In this post we will try to clarify these concepts and move them to everyday situations to help understand them better.
We begin with the sound absorption, this is a property that present all materials which absorb part of the acoustic energy index on them in the form of sound pressure waves, transforming it into other forms of energy (usually heat).
The following graph (obtained courtesy of World of acoustic) illustrates these concepts, part of the incident energy (Ei) is reflected (Er), another part is absorbed by the material (Ea) and some is transmitted (Et), fulfilling provided that Ei = Ea + Er + Et
Most of the materials identified with the label "absorbent material" acoustic property should this entrapped air within as small cells. The acoustic energy is converted to heat energy due to rubbing. The advantage of such materials is that their good properties as combine sound absorbers with a reduced weight due to its greater part are formed by air. Examples of such materials are rock wool and glass widely used in construction.
The manufacturers of absorbent materials apport the absorption coefficient curves in function of the frequency of the incident sound wave, ls usual values of the absorption coefficient is in the order of 0.9 to 0.95 for medium and high frequencies. This means that 90% of the incident acoustic energy is dissipated by the material in this frequency range.
The manufacturers of absorbent materials apport the absorption coefficient curves in function of the frequency of the incident sound wave, ls usual values of the absorption coefficient is in the order of 0.9 to 0.95 for medium and high frequencies. This means that 90% of the incident acoustic energy is dissipated by the material in this frequency range.
Although acoustic absorbing materials dissipate a high percentage of incident sound energy by themselves do not solve the problems of acoustic isolation
Sometimes absorbent materials are attached directly to the walls of the enclosures to be treated, this treatment improves acoustics barely inside the premises diminishing its reverb but does not improve the sound insulation of the fences. This is due to the nonlinear nature of the sound.
But what does it mean to "non-linear"?, I will try to explain as clearly as possible with an example. If you have a stereo emitting a sound level of 60 dB and bring another team to 60 dB emitting identical the result will be 120 dB (thank God) but will have only 63 dB.
If the same thing happens absorbent materials, dissipating much energy even fail to dissipate enough to get rid of the noise transmitted to the trouble (just cut a few decibels of noise incident).
Absorbent materials are useful in architectural acoustics, but as we will see always in combination with other materials.
With regard to acoustic insulation property is presented a material or set of materials that form a closure to prevent the sound passing through ensuring the comfort across the enclosure in which sound is generated.
The mechanism of action is as follows: part of incident sound wave is reflected by the material while another portion thereof is irradiated by the material in the form of vibration, this vibration causes starts moving the air in the side material opposite the sound. A fraction of the energy that is dissipated through the material.
The sound insulation of a material has a strong dependence on the mass because the heavier material greater fraction of incident sound energy is reflected.
The materials have different characteristics in terms of energy dissipation through them, resulting generally best for soundproofing those which combine a high mass with a high energy dissipation capability.
The materials have different characteristics in terms of energy dissipation through them, resulting generally best for soundproofing those which combine a high mass with a high energy dissipation capability.
The best results in terms of soundproofing materials are combined with consequent high surface mass with absorbent materials.
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