There is a common misunderstanding that horns must be 1/4 wave long and mouth area must be 1/4 wavelength in circumference. This is only a rule of thumb. If a horn is flown alone, that's true, and length should really be 1/2 wave. However, that is rarely the case and almost never for basshorns.

Basshorns are almost always used on the ground, which cuts these values in half. Use a pair of basshorns on the ground and the size is cut by 1/4. In fact, the most common basshorn is actually 1/8th size. It is smaller both in length and in area. If used in groups, 1/8 size horn is all you need. This will be both shorter in path length and smaller in mouth size than 1/4 wave.