The speaker box plus tuning port CAD files can be downloaded here:
http://files.chumby.com/bunnie/spkrbox.zip
It's included in EASM, IGES, STEP, parasolid and STL formats -- your tool ought to be able to open one of these!
The box's purpose is to set a resonant frequency that extends the bass response of the driver, and to provide some backside acoustic mass at other frequencies. The box is designed to be a helmholtz resonator (the type of resonator you have when you blow across the top of a beer bottle), tuned to, in this case, 140 Hz -- it shoots a little lower than the canonically "perfect" value actually, to create the perception of a bassier speaker. Given a particular volume, you need a certain constant aperture area to length ratio for the tube. So in this case, the volume is 83000 mm^3, which leads to a ratio of 0.54, so roughly speaking the tube is 25 mm long, with a surface area of 13.53 mm^2, or a radius of about 2.1mm (in reality the numbers are slightly tweaked from here to compensate for draft angles, filleting to reduce rasping, and the volume of the tube itself). Going from volume to the ratio is a harder formula, which I don't remember at this time, and I've lost my notes on how I calculated it. It's a small box anyways, which means that second order effects come in to play in a big way so I think the math is overrated anyways; you'll have to tune with a sweep generator and your ears in the final sum of things no matter what you do, but at least you know the general shape of things if you want to tune things up a bit.
Also, note no two sides of the inside of the speaker box are exactly parallel, there's a minimum of 1.5 degree offset on all sides. That's to detune any strong resonant modes that can occur inside the box. I haven't used shapeways for fab, but it's also extremely important that the box be very stiff and entirely airtight. If shapeways is using an extruded 3D printing process, you'll want to lacquer the inside of the box to make it air tight and use hot glue around the seal between the halves and a gasket under the speaker and the box. When you run the numbers you'll find that even a tiny gap or seam can noticeably degrade the speaker's performance. The chumby one's two speaker box halves are ultrasonically welded for a uniform seal, an EVA gasket is used under the speaker, and a low-viscosity glue is used to seal the gap for the speaker wires to keep the box air-tight, except for the tuning port.
7BAA 2E53 01C1 DCFF 497B E7F0 9699 A303 78F0 D9B9
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