So very true! Heres a quicky method (accurate, no way, but it gives an idea of a basic BLH low FR concept). Take the tuning length until just before the final flare section. Calculate the TL response based on 1/4 wave action(straight TL), add 10 Hz. This will give the lowest frequency (approx) when wall/floor loaded. Corner loading will mean subtracting 10 hz.(given the proper room dimensions). Even Dr Bruce has stated that 1/8 mouth size had never given the calculated response when corner loaded.
Yea, its a rough silly Kentucky windage/SWAG type calculation, but i have found it to be very close in many horn designs.
In my designs and sims i see that 1/4 wave gives the lowest initial boost then horn action kicks in then the compressed 1/4 wave action (harmonics) enters into the picture(later in frequency). Thats the upper ripple that so many see at the limits of the horns BW. The 1/4 wave action (upper harmonics) and the horn action combine. And if its designed correctly there will be minimum ripple.
ron