Science – Soundboards in Musical Instruments

October 14, 2010 by Leave a Comment
Makers and sellers of violins, pianos, guitars and other acoustic instruments are very particular about what materials their products contain. Piano manufacturers often advertise that their soundboards are only made from the “finest Alaska Sitka spruce”. The reasons given for this often have something to do with the short growing season, and limited moisture in the soil where the trees grow, which causes the wood to have a very close grain. Growth ring science has proven that the spruce tops of Stradivarius violins were made from trees that grew during a “mini ice age”, when winters were especially long and cold.

It is sometimes advertised that piano soundboards and violin parts act as resonators, amplifying the vibrations of the strings. This is not scientifically accurate. The air inside a violin or guitar and inside the case of a piano acts as a resonator, but the soundboard is an amplifier. Vibrations of the strings are transmitted through the bridge of a piano, guitar or violin to the wooden soundboard or top of the instrument. The soundboard vibrating at the same frequencies as the strings efficiently transmits the vibration into the surrounding air, due to its flat shape.

It has been claimed that spruce has a peculiar cellular structure, of “cells within cells”, that vibrate in sympathy with the strings of an instrument. Science can verify this structure, but microscopic cells cannot account for the way all the different pitches of the vibrating strings are amplified for listeners to hear. Listeners hear the vibrations through the air in the room, which is set in motion by the vibration of the soundboard. This is easily demonstrated by comparing an electric and acoustic guitar. The electric guitar has a solid body, with no soundboard. With an electric amplifier, the strings are barely audible. Put the same strings on an acoustic guitar, and you’ll hear plenty of sound. The real reason spruce works well as a soundboard is its high strength to weight ratio. It can be cut thin enough to vibrate easily, while retaining sufficient strength to be structurally sound.

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Science and the Invention of the Piano

September 30, 2010 by Leave a Comment
The Oldest Surviving Piano
Image by 1gl via Flickr

Science and art are inseparably connected. Consider the piano. The development of the modern piano is heavily dependent on scientific principles. Its forerunner, the harpsichord, produced sound when thin strings were plucked by feather quills activated by levers known as keys. No matter how much or how little force was used to depress the key, the volume of tone was always the same.

Around the year 1690, using the scientific method, an Italian harpsichord maker named Bartolomeo Cristofori might have asked, “Is it possible to make a harpsichord that can play soft and loud?” That may not be the question he asked; perhaps he wanted to know if leather hammers could be made to work on a keyboard instrument, for a different kind of sound than the plucked harpsichord.

The Science of Physics: Levers Allow the Piano to Play Soft and Loud

Cristofori knew that if the hammers were directly connected to the back end of a key, depressing the front end would hold the hammer pressed against the string, preventing it from continuing to vibrate. He experimented, connecting the hammer to a second lever, separate from the key. The levers were arranged so that the hammer would move eight times as fast as the front end of the key, to give it sufficient force to cause the string to vibrate when struck. A crucial feature was that when the hammer came almost to the string, the key would disengage from the lever to which the hammer was attached. This allowed the hammer to move freely during the last two millimeters of its travel, then fall back after striking the string, so the vibration could continue. With a small amount of force applied to the key, the hammer would strike gently, producing a soft tone. More force would move the hammer faster, resulting in a louder sound. This phenomenon made all the difference, allowing the piano to gain supremacy over the harpsichord. Cristofori experimented and refined his invention, and others continued until the piano reached its current form. Without science, we might be making music by banging rocks together.

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Science ‘ Physics of Piano Strings ‘ Why Partials are Sharp

September 3, 2010 by Leave a Comment
Piano strings
Image via Wikipedia
The piano is an amazingly complex musical instrument. Science offers a lot of help in understanding how the piano works and why it behaves as it does. To begin with, piano strings are really wires, and they are rather stiff wires, when stretched over the cast iron plate of a piano. When any cord vibrates, whether it is a piano string, harp string, guitar string, or clothesline, it behaves in an interesting way. Besides the entire length of the string moving as one piece, (fundamental vibration) with its widest amplitude (distance from its silent resting position) being in the middle of its length, each string also vibrates in sections. Any vibrating cord moves in two, three, four, five, etc. equal sections, simultaneously with its fundamental vibration. The vibration in two sections produces a pitch of a frequency twice as fast as the fundamental pitch, the vibration in three sections is three times as fast, and so on. The unique quality of sound of any vibrating cord is determined by the relative strength of each of the partial vibrations. That is why violin, piano, guitar and harp strings all sound different. A strong fundamental vibration with very weak upper partials will sound clearer than a weaker fundamental with relatively strong upper partials, which will be richer, or fuzzier, depending on its physical qualities.

With the piano, the strings are so stiff that there are small portions of each string which do not move, between the vibrating sections of wire in each partial. These tiny dead zones are called nodes. Because the vibrating portion is slightly less than half, (or a third, or fourth, etc.) of the whole length of the string, the partials are sharp- their frequency of vibration is a little faster than that of a perfectly in-tune partial would be. Because each partial has one more node than the one before it, it is also slightly sharper, because of the increase in the non-vibrating portion of the string. This out-of-tune quality of piano strings is called “inharmonicity”.

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Science’ Physics of Piano Strings’ Placement of Hammer Striking Point on String

September 1, 2010 by Leave a Comment
Each string in the piano is struck by a hammer, which is a felt-covered mallet, to start it vibrating. Each of the 88 keys on a standard size piano keyboard activates one hammer, but each hammer strikes one, two or three strings, depending on its pitch. The lowest pitches only require one heavy bass string, some notes require two strings tuned to the same pitch, and most notes on the piano require three strings. This design is a balance of science and practicality.

In order to produce the best quality of sound, each string of the piano must be struck at a particular point along its length. This point has been found to be between 1/8 and 1/7 of the distance from one end of the vibrating portion of the string. Exactly 1/8 of the distance would not be optimal. The reason for this may be explained by a principle of the science of physics, concerning the nature of vibrating cords. Each cord vibrates in equal sections at the same time as it vibrates as a whole. That is, it vibrates in two equal sections, three equal sections, and so on. If a hammer struck a piano string exactly on one of the “nodes” between vibrating sections, that particular set of vibrations would not be effectively activated. For example, if you struck the string in the exact middle, it could vibrate as a whole, and in thirds, but not very well in halves or quarters, because the middle is a node between the vibrating sections of those partials.

A striking point between 1/8 and 1/7 of the distance from the end avoids all the nodes for at least the first seven partials, which are the strongest. To obey this principle of science, it is only necessary to arrange the geometry of a piano in such a way that a row of hammers in a straight line will all strike their respective strings at the appropriate “sweet spot” where the best tone will be produced.

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