Line Length of a ML-TQWT

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Hello Forumites

I would like to build a ML-TQWT cabinet for the Alpair 10, similar to Cyburgs Needle. I am still reading about that type of enclosure, trying to understand the underlying physics.

I wonder if there is a method of calculating the length of middle line of the cabinet. So far I have not found any information about the math of that most important parameter of a ML-TQWT.

The Alignment Tables of Mr. King may be a first start to look at, but I am not sure if I can use that information.
The effective length of a tube (tuned to 45 Hz, SL/So=3) would be 232 cm (91.4 inches), but that length only applies to a tube with an open end. The terminus of my project, that has the properties of a Helmholtz Resonator, seems to act as an additional acoustic impedance that reduces the effective line length.

At this point I do not know how to proceed. Should I use the unsatisfactory rule of the thumb L=c/(4*f), in the hope that the too short line length is compensated by the acoustic impedance of the port?

Or are there any Alignment Tables for ML-TQWTs?

Thank you for your help!
 
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