Acoustics

Acoustics, pronounced uh KOOS tihks, is the study of how sounds are created, transmitted, and received. The word acoustics also refers to the quality of sound as heard or transmitted in a room or concert hall. Two of the major fields in the study of acoustics are architectural acoustics and environmental acoustics.

Architectural acoustics deals with making rooms and buildings quiet and providing good conditions for listening to speech and music. It plays an important role in the planning and construction of auditoriums, churches, halls, libraries, and music rooms.

The acoustical quality of a room is affected by various factors. These include (1) the size and shape of the room; (2) the ability of the ceiling, walls, and floor to keep out unwanted sound; and (3) the use of furnishings made of sound-absorbing materials.

Another factor in the acoustical quality of a room is the way the room reflects sound. Sounds made by a speaker or a musical instrument bounce back and forth against the ceiling, walls, floor, and other surfaces. These reflections of a sound make up its reverberation. The reverberation time of a room is the time in which a sound dies away to one-millionth of its original energy. Reverberations should last about one second in an auditorium designed for speech, and about two seconds in a music hall. But no single strong reflection should arrive at a listener's ear later than about 1/20 of a second after the arrival of the direct sound from a speaker or instrument. Otherwise, the listener hears the strong reflection as a disturbing echo of the original sound.

Furnishings made of sound-absorbing materials control reflection in a room. These include acoustical tiles, carpets, drapes, and upholstered furniture.

Environmental acoustics involves the control of noise pollution, a widespread problem in many residential areas. Major sources of environmental noise include automobiles and other motor vehicles, aircraft, industrial plants, and heavy construction equipment.

Noise pollution can be controlled in three ways: (1) by quieting the source of the noise, (2) by blocking the passage of noise from one place to another, and (3) by absorbing noise energy. For example, mufflers quiet the noise of automobile engines, heavy walls that have no cracks or pores block noise, and furnishings made of acoustical materials absorb noise.

Frequent exposure to intense noise can damage a person's hearing temporarily or permanently. The intensity of noise is measured in units called decibels. Federal laws require industries to reduce factory noise to 90 decibels or lower or to order workers to use protective earplugs or earmuffs.

Other areas of acoustics include (1) physiological acoustics--the way we hear sounds; (2) psychological acoustics--the way we interpret sounds; (3) musical acoustics--the way instruments and voices produce sounds; and (4) speech communication--the way we produce and hear speech. Acoustics also includes the study of sound waves that we cannot hear. For example, infrasound is too low in frequency for the human ear, and ultrasound is too high in frequency. Sound waves within the earth and underwater also fall outside the range of human hearing and form fields of study.

Contributor: James D. Chalupnik, Ph.D., Prof. of Mechanical Engineering, Univ. of Washington.

Acoustics

Master Index