American Brass Quintet Makes Sure It Doesn't Shrink to a Trio Among North American brass ensembles none is more venerable than the American Brass Quintet, which was founded in 1960 and has been a resident ensemble at the Aspen Music Festival since 1970, and at the Juilliard School since 1987. But rosters change, and the retirement of the trumpeter Raymond Mase and the hornist David Wakefield has created two openings in the quintet in quick succession. As of Monday both spots have been filled: the trumpeter Louis Hanzlik joined the ensemble on Dec. 1, and the hornist Eric Reed will take over from Mr. Wakefield on March 23. They are the 25th and 26th members of the ensemble, which has seen several distinguished players pass through it, among them the trumpeters Gerard Schwarz (who traded in his trumpet for a baton), Allan Dean and Chris Gekker, and the hornist Edward Birdwell. The current roster includes, along with Mr. Hanzlik and Mr. Reed, the trombonist Michael Powell (who joined in 1983), the bass trombonist John D. Rojak (1991) and the trumpeter Kevin Cobb (1998).