John has written another post on his blog, concerning the "Live Room" mentioned in the entry on the Almighty instrumentals, with more details on how the room came to be and how it originally had a different purpose. He says that his omission of the intended purpose of the room in the said written piece was an oversight, so he thought he'd mention it.
He reveals that the room was originally his control room from back when his studio was a "rock" studio and then goes on to describe its transformation through a series of events that led him to a very interesting semi-accidental (?) discovery:
By the time the room was finished, I had it in mind to use it for this secondary purpose, and I clapped in there for the first time and was disappointed. It sounded almost dead, with no real bounce to speak of. But when I sent very loud sounds into it and placed microphones in specific positions I became very excited. I’ve been able to make that room sound like reverb by being creative. It’s not a reverb chamber. It’s also not a very large or high-ceilinged room, but I’ve managed to make it sound like one by being resourceful.
Addendum, July 14th, 2016: John previously spoke about the live room and how he made it "swell into Rugged Monk's voice in the 2014 Guitar Player interview.
*I'm not good with summaries of things beyond my expertise and this is why the previous post was never published and is up now. But backdated posts are cool, so yeah. ^_^