Since my last post I have come to the conclusion that the only John Turle Cave was in fact the John Thomas Cave born Q2 1856 St George in the East 1c 441 according to FreeBMD. I've checked his census returns from 1871 to 1901 showing his birth family and spouse family. He actually names himself “John Turle Cave” only once, that is in the 1891 census but he can be tracked with the other family members up and down from there. I believe this is the only John Turle Cave that there was. Perhaps he decided to improve his musical credentials by taking the name Turle from the musical side of the Turle family which originated in the West Country; see
http://www.turle.name/Even though he described himself as a Vocalist on the August 1877 birth certificate for his son William John Cave by Ruth Susan Osborn, and perhaps he had aspirations in that direction, nevertheless his singing appears to have been something of a side-line, as from 1871 to 1891 inclusive the census consistently describes him as a clerk.
Ruth Susan Osborn appears to have been another side-line as their 2nd child - a daughter Maud, was born after the census date in 1881 and John's census return for that year shows he already had a 5 year old daughter and a 2 year old son by his wife Harriet!
Another skeleton comes clattering out of the closet!
Fortunately, as the censuses also show, Ruth Susan's parents were on hand to bring up the two children. Grandparents - what would we do without them?