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Architectural Acoustics by David Egan: A Review
Architectural acoustics is the science and art of designing buildings for good hearing and freedom from noise. It is an essential aspect of architecture that affects the comfort, health, productivity, and enjoyment of occupants and users. Architectural acoustics deals with both natural and artificial sound sources, as well as indoor and outdoor environments.
architectural acoustics david egan pdf
David Egan is a consultant in acoustics and Professor Emeritus at the College of Architecture, Clemson University. He has been a principal consultant of Egan Acoustics for more than 35 years. He has a bachelor's degree from Lafayette College and a master's degree from MIT. He has also taught at Tulane University, Georgia Institute of Technology, University of North Carolina at Charlotte, and Washington University. He is a fellow of the Acoustical Society of America, a member of the National Council of Acoustical Consultants, and an Association of Collegiate Schools of Architecture Distinguished Professor.
His book Architectural Acoustics is a widely used reference that presents in a highly illustrated format the principles of design for good hearing and freedom from noise in and around buildings. The book covers basic concepts of sound and hearing, sound absorption and noise reduction, sound isolation and criteria for noise, control of HVAC systems noise and vibrations, auditorium acoustics design, and electronic sound systems. The book is written for architects, interior designers, engineers, and all others concerned with the design and construction of buildings who need to know the basics of architectural acoustics.
Basic Principles of Sound and Hearing
Sound is a form of energy that travels as waves through a medium such as air or water. Sound waves have three main properties: frequency (or pitch), amplitude (or loudness), and phase (or timing). Frequency is measured in hertz (Hz), amplitude in decibels (dB), and phase in degrees.
Hearing is the process by which humans perceive sound through their ears. The ear consists of three parts: the outer ear (or pinna), the middle ear (or tympanic cavity), and the inner ear (or cochlea). The outer ear collects sound waves from the environment. The middle ear amplifies them by transferring them to three small bones called ossicles. The inner ear converts them into electrical signals that are sent to the brain via the auditory nerve.
The quality of hearing depends on several factors such as frequency range (or bandwidth), dynamic range (or threshold), sensitivity (or loudness level), masking (or interference), localization (or direction), reverberation (or echo), diffraction (or bending), reflection (or bouncing), refraction (or changing speed), absorption (or damping), transmission (or passing through), attenuation (or weakening), resonance (or amplification), interference (or superposition), diffraction (or scattering), dispersion (or spreading), refraction (or changing direction).
The main acoustical parameters that describe sound in a space are: sound pressure level (SPL), sound power level (SWL), sound intensity level (SIL), sound exposure level (SEL), equivalent continuous sound level (Leq), maximum sound level (Lmax), minimum sound level (Lmin), peak sound level (Lpeak), day-night average sound level (Ldn), community noise equivalent level (CNEL).
Sound Absorption and Noise Reduction
Noise is any unwanted or harmful sound that interferes with communication, concentration, relaxation, or sleep. Noise can have negative effects on human health such as hearing loss, stress, annoyance, fatigue, headache, hypertension, cardiovascular disease, cognitive impairment, sleep disturbance, etc.
Sound absorption is the process by which sound energy is converted into heat or other forms of energy when it strikes a material or surface. Sound absorption reduces the amount of reflected sound in a space, thus improving speech intelligibility, musical clarity, privacy, etc.
The different types of sound absorbers are: porous absorbers (such as fibrous materials or open-cell foams), panel absorbers (such as thin plates or membranes), resonant absorbers (such as Helmholtz resonators or quarter-wave tubes), reactive absorbers (such as perforated panels or slotted panels).
Sound absorption can be incorporated into architectural design by using appropriate materials for walls, ceilings, floors, windows, doors, furniture, etc. Sound absorption can also be enhanced by using irregular shapes or textures for surfaces or adding decorative elements such as curtains, carpets, plants, etc. Sound Isolation and Criteria for Noise
Sound isolation is the process by which sound transmission between two spaces or sources is prevented or reduced. Sound isolation protects occupants from external noise such as traffic noise or aircraft noise. It also protects occupants from internal noise such as speech noise or music noise.
The different types of sound transmission paths are: airborne transmission (such as through walls or windows), structure-borne transmission (such as through floors or ceilings), flanking transmission (such as through joints or gaps).
The criteria for acceptable noise levels depend on the type of space or activity involved. For example: residential spaces require lower noise levels than commercial spaces; sleeping spaces require lower noise levels than living spaces; quiet activities require lower noise levels than noisy activities; etc.
The common criteria for acceptable noise levels are: noise rating curves (NR curves) which specify maximum SPLs for different frequency bands; room criterion curves (RC curves) which specify maximum SPLs for different frequency bands plus background noise; balanced noise criterion curves (BNC curves) which specify maximum SPLs for different frequency bands plus background noise plus room response; speech interference level (SIL) which specifies maximum SPLs for speech intelligibility; speech privacy index (SPI) which specifies minimum SPLs for speech privacy; speech transmission index (STI) which specifies a numerical rating for speech intelligibility.
