I'm working on BIB Fostex FF165K sim, but I have some problems, or missuderstanding.

When I put T/S data into BIB_166_GM_v2 sheat , I get L=168,31 in. and Sm=93.50 sq.in. (more that on Zilla site - Sm=88.125 sq.in.)

If I shorten L and change Fr to 50Hz, then Sm become bigger (Sm=116.87 sq.in.)

What I'm doing wrong?

How to calculate shorter pipe?

I think that Sm must be the same - not bigger if pipe L shorten?

When I put T/S data into BIB_166_GM_v2 sheat , I get L=168,31 in. and Sm=93.50 sq.in. (more that on Zilla site - Sm=88.125 sq.in.)

If I shorten L and change Fr to 50Hz, then Sm become bigger (Sm=116.87 sq.in.)

What I'm doing wrong?

How to calculate shorter pipe?

I think that Sm must be the same - not bigger if pipe L shorten?