John Gill Commentary 1 Chronicles 9:34

"These were heads of fathers` [houses] of the Levites, throughout their generations, chief men: these dwelt at Jerusalem." — 1 Chronicles 9:34 (ASV)

These chief fathers of the Levites were chief throughout their
generations
Even all before made mention of in this chapter:

these dwelt at Jerusalem ;
always resided there, and did not in turns go into the country villages, as the inferior Levites did; their office requiring them to be constantly there, being chief of the porters, singers who had the superintendency and direction of the rest.