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As you can see from Figs. 25 and 26, a modern grand case is very substantially made. The rims of the best modern grand pianos are usually made from heavy hardwoods such as maple or beech, and may have a total thickness between 80 - 90 mm. The case for a piano of this size may weigh 150 - 200 kg. The acoustical benefit of this is that it provides a massive termination for the edges of the soundboard. This means that the vibrational energy will stay as much as possible in the soundboard instead of dissipating uselessly in the case parts, which are inefficient radiators of sound.
Fig. 25. Grand rim with keybed attached.
Fig. 26. Grand rim nearly completed.
Cristofori had a totally opposite idea about the soundboard as the sketch in Fig. 27 shows (Pollins 1984). His soundboard, 3.5 mm thick, was glued to an extra inner vertical case wall, only about 4 mm thick. This was mechanically decoupled from the main outer walls of the case. Cristofori must have felt that connecting the soundboard directly to the outer case would impede its vibration. Fig. 28 is a view of the underside of the 1720 piano with its bottom board removed. The large cross members are not ribs but rather stiffening members that are connected to the sides of the outer case.
Fig. 27. Cross section of Cristofori case. (By permission of the Journal of the American Musical Instrument Society).
Fig. 28. Close-up of underside of 1720 Cristofori piano. (By permission of the Journal of the American Musical Instrument Society).
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This lecture is one of Five lectures on the Acoustics of the piano
© 1990 Royal Swedish Academy of Music