Physics of Sound: Waves, Frequencies, and Intensity

Acoustics Fundamentals

Acoustics is the part of physics that deals with the study of sound from sound waves.

Sound Waves

Are those that produce sound.

Mechanical Waves

These are waves that produce due to a disturbance, and their propagation in the form of oscillation requires a material medium.

Classification of Mechanical Waves

This classification agrees with the direction in which a wave vibrates the particles of the material medium.

Longitudinal Waves

They occur when material particles of the medium vibrate parallel to the direction of wave propagation.

Transverse Waves

They occur when material particles of the medium vibrate perpendicular to the direction of wave propagation.

Sound Definition

A longitudinal mechanical wave that propagates through an elastic medium (solid, liquid, gas).

Speed of Sound

331 m/s

Doppler Effect

The change in frequency of a wave produced by the motion of the source relative to an observer.

Sound Frequency Ranges

• Infrasound: A wave or sound whose frequency is below the audible range of human hearing (about 20 Hz).
• Ultrasound: A sound wave or sound whose frequency is above the audible range of human hearing (approximately 20,000 Hz).

Timbre of Sound

This is the characteristic tone of a sound, which can be acute or severe depending on the height of the note that corresponds to its dominant resonator.

Sound Intensity

The power transferred by a sound wave through a unit area perpendicular to the direction of propagation.

Thresholds of Sound Intensity

• Threshold Sound (Reference): Represents a standard zero sound intensity; its value is $1 \times 10^{-4} \text{ mW/cm}^2$ for a frequency of 1000 Hz.
• Pain Threshold: Represents the maximum intensity that the human ear can register without pain. Its value is $100 \text{ mW/cm}^2$ or $1 \times 10^{-4} \text{ W/cm}^2$.

Note: The definitions for Ultrasound, Timbre, Sound Intensity, Threshold Sound, and Pain Threshold were repeated in the original text and are consolidated above.