The sound is any change in air pressure that can be detected by the human ear. By definition, noise is unwanted sound. More particularly, the noise is an annoying sound to distinguish the sounds pleasant. When you say junk should be clear what makes him undesirable noise, or when they say it’s inconvenient, it should quantify what the value of the nuisance, and who bothers a few, many , how long, etc.
The number of pressure variations per second is what is called sound frequency and is measured in Hertz (Hz). Each frequency of a sound produces a different tone.
Sound Level Meters
The instruments used to measure the noise level are called sound level meters and provide an indication of noise level (averaged over time) of sound waves incident on the microphone. The sound level is displayed on a scale usually with a moving needle indicator or digital display.
The ear is not equally sensitive to all frequencies. For this reason, even though the sound pressure level of two sounds may be the same, can be interpreted as different levels if one has a greater concentration on the frequencies that the ear is most sensitive. For this reason, sound meters are incorporated into the frequency weighting filters that modify the sensitivity of sound level on frequencies that are less audible to the ear. Many sound level meters are equipped with different weighting filters-frequency sensitivity.
The weighting scale is used most frequently. The scale A is internationally standardized and adjusted its weighting curve to the response of human hearing. The sound level values measured with this scale are known as dB (A).
There are other rating scales used less frequently such as the B scale, used for medium-intensity sounds, the C scale, used to loud sounds, and the D scale, used to measure the noise of jet aircraft. Because of its good agreement with the subjective response, the scale A, is commonly used for all levels, still relatively rare use of scales B, C and D.
Often, the sounds emitted by the sound sources fluctuate widely over a period of time. Can you measure an average value of noise during the period known as the equivalent sound pressure level Leq. The Leq is the equivalent continuous sound level that it provide the same acoustic energy to the fluctuating noise measured over the same period of time.
Pathways
Noise can be transmitted through multiple paths. Through the air or through a solid medium in which part of the sound is reflected, part will be absorbed, and the rest transmitted through the object. The amount of sound reflected, absorbed or transmitted depending on the properties of the object, its shape, thickness and method of assembly as well as the angle of incidence and the incident acoustic wave. The propagation of sound in air depends mainly on the type of noise sources, their distribution in space and topography, as well as the conditions of the atmosphere in which the propagation takes place. The sound intensity level to get away from the sound source decreases by 6 dB every time you double the distance from the source in a free field.
Vibrations
We say that a body vibrates when you perform an oscillating motion about a reference position. The movement may consist, in practice, a component to a unique frequency, like a tuning fork, or several of them simultaneously with different frequencies.
Since the machines began building must isolate and reduce vibration.
By piezoelectric accelerometers, which convert the vibration into an electrical signal, it can make the measurement and vibration analysis.
Isolation and acoustic conditioning
The sound isolation is to prevent the spread of it through more or less reflective barriers, however absorption is the energy dissipation within the propagating medium. It is therefore very important to distinguish between the insulation and acoustic conditioning.
The soundproofing is to get the energy passing through a barrier as low as possible, which means installing materials that have an impedance as different as possible to the medium that carries the sound. Thus, if the transfer is made through the air, the barriers should be dense and heavy materials. The isolation of a construction element is a function of their mechanical properties and the “Law of Mass, by which the increase of mass is doubled, an increase of 6 dB (A) in soundproofing.
When sound waves come in direct contact with the building structure, conveying the excitement of this, we speak of structural noise or impact. These are noises generated by the impact between solids such as objects falling to the floor, footsteps, etc..
The acoustic conditioning should take into account in the construction and restoration of churches, theaters, auditoriums, libraries, etc.., In short in all types of venues where you are going to need a good intelligibility of speech or good hearing of the music for its normal functioning.
Each location has different acoustic characteristics and individuals. One of these features is the reverberation time measured in seconds. The reverberation time is the time required in a confined space for a sound frequency or band of frequency, so that the sound pressure level inside it decrease by 60 dB, after leaving the source.
The acoustic materials can be used to reduce the reverberation time of an enclosure or used as a barrier to reduce the intensity of sound that travels from one point to another. In the first type of these materials are absorbent materials. Perhaps the most important of these materials are porous materials, which consist of a solid structure within which there are a number of cavities or pores interconnected with each other and with the outside. Among the materials are porous rock wool, polystyrene foams, carpets, etc..
Speakers
To prevent transmission of sound waves in free field, shielding can be interspersed between the transmitter and receiver.
There are many variations of shielding, planting vegetables, acoustic screens themselves, and so on.
Silencers
To mitigate the propagation of sound waves that accompany a flow of air or gas in motion without impeding the passage of these are used silencers. These tend to be formed mainly by an absorbent material that dissipates acoustic energy transmitted through the muffler together with the fluid flow silencers or where the attenuation is mainly due to the internal geometry of the muffler, that is, forms and volumes of the indoor enclosures.
Regulations
The need to protect the occupants of the buildings of the physical and psychological discomfort caused noise issue has led to the Basic Standard Building (NBE-CA-88) which sets minimum requirements for buildings to keep them acceptable noise level, and the enactment of municipal ordinances for environmental protection and comfort of citizens against any disturbance by noise and vibration nuisance generated by machines and equipment.
Royal Decree 1316/1989 is the protection of workers against risks arising from exposure to noise at work.
The primary purpose of that R.D. is to protect workers against risks from exposure to noise at work, and particularly for the hearing. Employer’s duty is to reduce to the lowest level technically and reasonably possible risks from exposure to noise, given the technical progress and availability of noise control.
It must assess the exposure of workers to noise in order to determine if they exceed the limits, including assessment of existing jobs at the date of promulgation of the standard or the existing ones which have undergone modifications involving significant variation in the exposure of workers to noise, periodic assessments as annual maximum.
Tags: Notions of Acoustic, oscillating motion
