WHAT IS A NOISE? >>
Noise is today one of the main causes of pollution: men, who cannot insulate himself from noise as he can do from light just closing his eyes, felt the need to protect himself from sounds. The first means able to manage noise within buildings are linked to the following rules:
- realization of building
- acoustic features of building
and of its materials.
A noise represents a set of sound vibrations corresponding to the variations of air pressure man is able to hear.
ARCHITECTURAL ACOUSTIC >>
- Interior air noises (conversations, hi-fi channels, TV…).
- Floor impact noises (falling objects, footsteps, dragging furniture …).
LEVELS OF NOISE >>
Sound level, expressed in Decibel (dB), indicates the intensity of a noise or a sound referring to a scale. From 10 to 120 dB, acoustic pressure is equivalent to noise sources of different origin and generates sensations ranging from calm (10 dB) to pain threshold (120 dB). This evaluation or measurement of noise allows to define an objective, starting from a certain sound, towards an established sound level. To be perceptible, every acoustic improvement must be above 1 dB minimum. In case of simultaneous noises having the same or different sound intensities, the final noise level is the sum of all of them
In particular, two noises having the same intensity will produce a noise of 3 dB higher (i.g., 60dB+60dB=63dB), and two noises having different intensities will produce a noise equal to the stronger one (60dB+80dB=80dB).
ACOUSTIC INSULATION >>
The acoustic insulation is the set of measures to reduce energy transmission, starting from its souces to the places to protect.
- As air noises are concerned, the unit of measurement is Rw: phono-insulating power of separation elements between rooms
- As footsteps sounds are concerned, the unit of measurement is Lnw: level of sound pressure caused by footsteps of the slab.
IMPACT NOISE: FLOORS >>
Impact noise on floors can be caused by:
- percussion (falling objects, footsteps, etc.)
- vibrations (machines)
- friction (dragging furniture).
Because of the rigid continuity of structures, the transmission of impact noise reaches parts of the building distant from the sound source itself, unlike airborne noise.
The most efficient solution both in terms of acoustic and economic results consists in the use of the so-called “floating floor”, the purpose of which is to obtain a flooring free from rigid connections with other structures. This total desolidarization is obtained by placing a suitable elastic material between the flooring, side walls and load bearing floor.
The quality of the construction of the floating floor is very important, since even small rigid connections considerably reduce the sound absorption performance of the system..
EVALUATION INDEX >>
L’nw is calculated taking into account the lateral transmissions. The function to measure it could be:
L’nw = L nw0 – ∆ Lnw + K
- L nw0 is the index of sound level of naked slab
- ∆ Lnw is the increase in acoustic insulation to footsteps depending on the type of building (i.g. floating floor)
- K is the correction to consider the lateral transmissions (dB). K can range 0 < K < 4, generally it is equal to 2 dB.
- The higher the ∆Lnw, the lower the L’nw, the better the performance!