Acoustics

Reflection-Sound wave changed in direction of propagation due to a solid object obscuring its path. Sound AbsorptionThe ability of a material to absorb sound energy through its conversion into thermal energy. Reverberation is the persistence of sound in a particular space after the original sound is removed.[1] A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air.[2] This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard. The length of this sound decay, or reverberation time, receives special consideration in the architectural design of large chambers, which need to have specific reverberation times to achieve optimum performance for their intended activity.[3]

Absorption refers to the absorption of sound waves by a material. The absorption is the "missing piece", when comparing the total reflected and transmitted energy with the incident energy. It is the property of a material that changes acoustic energy into usually heat energy. A material or surface that absorbs sound waves does not reflect them. Absorption of a given material is frequency-dependent and is affected by the size, shape, location, and mounting method used. A good sound absorber is normally a porous material. Mineral wool, glass wool, and micro perforated plates work as sound absorbers. Absorption is not a single mechanism of sound attenuation. Propagation through a heterogeneous system is affected by scattering as well. Acoustical absorption is represented with the symbol A. Acoustical absorption in the ocean is an important part of the analysis of Sonar. The primary substance in seawater that is responsible for absorption is Magnesium sulfate. The secondary substance is boric acid. The most common sea salt, sodium chloride has virtually zero effect on sound absorption.