John Gill Commentary 1 Chronicles 15:16

"And David spake to the chief of the Levites to appoint their brethren the singers, with instruments of music, psalteries and harps and cymbals, sounding aloud and lifting up the voice with joy." — 1 Chronicles 15:16 (ASV)

And David spoke to the chief of the Levites
The six before mentioned, (1 Chronicles 15:11)

to appoint their brethren to be the singers ;
before the ark, as they brought it up:

with instruments of music, psalteries, and harps, and cymbals ;
which were used in those times, see (2 Samuel 6:5) (13:8)

sounding by lifting up the voice with joy ;
the instrumental music was to be attended with vocal music, and that very sonorous and loud, and performed with all tokens of inward joy and gladness, as the occasion required.