Acoustics: Sound and Vibration

Acoustics

• Acoustics focuses on the production, transmission, and absorption of sound in buildings to ensure optimal conditions
• Acoustics is the science of sound and vibration related to stress fluctuations and waves in material mediums
• It is a branch of physics dealing with the production, control, transmission, reception, and effects of sound

Types of Acoustics

• Psychoacoustics studies how the brain processes and perceives sound, and its psychological and physiological influences on auditory experiences
• Environmental acoustics focuses on the study and control of sound in the environment addressing noise pollution and its human impact
• Architectural acoustics focuses on designing and optimizing building structures to control and enhance sound in enclosed spaces for optimal acoustics
• Landscape acoustics examines the interaction between sound and outdoor settings, considering factors such as topography and vegetation that influence sound propagation
• Electroacoustics is the study and application of electronic devices and systems involved in the production, transmission, and reception of audio signals
• Sonics studies sound including generation, propagation, and effects, used interchangeably with acoustic in a general sense

Applications of Acoustics Types

• Psychoacoustics are used to maximize perceived audio quality on music streaming platforms
• Environmental acoustics is applied to urban noise pollution via sound barriers, traffic regulation, and impact studies on public health
• Architectural Acoustics optimizes theaters, concert halls, and auditoriums to improve clarity and fidelity
• Landscape Acoustics utilizes planning and management of outdoor spaces to minimize noise impact, and designs parks for natural soundscapes
• Electroacoustics are used to develop high-fidelity audio equipment and design audio systems for many different venues
• Sonics applies sound wave knowledge to medical imaging, underwater acoustics research, and creates noise-canceling technology

Architectural Acoustics

• Architectural acoustics encompasses the study of the generation, propagation, and transmission of sound in rooms, dwellings, and buildings
• Applying architectural acoustics principles can greatly improve the quality of life at work, during leisure, and at home.
• Desirable sounds can be enhanced in concert halls, and a speakers voice in debating chambers, while undesirable sounds (noise) are reduced

Historical Aspects

• Ancient Open-Air Theaters have significant research on their acoustics
• The Greeks and Romans are given too much credit for acoustical sense in planning
• They tried to solve only the line-of-sight problem and obtained reasonable hearing at the same time.
• They located audiences close to the acting area or "logion" by shaping a steeply banked seating area in a semi-circle for good hearing
• Romans built large slanting roofs above acting areas, as sound reflectors for better sound to remote seats

Historical Buildings

• The Theatre at Orange, in France, built about 50 A.D. by the Romans is a typical example of open-air theaters
• Theaters were to be sited away from winds and "marshy districts and other unwholesome quarters" according to Vitruvius
• Vitruvius planned sight lines, numbers/locations of entrances/exits, and finally considered the acoustics subject
• Vitruvius made the first recorded reference to architectural acoustics in his book "De Architecture", about sounding vases ("echeia")
• Middle Ages acoustics of medieval Church Halls suffered overwhelming fullness of tone, excessive reverberation and poor intelligibility
• The Teatro Olimpico at Vicenza(Italy), designed by Palladio and built in 1589 by Scamozzi, had an audience of 3000
• The Teatro Farnese at Parma (Italy), designed by G.B. Aleotti and built in 1618, had a capacity of 2500

Wallace Clement Sabine

• Wallace Clement Sabine is considered the "father of architectural acoustics"
• In 1895, he was summoned to improve the poor acoustics of a theater
• Need for intelligibility, he focused on maintaining the direct sound volume that reached the listeners ear
• The relationship between the room's dimensions
• The rate the sound quieted to inaudible, also determined (rate of decay)
• His contour maps showed the distribution of sound intensity as he identified worst source reflections using sound absorbing panels
• Sabine turned to new theater designs, aiming for near-uniform acoustics for the audience

Sound Characteristics

• Sound is the sensation perceived by the human ear from rapid fluctuations in air pressure, typically created by a vibrating object
• Pitch is the frequency of its vibration
• Loudness is the strength of sound received through the ear
• Tone quality distinguishes itself from other sound of the same loudness

Elements of Sound

• Source can be natural or man-made and can be louder or quieter
• Transmission Path can allow sound to transmit more or less
• Receiver is the listener's reception of sound
• Healthy young ears have a detection range of 20 to 20,000 Hz

Sources of Sound

• Biological Sources: Sounds from living organisms, animals, birds, and insects
• Geophysical Sources: Natural events like earthquakes, thunderstorms, and volcanic eruptions generate sound
• Atmospheric Sources: Wind, rustling leaves, and atmospheric phenomena produce sound
• Industrial Sources: Machinery, manufacturing, construction activities are significant noise sources
• Transportation Sources: Vehicles, airplanes, trains, and ships make noise during operation
• Urban Sources: Sounds from urban activities, traffic, construction, and human-related activities in cities/towns
• Electronic Devices: Computers, televisions, radios, and other electronic devices can emit sounds
• Recreational Sources: Concerts, sports events, and fireworks produce significant sound levels
• Musical Instruments
• Noise: Noise is vibration caused by bodies, speech or music, loud, unpleasant, and causes disturbance

Sound Classification

• Music: Pleasing arrangements of sound for entertainment purposes are wanted sound
• Speech: Spoken word communication is intentionally and wanted in most settings
• Nature Sounds: Sounds such as birds, flowing water and wind are often desirable
• Traffic Noise: Vehicles generate unwanted noise on roads often considered disruptive
• Industrial Noise: Machinery/processes making intrusive, detrimental industrial noise
• Construction Noise: Disturbing construction noise to nearby residents
• Electronic Interference: Noise that effects quality/communication signals on electronics
• Crowd Noise: Gatherings cause unwanted disturbance

How Hearing Occurs

• Sound waves travel into the ear, reaching the eardrum
• The eardrum sends vibrations through middle ear bones into the inner ear
• The inner ear (cochlea) contains tiny hair cells that turn vibrations into electrical signals which are sent to the brain for interpretation.

