What is Sound
Sound is the vibration of an elastic medium, whether gaseous, liquid or solid. When we refer to audible sound by the human ear, we are talking about the sensation detected by our ears, which produce rapid variations in air pressure above and below a static value. This value gives us static atmospheric pressure (about 100,000 pascals) which has some smallvariations and very slow, as is apparent in a barometer.
How are small and fast changes in pressure that cause sound?. When the rapid variations of pressure is centered between 20 and 20,000 times per second (equal to a frequency of 20 Hz to 20 kHz) the sound is potentially audible even though the pressure variations can sometimes be as small as a millionth of a pascal . Loud noise is caused bylarge variations in pressure, such as a variation of 1 pascal would hear a loud sound, as long as most of the sound energy was contained in the midrange (1kHz - 4 kHz) which is where the human ear is most sensitive.
The sound you can produce different sources, from a person speaking to a loudspeaker, a mobile membrane that compresses the air produced sound waves.
What is the frequency PHZ
Aswe have seen the sound is produced as a result of compression and expansion of an elastic medium, ie the vibrations generated in the.
The frequency of a sound wave is defined as the number of pulses (cycles) per unit time is (second). The unit corresponding to one cycle per second is hertz (Hz).
The lower frequencies correspond to what we usually call sounds "serious" sound vibrations areslow. The higher frequencies correspond to what we call "acute" and are very fast vibration.
The audible frequency spectrum varies according to each person, age etc. Without a normal clutch is accepted as the intervals between 20 Hz and 20 kHz.
What is a Decibel dB
The decibel is a logarithmic unit of measurement used in different disciplines of science. In all cases, is used to comparea number with a call reference. Normally the reference value is always taken as the lesser of the amount. In some cases it may be an approximate average value. In Acoustics most of the time the decibel is used to compare sound pressure, in air, with a reference pressure. This reference level taken in Acoustics, is an approach to the minimum pressure level that makes our hearing is able toperceive. The reference level varies depending on the kind logically as we are doing. Not the same reference level for sound pressure, which for the loudness or sound power. Here are refeerncia values.
Level for the sound pressure (in air) = 0.00002 = 2E-5 Pa (rms)
Level for the loudness (in air) = 0.000000000001 = 1E-12 w / m ^ 2
Level for the Sound Power (air) = 0.00000000001 = 1E-12 w
As itsname implies, the decibel is a tenth of Bel. The Bel is the logarithm base 10 of the ratio of two powers or intensities. However this unit is too big so that was standardized using a tenth of Bel, with the decibel and decibel. The formula for its application is as follows, based on the acoustic intensity in the far field is proportional to the square of acoustic pressure, is defined as soundpressure level:
Lp = 10log (p ^ 2/pr) = 20 log p / pr
As Lp = sound pressure level, p the pressure measurement; reference pressure pr (2E-5 Pa)
As is easy to see the baseline always correspond to the level of 0 dB:
Lp = 20log (0.00002/0.00002) = 20log (1) = 20 * 0 = 0 dB
At both 0 dB threshold of hearing have the human ear, it is assumed that you can not hear below this level, or levelvariations in air pressure less than 0.00002 pascal.
The reason why the decibel is used is that if I would have to be driving or very small numbers or exes, which were filled with zeros, so that the possibility of error would be too big to make calculations. You also must take into account that the behavior of the human ear is closer to a logarithmic function than a linear, and who does not...