Intensity, pitch and timbre are the physiological qualities of sound and are related to how the auditory system perceives sound waves.
It is common to give more value to the sense of sight . However, if we mix two pure radiations , such as red and yellow , our vision is not able to distinguish them, that is, we will see an orange color. On the other hand, with our ears , we can distinguish different sounds, even those that we receive together. For example, if we hear an orchestra play, we have the possibility to identify each of the different musical instruments that are playing at the same time.
Sound waves are longitudinal mechanical waves . This means that a sound wave propagates in various material media, but does not propagate in a vacuum. The sensitivity of the human ear to sound waves varies from person to person.
We can say that there are countless physical quantities that characterize a sound. One we know very well is intensity . Sound waves can be more intense (it’s the same as saying strong sound) or less intense (it’s the same as saying weak sound). Therefore, we define intensity (I) as the energy transported perpendicularly by the wave across a surface per unit time and also per unit area .
Simplifying this whole statement, we say that the intensity is nothing more than the power per unit area, which in the International System of Units ( SI ) is given by watt per square meter (W/m 2 ).
Therefore, we say that the human ear has the ability to detect sounds with intensities ranging from 10 -12 W/m 2 to 1 W/m 2 . This means that between the minimum sound intensity that we hear and the maximum that we can hear there is a gap of 10 12 . Because of the size of this interval, the intensity can be expressed by using a more appropriate quantity. This quantity was called intensity or sound level ( β ) , it is given in decibel ( dB ) and is defined by the following expression:
The reference value for the minimum sound intensity, that is, the weakest sound that we can hear is called the hearing threshold and has a reference value of I 0 = 10 -12 W/m 2 . The decibel unit was given in honor of Alexander Graham Bell . The table below provides some representative values of intensity and sound level.
Intensity and sound intensity level
Daily, we see people talking in the parks, on cell phones, etc. If we pay attention, we will hear a difference between a man’s voice and a woman’s voice. The basic difference is that a man’s voice is thicker , and a woman’s is thinner . As for sound waves, the terms “thick” and “fine” are classified into low sound and high sound, so we can say that man has a deeper voice; and the woman, a higher voice. Height is also another sound quality .
A third quality that we can highlight about the sound is the timbre . It is what allows us to distinguish between two sounds with the same frequency ( same pitch ) and intensity, emitted by the same sound source. For example, if a piano and a flute play the same musical note, we can perceive it, because our auditory system perceives different sensations, that is, the two instruments have different timbres.