Focal Point, very cool idea, with the focal point you may need to play with the mounting. 
maybe make the cone clip on as to have the ability to clip on larger "ears" for ability to capture audio at a much larger directional distance. This would be good for wildlife or spying purposes 
or make a capture cone for an external microphone that plugs into the jack, This would drastically improve the ability to capture the audio as you would be able to utilize the entire shape
I started out with a version with a clip on "ear", but this took up more space, blocking the top button, so I decided to stick to the fixed setup. Wil try to make a more horn like shape...
maybe a large half sphere/ellipse where the camera mounts in the focal point would be cumbersome but it would function
I could try something like this but it would be very fragile.... think i'll give up on the idea and go look for some "real" external microphones ....
It should still give improved function if you just make a 1/4 sphere on top. It will be an improvement either way, Try some sound tests?
ok, I'll give it another go.... printing right now....
That looks like a possible winner
Bad news :(
Nice print, nice design, bad functionality..... tested it by talking and walking around it, the sound from the back seems just as loud as sound from the front.
I'll have a look at external mic's. At least the good thing is I now have a good model of a perfectly fitting "frame" if I want to design one later for mounting an external mic...
Maybe as a last try I need to test it out in the open... as the sound is really dampend when you put a finger on the mic holes.... so theoretically it should have some effect...
It should have a benefit but not one you would notice in a closed room. Try outside where sound cannot reflect off the walls
Set up a tripod. Go a set distance away and play a recorded sound at a set volume. Repeat with and without.
Wil do at test somewhere outdoor ... later ....
Tried it again outdoors, there is an effect but I find it rather minimal.
If you want to try for yourself i've just uploaded the file;
https://www.youmagine.com/designs/audio-frame-for-gopro-3
Maybe attach some foam rubber to the backside of your dome? Since it's so small of an area, if sound hits that plastic from the back, it could be resonating the entire dome, which then directs the sound down into the mic because of its shape. Maybe 1/2" to 1" thick might deaden anything from that side.
If that does have an effect, then maybe printing your reflector in something softer, like soft pla, would also work better? If it does, then try making the dome thicker, say 1/4"~1/2" with maybe 25% infill. A solid object will pass sound better than one with an air cavity.
First of all you need to model a parabolic curve where the focal point is just inside the mic. Not a sphere. Not an ellipse. A parabola with the axis of the parabola facing towards where the sound is coming from.
Second of all I'm not sure how well this will work at typical audio frequencies. The wavelength of middle A is 440 Hz and where sound is about 300 meters per second 300/440 is (very roughly) a meter in wavelength. I'm not sure if such a tiny parabola has much effect. Of course if you go up to 10KHz (almost 5 octaves higher on the piano! Well that's above all the notes on a piano but still can hear it) I would expect a huge improvement. But again if you get the shape of the parabola wrong by even just 3mm here and there it won't work at all. In other words a sphere shaped surface won't work any better than a cube shaped.
Try tones from your watch and line them up exactly with the axis of the parabola - at least 20 feet in front of the camera. Very high pitches.
Most parabolic microphones are seen at sports events and are at least a half meter in diameter.
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Dim3nsioneer 557
You have to change the shape of the ear in such a way that reflected sound waves are directed into the mic. With the present shape you somehow concentrate the sound in the center of the hollow sphere.
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