Since Mozart's time, piano wires have changed in content -- but very little in quality, research shows.

THE GIST

The wire inside pianos has undergone significant changes between the piano's origins in the early 1700s until the late 1880s.

Research suggests that piano designers used music wire to reach similar harmonic levels despite working with different metals.

Piano designers balance tension and stiffness of music wire, but many other factors are considered as well.

When Wolfgang Mozart sat down to perform his masterpieces to audiences, he tapped out the notes on a much different instrument than most pianos used today. Among the differences was the wire inside his instrument.

While piano wire has changed over the centuries from iron to steel of varying qualities, researchers were surprised to find that the sound produced by the instruments' wires has remained largely unchanged.

"I thought as the wire evolved -- as the tension evolved -- harmonicity would also change over time," Purdue University physics professor Nicholas Giordano told Discovery News. "I was surprised to find all these makers held the same value of harmonicity (quality of sound)."

After studying the sounds of four pianos crafted between 1815 and 1912, two with music wire made of iron and two composed of steel, Giordano discovered the pianos had similar harmonics with predictable ranges of notes -- despite using different metals, string tensions and diameters.

His findings, which will be presented at the Acoustical Society of America's meeting this month, show how piano designers have always had to strike a balance between increasing the tension of the wires (which requires wire of greater tensile strength or a larger diameter) and achieving a good tone quality (which requires a small string diameter).

And even though piano designers have been walking that line for centuries, Giordano believes there's still room for improvement. He said carbon fiber might be worth exploring in the future because of its added strength.

During the piano's genesis in the early 1700s, iron was used to make music wire, but the material's tension and strength limited its ability to produce loud sound, Giordano said. As metallurgy practices improved by the 1850s, it became easier to make music wire out of steel, and by the 1880s music wire steel was nearly identical to what's still in pianos today.

Findings aside, Giordano said he still thinks musical tastes are subjective.

"You ask what does it mean when two notes sound good to a person." he said. "Then, you're getting into psychoacoustics, and that's a topic that gets a lot fuzzier."

Others working with pianos on a daily basis hold different views about music wire, said craftsman and piano builder Arno Patin, who owns a piano business in Ann Arbor, Mich. In addition to tension and stiffness, he said music wire's stress rate is an equal, if not more critical parameter.

Defined as the breaking point of a given material at a certain diameter, stress rate is determined by the content of a material, its alloy properties and the quality and speed of wire drawing. All of these factors create different types of wires, especially when steel is used.

Patin said one cannot consider the evolution of music wire without looking at these other properties.

"You have the same tension, inharmonicity and stiffness, but the acoustical output will be very different," he told Discovery News.

Only a handful of wire producers take these parameters into consideration, which drives Patin to believe that music wire is still evolving, while piano design is not since it has mainly remained unchanged since the 1880s.

Even with math models and calculations, there will never be an "ideal string" because of the physical parameters inherent to the piano, Patin said. He also believes that pianos are far too complex to generalize about the execution of design.

For every individual piano, each string varies by length and has to achieve different tension and stiffness. But this becomes increasingly complicated when each string has to harmonize with others.

"It's not one note." he said. "It's 88 notes that have to be beautiful."