You said acoustics?

.01

Noise, molecules of air creating a vibration that propagates up to the brain.

When not chosen, noise is an acoustic phenomenon producing a hearing sensation considered as annoying and unpleasant (International Organization for Standardization)

.02

A sound, characterized by its frequency (number of vibrations of the molecule of air per second) and its sound level (clear energy associated with the variation of the atmospheric pressure) is amplified by the external ear: the auricle at first, then passes in transit by the auditory canal up to the eardrum.

.03

The middle ear, a cavity filled with air, reacts like a pre-amplifier: it plays the role of an adapter between the air environment (external ear) and the liquid environment (internal ear). It also protects the hearing system from too intense noises.

.04

The internal ear, the center of the organs needed for balance in particular, amplifies the sound vibrations and selects them by frequency, from the gravest to the most acute. They are then delivered in the brain in the form of electric impulses that it will only have to decode.

.05

The ear is an extraordinarily sensitive organ which can perceive a wide range of noises from the wind in the leaves to the sound of thunder.

.06

To ease calculations, acousticians invented the decibel (dB), the unit to measure the level of sound.

.07

The sound sensation and the sound energy are not proportional but bound by the logarithmic decibel law: two identical sound levels are not equal to a doubled sound level but to a sound level increased by 3 decibels.

.08

The decibel A allows to reproduce the sensibility of the ear. It recreates the heightened sensibility of the ear with the average frequencies. The mesuring instruments are equipped with this level-headedness. It is called dB (A).

.09

An few hours exposure to an intense noise induces hearing tireness provoking a temporary reduction in the hearing acuteness, which will last between 12 and 36 hours in certain conditions. If the exposure is longer or if the noise is very intense, this tireness is transformed into permanent hearing loss which can lead to deafness.

.10

Hearing loss comes along with recruitment (hyper sensibility towards the variations of sound level and in the pain), with acouphenes (irregular or continuous) and with troubles in understanding the messages each sound conveys.

.11

Professional deafness is a consequence of an exposure to high sound levels or of a sound trauma: the ear continues to receive sound waves but does not have the means any more to convert them in nerve impulse.

.12

At first, only the zone where the hearing is the most sensitive is affected.

.13

Then, deafness settles down and the acute frequencies of the conversation are affected…inducing troubles in social and professional life for the individual.

.14

Eventually, deep deafness settles down: we note a sensitive hearing loss towards the sound of voice. Deep deafness is due to an irreparable and definitive destruction of the ciliated cells of the internal ear that no surgical operation can restore.