Charles Ellicott Commentary 1 Chronicles 9:33-34

"And these are the singers, heads of fathers` [houses] of the Levites, [who dwelt] in the chambers [and were] free [from other service]; for they were employed in their work day and night. These were heads of fathers` [houses] of the Levites, throughout their generations, chief men: these dwelt at Jerusalem." — 1 Chronicles 9:33-34 (ASV)

A general concluding statement, with reference to the preceding account of the Levites (1 Chronicles 9:14–32).