When we talk about sound or noise , the magnitude that is used most frequently is dBA , and hardware manufacturers use it a lot in audio systems but also to define how much noise a fan emits, for example. In this article we are going to tell you what this magnitude is , how it is measured and why it is important to know its scale .
Has an overly noisy situation ever made your ears ring? Even to the point of having to cover them because it caused you pain? There are many factors that influence the intensity of sound and how we perceive it, including how long it lasts, the frequencies or tones, and the environment in which it is heard. For this reason it is important to be able to measure the intensity of sound and know the scale of that magnitude, and that is what we are going to talk about next.
What are dBAs and how are they measured?
Decibels (dB) are a unit of sound pressure, a measure of force, and more specifically a measure of force per unit area . Every time the source of the sound moves away from us, it loses intensity with a ratio of 6 dB each time the distance doubles (for example, if at one meter we perceive 80 dB, at two meters we will perceive 74 dB). For this reason, it is important that when measuring the intensity of the acoustic pressure the distance at which it is measured is indicated, and that is where dBA comes into play.
The suffix “A” of dBA is because the measurement uses a weighting filter for the human ear that only captures frequencies between 20 and 20,000 Hz and at a distance of 50 centimeters . It is, therefore, a reliable and objective magnitude to be able to measure any intensity of sound.
The particularity is that decibels are different from other known measurement scales. While many standard measuring devices like a ruler or meter are linear, the decibel scale is logarithmic . This type of scale best represents how changes in sound intensity are actually felt in human ears.
To put this in perspective let’s take an example: imagine a building 80 meters high. If its height is extended by an additional 10 meters (90m in total), it will appear to be only slightly taller to the eye because we have actually increased its height by 12.5%. If we translate these magnitudes into decibels, if a sound is 80 dB loud, adding an additional 10 dB would make the sound 10 times more intense and approximately twice as loud for our ears.
To measure decibels, devices called sound level meters are used, which are capable of capturing sound pressure quite accurately and there are actually very cheap ones (even mobile phone applications are quite reliable, although logically less than professional devices designed specifically for it).
How loud is the noise?
Since as we have explained the dB and more specifically the dBA are a logarithmic scale that depends on where we are in front of the sound source, it can be difficult to evaluate how many dBA is a lot of noise, and how many is little. Fortunately and since it is a subjective scale of perception of the human ear, it is very easy to extrapolate this in a table.
| dB | Example |
|---|---|
| 140 | An airplane taking off, 30 meters away |
| 130 | Pain threshold |
| 120 | Discomfort threshold |
| 110 | Chainsaw one meter away |
| 100 | Disco within 1 meter of speakers |
| 90 | Truck 10 meters away |
| 80 | Noisy and busy street |
| 70 | Vacuum cleaner 1 meter away |
| 60 | Speech 1 meter away |
| fifty | Average noise of a home |
| 40 | Silent library |
| 30 | Bedroom at night |
| twenty | Background noise in a recording studio |
| 10 | A leaf falling in the wind |
| 0 | Hearing threshold |
So that you understand this scale in a better way, we are going to put a scale of 10 in 10 dB with the effects that they can cause.
| Sound source | dB | Effect |
|---|---|---|
| Plane taking off at 25 meters | 150 | Eardrums rupture |
| Take-off runway from an airport | 140 | Pain threshold |
| Take off of a military fighter at 20 meters | 130 | Pain. It is 32 times more intensity than 70 dBA. |
| Horn of a truck at 1 meter. Live concert. | 110 | Average of human pain. 16 times more intensity than 70 dBA. |
| Electric lawn mower. Helicopter 30 meters. | 100 | Eight times more intensity than 70 dBA. Maintaining this level for 8 hours causes damage to the eardrums. |
| Motorcycle 10 meters | 90 | 4 times more intensity than 70 dBA. It can damage the eardrums if it is exposed for more than 8 hours. |
| Dishwasher. Factory (average). | 80 | Double the intensity of 70 dBA. Threshold of what is usually annoying. |
| TV audio | 70 | From this intensity, it is already annoying for many people. |
| Conversation in a restaurant | 60 | Half the intensity of 70 dBA. |
| Normal conversation in a house. | fifty | Four times less intense than 70 dBA. |
| library | 40 | One eighth the intensity of 70 dBA. |
| Rural zone | 30 | Sixteen times less intense than 70 dBA. |
| Whisper | twenty | Barely audible if you are not very close. |
| Breathing | 10 | Inaudible to most. Humans do not normally listen to their own breathing. |
| Absolute silence | 0 | It is literally impossible for a human being to “hear” absolute silence, but this is the threshold of hearing. |
In case you are wondering, it is literally impossible for human beings to capture absolute silence. Although it may exist in deep space, a human being always, always hears something (unless he is completely deaf, obviously), and in situations of extreme silence he will begin to hear (in addition to his own breathing) even the blood stream flowing through his veins.
