As an example of what I am trying to say, please refer to Appendix C of my TL alignment tables article. I have displayed the results for three TL's (tapered, straight, expanding) all tuned to 30 Hz. The fundamental 1/4 wavelength resonance is at 30 Hz for each geometry but the 3/4 wavelength resonance is at 120 Hz only for the straight TL. I won't go into the mode numbering schemes because I use a different method of labeling. Maybe we are talking about different things or I have misunderstood the thread discussion.

Martin