Acoustics is the study of the production, transmission, and effects of sound. Acoustics plays an important role in the design of building, machinery, musical instruments and sound-reproducing equipment. Other important applications include the study of metals and the location of underwater objects.
Architectural acoustics, the best-known branch
of acoustics, deals with the design, construction, and furnishing of a
room to achieve the clear transmission of a sound produced within the
room. Good acoustical qualities are especially important in churches,
auditoriums and theaters.
The sound produced within a room is reflected by the walls, ceiling, floor, and other surfaces. This reflection produces reverberation, echo, and interference that affect the quality of the sound.
Reverberation is the persistence of a sound after it has been made. It is caused by repeated reflections of the sound from smooth surfaces. Reverberation lasting one or two seconds improves the quality of sound, but longer-lasting reverberation causes one sound to merge into the next, making speech indistinct and music blurred. Absence of reverberation results in a dry sound that lacks richness.
Echo is a distinct repetition of the original sound. Part of the sound comes to a listener in a direct path from the source of sound, while part is reflected from walls and other surfaces and travels in an indirect path. An echo is heard when the distance traveled by the reflected sound is at least 65 feet longer than the distance traveled by the direct sound.
Interference occurs when sound waves are reflected in such a way that some waves either reinforce or weaken other waves. Interference produces an unequal distribution of sound in a room. Interference is particularly likely to occur in rooms that have large curved surfaces. The same is true of echo.
To reduce reflection, the surfaces of a room should be covered with sound-absorbing materials, such as carpets, draperies, porous plasters, and acoustical panels with many tiny holes. Relatively uniform distribution of sound may be achieved in a rectangular room whose length is no more than double its width.
Noise control is a branch of acoustics that has an important role in the design of machines and the planning of cities, as well as in the design of home, office, and factory interiors.