Are absorption and attenuation the same thing?

Question

Are absorption and attenuation different words for the same thing? Wikipedia separate has articles on Absorption (Acoustics) and Accoustic Attenuation. I don't see a clear physical distinction between these two concepts, but I also don't know much about acoustics. Both seems to measure how much energy is dissipated from a wave passing through a material. Are they genuinely different, or is this a case of different areas having their own terminology?

Answer 1

Attenuation is the reduction of power in a signal/wave/whatever-suits-your-field, and absorption is one process of attenuation. However, there are other sources of attenuation as well, such as scattering/reflection of acoustic waves off of surfaces for example.

Attenuation and absorption are both terms used in a variety of different fields. In my own for example, photonics we experience attenuation through absorption, scattering and reflections as well. These three are different processes with results in attenuation of a signal. You can view maybe attenuation as the opposite of gain/amplification.

Answer 2

In the acoustic nomenclature, attenuation and absorption describe two different things, both related to loss of the sound wave energy.

Attenuation is the continuous dissipation of energy in an acoustic wave as it is propagating through a medium. If you have a sound wave in air travelling from A to B, it will be weaker when it arrives at B. The reason is that energy has continually been dissipated on the way by the medium's viscosity, thermal conduction, and (in air) molecular relaxation.

Absorption is when the sound wave suddenly loses a lot of energy after encountering an object. For example, when a sound wave hits the wall of a room, it will be reflected back, but the reflected wave will be weaker because the wall absorbs part of the energy. Different materials absorb energy to different amounts. Concrete absorbs very little, wood absorbs more, and the walls in an anechoic chamber absorb almost all of the energy in the impinging sound wave, so that the reflected sound is extremely weak.

Thus, in short, attenuation is a continuous energy loss as the sound wave is propagating, while absorption is a sudden energy loss when the sound wave encounters an absorbing object.

Answer 3

They are not really the same thing, attenuation is the loss in sound energy could be due to absorption, reflection, scattering...etc. Absorption is converting sound energy into heat energy when the sound wave hits the absorptive object.

So absorption is part of the attenuation but the attenuation is not necessarily absorption.

For example, noise barriers in the street, attenuate the sound mostly by reflecting it, but in big spaces like lobbies, the absorptive materials on the walls and ceiling attenuate noise by converting sound energy to heat energy in the absorptive material.