1. Felt hammers controlled by keys, each hammer striking two or three strings (which are tuned in unison) and immediately rebounding from these strings, allowing them to vibrate as long as the key is held down. The mechanism that allows the hammers to rebound from the strings and fall into position for another blow is called the escapement.
2. A damper (made of softer felt) pressing against each string and preventing it from vibrating until it is wanted.
3. A keyboard action that controls both hammers and dampers, causing the damper to leave the string at the same instant that the hammer strikes it.
4. A pedal (damper pedal) controlling all of the dampers, so that at any moment all the strings may be released so as to be free to vibrate.
Other interesting details are:
1. The strings are stretched over a thin sheet of wood called the sound-board. This aids greatly in intensifying the tone.
2. The soft pedal (the one at the left) in an upright piano causes the hammers to move up nearer the strings, and the shorter swing thus afforded causes a less violent blow and consequently a softer tone. In the grand piano this same pedal shifts the mechanism to one side so that the hammers strike only one or two of the strings, this resulting in a softer tone of somewhat modified quality.
These details regarding the mechanism of the piano can easily be verified by removing the front of any ordinary upright piano and observing what takes place when the keys are struck or the pedals depressed.
3. There are two familiar types of organ in use at the present time, (1) the reed organ, (2) the pipe-organ.
The reed organ is very simple in construction, the tone being produced by the vibration of metal reeds (fixed in little cells), through which air is forced (or sucked) from the bellows, the latter being usually worked by the feet of the player. More power may be secured either by drawing additional stops, thus throwing on more sets of reeds, or by opening the knee swells which either throw on more reeds (sometimes octave couplers) or else open a swell box in which some of the reeds are enclosed, the tone being louder when the box is open than when closed. More tone may also be secured by pumping harder.