Sound absorption: sound absorption coefficients. Sound absorption materials: table

In rooms where a large proportion of surfacesmake up an open brick, plaster, tile, concrete, glass or metal, always hear a long echo. If there are several signal sources in such a room: musical accompaniment, production noise, conversations of people, direct sound is superimposed on its reflection from the walls.

This entails promiscuity of speech andincrease the noise level in the room. In most situations, this effect is undesirable. For example, the halls of railway stations and airports, as well as large supermarkets and subway lobbies are designed to minimize the after-sounding time (otherwise it is called the reverberation time), because otherwise it is simply impossible to understand the content of the ads. Also within the specified limits should be reverberation in theater, concert and lecture rooms. The increased reverberation time distorts the perception of music and speech. On the contrary, a small time entails the "dryness" of the hall and the lack of depth of sound. Sound-absorbing materials and structures are used to reduce or change the reverberation time in interior decoration.

To protect the room from noise, applya variety of materials that are able to create an obstacle in his path. Their choice is determined by the task. The task may include both sound insulation and sound absorption. We will talk about them.

Soundproofing

The goal of soundproofing is -reflection of noise waves in order to prevent them from penetrating the wall of the room. The special structure of the soundproofing materials erects a barrier in the way of the waves, which reflects them. The ability of the structure to sound insulation depends primarily on the mass. The thicker and thicker the wall is, the harder it is for sounds to penetrate the room. To assess the ability of enclosing building structures to sound insulation use such a value as the sound insulation index. This parameter is measured in dB and should be in the range of 52-60 dB. Soundproof materials are considered to be dense. Among them, drywall, brick, concrete.

Sound absorption

The purpose of sound absorption is to absorb the noise without giving itbounce off the surface back into the room. It is measured by such a parameter as the sound absorption coefficient of materials, varying from 0 to 1. If the value of this coefficient is zero, the signal is reflected from the walls in full. When all noise is completely absorbed, the coefficient is one. The materials with the considered properties include those that have a certain level of sound absorption. Sound absorption coefficients should be more than 0.4.

Silencers come in the following groups:

• layered structures;
• three-dimensional;
• porous (including fibrous);
• porous with perforated screens;
• resonant.

The higher the coefficient value, the higher the sound absorption class.

Porous Sound Absorbers

Porous sound absorbers are produced inthe shape of slabs of porous lightweight materials attached directly to the enclosing surfaces or at a distance from them. These materials are produced on the basis of kaolin, pumice, slags, vermiculite, using cement, lime or gypsum as a binder. These materials have sufficient strength and can be used to reduce the noise level in the foyer, lobbies, corridors, and on the stairs of public buildings and industrial buildings.

Fibrous sound absorbers

In those rooms where the appearancesound absorbers should be more aesthetic, materials are applied from fibers, treated in a special way. Mineral wool, glass wool, as well as wood and synthetic fibers are used as raw materials for their manufacture. Such sound absorbers have the form of ceiling and wall panels or elements of curved and volumetric shape. Special porous paints are applied to the surface of sound absorbers, which can pass air, or they are coated with special materials or fabrics that also have the property of air permeability.

In modern construction fibroussound-absorbing panels are most in demand. They have proven to be effective in terms of acoustics and meet the increased requirements for room decoration.

Sound absorption nature

Dispersion energy of acoustic oscillations infiber absorbers with heat (sound absorption of materials) has several reasons. Firstly, due to the viscosity of air, which is quite abundant in the interfibral gaps, the oscillation of air particles in the internal volume of the absorber is accompanied by friction. Secondly, there is air friction on the fibers, which also have a significant total surface area. Next, the fibers rub against each other, and energy is dissipated due to the friction of the fiber crystals between themselves. Therefore, at medium and high frequencies, particularly effective sound absorption occurs. The sound absorption coefficients of materials are within 0.4 ... 1.0. At low frequencies, it is harder to achieve.

Отметим, что коэффициент звукопоглощения calculated as the ratio of the signal not absorbed by the surface and transmitted through it to the total energy that acts on the surface. A table of sound absorption coefficients is used to obtain reference data on sound absorption of basic building materials. It is listed below.

Table. Sound absorption, sound absorption coefficients

Material	Noise absorption coefficient at 1000 Hz
Plate Hardboard	0,40-0,80
Perforated Acoustic Sheet	0,4-0,9
Fibrolite	0,45-0,50
Foam glass	0,3-0,5
Concrete wall	0,015
Fiberglass	0,76-0,81
Wooden wall	0,06-0,1
Brick wall	0,032
Basalt fiber	0,94-0,95

Sound absorbing structures

Звукопоглощающие материалы волокнистого и Porous type is used most often to improve the acoustic properties of theaters, cinemas, concert halls, recording studios. They are also used to make less noise in kindergartens, hospitals, schools.

In order to increase noise absorption in the low frequency range, the thickness of the materials must be increased or a gap in air between the absorber and the sound reflecting structure must be planned.

If no dye is applied to the fibrous sound absorbers and there is no outer layer of fabric on them, they can be used to protect them from damage based on perforated material.

В промежутке между экраном и материалом из the fibers place an air-permeable canvas to avoid getting fiber particles in the air. Sound absorbing structures, equipped with a perforated coating, make it possible to obtain sound absorption of good quality at all frequencies. Adjusting the frequency characteristics of sound absorption occurs by selecting materials. And also by varying their thickness, size and shape, the distance between the holes. Sound absorbing structures, equipped with a perforated metal screen, are widely used as anti-vandal coatings. One of the modern materials of this kind is "Schumanet Eco".

The best noise absorbing materials. Glass wool

Fiberglass based materialpossessing high durability and elasticity. Glass wool also emits high vibration resistance. Sound absorption of glass wool occurs due to the presence in the gaps between the fibers of a large number of voids filled with air. Advantages of glass wool are fire safety, low weight, high elasticity, lack of hygroscopicity, vapor permeability, chemical passivity. Glass wool serves as an element of acoustic partitions of rolls or plates, as one of the layers of multi-layer sound-absorbing structures.

Mineral wool

Mineral wool is a fibrous material, the raw materials for which are silicate rock melts, metallurgical slags, and mixtures thereof.

Advantages of the material:incombustibility, chemical passivity and, as a result, the absence of corrosion on metals in contact with mineral wool. The quality of sound absorption is realized due to the chaotic arrangement of the fibers.

To get a high ratiosound absorption (from 0.7 to 0.9) in the entire frequency band, using multi-layer resonant type structures, which consist of several parallel screens with different perforations with air gaps of different thickness.

Materials "Shumanet Eco"

They are a sound insulation layer,designed for use in frame partitions, plasterboard linings or suspended ceilings. They are made in the form of hydrophobic fiberglass plates, which are covered with fiberglass. The material used inert binder based on acrylic, which makes sound-absorbing panels non-combustible.

Features of large premises

It is necessary to take into account that in rooms that havelarge volume, the effect of reducing the reverberation time due to the structures of additional sound absorption is not so great. Such rooms regulate the reverberation time due to the shape of the ceilings and walls. For example, the use of not flat, but rounded ceilings and pilasters of various shapes or balconies on the walls makes sound absorption greater. This form of architectural details makes it possible to obtain an acoustic field of greater diffusion, which has a positive effect on the acoustic climate in the room.

It should also be noted that the overall noise absorptionhall increases with the presence of decorations, soft chairs, curtains. This should be taken into account when choosing finishing materials in order to pick up sound absorption. Sound absorption coefficients will increase in this case.