The sounds that 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 tones, low frequencies produce low tones. These different frequencies are superimposed to form the noise spectrum analyzed by the auditory system, perceived with more or less intensity according to the emission pressure. Theintensity sound is measured in decibels (dB).
Complementarity of sound and thermal insulation solutions
The thermal and acoustic insulation solutions meet different criteria. However, certain materials fulfill these two functions satisfactorily. Renovation work (excluding extensions or elevation) is subject to special provisions for the replacement of floor coverings, facades, openings, heating or ventilation.
Qualities of a good sound insulation
The degree of sound insulation of a built space is defined by the coefficient acoustic damping walls (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 a 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 and fibrous absorb frequencies acute, the materials perforated absorb frequencies medians and the membranes absorb them 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, i.e. 35 dB (A) pfor general uses, 38 dB (A) for living quarters, including utility rooms and 70 dB (A) for floor noise.
Structural insulation techniques for walls
The structural sound insulation of vertical or horizontal walls is usually obtained by the use of concrete. The mass of the concrete gives it a good quality of airborne sound insulation, but poor absorption performance. The brick, breeze blocks and the Aerated concrete are also efficient load-bearing materials in acoustic insulation.
The biobased concrete are new materials containing high proportions of plant fibers and pozzolan. They are not load-bearing, but more ecological, light, hygroscopic, permeable to water vapor and flame retardant, they are particularly indicated in renovation, for the exterior dubbing new or old buildings and the filling of timber frame buildings. The most common green concrete is loaded with fibers of hemp. This material has excellent acoustic and thermal absorption characteristics, but many other plant aggregates are being marketed or still being tested.
Freshly kneaded, it can be closed, spread out or projected. In the form of bricks, it is masonry using thin lime joints. The exterior surfaces are plastered 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 interior lining of residential buildings. Often excellent for thermal insulation, they can be poor for sound insulation. However, some products combine these two functions brilliantly. Their sound absorption coefficient is specified on the labels.
Whatever the installation system, avoid all polystyrenes and the polyurethane, with acoustic properties mediocre. Prefer:
- Rock wools, natural wools in dense panels
- Cellulose wadding, known best sound insulation
- Wood fibers and expanded cork panels
- Panels and rolls of synthetic materials
For this use, avoid glass wools, because of unequal qualities, they prove to be disappointing and less stable over time.
Bonded composite panels
Glued panels are ready-to-install wall linings. They consist of a cardboard plasterboard with thinned edges of different widths, 2.50 m long and 10 to 13 mm thick, to which the absorbent is glued in the factory.
They are fixed to the walls by pads of glue.
Frame counter partitions
The most efficient interior lining system, it consists of a wooden or metal frame to which earth plates are screwed. The sound absorber must fill, without breaking continuity, the gap between the framing elements. For more efficiency, the assembly must be fixed to the ground and the ceiling, but detached from the wall.
The acoustic performance of frame counter partitions and glued panels can be significantly improved by doubling plasterboards or by replacing them with cellulose sheets.
The masonry partitions
Masonry acoustic counter-partitions consist of a thin partition, made of bricks or concrete blocks, offset from the wall by a value equal to the thickness of the insulating layer. The absorbent is either fixed against the wall before building the partition, or removed during assembly, or blown afterwards.
Insulation of partitions
Green concrete is a material ideal, but expensive, to soundproof partitions. Like wall counter partitions, metal frame systems are efficient and more affordable solutions. There are also prefabricated soundproof partitions, consisting of an absorbent layer sandwiched between two plasterboards. Their installation, simple and fast, is within the reach of a good handyman.
To reinforce the sound insulation of a particular room at a lower cost, glue an underlay of cork in rolls on the walls, then apply a paint called “phonic“to complete the finish of the work. The glazed surfaces will be advantageously lined with thick curtains.
Sound insulation of floors and floors
To avoid phonic bridges, the insulation of floors and floors must be in continuity with that of the walls. On 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 done using a floating screed in green concrete. Isolation of floors on joists is made of reconstituted wood panels, placed on mineral wool panels or synthetic acoustic underlays. A simple glued flexible coating effectively dampens footsteps.
The mineral wool blowing 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-vibration“, in order to separate from the upper mass. As for walls and partitions, the system of mass boards in cardboard plaster supplemented with a flexible absorbent material is the most used. composite plates plant fibers, expanded wood or synthetic foams bonded to finishing surfaces in cellulose or hardboard, specially designed for this use.
Sound insulation of openings
Doors and windows are sources of significant noise pollution. Current joinery in double or triple glazing, are waterproof and very effectively reduce airborne noise. To perfect their performance, choose silencer air intakes. The openings are classified AC1, AC2, AC3 and AC4, according to their increasing sound insulation capacity.