HF absorption by the air, room size & volume, reflective & absorptive surfaces, directivity of the sound source, critical distance, reverberation - all affect what we hear and whether we can hear the words. These factors can also affect the performance of the artiste.
So using a system that deals well with mids & mid highs, and allows most of the audience to be on-axis with a loudspeaker is helpful. Jim harks back to “the older way of doing things” with multiple horn systems and the rule of thumb - wherever you are sitting you should be able to look up a horn.
Room & system assessment, using diffusion instead of absorption so as to keep the liveliness of a room but lose undesired effects such as flutter echos, Fourier analysis, impulse response, comb filtering, the difference between clarity and intelligibility is also discussed by Jim.
John applies these concepts to sound systems in practice – particularly touring systems. If measurements are taken using an omnidirectional speaker, then directional speakers are put into the room, do these measurements really still apply? John also talks about horns, loudspeaker arrays, touring with Underworld, using drapes and building the system to suit the room – using examples from the Paradiso in Amsterdam, the Ancienne Belgique, the Philips Building in Eindhoven, the Sage in Gateshead and the Manchester Albert Hall.