ACOUSTICS SLIGHT KNOWLEDGE 
The sound is
any variation of the pressure in the air that can be detected by the human ear. By
definition, the noise is a sound nonwished. More particularly, the noise is an annoying
sound, to distinguish it of the pleasant sounds. When it says not wished agrees to know
clearly what is what noise does to be to not desirable, or when it is said that he is
annoying, agrees to quantify as it is the value of the annoyance, as well as to whom
annoying one, few, many, how long, etc.
SOUND LEVEL METERS
The used
instruments to measure the noise level denominate Sound
level meters and provide an indication of the acoustic level (mediated in the time) of
the sonorous waves that affect the microphone. The level of the sound visualizes normally
on a scale graduated with an indicator of movable needle or in a digital indicator.
The
ear is not equally sensible for all the frequencies. Therefore,
although the sound pressure level of two sounds even can be the same one, can be
interpreted like of different level if one of them presents/displays a greater
concentration in the frequencies in which the ear is more sensible. Therefore filters in
frequency are gotten up in the sound level meters that modify the sensitivity of the sound
level meter with respect to the frequencies that are less audible by the ear. Many sound
level meters are provided with different filters from
sensitivity-frequency.
The two sum of dB never can be more than 3 dB more than the greater one of If the difference that there is between both 10 the two values to add is greater of dB the sum does not have practical value and the value is taken from the greater one of both.
PROPAGATION CHANNELS
The noise can be transmitted through multiple channels. Through the air or an average solid in which it leaves from the sound will be reflected, part will be absorbed, and the rest transmitted through the object. The amount of sound reflected, absorbed or transmitted depends on the properties of the object, its form, of the thickness and the method of assembly, as well as of the angle of incidence and the incident acoustic wave. The propagation of the sound in the air depends mainly on the type of sources of noise, its distribution in the space and the topography, as well as of the conditions of the atmosphere in which the propagation is made.
The speed of
propagation of the sound in the Air is of about
334 m/s. and to 331.6 0ºC m/s is of. The speed of propagation is proportional to
the square raiz of the absolute temperature and is near 12 m/s. greater to 20º . The speed is always
independent of the atmospheric pressure.
In the Water the speed of propagation is of 1500 m/s . The speed difference is possible to obtain measures of temperature of the oceans measuring on great distances.
VIBRATIONS
One says that a body vibrates when it makes an oscillating movement
with respect to a reference position. The movement can consist, actually, of a component
to a singular frequency, like in a tuning fork, or of several of simultaneous them with
different frequencies.
Ever since they began to construct machines must isolate and reduce
the vibrations.
By means of the piezoelectric accelerometers, that turn the vibratory
movement into electrical signal, it is possible to be made the measurement and analysis of
the vibrations.
ISOLATION & ACOUSTIC PREPARATION
The isolation of
the sound consists of more or less preventing the propagation of same by means of
obstacles the reflectors, however absorption is the dissipation of energy in the interior
of propagation means. It is then very important to distinguish between the isolation and
acoustic preparation.
When the
sonorous waves enter direct bonding with the structure of the building, transmitting the
excitation to this, speech of structural noise or impact. These will be noises generated
by the impact between solids such as the fall of objects to the ground, footsteps, etc.
The acoustic
preparation is due to very consider in the construction and restoration of Churches,
Theaters, Audiences, Libraries, etc., really in all type of enclosures where it goes away
to need a good understanding of the word or good hearing of music for his normal
operation.
The materials in acoustics can be used to reduce the time of
reverberation of an enclosure or are used like barrier to reduce the intensity of the
sound that travels from a point to another one. As far as the first type of these
materials they are the absorbent materials . Perhaps most important of these materials
they are the porous materials, that are constituted by a solid structure within which a
series of cavities or intercommunicated pores exists to each other and with the outside.
Between the porous materials they are the rock wools, polystyrene foam, moquettes, etc.
ACOUSTIC SCREENS
In order to avoid the transmission of the sonorous waves in free field, a
screening between the transmitter and the receiver can be put in.
Many vegetal variants of screenings, plantations, acoustic screens exist properly happiness, etc.
. SILENCERS
In order to attenuate the propagation of the sonorous waves that accompany gas or a air flow in movement without preventing the passage of these, silencers are used. T
NORMS
The necessity
to protect the occupants of the buildings of the physical and psychic annoyances that
cause the noises has taken to dictate the Norma
Básica de Edificación
PREVENTION
In the jobs
in which the equivalent daily level surpasses 80 dB(A) the following measures will have to
be adopted: To provide to each worker a information, and when it comes, a formation
adapted in relation to the potential evaluation of its exhibition to the noise and risks
for its hearing, the preventive measures adopted, with specification of which they must be
carried out by the own workers, and the results.
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