Your speaker placement is based on your seating
No, not just the captain's chair but all the chairs....
Yes, we have all seen the Dolby charts, guides, and even the detailed Dolby design tool.* DTS has a similar description of where to place speakers in relation to a single listening position. But most of us have at least two or three seats, if not two or three rows of seats, in our home theaters. And many of us want more than one format to sound good in all those seats. So there is some nuance to following the guidelines based on one technology and one listener....
.....which boils down to placing the speakers based on the seating locations, rather than based on strict angles derived from (and optimized for) a single listener.
Trinnov published a white paper on this several years ago. More recently, CEDIA has codified this approach in RP22, and I will quote from it, here.
The front speakers relate to the screen size, whether you are using a flat panel or a projections system and with the projection system whether it is an acoustically transparent screen.
But the rest of the speaker positions are related to seating and not the screen.
For example, the surround and the back speakers go in these general areas specifically related to the seating:
And the overhead speakers location is directly related to the whole area where people sit:
And, finally, other elements like the number of rows, seat back height, and riser height determine the best height of the surround speakers:
In short you won’t know the right spots for the speakers until you make decisions on the seating location(s).
Caveats: This post doesn't cover subwoofer location. There is a whole separate post about that. And this post doesn't account for informal living room setups where some casual seating locations may be far aware from the rest of the seats.
Footnotes
*The official description: The Home Entertainment Dolby Atmos Room Design Tool v6.0.0 HE+Music (HE DARDT) is an interactive Microsoft Excel tool which allows the user to input the room dimensions, speaker locations, and speaker and amplifier details to help design and model a Dolby Atmos mix studio for music, post, gaming, podcasting, and other uses. This tool adheres to and represents Dolby’s technical guidelines which should be reviewed in parallel. The late 2023 version can be downloaded via this link and full release notes via this link. To partner with the new DARDT v6 Dolby also published a new guideline document on ‘How to Design a Dolby Atmos Mix Room’. The document focuses on 7.1.4 and 5.1.4 speaker placement in music and non-theatrical postproduction applications and also covers the high-level requirements for audio interfaces and speaker management. In most circumstance the new document can be considered a replacement for the full technical specification document (Dolby’s technical guidelines) according to Dolby. Access is via the Professional Support knowledge base and forums, specifically: https://professionalsupport.dolby.com/s/article/Dolby-Atmos-Home-Entertainment-Studio-Technical-Guidelines?language=en_US