I think Abbey Road (and probably other studios of the era) had an ambiphonic system similar to as described in the paper. They had an array of speakers built in

I think Abbey Road (and probably other studios of the era) had an ambiphonic system similar to as described in the paper. They had an array of speakers built into the walls of their recording room so that could feed back signals from it, artificially changing the length of the reverb decay of the room. https://soundgas.com/pages/grampian-ambiophonic-unit-type-666 https://soundgas.com/pages/grampian-ambiophonic-unit-type-66... http://www.sydbarrettpinkfloyd.com/2009/08/unforgotten-hero-peter-bown-and-piper.html?m=1 http://www.sydbarrettpinkfloyd.com/2009/08/unforgotten-hero-...