Originally Posted by Ericglo
I thought Dolby said 100hz or so was good for the bottom end on the ceiling speakers.
There was a htgeek podcast about a year and a half ago. The guest was someone working in cinema audio. IIRC he said that 90% or greater of a movie's audio is coming through the center channel. It seems like a waste to spend a lot on surround channels. The Pioneer Atmos demo '14 convinced me that 5.1.4 is better than any number of surrounds without ceiling speakers.
I am going off the actual Dolby Cinema specs - here is the relevant portion from their commercial cinema white paper:
4.4 Surround Loudspeaker Sound Pressure Level: 99 dB
Each loudspeaker and associated amplifier must have a maximum output capability of 99 dB continuous SPL at the RLP (defined on page 1). Loudspeaker capability must be determined, as described in Section 6. We recommend an amplifier with 3 dB of headroom (that is, twice the required continuous power).
4.5 Surround Array Sound Pressure Level: 105 dB
Each surround array and the associated amplifiers must be able to produce 105 dB continuous SPL at the RLP. To meet this requirement for surround arrays with fewer than four loudspeakers, each loudspeaker must be able to produce more than 99 dB continuous SPL.
4.6 Surround Sound Frequency Response: 40 Hz to 16 kHz, +3/–6 dB Dolby Atmos auditoriums must support playback of full-range surround signals. To meet this specification standard, cinema
surround loudspeakers with limited bass response require bass management. If bass management is used, the surround loudspeakers frequency response (±3 dB) must extend to 90 Hz or lower. The crossover frequency should be set based on the capabilities of the surround loudspeakers, but must not be higher than 100 Hz.
In the cinema spec, there is no differentiation made between side and ceiling surrounds. All are full range channels. My post had to do with how they are likely to be implemented in an actual mix, where the ceiling channels are unlikely to be used (often) for intensely dynamic, full range signals.
RE: 90% of a movie coming from the center. This is not universally true, in fact it's very
rarely the case at all. Perhaps if we are talking about a drama where it's almost all dialogue (or a Woody Allen movie) that might be true. But almost every movie ever made has a music score, and the music score is almost exclusively mixed to left, right and surrounds. So are the big sound effects in action and SF films.
Even if most of the movie is carried by the dialogue, whenever the music or sound effects kick in, those go out to the sides and surrounds and THAT is where most of the crazy dynamics live. I've mixed two films in surround, and while these were both independent films without lots of money for big FX or elaborate sequences, most of the dynamic energy still ended up coming from the main left and right channels. It's clear even if you look at the waveform - the center channel is almost always active, but most of it is pretty restrained in dynamics, while the big peaks come on the left and rights (this is not always the case, though, which is why you really do want a good quality center speaker).
This is all very easy to test out at home - just disconnect your center speaker during a movie like GODZILLA or THE FORCE AWAKENS, and you will hear all kinds of very dynamic sounds coming from all around you.
Another excellent test - either BIRDMAN or THE REVENANT, both cases where dialogue is also mixed into the side and rear surrounds, discretely.
I think it's also important to point out that this is all evolving, so even if mixers are not taking full advantage of all channels yet, that does not mean they won't be. I think that "80 - 90% from the center channel" was true in the Dolby Surround past, but not really any more
Hope that helps!