Unit 3: Sound Notes PDF

# UNIT 3: SOUND ## General Properties of Sound - Sound waves can be transmitted through many materials, such as air, water, wood and biological tissue. - Sound waves require a medium for their transmission. - The sound cannot travel in a vacuum. - Because, the sound mechanical wave which requi...

# UNIT 3: SOUND ## General Properties of Sound - Sound waves can be transmitted through many materials, such as air, water, wood and biological tissue. - Sound waves require a medium for their transmission. - The sound cannot travel in a vacuum. - Because, the sound mechanical wave which required exist medium to propagation. - Sound wave spread outward as a longitudinal wave i.e. Sound waves are composed of compression and rarefaction patterns. ## Compression and Rarefaction - Compression happens when molecules are densely packed together. - Rarefaction happens when molecules are distanced from one another. ## Traveling Longitudinal Waves - A longitudinal wave is a wave in which the motion of the medium's particles is parallel to the direction of the energy transport. - Sound waves in air and fluids are longitudinal waves, because the particles that transport the sound vibrate parallel to the direction of the sound wave's travel. | Wave Type | Source Movement | Coils Movement | Energy Transport | |---|---|---|---| | Longitudinal Wave | Left and Right | Left and Right | | | Transverse Wave | Up and Down | Up and Down | | ## Longitudinal Waves - Music System Sound Waves ## Transverse Waves - Television Visible Light ## The Basic Terminology That Applies to a Sinusoid Vibration: - **Wavelength:** The distance between two successive crests or troughs of a wave. - **Amplitude:** The maximum displacement of an object from its equilibrium position during a cycle of periodic motion. - **Time Period:** The time it takes for one complete cycle of periodic motion to occur. - **Frequency:** The number of cycles described in one second. ## Speed of the Sound - The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium from particle to particle. - **Speed = distance / time** - The higher the density, the higher is the speed of the sound. - The speed of sound can be determined by this equation: - **c = fλ** - **c:** speed of the sound in meters per second. - **f:** frequency of vibration of the sound wave in Hertz. - **λ:** wave length of the sound wave in meters. | Medium | Speed of Sound Waves (m/s) | |---|---| | Dry Air (20° C) | 343 | | Water | 1437 | | Wood | 3850 | | Glass | 4540 | | Aluminium | 6320 | ## Spherical Waves - Spherical waves are waves in which the surfaces of common phase are spheres and the source of waves is a central point. - The property of a spherical wave is that it has a spherical symmetry. - The other property of a spherical wave is that they can be coherent, meaning that they have a constant phase relationship between two or more waves. ## Applications of Spherical Waves - In acoustics, spherical waves are used to model the sound field generated by a source, such as a loudspeaker or musical instrument. - In optics, spherical waves are used to describe the propagation of light, including diffraction and interference phenomena. - Spherical waves are also used in radar and sonar systems to detect and locate objects. ## Reflection, Refraction, Diffraction and Interference of a Sound Wave ### Reflection of Sound Waves - When a wave reaches the boundary of a new medium, a portion of the wave undergoes reflection and a portion of the wave undergoes transmission across the boundary. - Reflection of sound waves off surfaces can lead to one of two phenomena - an echo or a reverberation. - A reverberation often occurs in a small room with height, width, and length dimensions of approximately 17 meters or less. - Echoes are different than reverberations, often occurs in a large room more 17 meters and the sound wave reaches the ear more than 0.1 seconds after the original sound wave was heard. ### Diffraction of Sound Waves - Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path. - The amount of diffraction increases with increasing wavelength and decreases with decreasing wavelength. ### Relationship Between Wavelength and Obstacle Size - For diffraction to occur significantly, the size of the obstacle or opening should be comparable to the wavelength of the sound. - Longer Wavelengths: sound waves diffract more noticeably, making it possible to hear sounds even when not in a direct line of sight. - Shorter Wavelengths: sound waves tend to travel in more straight lines, and the ability to hear sounds around corners or through openings diminishes. ### Refraction of Sound Waves - Refraction of waves involves a change in the direction of waves as they pass from one medium to another. - Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. ### Interference: when waves affect each other - When two waves travelling in different directions meet, they combine their energies and form interference patterns. - This can result in regions of very high waves when they add up (constructive interference) alternating with regions of diminished or no waves when they cancel out (destructive interference). ## Characteristics of a Sound Wave (Intensity, pitch and quality) ### Sound Intensity - Sound intensity is the power per unit area carried by a sound wave. - The more intense the sound is, the larger the amplitude oscillations will be. ### Pitch - Pitch is a characteristic of sound by which a correct note can be distinguished from a grave or a flat note. - The term 'pitch' is often used in music. - Pitch depends upon the frequencies of the sound wave. ### Loudness - The loudness depends on the amplitude of the vibration. - The wide range of intensities the human ear can detect is so wide, it is convenient to use a logarithmic scale, where the sound level (β) is defined by the equation: - **β = 10 log ( I / I₀ )** - The constant (I₀) is the reference intensity, taken to be at the threshold of hearing (I₀ = 1.00 × 10⁻¹² W/m²) and (I) is the intensity in watts per square meter. ### Quality - Timbre (or Quality) is the characteristic of sound wave that distinguishes two sound waves (generally produced from different sources) having same loudness and pitch. - It depends on the shape of the waveform. - The shape of the waveform creates the differences in sounds between instruments such as a tuning fork, flute, voice, and guitar. ### Difference Between Pitch and Loudness - **Loudness Increases:** Higher Amplitude - **Loudness Decreases:** Lower Amplitude - **Pitch Increases:** Higher Frequency - **Pitch Decreases:** Lower Frequency