Hmm. It was quite late last night, so I’ll try to remember the steps.
I Googled “a cappella choral of tubular bells” (without the quotation marks and no commas) and it brought up 1) John Muelhleisen, an author of choral music. That wasn’t it. 2) was Tubular Bells Wikipedia.
So I went to the Wikipedia page which was rather long and it was getting late, so I pressed [“ctl” + “f”], then punched “a cappella” into the search box and it took me to the bottom of the page to “Cover Versions” and there, highlighted, was the listing for the Finnish a cappella rockband Pask‘s version of Tubular Bells.
I went back to Google and punched in “YouTube, Pask, Tubular Bells” (again without quotes) and the Pask version popped up. There were no other a cappella listings. But that wasn’t it. It was one guy just making a lot of off-key vocal noise way too close to the mic. Must be those long, dark Finnish winters with nothing to do.
But a few listings down was an a cappella version by somebody named Petra Haden. I listened and figured it was the best bet.