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Owning a home theater pushes irresistibly to increase the sound... But to limit noise between rooms, good sound insulation is essential.

## The principle of the mass law

In terms of sound insulation, the Rw attenuation index indicates the sound reduction level of a partition or insulating material, in decibels (dB). The more material is heavy or has a high sound reduction index (Rw), the more insulating it is.
A concrete partition isolates better than a brick partition. This is the principle of mass law. But it is possible to improve an insulating performance by applying the effect "mass / spring / mass" by doubling plasterboard (or better soundplates, denser) and mineral wool of glass or rock (Ursa, Knauf, Isover...). The latter intercepts the sound and absorbs it, serves as a damper and limits the transmission to the second mass that constitutes the wall, and therefore the nuisance to the outside. Only 14 cm thick in total, this solution is the equivalent in terms of performance of a concrete wall 20 cm thick... but ten times lighter!
The implementation on metal frame is classic: just make sure that it is not in direct contact with the wall (1 cm apart is enough to leave a blade of air that also serves as insulation) and not to compress the insulation during the installation so as not to reduce its properties. For reasonable cinephiles in terms of decibels, simple pasted doublings (doubling complexes) are largely sufficient. They are found in the form of a gypsum board + insulating mineral wool ready to install.

## How to reduce noise transmission

Sound insulation is the set of measures taken to reduce the transmission of noise from their source to places to protect or isolate. Isolation is a loss of noise (a gain therefore) expressed by an index (Rw) indicated in decibels (dB).

 Example 1Uninsulated brick wall 200 mm (Rw = 42 dB) Example 2Masonry wall insulated hollow brick + doubling (Rw = 68 dB)

The soundproof plasterboard placed between two rooms makes it possible reduce noise pollution by 50% compared to a standard structure, a gain of 3 dB. It can, as here, implement it on profiles to mount a partition with glass wool insulation, or doubling an existing wall.

## The principle of the "box in the box"

To isolate a room optimally, the most effective is to to separate wall, floor and ceiling: this is the principle of the "box in the box". However, this requires more work, since the entire room is treated and all acoustic bridges cut.
On the wall, the metal frame lining remains the most effective solution. On the ground, under the cladding and depending on its nature, we apply a resilient underlay (polyester foam, thickness of rock wool, cork or wood fiber). This method is particularly intended to reduce "solid" noise generated by shocks. The ideal is to complete these first works by the realization of a false ceiling metal frame with integrated mineral insulation. It must be fixed on antivibration hangers to prevent vibrations emitted by airborne noise. In contrast, closed-cell materials, such as polystyrene, too rigid, are to be avoided because they may amplify the sound.

## Solution to insulate a room

To eliminate any sound leak, the method called "the box in the box" is the most effective. It consists of doubling a room from floor to ceiling. The latter must be suspended by a system of antivibration hangers.

1. Fur
2. Anti-vibration hangers
3. Sound plasterboard
4. Insulating
5. Slab
6. Strip of dissociation (resilient)
7. cope
8. Undercoat