The point is to have coverage of the seating area. With a horizontal speaker, faced towards the middle of the seating area, it's fairly easy to get good frequency response. With a downward firing speaker, not so much. With the majority of speakers, the best frequency response (before starting to lose frequencies) is within 30 degrees off axis (picture a 60 degree cone of sound projected perpendicular from the face of the speaker). If all your seating is within that cone, for all your speakers, then you are probably home free.
There are some caveats. For instance, distance makes the cone area larger, so short ceilings are more problematic. In addition, the width and depth of the listening area makes a huge difference. The larger the seating area, the more important directionality becomes. Lastly, every speaker has it's own set of frequency response off axis characteristics, some narrower than 30 degrees, some greater. For instance, the Golden Ear AMT is designed to have very narrow vertical dispersion, but has larger than average horizontal dispersion (so it's more of an oval cone instead of a round cone).
Also, note that a movable tweeter does not help the dispersion characteristics of the frequencies served by the woofer. So, your frequency response might be fine down to the 3000Hz or 2500Hz crossover point, but below that it will drop off as the angle increases.
So, do the calculation of ceiling height to your seated ears in every seating position, at 30 degrees off axis (RSL is tilted 15 degrees, so you get 45 degrees to play with off axis). Paradigm has a model with a 30 degree angle built in (60 degrees of play). Triad has one with 45 degrees built in (75 degrees of play). These may be necessary in situations with low ceilings, or wide/deep seating, or issues with optimal speaker placement.
It's a VIRTUAL channel unless stated otherwise.
Last edited by RayGuy; 06-27-2019 at 02:55 PM.