Christoph Eschenbach conducts the National Symphony Orchestra in 2010. (Photo by Margot Schulman)

The announcement was made Sunday during the NSO’s Season Opening Ball, along with the news that NSO music director Christoph Eschenbach had extended his contract through the 2014-2015 season.

Rubenstein, the co-founder and managing director of private equity firm, The Carlyle Group. is the single largest donor in the center’s history. His donations total over $25 million. He called his latest gift a fitting one for the anniversaries. “It is my hope that the new organ will enrich concert life not only for the NSO, but for all of Washington musical groups for decades to come,” Rubenstein said in a statement.

The center chose Casavant Freres of St-Hyacinth, Quebec to building the organ. The new instrument will have 5,000 pipes ranging from the size of a pencil to over 30 feet in length. The installation is expected to begin in the summer of 2012.

The present organ dates to 1972 and was a gift from the late philanthropist Catherine Filene Shouse.

Eschenbach has become involved with every aspect of music at the center. In a statement, he took note of the NSO relationship.

“As for the NSO itself, the members arrive at every rehearsal prepared to make music of the highest caliber. I enjoy making music with them in every way possible--as conductor, soloist, and chamber performer--and their sense of ad­ven­ture is extraordinary.”