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Differences between acoustic absorbers and acoustic insulators

Within the world of acoustics there are names and concepts that are quite similar and that can give rise to misinterpretations by many people, as is the case with acoustic absorbers and acoustic insulators. At first they may seem the same thing, but in this article we are going to show the difference between one and the other.

Sound absorption and acoustic conditioning

Let’s start talking about the acoustic absorption, giving as an example when an acoustic wave hits the surface of a certain material. In this case, there is a part of its energy that is reflected and another part of energy (smaller) that is absorbed by this material. In this case, it must be said that the acoustic absorption volume of a certain material is the ratio between the energy that it has absorbed and that which has been reflected by it. This is represented by a value that can range from 0 to 1. Zero means all reflected energy and one means all absorbed energy. For its part, the term acoustic conditioning refers to the protection of a certain area against noise that may enter from outside or come out of it. Normally, the main sound transmission routes are the structural route, which is usually through solid materials, or also through the air, through the air.

Types of materials in terms of sound absorption

Among the materials that have acoustic absorption capacities are resonant, porous, those that have the shape of a panel or membrane, and the Helmholtz absorber. The resonant materials have the maximum absorption at a certain frequency, which is the frequency of the material itself. For their part, porous materials absorb more sound as the frequency increases. In this case, the more porous the material, the higher the absorption rate, but only up to a certain limit because later the material would behave as reflective. The absorbers in the form of a panel or membrane have the ability to absorb low frequencies more effectively than high frequencies. Finally, the Helmholtz absorber is a kind of artificial absorber that absorbs a certain defined frequency range. Regarding the materials that can be found to carry out acoustic conditioning, they can be very varied. Among them we can find lead, one of the best acoustic insulators there is because in addition to insulating from sound it also does so from vibrations. Despite this, today this material is prohibited and for this reason other alternatives are usually used, such as sheets of phonoacoustic wood, rubber, EPDM, etc. Although it sounds strange, the materials used in construction, such as terrazzo, steel or concrete, are sufficiently rigid and non-porous to become good insulators, especially since they are governed by the law of mass. Finally, the air chambers between walls are an effective acoustic insulator. In addition, an absorbent material can be added in the space between the two partitions, such as glass wool or rock wool, which significantly improves conditioning.