. When the key-pressing strength is moderate (for example, when the sounding volume is mezzo forte mf), the timing at which the hammer strikes the string and the timing at which the lower part of the key 000 strikes the shelf board are almost simultaneous. When the key-pressing strength is strong (for example, when the sounding volume is forte f), the lower part of the key 000 strikes the shelf board after the hammer strikes the string. Therefore, the 