A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
2 Chronicles 5:1
ch2 5:1THE DEDICATED TREASURES. (Ch2 5:1)
Solomon brought in all the things that David his father had dedicated--the immense sums and the store of valuable articles which his father and other generals had reserved and appropriated for the temple (Ch1 22:14; Ch1 26:26).
2 Chronicles 5:2
ch2 5:2BRINGING UP OF THE ARK OF THE COVENANT. (Ch2 5:2-13)
Then Solomon assembled . . . in the feast which was in the seventh month--The feast of the dedication of the temple was on the eighth day of that month. This is related, word for word, the same as in Kg1 8:1-10.
2 Chronicles 5:9
ch2 5:9there it is unto this day--that is, at the time when this history was composed; for after the Babylonish captivity there is no trace of either ark or staves.
2 Chronicles 5:11
ch2 5:11all the priests that were present . . . did not then wait by course--The rotation system of weekly service introduced by David was intended for the ordinary duties of the priesthood; on extraordinary occasions, or when more than wonted solemnity attached to them, the priests attended in a body.
2 Chronicles 5:12
ch2 5:12the Levites which were the singers--On great and solemn occasions, such as this, a full choir was required, and their station was taken with scrupulous regard to their official parts: the family of Heman occupied the central place, the family of Asaph stood on his right, and that of Jeduthun on his left; the place allotted to the vocal department was a space between the court of Israel and the altar in the east end of the priests' court.
with them an hundred and twenty priests sounding with trumpets--The trumpet was always used by the priests, and in the divine service it was specially employed in calling the people together during the holy solemnities, and in drawing attention to new and successive parts of the ritual. The number of trumpets used in the divine service could not be less than two (Num 10:2), and their greatest number never exceeded the precedent set at the dedication of the temple. The station where the priests were sounding with trumpets was apart from that of the other musicians; for while the Levite singers occupied an orchestra east of the altar, the priests stood at the marble table on the southwest of the altar. There both of them stood with their faces to the altar. The manner of blowing the trumpets was, first, by a long plain blast, then by one with breakings and quaverings, and then by a long plain blast again [BROWN, Jewish Antiquities].
2 Chronicles 5:13
ch2 5:13the house was filled with a cloud--(See on Kg1 8:10).