Introduction
Instruments that generate sound by following the laws of acoustics are called acoustic instruments. Examples of such are acoustic guitar, acoustic bass guitar etc.
The resonator and driver:
All acoustic instruments contain resonators. Anything which might vibrate for a reasonable length of time, as a reaction to an energy impulse is said to be resonating. The dimensions and material that the resonator is made up of may be the determining factor behind the frequency at which it vibrates. If the shuddering of the structure stops after a wee amount of time it may be termed as a damped oscillation. The type of vibration might be complex or as simple as simple harmonic motion. The vital factor is frequency matching. If the impulse frequency is equal to the resonating frequency then a cascade of impulses will be able to maintain the shaking or vibration. If the resonator reacts to a vast range of frequencies then it is given the epithet, ‘broadly tuned’. Conversely, if however the resonator reciprocates to a shallow range of frequencies then it is christened as ‘narrowly tuned’. Then there is a device called driver. This driver is the primary device that feeds energy to the resonator. The driver may be the hand of a person who is belting out strong tunes on a guitar. The driver might also be the stick with which to produce exquisitely beautiful sound from a violin etc. If the driver is utilized just once to procreate an amazing sound it is termed an ‘impulse driver’. On the contrary if a series of strokes are required from the driver it is labeled as a ‘sound generator’.
How pitch is controlled:
Most acoustic instruments have provisions for manipulating and controlling the pitch of the instrument. There are two levels, one being tuning and the other being performance. Depending on the tuning, the person controlling the instrument would be able to produce specific pitches when playing it. A pitch controller might be able to change the functions of the driver or resonator. Replication of a tuned structure might be used to provide pitch selection. In case of a string instrument the string acts as the device that administers the pitch, and hence the string frequency is quite imperative.
String instruments:
A firmly lengthened and stretched string acts as the driver in this category of acoustic instruments. The string can be set into a vibration by exerting a force on it by means of a pluck or a hammer-blow. The speed at which the quivering occurs depends on the mass, tension and length. It is a very intricate vibration that has energies from many harmonic frequencies. There is a connecting feature called a bridge. This bridge propagates the vibration from the driver to the resonator. The resonator might be a weird looking box, whose shape cannot be easily described. It may also be a flat board that is colored white. The whole surface area that the resonator has is utilized in radiating the sound of a particular frequency or an array of frequencies. A guitar is a great representation of string instruments.
There are instruments galore, and all of these play great parts in carrying forward the aura and magnificence of acoustic instruments.
