The Piano Strings



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by Don Kulak

When one compares the sound of the piano with that of any other stringed instrument (even though the piano is technically considered a percussion instrument, as the piano hammers strike the strings), the piano stands out with a sonic quality clearly it's own. 

Aside from the fact that the piano strings are struck, and not bowed, or plucked, their still remains a distinctly different sound, certainly less pure, or, shall we say dirty, and with an added brilliancy.  The primary reason for this difference lies in the strings themselves.  The following sections will break down the various components of the strings which lend themselves to this unique piano sound.

Tension The first piano was the harpsichord.  Its characteristic, soft, pure, almost fragile sound, was due largely to the vibrating characteristics of the thin and flexible strings.  The hammer dulcimer also bears some resemblance to the sound of the harpsichord, and once again, it is the vibrating tendencies of the light and flexible strings which produces that characteristic soft and delicate timbre. 

Through the years our musical taste leaned toward a more powerful, louder sound. This was most probably due to economic reasons as well, as concert halls were being built larger and larger, in order to accommodate more paying customers for each performance.  As the delicate sounds of the lighter stringed instruments were being lost in the vast spaces of these new halls, the louder forte piano was introduced. 

Consequently one of the first changes that had to be made was to have thicker strings, bridges, and soundboards in order to "beef up" the sound. One of the first piano builders to introduce the louder, forte piano was Anton Walter (1752-1826) of Vienna.  He installed thicker soundboards and strings as well as heavier bridges.  The sound was certainly louder, but also less clear and responsive.

The nature of these forte piano strings is such that they must be drawn to a very high tension, approximately 160-165 lbs. per string, in order to produce a suitable sound.  A tension too low would sound dead, and at the other extreme, a tension too great would produce a sharp, piercing, metallic sound.

The ideal tension, for optimal elasticity and tone, is near 70% of the string’s breaking point.  It is this elasticity which enables the string to divide itself more distinctly, as it breaks up into the smaller vibrating segments, or overtones. (see the following diagram) It is the proper development of these  overtones which creates the rich, "piano" sound. FFFFFF

Soundcraft Piano - Piano Strings and Restringing

This effect of increased tension (increased, as compared to the harpsichord is identical to that of hardening the wire.  At one extreme, this produces a partial structure more similar to that of a steel bar, i.e. a greater number of higher overtones which are predominantly odd numbered.  The sound is metallic and piercing. 

At the other extreme, a decrease in tension would decrease the overtones and increase the fundamental until just a simple tone remained. It would sound dull, flat, and uninteresting.    



All in all, the modern piano is metallic and sharper sounding relative toit's predecessor, the harpsichord, due mostly to the reasons mentioned above.  One might even say that we sacrifice tonal purity in favor of volume, which is essentially what had happened. Assuming there was an ideal piano, it would have at least 50% fundamental with the partials steadily decreasing in strength as they increase infrequency.  This is most efficiently done when the wire is drawn to a tension of160 -165 lbs. each.  It is also this tension which renders the wire most responsive with use, which is one of the reasons why pianos need to be played for some years before they reach their full potential. 

Piano strings have a memory that is they memorize the vibrating pattern created by the impact of the hammer at a given spot on the string.  The more a particular string vibrates a certain way, the more efficient it becomes, therefore conserving energy, and producing a longer, more rounded sound.  Once again, energy conservation and efficiency is the key.  Once the hammer hits the string, the energy and sound is dissipating at fast rate..  And since there are no external means of prolonging the note, short of playing it again, energy efficiency is a key factor which distinguishes a good piano from an excellent piano.                                                                

The effects of high tension, stiff piano wire does more than just change the number and intensity of certain harmonics, it actually alters them, making them slightly sharper than normal.  Consider the end points of vibrating string.  When completely flexible, it will vibrate over the entire speaking length.  A stiff wire becomes rigid at the end points and consequently does  not vibrate over the entire speaking length ), but rather stops short of the two termination points, creating, in effect, a shorter string.   This shorter length produces a higher frequency (frequency being inversely proportional to length).  Bear in mind, the speaking lengths we are referring to here are the speaking lengths of the individual partials, or subdivisions within the string itself.  This is why these subdivisions within each note are called partials, as opposed to harmonics, the latter always consisting of pure whole number ratios tithe fundamental.  Which is to say, they are in tune with themselves, as compared to the "partials" of a piano string which are slightly sharper, and out of tune with themselves.    
The degree to which this frequency is altered is called inharmonicity. So the stiffness and tension of modern piano wire produces 1) more emphasis on the odd numbered harmonics, and 2) inharmonicity - both contributing to a brighter, more metallic sound.  Metallic only in a relative sense, however, compared to, let’s say, a harpsichord, or hammer dulcimer.

To add to the scenario, the number of audible harmonics as well as the degree of inharmonicity also changes with each note.  The higher octaves of the piano have shorter strings, and are therefore even stiffer than the  lower octaves.  When this excessive degree of stiffness exists, the flexibility is decreased to such an extent that the string cannot subdivide in the usual complex manner.  Thus, the reflection of wave motion and consequent formation of segments (harmonics), will be reduced.  The sound will be thinner, almost like listening to one violin as compared to 5 playing simultaneously.

As mentioned earlier, in order to compensate for this thinner sound, the strike point of the hammer in the upper treble favors the few partials there, in order to make that section sparkle and stand out.

©2011 Don Kulak All rights reserved


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