A definitive formula for Basstrap ?

[zenzei]

Hello everybody thanks for your greeat help, Once I heard there is a formula to build a box of any shape in which the only important thing was air volume, I understand the principles of slat resonators as well as Ethans membrane basstrap, however Ive seen many pictures of nice studios featuring a large U shaped box attached to the ceiling in the back part of the control room, the legs of the "U" run across the upper part of the lateral walls, some times they seem 3 different boxes placed l _ l

Many Walter -Storyk studios or Pilchner Schoustal studios feature these kind of boxes. what are these? decorative? to support lights? Air conditioning ducts ? Bass Traps ?. I ve also seen stuffed cilinders or corner basstraps whith a smaller tube as air entrance , this make me guess there shold be a formula volume/frecuency. please help me.