Control of HVAC Systems Noise and Vibrations
HVAC systems are heating, ventilation, and air conditioning systems that provide thermal comfort and indoor air quality for buildings. HVAC systems can also generate noise and vibrations that can affect occupant comfort and building performance.
The main sources and characteristics of HVAC systems noise and vibrations are: fans, compressors, pumps, motors, ducts, pipes, valves, grilles, diffusers, etc.; broadband noise, tonal noise, impulsive noise, fluctuating noise, etc.; airborne noise, structure-borne noise, flanking noise, etc.; forced vibrations, resonant vibrations, harmonic vibrations, etc.
HVAC systems noise and vibrations can be reduced or eliminated at the source, path, or receiver. Some examples are: selecting quieter equipment; Auditorium Acoustics Design
Auditorium acoustics design is the process of creating an optimal sound environment for auditoriums and other large spaces that host speech, music, or other performances. Auditorium acoustics design involves balancing the following aspects: direct sound, reflected sound, reverberant sound, background noise, and electronic sound systems.
Direct sound is the sound that reaches the listener directly from the source without any reflection. Direct sound provides clarity and intelligibility of speech and music. Direct sound depends on the distance and angle between the source and the listener, as well as the directivity of the source.
Reflected sound is the sound that reaches the listener after bouncing off one or more surfaces such as walls, ceilings, floors, etc. Reflected sound provides loudness and spaciousness of sound. Reflected sound depends on the shape, size, orientation, and material of the surfaces, as well as the position of the source and the listener.
Reverberant sound is the sound that persists in a space after the source has stopped due to multiple reflections. Reverberant sound provides warmth and richness of sound. Reverberant sound depends on the volume and absorption of the space, as well as the frequency and duration of the source.
Background noise is any unwanted or distracting sound that interferes with the desired sound in a space. Background noise can come from external sources such as traffic noise or aircraft noise, or internal sources such as HVAC systems noise or audience noise. Background noise reduces speech intelligibility and musical quality. Background noise depends on the level and spectrum of the noise, as well as the masking effect of the desired sound.
Electronic sound systems are devices that amplify, process, distribute, or reproduce sound electronically. Electronic sound systems can enhance or supplement natural acoustics by increasing loudness, improving intelligibility, correcting defects, adding effects, etc. Electronic sound systems depend on the quality and placement of microphones, speakers, amplifiers, mixers, processors, etc.
Auditorium acoustics design can be improved by manipulating room shape, size, volume, materials, and furnishings to achieve optimal direct sound, reflected sound, reverberant sound, and background noise levels for different types of performances and audiences . Auditorium acoustics design can also be enhanced by integrating electronic sound systems with natural acoustics to provide better sound quality and intelligibility .
David Egan's book Architectural Acoustics is a valuable resource for anyone who wants to learn about the principles and applications of architectural acoustics. The book covers a wide range of topics from basic concepts of sound and hearing to specific design issues for different types of spaces and activities. The book is written in a clear and concise manner with more than 540 illustrations that explain and demonstrate acoustical phenomena and solutions.
The book is suitable for architects, interior designers, engineers, and all others concerned with the design and construction of buildings who need to know the basics of architectural acoustics. The book can also serve as a reference for students, teachers, researchers, and practitioners who want to deepen their knowledge and skills in architectural acoustics. The book can help readers understand how acoustics affects human perception, comfort, health, productivity, and enjoyment in buildings.
For more information about architectural acoustics and related topics, readers can visit the following websites:
The Acoustical Society of America: https://acousticalsociety.org/
The National Council of Acoustical Consultants: https://ncac.com/
The Institute of Noise Control Engineering: https://inceusa.org/
The International Commission for Acoustics: https://icacommission.org/
The International Institute of Noise Control Engineering: https://i-ince.org/
What is architectural acoustics?
Architectural acoustics is the science and art of designing buildings for good hearing and freedom from noise.
Who is David Egan?
David Egan is a consultant in acoustics and Professor Emeritus at the College of Architecture, Clemson University. He is also the author of Architectural Acoustics.
What are the main acoustical parameters?
The main acoustical parameters are: sound pressure level (SPL), sound power level (SWL), sound intensity level (SIL), reverberation time (RT), speech interference level (SIL), speech privacy index (SPI), speech transmission index (STI), etc.
What are the main types of sound absorbers?
The main types of sound absorbers are: porous absorbers (such as fibrous materials or open-cell foams), panel absorbers (such as thin plates or membranes), resonant absorbers (such as Helmholtz resonators or quarter-wave tubes), reactive absorbers (such as perforated panels or slotted panels).
What are the main sources of HVAC systems noise and vibrations?
The main sources of HVAC systems noise and vibrations are: fans, compressors, pumps, motors, ducts, pipes, valves, grilles, diffusers, etc.