The human ear reacts to various frequencies in a different way. The frequency range between 1 and 3 kHz is the most sensitive. Generally, high and low tones are perceived as mid-range sounds. The intensity of the sound also affects the hearing curve. With the increase in the volume of the signal, the hearing curve reaches an equilibrium value.
The "normal" hearing frequency range is between 20 Hz and 20,000 Hz. This range of hearing is influenced by age, occupation and gender. As we age, hearing sensitivity at high frequencies decreases by about 12 kHz. Sounds that are above the threshold of hearing are called ultrasound, those below infrasound. Young people can also perceive some kHz in the ultrasound band.
Since the ear, unlike other organs, does not regenerate, a gradual hearing loss occurs with advancing age. High frequencies are the first to be lost as they are processed in the initial part of the cochlea, which is more subject to wear and tear, thus allowing an estimate of the years. For example, if you can hear a sound with a frequency of 19000 Hz, it is estimated that the age of the ears is less than 20 years, unlike a lower frequency such as 3000 Hz that everyone can perceive.
In addition to the progressive decline in hearing sensitivity at high frequencies, 50% of over 60s have hearing loss for frequencies between 3-6 kHz. This means that older people perceive noise in the high frequency range very differently. It should be emphasized that with aging there is not only a loss of frequencies (high-pitched sounds are no longer heard), but also of sound intensity (it is more difficult to hear the low voices and sounds).
The human ear is capable of hearing very quiet sounds (low intensity) and extremely loud sounds (high intensity). It has an intelligent built-in mechanism that reduces its sensitivity as the sound level increases, and it also has the amazing ability to handle a wide range of sound power levels.
To significantly express specific sound levels and the relationship of intensity between silence and various noises in a simplified way, a logarithmic scale, base 10, is used instead of a linear scale. This scale is called the decibel scale. In terms of decibels, a doubling of the volume roughly equates to an increase of 10 dB. It doesn't matter if that increase is from 40dB to 50dB or 70dB to 80dB.
On the decibel scale, the lowest audible sound (perceived in almost total silence) is 0 dB. 10 times more powerful sound is 10 dB. A sound that is 100 times more powerful than near silence is 20 dB. Sound 1,000 times louder than near silence is 30dB, 40dB, and so on.
Here are some examples of noises in decibels:
The number of sound vibrations emitted per second is known as the frequency which is measured in hertz (Hz). The lower (or higher) the frequency, the lower (or higher) the pitch of the sound. The other consideration is loudness which is measured in decibels (dB).