it's a diy one off project by a friend who asked if I would like to try some hornloudspeakers.The bass-bin is for 400Hz and lower. The mids 400-5k and the highs >5k
The horns were calculated by Kees Soeters himself with a spreadsheet and made with his own DIY cnc machine.
For detailed questions you can email him via his site. Or just ask and I'll see if I know the answer.