Hi, I was thinking about building my own Helmholtz resonator based on the cylindrical model as shown in Everest's MH of Acoustics, but unfortunately he won't give the appropriate formulas for this model. I have ETF and it does the calculations for me, but when I go buy the material, I'd like to have the formulas on my PDA so that I can choose from whatever's available more easily. BTW, I see that many companies offer bass traps as a byproduct of polycylindrical diffusors, and I was wondering if that's a good solution. I already have a primitive-root diffusor on my ceiling that I'm experimenting with, and I wanted to have different toys for different applications for better control, but having stuff in the corners is not a bad idea, so I'm considering it. Thanks for any opinions.