Berlin's main concert hall built by architect Hans Sharoun (1960-1963) is universally regarded an emblem of the city for its excellent acoustic and exciting architecture. The main concert hall is round with the orchestra playing in the middle of the room. Every visitor is regarded equal, there are no special seats not even for the prime minister.
Classical concerts might be expensive but there are various opportunities to enjoy music for a reasonable price. If you are interested in Berlin's post-war history and architecture you should definitely visit the Philharmonie and the surrounding buildings of the so-called Kulturforum (planned by Sharoun + Neue Nationalgalerie by Mies Van der Rohe).
Free lunch concerts every Wednesday in the lobby! If you are under 28 years, get a cheap ticket for any performance!