Sound - Acoustics and Noise

Sound - Acoustics and Noise

from Ching Viz Dictionary of Architecture

reflecting surface = a non absorptive surface from which incident sound is reflected, used esp. to redirect sound in a space. to be effective, a reflecting surface should have a least dimension equal to or greater than the wavelength of the lowest frequency of the sound being reflected

attenuation = a decrease in energy or pressure per unit area of a sound wave, occurring as the distance from the source increases as a result of absorption, scattering, or spreading in three dimensions.

acoustical treatment = the application of absorbent or reflecting materials to the walls, ceiling and floor of an enclosed space to alter or improve its acoustic properties.

diffracted sound = airborne sound waves bent by diffraction around an obstacle in their path.

reflected sound = the return of unabsorbed airborne sound after striking a surface, at an angle equal to the angle of incidence.

live = highly reverberant or resonant, as an auditorium or concert hall

dead = without resonance, as a room free from echoes and reverberations.

soundproof = impervious to audible sound.

resonance = the intensification and prolongation of sound produced by sympathetic vibration.

sympathetic vibration = the vibration induced in one body by the vibrations of exactly the same period in a neighboring body.

reverberation = the persistence of a sound within an enclosed space, caused by multiple reflection of the sound after its source has stopped.

decay rate = the rate of decrease of sound pressure level after its source has stopped, usually expressed in decibels per second.

reverberation time = the time in seconds required for a sound made in an enclosed space to diminish by 60 decibels.

echo = the repetition of a sound produced by the reflection of sound waves from an obstructing surface, loud enough and received late enough to be perceived as distinct from the source

flutter = a rapid succession of echoes caused by the reflection of sound waves back and forth between two parallel surfaces, with sufficient time between each reflection to cause the listener to be aware of separate, discrete signals.

focusing = the convergence of sound waves reflected from a concave surface

noise reduction = the perceived difference in sound pressure levels between two enclosed spaces, due to the sound isolating qualities of the separating barrier as well as the absorption present in the receiving room: expressed in decibels

absorption = the interception and conversion of sound energy into heat or other form of energy by the structure of a material, measured in sabins or absorption units.

sabin = a unit of sound absorption, equal to one sq. ft. of a perfectly absorptive surface

metric sabin = a unit of sound absorption, equal to 1 square meter of perfectly absorptive surface, also called absorption unit.

absorption coefficient = a measure of the efficiency of a material in absorbing sound at a specified frequency, equal to the fractional part of the incident sound energy at that frequency absorbed by the material

noise reduction coefficient = a measure of the sound absorbing efficiency of a material, equal to the average of the absorption coefficients of the material, computed to the nearest 0.05 at four frequencies: 250, 500, 1000 & 2000 Hz.