Correct, click the Voigt pipe link. I see you got it work. WRT Excel 'clones', I'm only familiar with Open Office, which works fine except macros? don't function.BTW, since MJK's worksheets assume polyfil, if you input the values for a fiberglass fill it will predict an understuffed 'sinewave like' response. In reality, it will mimic the polyfil response since FG has greater density/ft^3.
GM