MUSIC, AND SOUND INSTRUMENTS 421 



vibrations produced will interfere in such a way as to annihilate 

 the sound, and the result will be silence. 



Singers very often find difficulty in striking a familiar pitch 

 because some instrument or wall of the room or pocket in the room 

 produces a resonance which causes the singer to respond sympa- 

 thetically, pitching the voice lower than was intended. A slight 

 change in position will often remedy this trouble. 



FIG. 308. If one fork is struck the other will begin producing a tone in sym- 

 pathy with the first. 



Sounding Board. Most stringed instruments are placed upon 

 some type of board to cause the air to vibrate, usually on a hollow 

 box called a resonance box or sounding board. The piano strings 

 are stretched over a sounding board. The vibrations of the string 

 are transmitted through the frame to the sounding board, forcing 

 it to vibrate with the strings. Since the sounding board is so much 

 larger than the strings, it is able to set a large amount of air in 

 vibration. This the string alone would be unable to do. 



. Wood in Musical Instruments. It is important for the piano 

 maker to select wood having tonal value, " singing wood," as it is 

 sometimes called. This really means wood which is responsive. 

 Some woods are not responsive. If struck with a hammer they do 

 not give any tonal value. Pine and spruce are examples of wood 



