Eli5: the differences between decibels (dB) and weighted decibels (dBA)
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dB are for energy of acoustic wave. dBA are for how loud sound is. Human ear hears different frequencies with different efficiency. Mechanical/ electronic sensors give you dB. Then you put data through filter, that accounts human ear characteristics to get weighted dB. There are many filters, most popular one is A, so dB weighted through A makes dBA.
Decibels (dB) is the “raw” measure of sound, whereas dBA take into account human perception. A person with normal hearing will not perceive all the frequencies of a sound equally. So dBA takes into account the natural filter of the human ear to give a more realistic idea of the sound’s impact on your health.
dBA used, for example, to measure the loudness of working environments to protect workers (if they’re exposed to X dBA for Y amount of time, they’re required to use hearing protection so they don’t end up deaf).
dBA refers to the dB measurement made after the sound has been run through a filter which rolls off a lot of the bass (very low frequencies) and some of the treble (very high frequencies), matching the reduced sensitivity of our ears to those frequency ranges.
The point is to make the measurement match our hearing, so it tells you how loud something *seems* to us, rather than how intense it actually measures as.
For example, we perceive a 70 dB deep bass tone to be at about the same volume as a 45 dB midrange (speech) tone. If we do a dBA measurement, they’ll both be 45 dB.
The response of the human ear to frequency isn’t flat – i.e. you would need a high or low frequency sound to have much more energy (be louder) to perceive it at the same loudness as a midrange sound.
When acoustic engineers measure noise, they are often looking to meet a numerical target in dB. If that target is in dBA they can filter out a lot of the junk noise that is there & has a high measurable noise level but we don’t really perceive.
To do this they use a set of values called the A weighting which, when summed with a measured noise level, mimic a human ear’s response to that level.
TL:DR dBA (A weighted decibels) are designed to more closely simulate how people respond to noise, which is not shown by just measuring a noise level in dB.
The ear response to sound pressure waves is different for various frequency.
There exists lookup tables to convert actual sound pressure in dB to more relevant perceived sound pressure in dBa.
[https://www.nexflow.com/blog/what-does-dba-mean/](https://www.nexflow.com/blog/what-does-dba-mean/)
>A dB(A) measurement has been adjusted to consider the varying sensitivity of the human ear to different frequencies of sound. Therefore, low and very high frequencies are given less weight than on the standard decibel scale. Many regulatory noise limits are specified in terms of dBA, based on the belief that dBA is better correlated with the relative risk of noise-induced hearing loss.
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>Compared with dB, A-weighted measurements underestimate the perceived loudness, annoyance factor, and stress-inducing capability of noises with low frequency components, especially at moderate and high volumes of noise. (Richard L St Pierre Jr and Daniel J Maguire, “The Impact of A-weighting Sound Pressure Level Measurements during the Evaluation of Noise Exposure” (paper presented at NOISE-CON, Baltimore, Maryland, July 12–14, 2004).)
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>db-C or the C-weighting scale is sometimes used for specifying peak or impact noise levels but there is generally not much of a difference between the two.
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