Please fill in these blanks. What is it specifically for each horn type?
60 degree horn:
Room geometry: _____
Treatment type: _______
Goal:_______
90 degree horn:
Room geometry:______
Treatment type:_______
Goal:________
It's not that easy. In what frequencies is the speaker constant at 60° or 90°?
And all these points influence each other, creating many variables.
For instance: Let's say you have a room that isn't very long but it's quite wide. Because of too close proximity to the rear wall, you can't place diffusers there. You have to primarily absorp the rear wall reflections. In that case, it's very likely that it would be favourable to place diffusers on the opposite side wall reflection points. And that would imply also having a speaker with sufficient wide beam width.
Or let's say you have a very narrow and long room and you can't place treatment on side walls due to windows, WAF, etc. In that case, a very narrow horizontal directivity is likely to be the better choice. But you also have to weigh the directivty up against the size of horn you can live with. If the widest you can live is 60 cm, I probably wouldn't choose a direcitvity of 60° because it would collapse too high in frequency.