The vibrations will through the middle ear and in the inner ear - be transformed into nerve impulses that the brain perceives as sound.
The ear can perceive a very big sound scale - from the sound of a tiny pin falling to the ground, up to the noise from a jet plane.
The sound is perceived as deep or high, depending on how many times the pressure varies per minute. That is what we also call frequency and frequency is measured in Hertz.
An average young person can hear frequencies between 20 Hz and 20,000 Hz.
Sound strength corresponds to sound pressure. Quite literally, the pressure the eardrum is exposed to when the sound hit the ear.
To describe the sound strength we often use the decibel scale.
The Decibel scale is from 0 dB, which is the limit for audible hearing, up to 140 dB, where the sound pressure becomes so strong that it becomes truly painful.
The Decibel scale shall contain all of these sound pressure levels, and therefore it has been necessary to make a particular subdivision.
When you go up or down in the scale, it is always a 3 dB doubling or halving of the sound.
This means that twice the 80 dB is not 160 dB, but 83 dB.
If you measure the level of a kindergarten, it is very important to know if the measurement was 80 or 83 dB. At the same time, reducing the load of 3 dB will have a very important effect for the working environment.
What is a sound wave?
A sound wave is defined by the speed, amplitude and frequency.
The sound speed depends strongly on the media through which it moves, but also by the temperature. Sound speed is approx. 340 m/s in air - and 1500 m/s in water.
The Wavelength is equal to the distance between two peaks of a wave. Sound wavelength, λ is related to the sound speed c and its frequency f by the formula:
λ = c/f
λ = wavelength of the sound,
c = speed of the sound
f = frequency of the sound
Interpretation of texts and quotes by Brüel & Kjær: Grundbog i Lydmåling, Uffe Jørgensen, 1987