Charles H. Spurgeon on Psalms 149:3

Harp. Of the kinnor the Scripture affords little further information than that it was composed of the sounding parts of good wood, and furnished with strings. Josephus asserts that it was furnished with ten strings, and played with a plectrum; which, however, is not understood to imply that it never had any other number of strings, or was always played with the plectrum. David certainly played it with the hand (1Sa 16:23 18:10 19:9); and it was probably used in both ways, according to its size. That this instrument was really a harp is now very generally denied (Kitto). The reader will, by this time, have balanced the probabilities as to the nature and construction of the kinnor; and most likely he will be led to think that it was either a guitar or lyre, a belief which seems to be gaining ground, on account of the aptitude of such instruments for the uses to which the kinnor was devoted. —J. Stainer.