Thank you. There exists another Video with a view inside. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-e-HErWL4Qsg.html A short explaination: The four little vents blow air in the box, the big in the middle sucks it out. Therefore i drilled holes in the box under the vents. There are two effects. First the resonance of the different blowers that changes depending on the turnung speed. Second is the sound of the air flowing through the holes, a little bit like white noise. The mix makes the sound and that's the reason for my upgrade. The first try didn't make the sounds that i expected.
