Linked in turn to a post by Dwight Newton of the University of Kentucky at his Mewzik.com organology website:
... His vocal style is rhythmically free and declamatory, with great emotional expression, especially as he employs his stratospheric falsetto. The instruments were used in a minimalist way, strumming the strings in a simple down- down-down-down... stroke, or in some cases in a single rolled stroke at certain moments for emphasis in an otherwise a cappella performance.Link to http://mewzik.com/research/niles/index.php. Newton adds Niles' dulcimers "... are all clearly the work of a folk artist, not a luthier. But their musical function was secondary to their function as theatrical props. He rarely played melodic tunes on his large dulcimers. In all cases the real star of the show was Niles himself -- his voice and his expression."
JJN, introduction to The Ballad Book (1961. Lexington: UP of Kentucky, 2000): xxii
Seldom did I encounter the use of harmony in folk singing. However, I have heard folk hymns, carols, ballads, work songs, and nursery rhymes in which one voice sang the melodic line and others, numbering from 1 to 25, sang a monotone that occasionally harmonized. The effect was not unlike some of the results gained when a singer supports himself with dulcimer accompaniment, for the dulcimer actually produces as much dissonance as consonance.
Robert Pen, I Wonder as I Wander: The Life of John Jacob Niles (Lexington: University Press of Kentucky, 2010) discusses dulcimers :
... One reviewer in Amsterdam's Algemeen Handelsblad raised an interesting point of interpretation and performance practice, observing, "We have heard negro songs sung in different ways by Roland Hayes, Edna Thomas, Layton and Johnson, the Fisk Jubilee Singers and the Utica Singers, but so realistically and no negro like we have never heard it yet. This is a revealing comment: the reviewer is crediting [opera singer Marion] Kerby and Niles with being more "black" than actual African Americans. At a time when solists like Robeson and groups such as the Fisk Jubilee SIngers were attempting to "pass" in their per romance style and repertoire, Kerby and Niles were attempting a "reverse pass" by simulating African American style. (122)Pen adds, "It is the art that conceals art, the seemingly natural way of conjuring the essence of a Beth Holcolmb [note corrected spelling] in any discernible way. It is the art of creating a distinctive personal style in which is contained the souls of hundred of singers, each with her or his own unique personality, and their songs. That was the foundation of Niles's art, which made him one of America's most sought-after performers during the next several decades. Although he was later faulted as an "inauthentic" folksinger, it is clear that his intent was not to Be the authentic folksinger but rather to interpret the essential experience of the original folksinger through the lens of his own personality." (222) JJN recorded her July 9, 1932, in Whitesburg, Ky.
... The sweet timbre of the dulcimer was designed for solo use in intimate gatherings and did not project well in a large hall. Since electronic amplification had not been effectively developed yet, Niles had to build larger instruments with more strings and to cultivate a unique performance styles consisting of sharply strummed chords and drones, rather than the traditional finger-picking of strumming with the use of a "noter" and a goose quill. (166)
[Niles wrote in his autobiography of his solo career in 1939] The problem was the projection of personality and the employment of dramatic methods, remembering all the while that every time I sing a single line of one of the great ballads or carols, I must have somewhere in my vision of what I thought a medieval bard looked like, also the personality of the singer whom I knew. Although I had been in the great world of the concert stage as a singer singing alone only a short while, I knew that I had to blend two powerful forces, my person and the personality of my inforant. For example Johnnie Niles, dulcimer and all, and Beth [/] Holcum, my mature informant. (221-222)
Cf. John Lovell Jr., Black Song: The Forge and the Flame (1972. New York: Paragon House, 1986), quoting a Dutch scholar named H.R. Rookmaaker, "The Afro-American spiritual, he believes, must be sung like Mahalia Jackson sings, not in the "Schubertized, concertized manner of the Fisk Jubilee Singers and Marian Anderson" (575).