In rooms where a large proportion of the surfaces are open brick, plaster, tile, concrete, glass or metal, a long echo is always heard. If there are several signal sources in such a room: musical accompaniment, industrial noise, people talking, direct sound is superimposed on its reflection from the walls.
This entails speech illegibility and an increase
in the noise level in the room. In most situations, this effect is undesirable. For example, the halls of stations and airports, as well as large supermarkets and metro lobbies, are designed in such a way as to minimize the time of an aftertone (otherwise called the reverberation time), because otherwise it is simply impossible to understand the contents of the announcements. Also within the specified limits should be reverb in theatrical, concert and lecture rooms. The increased reverberation time distorts the perception of music and speech. On the contrary, short 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 room decoration.
To protect the room from noise, a variety of materials are used that can create an obstacle in its path. Their choice is determined by the task. Sound insulation and sound absorption may also be included. We’ll talk about them.
Soundproofing
The goal that soundproofing faces is the reflection of noise waves in order to prevent them from penetrating the room wall. The special structure of soundproofing materials erects a barrier to the advancement of waves, which reflects them. The ability of a structure to soundproof depends primarily on mass. The more massive and thick the wall is, the more difficult it is for sounds to penetrate the room. To assess the ability of building envelopes to noise 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. Soundproofing is considered dense materials. Among them are drywall, brick, concrete.
Sound absorption
The purpose of sound absorption is to absorb noise, preventing it from reflecting from the surface back into the room. It is measured by a parameter such as the sound absorption coefficient of materials, varying in the range from 0 to 1. If the value of this coefficient is zero, the signal is reflected from the walls in full. When all the noise is completely absorbed, the coefficient is unity. To materials with the considered properties are considered those that have a certain level of sound absorption. Sound absorption coefficients should be more than 0.4.
Sound absorbers are of the following groups:
- layered structures;
- voluminous;
- porous (including fibrous);
- porous with perforated screens;
- resonant.
The higher the coefficient value, the higher the sound absorption class.
Porous Sound Absorbers
Porous-type sound absorbers are produced in the form of slabs of porous lightweight materials fixed directly to or at a distance from enclosing surfaces. These materials are produced on the basis of kaolin, pumice, slag, vermiculite, using cement, lime or gypsum as a binder. These materials are robust enough and can be used to reduce
noise in the lobby, lobby, hallways and
staircases of public buildings and industrial buildings.
Fiber absorbers
In those rooms where the appearance of sound absorbers should be more aesthetic, fiber materials processed in a special way are used. Mineral wool, glass wool, as well as wood and
synthetic fibers are used as raw materials for their manufacture
. Such sound absorbers are in the form of ceiling and wall panels or elements of a curved and three-dimensional shape. On the surface of the sound absorbers, special porous paints are applied that can let air through, or they are coated with special materials or fabrics that also have the property of breathability.
In modern construction, fibrous sound-absorbing panels are most in demand. They have proven their effectiveness in terms of acoustics and meet the increased requirements that apply to the decoration of premises.
The nature of sound absorption
The dissipation of the energy of acoustic vibrations in fiber-type absorbers with heat generation (sound absorption of materials) has several reasons. Firstly, due to the viscosity of the air, which is quite a lot in the interfiber spaces, 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. Then, the fibers rub against each other, and the energy is dissipated due to the friction between the fiber crystals. Therefore, at medium and high frequencies, a particularly effective sound absorption occurs. Sound absorption coefficients of materials are in the range of 0.4 ... 1.0. At
low frequencies, it is more difficult to achieve.
Note that the sound absorption coefficient is calculated as the ratio of the signal energy not absorbed by the surface and the energy passed through it to the total energy that has an effect on the surface. To obtain reference data on sound absorption of basic building materials, use the table of sound absorption coefficients. It is given below.
Table. Sound absorption, sound absorption coefficients
Material | Noise absorption coefficient at 1000 Hz |
Fiberboard plate | 0.40-0.80 |
Perforated Acoustic Sheet | 0.4-0.9 |
Fiberboard | 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
Sound-absorbing materials of the fibrous and porous type are most often used to improve the acoustic properties of the premises of theaters, cinemas, concert halls, recording studios. They are also used to make less noise in kindergartens, hospitals, schools.
To increase sound absorption in the low frequency range, the thickness of the materials must be increased or a gap of air is planned between the absorber and the sound-reflecting structure.
If there is no paint applied to the fibrous absorbers and there is no outer layer of fabric, they can be used with protection against damage based on perforated material.
Between the screen and the fiber material, an air-permeable canvas is placed to prevent the entry of fibrous particles into the air. Sound-absorbing structures equipped with a perforated coating make it possible to obtain sound absorption of good quality at all frequencies. The frequency response of sound absorption is adjusted 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 sound absorbing materials. Glass wool
Fiberglass-based material with high strength and resilience. Glass wool is also distinguished by high vibration resistance. Sound absorption of glass wool occurs due to the presence in the spaces between the fibers of a large number of voids filled with air. The 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 made of rolls or plates, as one of the layers of multilayer sound-absorbing structures.
Mineral wool
Mineral wool is a fibrous material, the raw materials for which are silicate melts of rocks, metallurgical slag and mixtures thereof.
Advantages of the material: incombustibility, chemical passivity and, as a consequence, the absence of corrosion on metals in contact with mineral wool. Sound absorption quality is realized due to the random arrangement of fibers.
To obtain a high sound absorption coefficient (from 0.7 to 0.9) in the entire frequency band, resonant-type multilayer structures are used, which consist of several parallel screens having different perforations with air gaps of different thicknesses.
Materials "Shumanet Eco"
They are a soundproofing layer designed for use in frame partitions, gypsum plasterboard claddings or suspended ceiling structures. They are made in the form of hydrophobized fiberglass plates, which are laminated with fiberglass. The material uses an inert binder based on acrylic, which makes the sound-absorbing panels non-combustible.
Features of large premises
It should be noted that in rooms that have a large volume, the effect of reducing the reverberation time due to additional sound absorption structures 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 great. This form of architectural details makes it possible to obtain an acoustic field of greater diffusivity, which positively affects the acoustic climate in the room.
It should also be noted that the total sound absorption of the hall increases with the presence of decorations, soft chairs, curtains. This should be taken into account when choosing finishing materials in order to select sound absorption. Sound absorption coefficients in this case will increase.