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A Dodecahedron Speaker: September 2014

Ever since I studied acoustics at uni I have wanted a dodecahedron speaker - not to use as an omnidirectional sound source which is what engineers use them for - but because they look bloody awesome, and I was really curious to hear what they sound like...
So one night a few months back I finally decided I was going to make one. The first thing I did was mock up what I wanted in CAD, it is about here I figured that the 12 pentagon faces were not going to be that easy to make.. The trick is the 58.28252558 degree bevel (ok we probably don't need all those decimal places)..

An Omnidirectional Point Sorce

omni cad angle

So I started talking to some of my suppliers at work, I was looking at rapid prototyping, cncing, laser cutting... Or anything that would not cost me an arm and a leg. Just about when I was starting to think it was all too hard I got a text from my Dad who is pretty clever with the circular saw, apparently he woke up one night and figured he could make that!

Some Precision Circular Saw Work

omni taped up

For the next couple of weeks, my weekend distraction became my Dads weekend distraction and I got the updates as he glued and painted the dodecahedron.

Taking Shape

omni glued
omni paint

After a couple of coats of gloss black paint the box was complete - Thanks Dad! - now I had the dodecahedron it was time to install the drivers and build a frame to hold it. The drivers I went with were the 3.5" 8Ohm Tectonic BMR drivers. I am in no way an audiophille so I am not sure how you are ment to describe the sound of a speaker, but these little drivers sound great! Nice high notes and plenty of bass for such a tiny driver

I wired up the 12, 8 Ohm drivers to give me a single 10.67 Ohm speaker. Deciding how to make the frame was not entirely trivial, the speaker weighs about 15kg and it has drivers on every side. I ended up going with galv pipe and fittings from the hardware shop and some heavy duty speaker cable to hang it from, all I needed to do was to clean up the pipe with turps and give it a couple of coats of paint.

Wire It Up

wiring

Lick of Paint

painting the frame

Looking... Unique..

finished

finished

I love the sound from this thing, because the speaker is completely ballanced and because it is isolated from any objects it actually doesn't produce any unwanted vibrations. It is still capable of producing plenty off nice punchy bass, just without the floor shaking or that horrible farting noise from sub woofer ports.


Some Boring Rectangular Speakers

I wasn't sitting on my hands while my Dad was slaving away over MDF pentagons, I decided to build some more traditional rectangular speaker boxes to try out the 12 drivers I had sitting on my desk. I have done some reading up about speaker enclosure design, and eventually I do want to try and do it properly. For my first enclosures though I just screwed together some pine rectangles and cut some holes in them, I did manage to make them look pretty shmick with some veneer and a coat of varnish.
A couple of lengths of 190x19 pine, a cheap 90mm hole saw and a pack of screws and there we have it.

A Bit Rough

pine rectangle

Now I definitely didn't have anything to write home about just yet, so I decided to have a go at applying a nice jarrah veneer. I got my veneer online from Top Veneer Supplies I found some 0.6mm thick jarrah that I though would work just right.
The guys at Top Veneer suggest the hide glue method - I'll try it next time - but this time I decided use PVA and an iron instead.

A Healthy Coat of Glue

glue
glue

I didn't take any photos as I went this time but the process is easy enough, and with the PVA glue it is so forgiving bacause you can always just use an iron to re-melt the glue and press out any bubbles.
I am actually pretty happy with the finished product, I did make a bit of a mess on a couple of the edges when trying to trim the veneer with a knife. I found that using a file gave me the best results, and I just filled in the gaps with some wax filler sticks after varnishing.

Getting There

veneer

Local Magpies Will Varnish Speakers for Bread

veneer

Not to Shabby

veneer

Summing Up

Maybe I just don't know good speakers, but dispite the fact that I have probably broken every rule in the speaker building book I am really happy with both my dodecahedron and the boring rectangles. They sound brilliant driven from my little Dayton Audio DTA-120 amp, even driving them loud enough to be uncomfortable they sound solid.
Now I am curious to see what I can make if I actually ready the speaker building book...