Sound - Audible and Inaudible Sounds

Vibration is the back-and-forth motion of an object. The number of oscillations per second is called the frequency ($f$), measured in $\text{Hertz (Hz)}$.

Audible sounds are those that can be heard by the human ear. This range is typically between $20\text{ Hz}$ and $20,000\text{ Hz}$ ($20\text{ kHz}$).

Inaudible sounds fall outside the range of $20\text{ Hz} - 20,000\text{ Hz}$.

Infrasonic sounds (Infrasound) have frequencies lower than $20\text{ Hz}$. These are produced by objects like pendulums or animals like whales and elephants.

Ultrasonic sounds (Ultrasound) have frequencies higher than $20,000\text{ Hz}$. Animals like dogs, bats, and dolphins can hear these frequencies.

The loudness of sound is determined by its amplitude ($A$). Loudness is proportional to the square of the amplitude: $Loudness \propto A^2$.

The pitch or shrillness of a sound is determined by its frequency ($f$). A higher frequency result in a higher pitch.