Voice, that is, the human voice, is an instrument in its own right. A singer generates sounds when airflow from the lungs sets the vocal cords into oscillation. The fundamental frequency is controlled by the tension of the vocal cords and the tone quality by the formation of the vocal tract; a wide range of sounds can be created.
A steel string acoustic guitarString instruments generate a sound when the string is plucked, strummed, slapped, etc. The frequency of the wave generated (and therefore the note produced) usually depends on the length of the vibrating portion of the string, its linear density (mass per unit length of string), the tension of each string and the point at which the string is excited; the tone quality varies with the construction of the resonating cavity. Examples: guitars, violins and sitars. Electric string instruments generate sound by a pickup placed under strings. The electric guitar and the electric bass are the most famous examples, but there is a wide variety of new instruments, because the electro-magnetic amplification generates new possibilities. Other Examples: 3rd bridge overtone koto, electric baritone, electric cymbalom.Percussion instruments create sound when struck. The shape and material of the part of the instrument to be struck and the shape of the resonating cavity, if any, determine the sound of the instrument. Examples: drums, bells and cymbals.Friction instruments are any instrument that use friction to create sound. For example the Glass harmonica.Lamellophones create a sound by the plucking of lamellas made from different materials (metal, raphia etc.). These Instruments are tunable, so they do not belong to the idiophones. An example is the Mbira.