Something that has been bothering me lately is the variable playback loudness in cinemas, with most cinemas playing back well below the Dolby Reference standard level of 7 (or calibrated to 85dB SPL), but seemingly there pretty much being no standard anymore. Unfortunately films being mixed at lower levels, to make for louder mixes, which then has cinemas turning down their volumes, has triggered a downward spiral in this regard. Anyway, the following page has a neat table of reference volumes/loudnesses as well as some useful definitions for some of the basic terms relevant to deliverables specs for film.
