Noise meter - the size of the sound in dB, what is the unit?
First of all, let’s talk about the unit of sound size, dB. The unit of dB can actually be called no unit, because it actually represents a proportional relationship. The calculation formula is given:
SPL=20 x log10[ p(e) / p(ref) ]
SPL is what we usually call decibels, p(e) is the sound pressure to be measured, and p(ref) is the reference sound pressure. In other words, what we call XXdb is actually the ratio of the sound to the size of a sound we stipulated, and take the logarithm to the base 10 and multiply it by 20. The reason for taking the logarithm is that this ratio can be very large. For example, the weakest sound that the normal human ear can hear is called the "auditory threshold", which is a pressure change of 20 micropascals (μPa), which is 20 x 10-6 Pa (twenty parts per million Pascal). And a space shuttle at full horsepower can generate a noise of about 2,000 Pa or 2 x 109 μPa at close range, which is very inconvenient to deal with. If the form of db is used, the gap between them will only be 160db.
So the unit of DB brings simplicity in form, but at the same time it also intuitively makes us feel that it seems very simple to measure a sound from 30db to 90db. The difference in height between Xiaolou and Mount Everest, the difference in sound pressure between the two sounds is 1000 times.
After understanding the above principles, let’s talk about how the sound volume is calculated in engineering.
We know that the human ear's perception of sounds of different frequencies is inconsistent, similar to a band-pass filter, first of all, it only responds to frequencies between 20-20000HZ, resulting in the same sound pressure, different frequencies, and the impact on human hearing Also different. The figure below shows how the human ear responds to different frequencies. Note that the unit is also dB.
