Page 18 - 2016Spring

Evolution of the Piano
are produced by three strings. This general pattern is fol- lowed in all modern pianos, although the precise number of notes which employ one, two, or three strings can vary from model to model. Some pianos even have four strings per note in the treble, a feature that has been used occasion- ally but is not common.
In Cristofori's day, the strings used in harpsichords and pia- nos were composed of either brass or iron. His brass wire was essentially the same as modern brass wire, but the tech- nology of iron wire-making had very significant changes during the eighteenth and nineteenth centuries. An advan- tage of iron (as compared to brass) is that iron wire has a greater tensile strength. For a piano, it is desirable for the strings to function at as great a tension as possible (for a given string diameter), as a string at higher tension will have less inharmonicity and can be hit harder by the ham- mer to produce a louder tone. Increasing the tensile strength of iron wire was of great use in many applications (beyond musical instruments), and metallurgists during the 1700s and early 1800s discovered how to make iron wire with con- trolled amounts of impurities (mainly carbon) to make ever stronger wire. This wire was adopted quickly by piano mak- ers when it became available, and one finds that the string tension used in pianos increased substantially from about 150 N in 1770 (the pianos Mozart played) to 200 N in the early 1800s (Beethoven), to 400 N in 1840, and then to 600 N in the earliest Steinway pianos built in the late 1850s. These latest pianos employed steel strings that were then just be- coming available. Steel had been invented much earlier, but the advent of new fabrication methods made steel wire at- tractive for application by piano makers. While the tensile strength of steel wire has improved some since the 1860s, the improvement has been modest, and the string tension and other design parameters used in pianos from that era are similar to those in instruments made today.
The improvement in string materials led to instruments that could produce more sound but led to another problem. The earliest pianos had cases made solely of wood, which were strong enough to withstand the tension forces for an instru- ment with perhaps 6 octaves and strings held at a tension of 200 N. As the number of notes and strings increased, and as the string tension also increased, wood cases were no longer satisfactory. Beginning around 1820, piano makers began incorporating metal rods to reinforce the case, followed by metal plates to strengthen portions of the instrument, usu- ally on the back side of the case (away from the keyboard). Eventually, the full metal plate was invented, which extend-
16 | Acoustics Today | Spring 2016
ed from the area of the tuning pins in the front section all the way to the back and sides. This plate is now made of iron, which has excellent strength when placed under tension (so there is no advantage gained by using steel). Interestingly, the full metal plate was the first important contribution to piano design from an American maker, Alphaeus Babcock, who created this invention around 1825. Piano makers ini- tially objected to the metal plate fearing that it would give a "metallic" character to the tone. The fact that the strings were metallic evidently did not matter according to their "logic." These objections stopped for good with the success of pianos made by the Steinway family and a few other makers.
There was one other important change in the overall layout of strings that was introduced around 1850 by the Steinway family makers. Before that time, the strings were aligned straight from the front to the back on the instrument, that is, parallel to the long straight left side of the case. This pattern was used in harpsichords and continued with grand pianos until the Steinway company introduced the idea known as overstringing. For the piano in Figure 2, the strings for the notes from an octave below middle C to the extreme treble run are not strung straight from front to back, but slant to- ward the back left side of the case (the upper left in Figure 2). This allows those strings to be slightly longer than if they had been strung straight from front to back. It turns out that all else being equal, longer strings exhibit less inharmonic- ity than shorter strings, which gives an improved tone, as described previously. The strings for lower notes then slant in the opposite way, toward the upper right in Figure 2. These are bass strings, and they lie in a plane above the treble strings. To keep these two string layers separate, there are two bridges, one for the treble strings and another taller one for the bass strings. This layout allows the bass strings to be longer than would otherwise be possible for a case of a given size, which again improves the quality of these notes. This layout of two string planes, one for the bass and another for the treble, with separate bridges, is now standard for both grand and upright pianos.
Redesigning the Hammers
The piano differs from its keyboard ancestor, the harpsi- chord, in its use of hammers to strike the strings instead of plucking them. The hammers in Cristofori's pianos would thus seem to be a completely new invention. In some ways they were entirely new, but in other ways they were not. Leg- end has it that the idea of introducing hammers in a keyboard instrument was inspired by an outstanding dulcimer play-