I went to brunch with friends and there was an Old Harp event going on in the atrium. The acoustics made the old, rural type of a capella singing sound just lovely. Old Harp singing, or shape note singing, is an American folk tradition (still vibrant in the rural south and in the mountains) of singing hymns and gospel songs from The Sacred Harp, a 150 year old songbook that uses shaped note heads to indicate position in the scale. It's participatory and seats are arranged in a hollow square. Wikipedia says: "Shape notes are a system of music notation designed to facilitate congregational singing. Shape notes of various kinds have been used for over two centuries in a variety of sacred music traditions practiced primarily in the Southern region of the United States."
And so it is.
The Sacred Harp is an oblong tunebook first published in 1844 by B.F. White and E. J. King. No harps, or instruments of any kind are used in shape note singing.