“Moreover David and the captains of the host separated to the service of the sons of Asaph, and of Heman, and of Jeduthun, who should prophesy with harps, with psalteries, and with cymbals: and the number of the workmen according to their service was:”
The singers were divided into 24 courses, so that every course or order contained twelve, and in all there were 288, as verse 7.