The soundboard is the single largest piece of wood and the most important part in a piano. A proper constructed soundboard has a crown or a slight dome shaped curvature to the top of the board to help it resist the down pressure of the strings on the bridges and to transmit sound better. The soundboard is made from either compression or rib-crowning method. Over the years, piano soundboard can lost their crown or their curvature caused by fluctuation of humidity in the surrounding air. As a result, the wood of the soundboard panel expands and contracts and eventually becomes damaged.
You will see this damage in form of cracks on the soundboard. However, in some cases the soundboard shows no visible sign of damage. If that is the case, only a careful evaluation of the sound of the piano can determine the damage; for instance losses power, lack of dynamic range and weak sustain qualities. These are very important because they are the foundation of the piano personality in producing a good musical tone.
The repairing of cracks on the soundboard is merely a cosmetic work and does little if anything to restoring the soundboard performance. Once the wood cells have undergone permanent crushing (compression set), as a result of stress cause by repeated swings in humidity, the soundboard is damaged and should be replaced.
To replace a soundboard can be very expensive. Other than the high repair bill, it is largely depends on the skill and the experience of the person doing the work and the working facilities. A skill person will be able to make the soundboard to sound better and last longer than before.
This is completely false. The wood being used today is no different that in the past. Of course, there are some manufacturers have switched to using less-expensive wood in order to stay competitive as top quality wood is getting more scarce and expensive all the time. The fact remains that top piano manufacturers in Europe continue to seek and use the same type of wood as in the past. Also, with new technology being introduced today, a great deal more is known about how to make the soundboard sound better and last longer than before. And, modern glues used in piano making today last much longer than the animal glues used in the past.
You should ask yourself about the value of a new piano of a brand similar in quality. The value of a used piano will never be, in cost, of a comparable new one. And if you decide to sell later, the ability of recoup the expenses spent on the repairing or replacement will be limited. In our opinion, if not for sentimental or historical reasons, older pianos should not be rebuilt. It will be better off to trade-in for a new good quality piano where it can produces powerful tone, wider dynamic ranges and good sustain qualities.