Hi R,
Issues
The principal determinants of the acoustics of a low frequency horn are its length and mouth size. If you change either you have a different horn no matter how you ‘slice and dice’ it. Furthermore, as soon as you position a horn along a room wall, floor or more, you have also changed it acoustically. Its low frequency response will be extended, irrespective of what regimen you choose to use to design it.
Method #4, al la Klipsch
The best approach would be to lower design [fc] and extend horn length to support the longer wavelengths that are now possible. The number of drivers used is related only to the magnitude of [vd] that you require. If you cannot get it by increasing [xmax] of a single driver of a given [sd], then as you increase [sd], with larger or multiple drivers, you foreshorten horn length only, while holding dimensions of the horn mouth constant. Sometimes driver [sd] is increased to mitigate packaging constraints as horn footprint is reduced by bifurcating and folding it up into a room corner. In this case driver [xmax] may be reduced.
Regards,
WHG
