The lowest key on a piano plays a note called A0 (27.5 Hz). If you push that key down very slowly and hold it, the felt hammer below won't have enough energy to strike the string but the wool damper, which usually rests on top of the string to stop it from vibrating, will stay lifted leaving the string "open." If you then play an A major chord one octave op, consisting of A1 (55 Hz) - C#2 (68.75 Hz) - E2 (82.5 Hz) - A2 (110 Hz), with a quick, hard strike and sudden staccato release, you will hear a soft, long-lived echo of the chord even though the dampers have stopped vibration in the strings of the chord. What is going on here? Explain in a few sentences.