|People impact the sound at a cinema|
It is debatable as to how much the audience impacts the sound but it does impact it. As the sound in an occupied auditorium is different than one unoccupied.
First, there are acoustic changes due to the sound absorption introduced by the audience.
Second, there are transmission changes to the sound patterns (direct and reflected) caused by the audience absorption and associated temperature and humidity changes.
Third, ambient noise increases due to the audience itself and the accompanying chatter, movement, laughing, eating, etc.
Although all of these affects are known, there has been little written or discussed about them within the context of cinema sound issues.
People are very sound absorbing. How much they absorb is open to debate as it depends on the activity and posture of the person, as well as, if they crowded together or spread throughout the auditorium? Also a group of occupied seats in one auditorium will not sound the same in a second auditorium. It's also a fact that people absorb more mid and high frequency sounds than low - particularly when sitting in upholstered seats.
So, it is easy to see that the introduction of large sound absorbing objects (people) will have a big impact on the sound within the auditorium. Introducing an audience into a space has a complex affect on the sound in terms of reverberation and reflection.
The next time your viewing a movie in a crowded auditorium it will sound very different if you viewed that movie two weeks later is a sparsely attended screening - and that difference will be substantial.
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