14 DAY TRIAL // Sounds are vibrations transmitted through the air as waves to our ears. The frequency of the sounds is given by the number of vibrations per second, measured in hertz (Hz). Humans can perceive only sounds with a frequency of 16 Hz to 20 kHz (20,000 Hz). Most musical instruments produce sounds with frequencies of 27.5 Hz to 4,186 Hz. Doubling the frequency produces a note with an octave higher on the musical scale. Tonality refers to how high or low a note is for the human ear. A low note, like that produced by a contrabass, has a grave tonality, while a note produced by violin upper string has an acute tonality.
Various instruments emit sound of different qualities for the same note. The frequency is the same, and note tonality identical, but, beside the main frequency, there are other vibrations also, differing from one instrument to another and giving a specific sound. The secondary vibrations are named harmonies, being multiples of the basic frequency. Also, the way a note is produced makes the start of the note to be different from the rest of the note, and this enables us to differentiate between instruments. For example, the start of a piano note is relatively loudly heard, because the piano spring is hit by a small hammer. The rest of the note is lower, because the string can vibrate further. Instead, the pipe organ produces smaller differences, because air is blown continuously through the pipes.
Percussion instruments. The large drum was initially a cooking pot covered by a stretched, tensioned skin. Modern large drums, called tympani, can generate a larger array of notes. By pressing a pedal, the tension of the membrane is modified, changing the tonality of the emitted sound.
Bells are made of dense and heavy metals, which vibrate a relatively longer period of time after being hit. Large bells cannot be used in orchestras, that's why lighter cymbals and tubes are used. Cymbals are made of brass and produce many sonic vibrations simultaneously, coming with a well defined tonality.
Brass instruments are made of a tube, having at one end a mouthpiece, while the other end is a large opening. The musician must make the mouthpiece vibrate. This vibration, in its turn, causes the vibration of the air inside the tube, and the sonic waves cause an up and down movements inside the instrument, called "stationary waves".
The lowest note that can be produced by a tube is called fundamental and it is generated by the simplest type of stationary wave. More complex models generate higher tonality notes, harmonies of the fundamental frequencies. The musician achieves the desired note by puckering its lips and modifying their tension.
The simplest brass instruments can produce just a few notes, like the bugle, which can emit just 7-8 notes. Other brass instruments are much more performing, due to modifications made to the tube length. The trumpet has valves that direct the air through additional sections of the tube when pressed.
Wind instruments are of two categories: pipes and reed instruments. Modern pipes have a hole located to the proximal end, and the musician directs the air using its lips. The stronger the blow, the higher the frequency of the emitted sounds. The pipe has 6-7 holes that can be covered or uncovered by the fingers, obtaining certain notes. When a hole is covered, the effective length of the air column that vibrates is reduced, resulting a higher tonality note.
Reed instruments work differently. Musician's blow makes the reed vibrate, producing vibrations of the air column inside the instrument. The combination between the reed and the carved wood cylinder produced a new family of reed instruments, comprising the clarinet, bassoon and oboe. Saxophone was invented in the 19th century by Adolph Sax. Even if made of brass, it is a woodwind instrument.
String instruments. When a tensioned string is made vibrate using a bow, it forms a stationary wave. The tonality of the produced note depends on the string length and its tension. The string can be tensioned using a string board, so that the tonality of the note is increased. By pressing a string at its half length, a frequency twice higher than that of the whole string is achieved, meaning an octave higher than the fundamental frequency of the string.
The sound produced by string must be amplified, in order to be heard. This is achieved using a wooden resonance box, that form the body of the instrument. In the family of modern violins (including violin, viola, violoncello and contrabass), 4 strings are used, being raised over the resonance box with the help of a deck. The deck transmits the vibrations from the strings to the resonance box. Formerly, strings were made of sheep intestines, but currently they are covered by a thin thread of silver (the lower strings) or steel (the higher strings).
Bar instruments. Of this type are the guitar, banjo, mandolin, balalaika and others. Their string board has prominent metal elements that ease the achieving of the desired note. The musician has to press the string in any point between two successive bars and the length of the string vibration will be reduced.
By the '30s, the sounds of the guitars could be amplified by electromagnetic translators placed behind the strings, producing electric signals that allow to be amplified and reproduced by a loudspeaker at the desired volume. Many of the modern electric guitars are especially made for achieving this effect, and, in this case, the guitar's body does not have the role of resonance box anymore, so it can be made of massive material. Bass guitars replaced massive contrabasses in pop groups.
Keyboard instruments. These are the most complex instruments, from a mechanical point of view. The harpsichord, the predecessor of the piano, had appliances called plectra, that, acted by the keyboard, pinched the strings. This could not allow great variations in volume.
But a piano key is pressed acting a small hammer wrapped in felt that hits a string. The speed of the hammer's movement is controlled by the force with which the musician presses the key. This allows the control of the volume.
Pipe organ is a wind instrument controlled through keyboard and pedals. The air flow is produced mechanically and directed to the desired tube via valves. At the beginning, the flow was ensured by apprentices using bellows, but currently electric air pumps are used.
The electronic organs mimic the sounds produced by pipe organs using electronic generators of tone and amplifiers. This way the Hammond organ emerged, giving the possibility to mimic any other instrument or create new, original sounds. It uses electronic circuits to generate sonic signals.