A century ago the Penrhyn Male Voice Choir visited Chicago as part of the Columbian Exposition. Now its artistic heirs are making their first return trip. Times have changed, as the current 70-man roster can attest. The Penrhyn traces its roots to the Penrhyn State Quarry in the northern Welsh village of Bethesda. Its first members were miners in the quarry, which at the time had the dubious distinction of being the largest man-made hole on earth. Like other quarrymen's choirs, the Penrhyn was a fraternal order and a glee club rolled into one. These choirs specialized in harmonized hymn singing, but they also directed attention to the plight of the miners with songs of protest; historians credit them with having swayed public opinion in favor of child-labor and mandatory-education legislation around the turn of the century. These days the choir's membership isn't exclusively tied to the quarry, though the prestigious Penrhyn slate is still being produced, and the singers, mostly men in their 20s and 30s, have taken on the role of revivalists of a bygone tradition. Their extensive repertoire includes nonconformist Welsh hymns and traditional folk songs plus works by contemporary Welsh composers. But this visit also offers a rare chance to hear the Welsh style of singing, with its down-to-earth quality and its mix of melancholy and defiance. Each song will be introduced by noted Welsh actor John Ogwen. A portion of the program will be sung by soprano Leah Owen. Alun Llwyd is the conductor. Monday, noon, rotunda, Museum of Science and Industry, 5700 S. Lake Shore Dr.; 684-1414. Tuesday, 12:15 PM, Preston Bradley Hall, Chicago Cultural Center, 78 E. Washington; 346-3278. Thursday, 7 PM, Episcopal Cathedral of Saint James, 59 E. Huron; 787-7360.