The sounds we perceive are vibrations produced by the friction of moving elements in the air. Each induces a singular wavelength of vibrations, measured in number of pulses per second (frequency in Hertz). High frequencies produce high pitched sounds, low frequencies low pitched sounds. These different frequencies overlap to form the noise spectrum analyzed by the auditory system, perceived with more or less intensity depending on the emission pressure. L’intensity Sound is measured in decibels (dB).
Complementarity of sound and thermal insulation solutions
Thermal and acoustic insulation solutions meet different criteria. However, some materials fulfill these two functions satisfactorily. Renovation works (excluding extensions or elevation) are subject to specific provisions, in terms of replacement of floor coverings, facades, openings, heating or ventilation.
Qualities of a good acoustic insulator
The degree of sound insulation of a built space is defined by the coefficient acoustic damping of the partitions (walls, floors and ceilings) that surround it. When a sound hits a wall, part is reflected, part diffuses into the wall and part passes through it. The effectiveness of sound insulation depends on the following characteristics:
- Its air permeability,
- Its volume content of air (porosity) expressed in % or by a physical quantity between 0 and 1,
- The structural shape of its air cavities, open or closed (tortuosity),
- Its thickness,
- The continuity of the insulating layer
In general, the materials porous et fibrous absorb frequencies watersthe materials perforated absorb frequencies medians and the membranes absorb the low frequencies. The universal material for optimizing insulation over the entire frequency range has yet to be invented. In practice, we limit ourselves to applying the conventional compromises, that is, 35 dB(A) pfor general purposes, 38 dB(A) for living quarters, including utility rooms and 70 dB(A) for ground noise.
Structural wall insulation techniques
Structural sound insulation of vertical or horizontal walls is usually achieved by the use of concretes. The mass of the concrete gives it a good quality of insulation against airborne noise, but poor absorption performance. The brick, the concrete blocks and the Aerated concrete are also high-performance carrier materials for acoustic insulation.
The bio-based concrete are new materials containing high proportions of vegetable fibers and pozzolan. They are not carriers, but more ecological, light, hygroscopic, permeable to water vapor and flame retardant, they are particularly indicated in renovationfor the exterior lining new or old buildings and the filling of timber frame buildings. The most common vegetable concrete is loaded with fibers of hemp. This material has excellent acoustic and thermal absorption characteristics, but many other plant aggregates are marketed or still being tested.
Freshly kneaded, it can be banché, spread out or projected. In the form of bricks, it is bricked using thin joints with lime. The exterior surfaces are coated with lime mortar.
Materials used for the interior lining of the walls and the partitioning
Ready to install, composite panels have become the standard for the interior lining of residential buildings. Often excellent in terms of thermal insulation, they can be mediocre for sound insulation. However, some products brilliantly combine these two functions. Their sound absorption coefficient is specified on the labels.
Whatever the installation system, avoid all the polystyrènes and the polyurethanewith acoustic properties mediocre. Prefer:
- Rock wool, natural wool in dense panels
- Cellulose wadding, renowned better sound insulation
- Wood fibers and expanded cork panels
- Panels and rolls of synthetic materials
For this use, avoid glass wool, because of unequal qualities, they are disappointing and less stable over time.
Glued composite panels
Glued panels are ready-to-install wall liners. They consist of a cardboard plasterboard with tapered edges of different widths, 2.50 m long and 10 to 13 mm thick, on which the absorbent is glued in the factory.
They are fixed to the walls by glue dots.
The most efficient interior lining system, it consists of a wooden or metal frame on which ground plates are screwed. The sound absorber must fill, without break in continuity, the space between the structural elements. For greater efficiency, the assembly must be fixed to the floor and to the ceiling, but separated from the wall.
The acoustic performance of framed inner partitions and glued panels can be significantly improved by doubling plasterboard or replacing them with cellulose plates.
The masonry partitions
Masonry acoustic counter-partitions consist of a thin partition, in bricks or concrete blocks, offset from the wall by a value equal to the thickness of the insulating layer. The absorber is either fixed against the wall before building the partition, or deposited during assembly, or blown afterwards.
Vegetable concrete is a material ideal, but expensive, to soundproof partitions. Like wall linings, metal frame systems are high-performance and more affordable solutions. There are also prefabricated soundproof partitions, consisting of an absorbent layer sandwiched between two plasterboards. Their quick and easy installation is within the reach of a good handyman.
To increase the sound insulation of a particular room inexpensively, glue an underlay of cork in rolls on the walls, then apply a paint called “phonic” to complete the finishing of the work. The glazed surfaces will advantageously be lined with thick curtains.
Sound insulation of floors and floors
To avoid the sound bridges, the insulation of floors and floors must be continuous with that of the walls. On the intermediate floors, sound insulation by the floor of the upper floor is to be preferred, in particular to deal with impact noise. It can be performed using a floating screed in vegetable concrete. The insulation of floors on joists is made of reconstituted wood slabs, placed on mineral wool panels or synthetic acoustic underlays. A simple bonded flexible covering effectively dampens the sound of footsteps.
The mineral wool blowing in a thick layer is the most effective and cheapest option for sound insulation in lost attics. The insulation of the ceilings under floors, is carried out by the installation of false ceilings screwed on metal rails, themselves fixed on hangers “anti-vibratiles“, in order to detach from the upper mass. As for the walls and partitions, the system of cardboard mass plates supplemented with a flexible absorbent material is the most used. There are also plaques composites vegetable fibers, expanded wood or synthetic foams glued to the finishing surfaces in cellulose or isorelspecially designed for this use.
Sound insulation of openings
Doors and windows are major sources of noise pollution. The current carpentry at double or triple vitrage, are waterproof and very effectively attenuate airborne noise. To perfect their performance, choose muffler air intakes. The openings are classified AC1, AC2, AC3 and AC4, according to their increasing sound insulation capacity.