Bob Flanigan, vocalist, trombonist and bassist for ’50s pop group the Four Freshmen, died of congestive heart failure in Las Vegas on Sunday. He was 84.

Flanigan founded the jazz-oriented quartet with his cousins Ross and Don Barbour and Hal Kratzsch in 1948 at Butler U. in Indiana.

The group reached the charts with such mellifluously harmonized singles as “Day by Day” and the top 20 hit “Graduation Day,” both of which hit in 1956. Five LPs — including “Four Freshman and 5 Trombones” (1956), “Four Freshman and Five Trumpets” (1957) and “In Person” (1958) — reached the national top 20. They were nominated for Grammy Awards six times.

The Freshmen’s sound had a marked impact on a young California musician named Brian Wilson, who later credited the act as a primary influence on the Beach Boys’ layered harmonies.

The unit prevailed despite the passing of original members Don Barbour, who was killed in a 1961 car crash, and Kratzsch, who died in 1970. Flanigan retired from performing in 1992 but kept his hand in the management of the group, who continue to appear today.

Flanigan is survived by his wife, Mary; six children; and 15 grandchildren.