JACK ROE predates sound in cinemas. Since then we have seen the introduction of mono sound, stereo, surround, digital and now uncompressed digital sound. Below in some information that we hope will help cinema enthusiasts to understand common questions.
The ".1" is the subwoofer. In addition to the actual speakers there are usually several subwoofers to help carry the low frequencies of the audio spectrum that are not so well covered by the smaller wide-range frequency speakers.
Dolby Atmos is a blend between the existing channel-based system and the more familiar channel-based systems that have been the staple of movie theatres for decades. In addition to the regular speaker channels there is the introduction also of object-oriented sound. This is where the final stage of mixing is essentially done onsite, and tailored to the room automatically by the sound processor itself. A sound (for example a helicopter) is included with the soundtrack and co-ordinates are attached to the sound. In this way the sound processo knows where the sound should be at different times in the auditorium and the Atmos logic determines how it should be blended into the specific speakers at the cinema in order to reproduce the highest possible spatial accuracy as intended by the director of the film at the sound stage. By having this final stage or mixing at the cinema the sound processor is able to help compensate for the differences between the cinema and the sound room. Barco Auro is similar to Dolby Atmos in that it improves upon the traditional 2D sound format (see 3D sound below) that is common to cinemas but does not include the object-oriented aspect of Dolby Atmos. Both systems increase the number of channels beyond 7.1.
Mono sound is point sound; the source is a single origin, with no axis to move along. Stereo introduces 1D sound; it is possible to move sound along the axis that connect the 2 speakers (that are behind a screen in a cinema). Surround sound is 2D sound because although the sound is all around the audience it is still only in a single plane. Although the speakers at at different heights around the auditorium to allow for the sloped seating they are not stacked so that 2 speakers are above/below each other. 3D sound (like Dolby Atmos and Barco Auro) introduce 3D sound to cinemas by introducing speakers above/below/suspended from the ceiling, with the configuration depending on the exact system and auditorium. Now it is possible to move sounds outside of the 2D plane of traditional surround sound.
There are more discrete channels in 3D cinema sound and so additional amplifiers are required, and new speakers too. With some systems/setups it is necessary also to replace some of the existing speakers. One of the most significant factors is the difficulty of safely and securely introducing speakers to the ceiling of the building. Given that the speakers must be suspended above the audience it is critical that there is no danger that they could fall. Structural engineers are required in order to assess and make recommendations for attaching this new weight to the ceiling, typically using some kind of truss and cabling. It is much more economical to factor these considerations into new construction as part of the overall build than to retrofit them as a standalone project to an existing auditorium.