I am trying to find the right info for the horn geometry, as this project is the coolest I have seen since quite a while. Not sure if I find the right source, but here is an interesting page with a very concise explanation why this project makes absolute sense: http://invalid.ed.unit.no/~dunker/why.html

There is one thing, though, that needs some looking into at a later point in time, and that is the low frequencies of the sound, which tend to be underrepresented in horn-shaped loudspeakers in general. My 'toilets' make up for this with an active subwoofer part.