My isobooth.
I was curious about how much and how well ”open sided polydiffusers” work. Inspired by
Yannick´s thread Polycylindrical diffusers offer useful LF absorbtion. So before I start to take care of the axial and tangential room modes I made some Polys.

Aprox dimensions 3,25 x 2,55 (8,3m2), pentagonic shape. Height 2,23 meter.
4 small ”open sided polysorbers” filled with Knauf Lambda 39 + 1 slotted panel.

For the measurement pictures please open the PDF, couldn't insert them here.

A couple of questions. First I thought of using VPR:s for the axial mode but then I thought of using convex plywood membranes, because I prefer reflections spread into different directions. But how do I calculate the resonant frequency on a convex cavity? I think Avare wrote somewhere that I can take the middle value. I e max depth 13 cm, lowest depth 9 cm. Calculate on 11 cm. Does it work?

After I have tamed the LF I plan to use som more diffusion for the higher frequencies, I don´t want to deaden the room. I have to add some insulation for better sound transmission loss. I thought of covering the insulation with ”half cupoles” but they are too expensive. I also thought about 2d QRD but I think they smear the phase. I think a good compromise would be something like these? What is Your experience with these kind of diffusers? See PDF for picture.

Finally I add 2 audio clips where You can compare the sound before and after this simple treatment.