Acoustics and Sound Waves

Acoustics

• Sound is a mechanical wave generated by disturbance/turbulence. It travels through a physical medium from a source to a receiver, causing a sensation of hearing.
• Acoustics is the branch of physics concerned with the properties of sound. It includes production, transmission, and effects (biological and psychological). The study focuses on generation, propagation, and reception of mechanical waves and vibrations.

Wave Types

• A wave is a transfer of energy from one point to another.
• Mechanical waves require a medium to travel (e.g., sound).
• Non-mechanical (electromagnetic) waves do not require a medium (e.g., light).

Sound Wave Properties

• Compressions: Crowding of molecules in a given space.
• Rarefactions: Thinning out of molecules in a given space.
• Compression and rarefaction make up a sound wave.
• Longitudinal waves: Sound waves are longitudinal waves. They are characterized by oscillations of particles parallel to the direction of wave propagation.

Objectives of Acoustics

• Noise reduction
• Privacy
• Sound intelligibility

Behavior of Sound

• Sound speed depends on the medium. It travels faster in denser materials (water, iron/steel) than in air.
• Sound waves can reflect, absorb, refract, diffuse, diffract, and transmit when encountering barriers.

Reflection

• Reflection is the occurrence of a sound wave striking one or more surfaces before reaching its receiver.

• In enclosed spaces, sound waves continuously hit surfaces until their energy is reduced to zero.

• The amount of reflected sound depends on the surface smoothness, size, and softness of the material.

• The angle of incidence equals the angle of reflection for flat surfaces; it differs for curved surfaces.

• Convex surfaces magnify reflected sound waves, making them seem bigger but weaker. They can be used to spread sound throughout a room.

• Concave surfaces make reflected sound waves appear smaller while amplifying them. They can concentrate sound waves at specific points.

Absorption

• Sound waves hitting an obstacle lose some energy by reflection and some by transferring energy to the obstacle's molecules. This lost energy is considered absorbed.
• Thickness and nature (softness/hardness) of a material affect the amount of absorbed sound energy.

Refraction

• Refraction is the bending of sound when it travels from one medium to another.
• The difference in the composition of the two media causes the sound to bend (change its angle of incidence into an angle of refraction).

Diffraction

• Diffraction is the bending of sound waves around edges of obstacles.
• Amount of diffraction depends on the size of the obstacle or opening in relation to the wavelength of the sound.

Transmission

• Transmission is when a sound wave is carried through an obstacle by its molecules, vibrating and re-emitting themselves without regard for the medium.
• Transmission can be structure-borne, air-borne, or impact sounds.

Interference

• Interference occurs when waves interact.
• Constructive interference occurs when compressions and rarefactions coincide, reinforcing the waves.
• Destructive interference occurs when compressions of one wave coincide with the rarefactions of another, weakening or canceling the waves.
• Interference can be reduced by sound-absorbing materials on reflecting surfaces.

Pitch and Loudness

• Pitch describes how high or low a sound is. It depends on the frequency of the sound source.
• High frequency means high pitch; low frequency means low pitch.
• Loudness relates to the amplitude of the sound wave. Larger amplitude means more energy, leading to louder sound.

This quiz explores the fundamentals of acoustics and the properties of sound waves. It covers the mechanisms of sound generation, transmission, and the distinction between mechanical and non-mechanical waves. Test your knowledge on the characteristics and behavior of sound waves.