Sound installation (related to sound art and sound sculpture) is an intermedia and time based art form. It is an expansion of an art installation in the sense that it includes the sound element and therefore the time element. The main difference with a sound sculpture is that a sound installation has a three dimensional space and the axes with which the different sound objects are being organized are not exclusively internal to the work, but also external. A work of art is an installation only if it makes a dialog with the surrounding space. A sound installation is usually a site-specific but sometimes it can be readapted to other spaces. It can be made either in close or open spaces, and context is fundamental to determine how a sound installation will be aesthetically perceived. The difference between a regular art installation and a sound installation is that the later one has the time element, which gives the visiting public the possibility to stay a longer time due possible curiosity over the development of sound. This temporal factor also gives the audience the excuse to explore the space thoroughly due to the dispositions of the different sounds in space.
Sound installations sometimes use interactive art technology (computers, sensors, mechanical and kinetic devices, etc.) but we also find this type of art form using only sound sources placed in different space points (like speakers), or acoustic music instruments materials like piano strings that are played by a performer or by the public (see Paul Panhuysen).
The simpler sound form is a repeating sound loop. This is mostly used in ambient art, and in this case the sound is not the determinant factor of the art work.
The most used sound structure is the open form, since the public can decide to experience a sound installation for just a few minutes or for a longer period of time. This obliges the artist to construct a sound organization that is capable of working well in both of the two cases.
There is also the possibility to have a linear sound structure, where sound develops in the same way as in a musical composition. In this case, the artist might risk not having the audience staying for the whole length of the sound.