Ten Speaker Layout Tips for Dolby Atmos, DTS.X & Auro

by Nyal Mellor November 14, 2015

Dolby Atmos has been a big thing with our client base. Since the format was announced >80% of our theaters have been designed to support Atmos and other next-generation audio formats such as DTS.X and Auro.

Here are some of our learnings and recommendations based on these experiences:

• Ensure there is a clear line of sight from all surround speakers to all seats.  Just because we have some new audio formats does not mean we should throw away the good speaker layout practices from the last 20 years of surround sound. High frequencies are easily blocked by seat backs, heads and other obstructions. To get balanced direct sound you need a clear line of sight to the speaker from each seat. 

• Do not put surrounds at ear level. See above. CEDIA (the industry trade association for contractors in the home theater design and installation market) is going to be updating their recommended audio practices to reflect this exact point later this year. 

• Keep surrounds as low as they can go without causing other issues (e.g. too much SPL variation over audience). Why? Because you want to keep the separation between the bed layer (the lower set of speakers) and the height layer (the ceiling speakers).

• Make sure surround speaker locations work for the speakers you are using and their coverage pattern. Don’t use dipoles for spatial audio, as by design they do not provide consistent coverage or support localization in the dipole “null”. If you are using narrow dispersion horns for surrounds then make sure will provide adequate coverage of each seating row. This is not really a new requirement, but with spatial audio being able to localize discrete effects in the surround field is more important.
  
  

• You may need to use “pan and tilt” speaker mounts to direct speakers at the right place (not necessarily the main listening position; there may be other locations that work better for best coverage). If you have two rows then a position between the two rows often works best in terms of where to point the speakers.

• Place ceiling speakers so they meet published standards but also provide good front to back angular spacing.  See below.

• If the front LCR and rear surrounds are raised above 0 degrees (likely) then the position of the ceiling speakers should change to provide more even spacing front to back. The screen LCRs are often raised above ear level in most dedicated theater in order to provide a good direct sound field to the second row. The rear surrounds are also often raised in order to provide clear line of sight over the seat backs of the second row to people in the first row. If you follow the Dolby Atmos layout angles exactly in this kind of configuration then you won’t have much angular separation between screen and first ceiling row and between rear surround and back ceiling row.

• More than two ceiling rows may be necessary for best coverage. If you are trying to provide a consistent experience in a multi-row home theater then you may need a third set of ceiling speakers. Generally you would position the first and second row of ceiling speakers based on the angles for the first row of seats. But if you do this then the second (and other) rows may have less-than-great angular spacing front-to-back (see above). A third row often helps ameliorate this issue.

• Ceiling speaker coverage requirements are challenging and with the exception of a coaxial there are going to be coverage holes due to crossover lobing and other things that need to be worked around. Ideally you need speaker off axis measurements (both horizontal and vertical) to do this. The main challenge is the need to provide great coverage both front-to-back in the room and left-to-right. This requires that ceiling speakers have a conical dispersion pattern. Most speakers are multi-way designs, using separate high and low frequency elements. These often have off axis phase cancellation issues, and it is important to know where these are. Speaker manufacturers are playing catch up with the dispersion requirement for spatial audio formats at the moment, so there isn’t much out there that really fits the bill for ceiling speakers. Note that we see many using mis-matched sets of speakers for spatial audio, such as LCRs and surrounds from one manufacturer and in ceilings from another. For spatial audio this is a big mistake, because soundtracks will increasingly have audio objects (the key part of these next generation formats) that can move from any speaker to any other. You do not want the timbre of that sound to change as it changes position spatially. 

• You may need to use pan and tilt brackets on the ceiling too. Because of the dispersion requirements, you may need to angle and point the ceiling speakers to provide good audience coverage.

 

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