Key Concepts of Sound Waves and Hearing

Sound Wave

A physical wave produced by the vibration of objects that travels through a medium (like air, water, or solids) as alternating regions of high and low pressure.

Longitudinal Wave

A type of wave in which the particles of the medium vibrate parallel to the direction of energy transfer Sound waves are longitudinal waves.

Compression

A region in a longitudinal wave where the particles of the medium are closer together than their equilibrium position, resulting in high pressure.

Rarefaction

A region in a longitudinal wave where the particles of the medium are farther apart than their equilibrium position, resulting in low pressure.

Medium

A substance through which a wave can travel. For sound, this can be a gas, liquid, or solid.

Density

The mass of a substance per unit volume. In the context of sound, a denser medium generally allows sound to travel faster.

Mach Number

The ratio of an object's speed to the speed of sound in the surrounding medium.

Outer Ear

The external part of the ear, including the pinna and ear canal, which collects and funnels sound waves towards the middle ear.

Middle Ear

The air-filled cavity between the eardrum and the inner ear, containing three small bones (malleus, incus, stapes) that amplify sound vibrations.

Inner Ear

The innermost part of the ear, containing the cochlea (responsible for hearing) and the semicircular canals (responsible for balance).

Basilar Membrane

A thin membrane within the cochlea that vibrates in response to sound waves, with different frequencies causing different parts of the membrane to resonate.

Intensity

The power carried by a sound wave per unit area in a direction perpendicular to that area. It is related to the loudness of a sound.

Frequency

The number of complete cycles of a wave that pass a point in a unit time, usually measured in Hertz (Hz). For sound, frequency determines the pitch.

Pitch

The perceived highness or lowness of a sound, determined by its frequency.

Loudness

The subjective perception of the intensity of a sound. It is typically measured in decibels (dB).

Decibel (dB)

A logarithmic unit used to express the ratio of two values of a physical quantity, often used to measure sound intensity levels.

Audible Range

The range of sound frequencies that can be heard by humans, typically from about 20 Hz to 20,000 Hz.

Infrasonic

Sound waves with frequencies below the audible range (below 20 Hz).

Ultrasonic

Sound waves with frequencies above the audible range (above 20,000 Hz).

Threshold of Hearing

The minimum intensity of a sound wave that can be detected by the human ear (approximately 0 dB).

Interference

The phenomenon that occurs when two or more waves overlap in space, resulting in a net wave whose displacement at each point is the sum of the displacements of the individual waves.

Constructive Interference

Occurs when waves overlap in such a way that their amplitudes add together, resulting in a wave with a larger amplitude.

Destructive Interference

Occurs when waves overlap in such a way that their amplitudes subtract from each other, resulting in a wave with a smaller amplitude.

Beats

Periodic variations in the amplitude (and thus loudness) of a sound produced by the interference of two waves with slightly different frequencies.

Doppler Effect

The change in perceived frequency of a wave (including sound) due to the relative motion between the source of the wave and the observer.

Vibrational Source

The initial object or mechanism that produces the vibrations that create a sound wave (e.g., a drumhead, vocal cords, a guitar string).

Standing Wave

A wave pattern created by the interference of two traveling waves moving in opposite directions, characterized by fixed points of zero amplitude (nodes) and points of maximum amplitude (antinodes). Musical instruments often rely on standing waves within a medium.

Harmonics

Frequencies that are integer multiples of the fundamental frequency of a vibrating object. They contribute to the timbre of a sound.

Fundamental Frequency

The lowest resonant frequency of a vibrating object or system, which determines the perceived pitch.

Timbre

The quality of a musical note, sound, or voice that distinguishes different types of sound production, such as the sound of different musical instruments or voices. It is determined by the presence and relative intensities of different harmonics.

Fourier Analysis

A mathematical technique that can decompose a complex waveform into a sum of simpler sine waves (harmonics) with different frequencies and amplitudes.

Sound Synthesis

The process of creating complex sounds by combining simpler waveforms, often based on the principles of Fourier analysis.