me the tricks.

Cheers
John

 

[planet10]

I plan on printing my small one as 2 pieces, drivers mounted from the back, 2 halves bolt together.

dave

 

[jgaupel]

John,
I have put together a table saw sled to cut the slots. Thanks for reminding me of that technique. I have never thought of it as a structural joint only as an esthetic one because at 90 degrees there are far more options for strength. But it is perfect for indexing obtuse angles like this..

Dave,
What dimensions are you thinking for the two shapes?

thanks
Jeremy

 

[planet10]

I haven’t worked it out yet.

dave

 

[jgaupel]

UUUUgggggggg Charlie Brown,
40 triangles to line up!

Just a friendly piece of advice. Even if you are just prototyping, the angles and edge lengths need to be waaaaayyy more accurate than a rectangular structure.

thanks
Jeremy

 

[Johno]

Well done Jeremy, looking good. Be able to call yourself a cabinet maker soon (😉)
Biscuits not needed?
Playing with the idea too, in my head at this point - but thinking a handful of the little TC9 3 inch FR with support from a THAM6 for the really low end for a small room. Very interested to see how your idea behaves.

 

[jgaupel]

John,

This project sis going to run real slow as it is a nightmare assembly. The sides are just to far out. That is why I could not use the biscuits. Each set of faces has to be maneuvered after glue tacks up.

I am also excited to see what this shape has to offer. I am only 35 min from Parts Express so once I get the cabs complete I will start researching what FR might be best suited.

I also had to make a wooden wine bottle out of slats for some instant gratification.

thanks
Jeremy

 

[Johno]

Not good Jeremy, but love the instant gratification. We are in a wine region so a decoration like that would go down well.
I am retired but also get paid to run a Men's Shed (a well provisioned workshop doubling as a space where old farts can get together socially away from the "kitchen"). Not sure if you have anything equivalent over your way.
Anyway it gives me opportunity to play! Thinking I must experiment a little. Like how to get back inside when its finished?, do the rear facing drivers get wired in reverse or is it a bookshelf type with only front facing?, how small can it be made etc? Also clear now that framing jigs are essential

 

[jgaupel]

Just couldn't wait

Random driver from a Panasonic center channel.
Box not sealed. Just threw the driver in and tested. Glue is just barely set.

Jeremy