Sound production and acoustics

The Violin - Sound production and acoustics

Any violin has a certain potential of volume, whose realization depends partly on ‘accessories’ – the type of strings and their tension, the type of bridge, the quality of the bow, even the type of chin and shoulder rests – and partly on the skill of the player.

Fingering, vibrato, bow speed and pressure, and the relative placing of the bow between the bridge and the end of the fingerboard all have a direct bearing on the dynamic and tonal characteristics of the sound.

When the bow sets the string or strings in motion, the vibrations are transmitted to the belly and the back via the bridge and the soundpost.

The soundpost renders the right foot of the bridge (the nearest to the E string) effectively immobile, leaving the left one relatively free to transmit vibrations to the bass-bar and belly (which functions as the soundboard of the instrument) and thence, through the sides to the back (whose primary function, however, is as a reflector). The total area of the soundbox then further amplifies the vibrations and transmits them eventually to the ear of the listener. The soundholes operate as a secondary and complementary acoustical system, adding considerably to the resonance.

The quality and character of the tone depend on the vibrating string and how well its fundamental pitch frequency and upper partials are received and transmitted by the wood of the violin's body. The string vibrates (for any given pitch) not only as a whole – that is, as stopped between nut and bridge by the player's finger – but also in various parts of its length so as to produce the other harmonics of the fundamental, thus giving richness and complexity to the timbre. Some individual tones are the result of the complex interaction of as many as 20 upper partials in addition to the fundamental.

The role of the violin body is to amplify and project the string vibrations to the outer air. What makes a particular violin good is the degree to which it transmits the string vibrations of the fundamental and its harmonics with equal response over the whole register of the instrument. The tone of the violin, then, depends initially on the capacity of the many resonance frequencies of the wood to respond to the string vibrations. Many makers, when adjusting the final thicknesses of the back and belly of a new violin, tap the plates (or fix them in a clamp and bow their edges) to tune them. The notes produced are known as ‘tap tones’. (The natural resonance of the interior air space – the so-called ‘air tone’ – has a frequency normally in the area of the D string in superior violins.)

Many experiments have been made, especially in the last 50 years, to determine which factors affect the timbre of a single note or of all the notes of a particular violin, thus distinguishing one violin from another. Modern acoustics, using electronic equipment, has shown that some previously accepted theories, including the ‘formant’ theory, will have to be modified or even discarded. There are still major questions regarding the acoustics of the violin (not to mention related areas in the physiology of hearing) that are not yet completely or satisfactorily answered – for example, what makes a violin a ‘good’ one, and whether old violins are better than modern ones (at present, the best available answer to the second question is ‘Not necessarily’).

Since its origins, the violin has undergone a considerable evolution of detail to meet the changing requirements of successive generations of performers and composers. The first century and a half of the ‘true’ violin culminated in the magnificent ‘classical’ model of Antonio Stradivari shortly after 1700. But this was not the end of the instrument's evolution; in the early years of the 19th century it was altered in a number of respects to attain greater power and a more mellow tonal quality (see §5 below). It was in this era, too, that the Tourte bow gained universal acceptance. Today the violin is a more powerful instrument, supporting greater tensions and pressures thanks largely to the move away from gut strings described above. These changes in the violin (and bow) were occasioned by new styles of music and new techniques of playing. Fig.6 juxtaposes the radically different approaches to violin playing in the 17th and 20th centuries. Whether we regard these changes as improvements is an entirely subjective matter. Many musicians now take the view that a particular repertory will be served best by performing it with instruments set up (and played) in the way the composers of the time expected. It is in response to this approach that so many violinists have now acquired ‘Baroque’, ‘Classical’, or even ‘Renaissance’ violins (while some, too, perform Romantic literature on violins strung as they would have been in the 19th century).