A piano is has more than 200 strings that are struck by hammers when you press the keys. These strings put more than 1000 pounds of pressure on the soundboard; also known as the "heart of the instrument," the soundboard amplifies the volume of the sound made when the hammers hit the strings. Having a working, high quality soundboard is therefore important to the integrity of the piano's sound. A bad soundboard will have many negative effects on a piano, and in some cases means the instrument is ruined.
The soundboard is a 5/8-inch thick wooden board that is curved at the center and sits at the back of the piano. The curve in the soundboard is also called the "crown." The soundboard is attached to the piano with glue around its perimeter. A good quality soundboard is imperative, as it has to withstand seasonal fluctuations in temperature and moisture. The crown of the soundboard will swell and put additional pressure on the strings in humid conditions; conversely, the soundboard will retract and reduce the pressure on the strings as the weather becomes cooler and dry. Good soundboards provide a clear, crisp amplified sound that is free of distortion or deflection.
You will notice the first sign of a bad soundboard in the sound of your piano. A bad soundboard is likely to make you cringe due to the distorted buzzing noises and "off" notes. Buzzing sounds are caused by cracks in a soundboard that has warped and started to pull away from its supports. If the soundboard loses its curved crown, it will also contribute to a very thin, poor sound.
A bad soundboard can also come from poor materials used in the piano's construction. Well-constructed soundboards are made from solid spruce; Italian red spruce is the most expensive, but also creates the cleanest sound. Soundboards made of cheaper wood can crack and deteriorate with age, as cheap soundboards will not be able to support the extreme pressure from the piano strings over time. Cheaply made soundboards are often made of plywood or laminated wood, and although they may not crack, they produce a dead, muffled sound as they are not quality tonal woods. The wood must also be properly cured, otherwise it will not be able to support the strings or tolerate seasonal climate changes.
Dirt and Grime
Over time, dirt and grime can also contribute to a bad soundboard. Cigarette smoke is very bad for a piano's soundboard, as it can build up in places that cannot be cleaned; the only way to reach these places is to take apart and rebuild the piano. After years of use, the soundboard will have a natural accumulation of dust; it is therefore important to have your soundboard cleaned regularly. Professional piano cleaners and tools are available to keep your soundboard in proper working order.
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