Jerry,
There are some US denominations that historically have not used instruments in church. Among those I'm aware of are Primitive Baptists, some Mennonites, and the Church of Christ. I have a seven shape Church of Christ hymnal that I've used as a source for early 20th cent. Gospel standards.

Not all saw the instruments as sinful, just not appropriate for church. I've heard of some that have decided to add instruments.

You mentioned shape note music. The 19th cent. shape note books kept alive the New England psalm singing of the previous century after it lost popularity there. The 19th century singing school movement was transatlantic. The British analog is usually called West Gallery or Georgian Psalmody. Both New England & British included instruments. I was only as it was preserved by those opposed to instruments (or just not having them) in church that the US versions became unaccompanied. Read Hardy's "Under the Greenwood Tree" or go to Bruce Randall's workshop at NOMAD for the connections.

I've read a little of some early 19th century music debates. The interesting thing to me was that organs were being introduced then & were not universally approved. Up until then, there were a variety of instruments, especially strings, used in churches. They seem to have lost out to the organ or been banned all together.

On the whole use of terms, unaccompanied is actually older & more accurate. Here's the Grove entry explaining the confusion that gave rise to the current usage of the term a cappella.


A cappella
(It.: 'in the style of the church [chapel]').

Normally, choral music sung without instrumental accompaniment. Originally (c1600) the term was used to distinguish works composed in the older polyphonic style of the Renaissance from those written in the newer concertato style of the early Baroque. During the 19th century the Roman Catholic Church idealized 16th-century polyphony and the works of Palestrina in particular. Noting that no instrumental parts were included in the sources containing this music, and unaware that instruments were often used during the Renaissance to double or substitute for vocal parts, musicians came to believe that a cappella referred to unaccompanied choral singing. Since that time, the term has become synonymous with 'unaccompanied singing', both religious and secular.
Holmes, William C.: 'A cappella', Grove Music Online ed. L. Macy (Accessed 11 Nov. 2003),