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Classification of Noise
Noise can be presented in the form of harmonic oscillations. Decomposition of noise in the harmonic components (for certain tones) is called spectral analysis.
The spectrum of noise - a tracker sound pressure level (L, dB) on the frequency (f, Hz).
Depending on spectrum type noise are divided on:
cease broadband spectrum width of more than one octave (octave - bandwidth, whose upper cutoff frequency is twice the lower);
tone, the range of which is expressed discrete tones.
According to the temporary noise characteristics are divided on:
constant sound level which is an 8-hour day has not changed in more than 5 dB;
constant, the sound level which is an 8-hour day time varies by more than 5 dB;
Steady noise is divided into:
oscillating at the time, the sound level which continuously changes over time;
intermittent, sound level which varies in steps (5 dB or more), and the duration of intervals during which the level remains constant is 1s or more;
pulse, consisting of one or more sounds, each of less than 1 s, and the level of sound, measured in decibels And according to the temporal characteristics of "Impulse" and "slow" sound level meter, differ by at least 7 dB.
The characteristic of constant noise in the workplace is a sound pressure level, dB in octave bands with average geometric frequencies 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz. For a rough estimate (eg, inspection supervisors, identifying the need to implement measures of noise insulation et al.) Is assumed as a characteristic constant broadband noise in the workplace apply sound level in decibels A, measured on a temporary characteristic "slow" and subject to correction A sound level meter.
The characteristic of volatile noise in the workplace is an integral criterion - the equivalent (for energy) sound level LA eq. DBA.
Valid sound pressure levels in octave bands, sound levels and equivalent sound levels in the workplace resulted in SDS 3.3.6.037-99  (see. Annex 1).
The structure of the human ear
Approximately 10% of the information we obtain through hearing. The human ear - very complicated and delicate mechanism, which is composed of various elements that long chain transmit from the ear to the cortex.
The ear is divided into three parts - outer, middle and inner (maze).
The outer and middle ear conducts sound waves towards the inner ear. Surround going to the ear and sent to the external ear canal. At the bottom of the course is tympanic membrane - a thin impermeable membrane varies when it get sound waves. Normal vibrations of the eardrum can occur only when both sides of the membrane is air that has the same pressure. The same pressure provided by a special channel auditory tube, which connects the tympanic cavity with the nasopharynx.
On the inside of the eardrum is attached to a chain of auditory ossicles (hammer, anvil and stirrup) that as a result of vibrations of the eardrum are also beginning to fluctuate. Stirrup, which is on the border between the middle and inner ear, fluctuating, transmits vibrations to the fluid filled ear labyrinth. There are special (hairs) cells that convert sound vibrations to nerve impulse energy. Auditory nerve impulses generated hair cells penetrate the brain, and passed several stages nerve pathways, these impulses reach the temporal lobe of the cerebral cortex, where the central section of the auditory analyzer. Here the final analysis is performed and heard we perceive surround sound as human speech or music magic, birds chirping or the howling wind, the roar of the engine or the noise of city streets during rush hour.