[justify]The acoustical design issues for buildings involve the principal issues like site noise considerations, including the control of noise transfer to a project’s neighbours, particularly if they are residential, establishing noise standards for each use space, including limitation of excessive ventilation noise, room acoustics considerations, sound isolation between various use spaces, vibration control for mechanical equipment, audio/visual system considerations.
Building planners should develop objective acoustical standards for library projects as an important component of the project program. The information contained in this article about library acoustics is intended as a source for these standards.
As the architectural and engineering design of the project evolves, the design should be reviewed in light of the agreed upon acoustical programmatic requirements for the building project. Since acoustics is typically not a code requirement, a city or state building official cannot be expected to comment on the correctness of the acoustical design in the contract documents. Therefore, it is the responsibility of the facility’s planners, user groups, architects, engineers, and others involved with the project to assure that the project acoustical needs are delineated and that there is follow-through, particularly for verification testing after the ventilation system has been installed and balanced.
Sound and Noise
Sound waves in air result from a physical disturbance of air molecules, such as when a truck drives by a building or when guitar strings are plucked. Sound waves combine and reach a listener via numerous direct and indirect pathways. The listener’s inner ear contains organs that vibrate in response to these molecular disturbances, converting the vibrations into changing electrical potentials that are sensed by the brain, allowing hearing to occur.
Acoustical analysis involves not only the sound source but also the listener and everything in between on the path of the sound. The perception of the receiver can be influenced by the treatment of either the path or the source. Some source sound is desirable, for example a lecturer’s voice, and some source sound is undesirable, such as the sound output from an idling truck outside a window. Undesirable sound is usually called noise.
Unless it is a pure tone, a sound wave is typically made up of vibrations at different frequencies. Like the impact of a stone in a lake, ripples in the water are created that are analogous to sound in the air. The frequency is basically the number of waves that pass a single point in one second, moving at the speed of sound in air. One wave per second is a frequency of one hertz (Hz). A frequency of 1,000 hertz is a kilohertz (kHz).
Human speech contains frequencies between 200 Hz and 5 kHz, while the human ear can actually hear sound generally between 25 Hz and 13 kHz, a wider range. Frequencies below 20 Hz can be sensed as a vibration, though not audible to most people.[/justify]