A closed conical bore resonates like a tube open at both ends

Evidence

Conical bores are a little subtle. The cone has its narrow end closed, but its resonances are the same as a tube of equal length open at both ends. Resonances in conical horns are discussed in every book and website on musical acoustics, but short of solving differential equations it seems no one tries to justify why a closed cone should act like an open tube. Here, we make the attempt with an intuitive argument starting from easily understood plane waves. — Eric J. Heller, Why You Hear What You Hear- An…, 1460

Categorization

• QUESTION: Why is the closed-cone-as-open-tube result so rarely justified intuitively in the literature? Worth chasing what the standard derivation actually is in Hellweg/other textbooks.
• XREF: connects to: A conical pipe closed at the narrow end behaves like an open-open pipe acoustically — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1214