The speakes above 80 Hz are all of Ex Eastern Germany production with a extremely high efficiency. But we are missing the frequency band below 80 Hz and considering to do a 18" Shearer Horn system (Don´t worry, we know it is big). Do you have any recommendations on construction / plans / drawings.

2nd questions: Does anyone have some verbal descriptions, what influence the several pieces of the horn do have in terms of efficiency, distortion, narrow band vs. wide band? Like throat area, volume behind the speaker, volume of the pressure chamber, horn length, mouth size?
Merry X-mas to all of you and might be someone can help me....