Sure, a quarter wavelength gives you an output, but it isnt a true CD. Also I dont think anyone was specifically referncing folded horns. While it had similarities, it really isnt the point. True CD horns can have phase that other speakers cannot.
Once the wavelength equal size of speaker then it’s P1
Horns of CD design will at low frequencies be dominated by higher modes perceptions, and the issues are clearly audible, as Dave C points out the CD horn advantages dissipate at low frequencies I have often wondered if this is the reason that JBL have never bothered with this in their low frequency transducers ?
Sure, a quarter wavelength gives you an output, but it isnt a true CD. Also I dont think anyone was specifically referncing folded horns. While it had similarities, it really isnt the point. True CD horns can have phase that other speakers cannot.