The story of Heil Sound
Did you know Joe Walsh of the Eagles was a ham? Joe Walsh was Bob Heil's beta tester. Bob Heil's traveled with the Who, the Grateful Dead and a bunch of rock groups fixing up and running their PA systems.
Fletcher Munson curve - what is it? Scientists from Bell Labs who were the pioneers in sound audio technology
There is QST article on a two level equalizer that he came up. Bob Heil since then invented the equalized microphone.
Man cannot hear 3dB difference. He demonstrated it. What is important is equalization to get an apparent gain in sound power level. Passed array is how to get 15dB on 75m and 40m.