Sound Properties

• Frequency refers to the cycles of sound wave per unit of time
• Frequency is measured in Hertz (Hz)
• Frequency determines the pitch of sound
• Amplitude refers to sound magnitude or intensity
• Amplitude relates to loudness or sound volume
• Measured in decibels (dB), amplitudes correspond to how quiet or loud sounds are
• Wavelength stands for the distance between successive peaks, inversely proportional to frequency
• Wavelength determines sound wave’s spatial extent
• High-frequency sounds have shorter wavelengths, reverse can be said for longer wavelengths.
• Speed of sound is the rate at which it propagates through a medium
• The medium's density, elasticity, and temperature are responsible for rate of travel
• Air at room temp: 343 meters/second (m/s) varies by altitude, humidity
• Phase identifies sound wave positions with a reference point measured typically in waves
• Phase describes waves peaks, troughs allowing them to interact for sound to occur
• Timbre (tone color/quality) has unique characteristics of sound distinguishing the similar sounds of pitch and loudness
• Timbre characteristics are; waveform, harmonics, waveform envelope, sound source characteristics and more

Measuring Sound

• Sound energy travels in waves, measured by frequency, amplitude
• Amplitude measures the wave's forcefulness, measured in decibels (dBA) of sound pressure
• The softest sound a person can hear: 0 dBA
• Normal speaking voices is about 65 dBA
• A rock concert can be about 120 dBA
• Frequency measures sound vibrations in one second
• Healthy ears hear low to high frequency, from 20 Hertz to 20,000 Hertz
• Piano lowest A: 27 Hertz
• Piano middle C: 262 Hertz tone.
• Piano highest key: 4186 Hertz.
• Sound intensity is expressed in decibels
• Loudness sensation in the ear is mesaured in Phons

Acoustic Terminology

• Airborne sound is radiated directly from a source, into the surrounding air
• Ambient noise is the total noise level in a specified environment
• Audible frequency ranges are sound frequencies heard
• The ranges spans 20 Hz to 20,000 Hz, but for engineering only frequencies between 40 Hz and 11,000 Hz
• Decibels (dB) express a sound intensity on a scale from imperceptible sound around 0 to 130 for the average pain level
• Diffraction has an acoustic wave disturbed, redistributing it in space
• Direct sound reaches a location by straight-line propagation from the sound source
• Frequency measures cycles per second.
• Noise is unwanted sound
• Noise Reduction (NR) has the difference of sound pressure in a sound path
• Reflection consists of Redirection of waves
• Refraction is a change in direction of sound caused by sound velocity changes
• Reverberant sounds happen via repeated reflection
• Sabin is a metric of absorption by one perfect absorbing square meter.
• Sound absorption is a process of sound energy being converted into heat, and reduction with hearing senses as well
• Sound Insulation is a material used to minimize sound passage.
• Sound insulation is a reduction to solid partitions
• Sound intensity is sound flow per unit area as w/m2

Wave Actions

• Reflection redirects off a surface
• Refraction direction is wave bending cause by speed changes
• Absorption is sound converted to heat
• Diffusion is the scattering/spreading out of sound waves against surfaces
• Transmission is the sound of propagation travelling in walls and flooring
• Diffraction occurs when sound weaves bend

Reflection Details

• Reflection redirects sound waves off of rigid, typically hard surfaces
• Flat surfaces have uniform reflection
• Convex surfaces disperse
• Concave surfaces concentrate sound

Absorption Details

• The process is material structure or object is taking sound when wave is encountered
• When waves are transmitted it's ether reflected, passes in the material or transferred to it

Refraction Details

• Sound refraction is bending as it passes though mediums density
• Phenomenon occurs sound changes by materials density
• Real-world is sounds change they hear underwater
• Air in water causes things to be distorted

Diffusion Details

• Scattering or spreading of sound waves that involves bounding creating acoustic environment

Transmission Details

• Sound diffusion refers to the scattering or spreading out of sound waves in various directions as they interact with surfaces or objects in an environment. Unlike sound reflection, which involves the bouncing of sound waves off a surface, diffusion causes sound waves to disperse more evenly throughout a space, reducing the perception of strong echoes and creating a more balanced acoustic environment.

Diffraction Details

• Phenomenon occurs bending in barriers, causes spreading in directions.
• It encounters object or corner bends dispersing areas behind objects.
• When waves are transmitted it's ether reflected, passes in the material or transferred to it.

Transmission Types

• Transmission sounds propagates separated sound waves with a wall and floor.
• Airborne/Structed sounds of materials used for separation of path.
• Primary method of sounds that travels an exterior with better soundproof materials
• Flanking sound transmission that travel adjacent around.
• Sealing of elements with improve mass.

Behavious in an Enclosed Space

• Incident or Direct sound comes directly from a source
• Reflected sound bounces surface
• Sound is absorbed to surface to be treated
• Diffused sound scattered and irregular reflections that distributes energy
• Diffracted Sound are bent sound waves
• Transmitted sounds travel via media
• The structure will hear the dissipated sounds inside.
• Structure can conduct sounds with inside.