A piano builder active in 18th-century Vienna, Walter created about 700 instruments and counted both Beethoven and Mozart among his clients.

Feltsman, a longtime Mannes faculty member, will play a fortepiano he commissioned from Paul McNaulty, a leading modern builder of historic keyboard instruments. McNaulty patterned the instrument directly after one of Walter's surviving fortepianos.

While the fortepiano, as befits its name, can produce a range of dynamic levels that its ancestors the harpsichord and clavichord cannot, its sound overall is much quieter than that of a modern concert grand. The fortepiano has a very light keyboard action: instead of playing it with the weight of the arm and body, the pianist uses primarily the fingers. "Switching to a modern piano after an hour on the fortepiano," says Feltsman, "can feel like weightlifting."

The Mozart sonata cycle includes five recitals from September 28 through October 12. The first and last concerts will be presented at The New School's Tishman Auditorium (66 West 12th Street), with the remaining three the Mannes Concert Hall (150 West 85th Street). Tickets are available by phone at 212-229-5488 or in person at The New School's box office at 66 West 12th St. Tickets for Mannes concerts will also be available at the door starting at 6:30 p.m. on performance evenings.

More information on the concerts, including the specific works played on each program, can be found at www.newschool.edu/feltsman/.