This was my very FIRST speaker build project that I did. I purchased the plans for and built the legendary TubaHT by Bill Fitzmaurice as the likely candidate as a subwoofer for future Hauptwerk use. This sub is SOLID down to the 20Hz range and is still audible down below that. This thing will absolutely rattle your teeth.
In the large A-Frame sanctuary of Greenwood UMC, placing this thing firing into a rear corner, I was able to utilize the walls, vaulted ceiling, etc. as an extension of the horn throat. This created a horn of epic proportions with results that, to be honest, has the potential to be too much for that space.
The plans start by laying out the side and tracing the outlines for the interior channels.