Originally Posted by westmd
I was only thinking in elevation angles from the MLP as this is the basis from the Denon diagram, and now the even better Dolby Atmos paper on speaker placement. So if a speaker is placed directly at the side of the MLP the azimuth is 90deg with reference to the center speaker. Now if I would put a surround height in top of that speaker then in regards to MLP is stays with 90 deg elevation angle, because it is directly above MLP!
You are correct. The Denon diagram shows a median section of the room at MLP position.The corresponding definition of elevation angle therefore differs from the one Auro uses in its spherical diagram, which is the elevation angle you get by taking a segment section following the azimuth of the speaker. My earlier presentation of Atmos angles which can be used for Auro does not take this difference in account. It is obviously more complicated than that.
Last night, I have been thinking about a better way to find the best compromise between Atmos and Auro speaker placement. It involves defining speaker placement with two variables, in a way similar to specifying a given location on earth: by degree of longitude (longitudal elevation, like in the Denon diagram) and degree of latitude (cross elevation, like in a cross section of the room at MLP position). Both azimuth and segment elevation (following azimuth of the speaker as in the Auro spherical diagram) are resultants of these two variables.
Now, as an illustration, back to the example of the side surrounds placed at an azimuth of 90 degrees. If you are putting elevated speakers above them using the exact same azimuth, the longitudal elevation will indeed be 90 degrees. We now take a typical room with 8 feet ceiling, a MLP at 3 feet from the floor, and front speakers 10 feet apart. Following the Atmos guideline to place top speakers in line with the fronts, the resulting cross elevation will be 45 degrees (5 feet to the side, and 5 feet up). In this case, since at 90 degrees the cross section is the same as the segment section, the segment elevation is also 45 degrees. This is presumably a bit too high to be used as surround heights for Auro. In this situation the compromise is to be found by either placing the top speakers a bit outside the Atmos recommended front-to-back line, or to placing them further to the back along the front-to-back line. I would in this case choose the latter and move the side surrounds also back from 90 to 110 degrees (see also Auro 13.1 speaker configuration).