Understanding Sound Waves and Propagation

• Sound results from vibrating objects creating sound waves.
• Sound waves travel through mediums like air or water.
• Once these waves reach our ears, our brain interprets them as sounds.

Sound Waves

• Sound waves are longitudinal, meaning the medium's displacement aligns with the wave's travel direction.
• Sound waves are made of compressions, which are high-pressure regions, and rarefactions, which are low-pressure regions.
• Sound waves need a medium to propagate, so they cannot travel through a vacuum.

Speed of Sound

• The speed of sound changes based on the medium.
• Sound travels faster in solids than in liquids and faster in liquids than in gases.
• Temperature affects the speed of sound; the speed increases with temperature.
• In dry air at 20°C, sound travels at approximately 343 meters per second.

Wavelength

• Wavelength is the distance between two consecutive compressions or rarefactions.
• The relationship between wavelength, speed, and frequency is expressed as: wavelength = speed / frequency.

Amplitude

• Amplitude is the maximum displacement of particles in the medium from their resting position.
• Amplitude corresponds to the sound's intensity or loudness; a higher amplitude results in a louder sound.

Frequency

• Frequency is how many complete wave cycles pass a point in one second.
• Measured in Hertz (Hz), 1 Hz equals one cycle per second.
• Frequency determines a sound's pitch, where high frequency is a high pitch, and low frequency is a low pitch.
• Humans typically hear sounds between 20 Hz and 20,000 Hz.
• Sounds above 20,000 Hz are ultrasound, and those below 20 Hz are infrasound.

Period

• Period is the time for one complete wave cycle.
• Period is the inverse of frequency, calculated as: period = 1 / frequency.

Relationship between Frequency and Pitch

• High-frequency waves are heard as high-pitched sounds.
• Low-frequency waves are heard as low-pitched sounds.

Properties of Sound

• Reflection is when sound waves bounce off surfaces, similar to light waves, creating echoes.
• Hard, smooth surfaces reflect sound well.
• Refraction is when sound waves bend as they move from one medium to another or through different temperatures, due to speed changes.
• Diffraction is when sound waves bend around obstacles or through openings.
• Diffraction allows sounds to be heard even when not directly in the sound's path.
• Longer wavelengths (lower frequencies) diffract more easily than shorter wavelengths (higher frequencies).
• Interference happens when two or more sound waves overlap.
• Constructive interference occurs when waves combine in phase, increasing amplitude and creating a louder sound.
• Destructive interference occurs when waves combine out of phase, decreasing amplitude and creating a softer sound or silence.

Intensity and Loudness

• Intensity is the power of the sound wave per unit area, measured in Watts per square meter (W/m²).
• Intensity is proportional to the square of the sound wave's amplitude.
• Loudness is the subjective perception of the sound's intensity, often measured in decibels (dB).
• The decibel scale is logarithmic, meaning small dB increases equal large intensity increases.
• A 10 dB increase is perceived as approximately twice as loud.

Threshold of Hearing

• The threshold of hearing is the minimum sound intensity detectable by the human ear and is defined as 0 dB, equivalent to 10⁻¹² W/m².

Threshold of Pain

• The threshold of pain is when sound intensity causes ear pain, around 120-140 dB.

Sound Production

• The human voice produces sound in the vocal cords, located in the larynx.
• Air from the lungs passes over the vocal cords, causing them to vibrate and produce sound waves.
• Varying vocal cord tension changes the sound's pitch.
• The tongue, teeth, and lips modify sound to produce speech.
• String instruments produce sound via vibrating strings (e.g., guitar, violin).
• Wind instruments produce sound via vibrating air columns (e.g., flute, trumpet).
• Percussion instruments produce sound when struck, shaken, or scraped (e.g., drum, cymbal).

Sound Perception

• The outer ear, or pinna, collects sound waves and directs them into the ear canal.
• The ear canal amplifies sound and directs it to the eardrum.
• The eardrum vibrates when sound waves reach it.
• These vibrations pass to three small bones: the malleus, incus, and stapes.
• These bones amplify vibrations and pass them to the oval window.
• The oval window is a membrane-covered opening to the cochlea.
• The cochlea, a fluid-filled, snail-shaped structure, contains hair cells.
• Vibrations in the cochlea cause the hair cells to bend, creating electrical signals sent to the brain.
• The brain interprets electrical signals as sound.
• Different brain regions process sound aspects like pitch, loudness, and location.

Applications of Sound

• Music is based on sound, which provides rhythm, melody, and harmony.
• Different instruments and vocal techniques create diverse sounds and musical styles.
• Communication relies on sound waves to transmit data.
• Devices like telephones and radios convert sound into electrical signals and back.
• Medical imaging uses ultrasound to visualize internal organs and tissues.
• It’s non-invasive and avoids ionizing radiation.
• Sonar (Sound Navigation and Ranging) uses sound waves to detect underwater objects, useful for navigation, fishing, and exploration.
• Acoustics studies sound production, transmission, and effects.
• Acoustics apply to optimize sound quality in concert halls, recording studios, and other spaces.