The financial gift will shift up to 300 concerts each year by UW faculty and students from the hard-to-find Mills Hall and Morphy Hall — both built in 1969 and tucked in the Mosse Humanities Building — to the new building at the northwest corner of University Avenue and Lake Street.

The location is the current site of several storefronts, with Brothers Bar and Grill being the most visible tenant. UW owns the property and plans to demolish those buildings for the performance halls' construction, said John Schaffer, School of Music director. It is uncertain when construction would begin. An architect will be chosen this winter.

Schaffer said the new 800-seat concert hall and 350-seat recital venue will be "world-class spaces."

"It's tremendously significant," said Marc Fink, a UW music professor and prominent Madison performer. "Our facilities are outdated. They served us well."

The donors will remain anonymous — for now, Schaffer said. He added that they likely would go public as construction progresses.

For the past three years, Schaffer and university officials developed plans for a new performance hall, but with "no donors and no money" the project seemed stalled. Even with the $20 million donations, the School of Music will need to raise another $18 million to complete the construction. Schaffer expects that task to be difficult but feasible. The entire building will be funded privately, he said.

Schaffer said complaints about the School of Music's current venues, Mills Hall and Morphy Hall, included small stages, acoustic faults and airflow issues from furnaces.

Chancellor Carolyn "Biddy" Martin made the donation announcement at an arts event honoring former Chancellor John Wiley in Overture Center on Monday night.

An employee at Brothers Bar and Grill declined to comment on the tavern's future — although it is uncertain when construction would begin. Brothers' owners could not be reached on Tuesday.

The School of Music's concert manager, Richard Mumford, was thrilled by the donation's news. He has handled UW concerts since 1999. "It will be so much more visible and inviting," he said.