The Decibel Scale

An explanation of the decibel scale and also related systems for measure up sound and loudness.

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Decibels (dB)

The ear has actually the remarkable capacity to handle an enormous selection of sound levels. In order to express levels of sound meaningfully in numbers that are more manageable, a logarithmic scale is used, rather than a linear one. This scale is the decibel scale. What is a decibel? Zero decibels (0 dB) is the quietest sound audible come a healthy and balanced human ear. Indigenous there, every rise of 3 dB to represent a copy of sound intensity, or acoustic power.

Loudness and also Sound strongness (Power)

The relative loudness that we perceive is a subjective mental phenomenon, no something that have the right to be objectively measured. Many of us perceive one sound come be double as according to as an additional one once they are around 10 dB apart; because that instance, a 60-dB air conditioner will sound twice as loud as a 50-dB refrigerator. Yet that 10-dB difference represents a tenfold rise in intensity. A 70-dB dishwasher will certainly sound about four times as loud together the 50-dB refrigerator, yet in terms of acoustic intensity, the sound it renders is 100 times as powerful.

Here"s another way of looking in ~ it: If the sound native one typewriter it is registered 60 dB, climate ten typewriters clacking away would register 70 dB (not 600 dB!), and they would sound only twice together loud as one typewriter. Girlfriend would require 100 typewriters to reach a noise level of 80 dB, and together they would sound only four times together loud as a solitary typewriter.

Sound LevelSound strongness (Power)Perceived Loudness 60 dB1x1y 70 dB10x2y80 dB100x4y

The potential because that a sound to damage our listening is proportional to its intensity, not its loudness. That"s why it"s misleading to count on our spatu perception the loudness together an indication of the threat to our hearing. Watch this chart for for sure noise exposure limits.

A-weighting (dBA) and C-weighting (dBC)

You will frequently see noise levels provided in dBA (A-weighted sound levels) instead of dB. Dimensions in dBA, or dB(A) together it is occasionally written, space decibel scale readings that have actually been readjusted to attempt to take into account the differing sensitivity the the human being ear to various frequencies of sound. (The main result of the mediate is that low and really high frequencies are provided less weight 보다 on the standard decibel scale.) many regulatory noise borders are stated in terms of dBA, based on the belief that dBA is better correlated through the family member risk that noise-induced hearing loss.


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Compared through dB, A-weighted measurements underestimate the perceived loudness, annoyance factor, and also stress-inducing capacity of noises v low frequency components, especially at moderate and high volumes of noise.*

Another system of convey is C-weighting, the dBC scale. DBC is sometimes used because that specifying peak or influence noise levels, such as gunfire. Unweighted dB readings are also used because that this purpose; over there is commonly not much difference in between the two.

Phons and also Sones

The phon is a non-standard noise unit the is designed to reflect viewed loudness, and is based upon psychoacoustic experiments in which volunteers were request to change the decibel level the a recommendation tone that 1 kHz until it to be the very same loudness as the signal being measured. So because that example, if a sound is 70 phons, that means it sounds together loud as a 70-dB, 1-kHz tone. The dBA range is now widely used instead of phons.

The sone is another non-standard, psychoacoustic unit of loudness. By definition, 1 sone = 40 phons, and from over there upward, the sone measure doubles because that every rise of 10 phons:

Phons405060708090100110120
Sones1248163264128256

The sone is a much more intuitive measure up of loudness, since a doubling in the number of sones to represent a doubling in perceived loudness (unlike the logarithmic phon scale). Noise level of household fans are frequently measured in sones.

Measuring Sound Levels

A sound level meteris the instrument normally used to measure noise level on the decibel scale. Numerous factors affect the noise level reading:


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The distance in between the meter and the source of the soundThe direction the noise resource is facing, loved one to the meterWhether the measurement is bring away outdoors (where noise deserve to dissipate) or indoors (where noise have the right to reverberate)

For a report sound level value to be most useful, the is important to specify the problems under i beg your pardon the reading was taken, particularly the street from the source.

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*Richard l St Pierre Jr and also Daniel J Maguire, "The influence of A-weighting Sound pressure Level Measurements throughout the testimonial of Noise Exposure" (paper gift at NOISE-CON, Baltimore, Maryland, July 12–14, 2004).

See also:Chart of sounds in Decibels

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