What is the piano soundbaord? It is a really important part of the piano and crucial in producing the sound that you actually hear coming out from the instrument.
As you have learnt in the post about piano strings and hammers, piano strings are pulled tightly across a wooden frame with pins. These pins can be tightened and loosened and produce the right note when hit with the piano hammers. However, the strings vibrating on their own would not produce enough sound.
In fact you would not be able to hear them outside the piano. The vibration of the strings is amplified by the piano soundboard. Like any other musical instrument that uses strings such as a guitar that uses a hollow sound box under the strings to amplify the sound, the piano uses the soundboard to the same effect.
The soundboard of the piano may or may not be any more important that its other parts, but it is difficult to make and expensive to replace. This piece of information is crucial if you are ever buying a second hand piano. When you have the piano looked over by an expert technician before buying, and you always must, the soundboard needs to be in good condition.
If the soundboard is not all right then you might as well pass over the sale because as mentioned it is very expensive to replace. And difficult to find even. The piano soundboard has to be made from the right wood, of the right thickness and cured for the right amount of time.
It is also a part that can get damaged if the piano is carelessly moved about and happens to take a heavy bump or two. The piano soundboard is slightly curved in shape. This curvature of the soundboard is called the Crown. This design feature helps in amplifying the sound of the piano to the right extent.