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.
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