The Burdizzos Mod
This mod was originally done on an Avatar B212. I swapped out the horn for a Galaxy Audio 5" driver. I have since used Galaxy's new Neo 5" driver and I think it sounds better than the standard driver. It has a claimed range of 150 to 18,000Hz and a claimed power handling of 100 watts RMS. If a crossover set at 500 Hz is used, it fills out the high frequency sound of the bass without being harsh, as horns often are.
This can be done in any cab where there is room on the front baffle to fit the new speaker. It has a 4.75